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Detonation of a nuclear weapon involves bringing fissile material into its optimal supercritical state very rapidly. During part of this process, the assembly is supercritical, but not yet in an optimal state for a chain reaction. Free neutrons, in particular from spontaneous fissions, can cause the device to undergo a preliminary chain reaction that destroys the fissile material before it is ready to produce a large explosion, which is known as predetonation.
To keep the probability of predetonation low, the duration of the non-optimal assembly period is minimized and fissile and other materials are used that have low spontaneous fission rates. In fact, the combination of materials has to be such that it is unlikely that there is even a single spontaneous fission during the period of supercritical assembly. In particular, the gun method cannot be used with plutonium (see nuclear weapon design). | 1 | Fission Products + Nuclear Fission |
In a normal thermal reactor, tin-121m has a very low fission product yield; thus, this isotope is not a significant contributor to nuclear waste. Fast fission or fission of some heavier actinides will produce Sn at higher yields. For example, its yield from U-235 is 0.0007% per thermal fission and 0.002% per fast fission. | 1 | Fission Products + Nuclear Fission |
Initially used to approximate chemical reaction rates, models of isotope fractionation are used throughout the physical sciences. In chemistry, the Urey–Bigeleisen–Mayer equation has been used to predict equilibrium isotope effects and interpret the distributions of isotopes and isotopologues within systems, especially as deviations from their natural abundance. The model is also used to explain isotopic shifts in spectroscopy, such as those from nuclear field effects or mass independent effects. In biochemistry, it is used to model enzymatic kinetic isotope effects. Simulation testing in computational systems biology often uses the Bigeleisen–Mayer model as a baseline in the development of more complex models of biological systems. Isotope fractionation modeling is a critical component of isotope geochemistry and can be used to reconstruct past Earth environments as well as examine surface processes. | 0 | Isotopes |
Caesium-134 is found in spent nuclear fuel but is not produced by nuclear weapon explosions, as it is only formed by neutron capture on stable Cs-133, which is only produced by beta decay of Xe-133 with a half-life of 3 days. Cs-134 has a half-life of 2 years and may be a major source of gamma radiation in the first 20 years after discharge.
Caesium-135 is a long-lived fission product with much weaker radioactivity. Neutron capture inside the reactor transmutes much of the xenon-135 that would otherwise decay to Cs-135.
Caesium-137, with a half-life of 30 years, is the main medium-lived fission product, along with Sr-90.
Cs-137 is the primary source of penetrating gamma radiation from spent fuel from 10 years to about 300 years after discharge.
It is the most significant radioisotope left in the area around Chernobyl. | 1 | Fission Products + Nuclear Fission |
Clumped isotopes present a distinct set of challenges for isotopic reference materials. By convention the clumped isotope composition of CO liberated from CaCO (Δ) and CH (Δ/ΔCH3DCH2D2CO for carbon dioxide and CH for methane. Standard isotopic reference materials are still required in clumped isotope analysis for measuring the bulk δ values of a sample, which are used to calculate the expected stochastic distribution and subsequently to infer clumped isotope temperatures. However, the clumped isotope composition of most samples are altered in the mass spectrometer during ionization, meaning that post-measurement data correction requires having measured materials of known clumped isotope composition. At a given temperature equilibrium thermodynamics predicts the distribution of isotopes among possible isotopologues, and these predictions can be calibrated experimentally. To generate a standard of known clumped isotope composition, current practice is to internally equilibrate analyte gas at high temperatures in the presence of a metal catalyst and assume that it has the Δ value predicted by equilibrium calculations. Developing isotopic reference materials specifically for clumped isotope analysis remains an ongoing goal of this rapidly developing field and was a major discussion topic during the 6th [http://www.ipgp.fr/en/iciw International Clumped Isotopes Workshop] in 2017. It is possible that researchers in the future will measure clumped isotope ratios against internationally distributed reference materials, similar to the current method of measuring the bulk isotope composition of unknown samples. | 0 | Isotopes |
Within the Fallout videogame universe many Nuka-Cola flavors are created using less than ethical ways. In particular the flavor, Nuka Cola Quantum, has a distinctive bright blue glow that comes from the added Strontium-90. This was also the last flavor to be created by Nuka Cola before the Great War. | 1 | Fission Products + Nuclear Fission |
Measurement of the abundance of clumped isotopes (doubly substituted isotopologues) of gases has been used in the field of stable isotope geochemistry to trace equilibrium and kinetic processes in the environment inaccessible by analysis of singly substituted isotopologues alone.
Currently measured doubly substituted isotopologues include:
*Carbon dioxide: COO
*Methane: CHD and CHD
*Oxygen: O and OO
*Nitrogen: N
*Nitrous oxide: NNO and NNO | 0 | Isotopes |
Strontium-90 is not quite as likely as caesium-137 to be released as a part of a nuclear reactor accident because it is much less volatile, but is probably the most dangerous component of the radioactive fallout from a nuclear weapon.
A study of hundreds of thousands of deciduous teeth, collected by Dr. Louise Reiss and her colleagues as part of the Baby Tooth Survey, found a large increase in Sr levels through the 1950s and early 1960s. The study's final results showed that children born in St. Louis, Missouri, in 1963 had levels of Sr in their deciduous teeth that was 50 times higher than that found in children born in 1950, before the advent of large-scale atomic testing. Reviewers of the study predicted that the fallout would cause increased incidence of disease in those who absorbed strontium-90 into their bones. However, no follow up studies of the subjects have been performed, so the claim is untested.
An article with the study's initial findings was circulated to U.S. President John F. Kennedy in 1961, and helped convince him to sign the Partial Nuclear Test Ban Treaty with the United Kingdom and Soviet Union, ending the above-ground nuclear weapons testing that placed the greatest amounts of nuclear fallout into the atmosphere.
The Chernobyl disaster released roughly 10 PBq, or about 5% of the core inventory, of strontium-90 into the environment. The Kyshtym disaster released strontium-90 and other radioactive material into the environment. It is estimated to have released 20 MCi (800 PBq) of radioactivity. The Fukushima Daiichi disaster had from the accident until 2013 released 0.1 to 1 PBq of strontium-90 in the form of contaminated cooling water into the Pacific Ocean. | 1 | Fission Products + Nuclear Fission |
In stable isotope geochemistry, the Urey–Bigeleisen–Mayer equation, also known as the Bigeleisen–Mayer equation or the Urey model, is a model describing the approximate equilibrium isotope fractionation in an isotope exchange reaction. While the equation itself can be written in numerous forms, it is generally presented as a ratio of partition functions of the isotopic molecules involved in a given reaction. The Urey–Bigeleisen–Mayer equation is widely applied in the fields of quantum chemistry and geochemistry and is often modified or paired with other quantum chemical modelling methods (such as density functional theory) to improve accuracy and precision and reduce the computational cost of calculations.
The equation was first introduced by Harold Urey and, independently, by Jacob Bigeleisen and Maria Goeppert Mayer in 1947. | 0 | Isotopes |
The earliest compelling evidence for human habitation of the Americas comes from the Clovis complex, between 11,050 and 10,800 C yr B.P. However, a series of human tracks were identified at White Sands National Park, New Mexico, which have been dated contentiously dated to between 23,000 and 21,000 years ago - during the Last Glacial Maximum. Alongside anatomically modern humans, the trackway shows impressions created by a Columbian mammoth and a giant ground sloth. The upper biostratigraphic limit for when the impressions were made could therefore be determined by consideration of the extinction dates of mammoths and ground sloths. More precise dates were able to be gained via radiocarbon dating of ditch grass (ruppia cirrhosa) embedded in the prints. These seeds produced a date of 23,000-21,000 years ago.
However, C dates are not infallible, and this remains a topic of debate. A recent counterproposal posits that the trackways were, in fact, created by the Clovis culture and the pre-existing proposed dates of first habitation should not be moved. False dates may have been produced as older strata containing the seeds could have been eroded and displaced onto the damp clay, before being impressed in by footsteps. Alternatively, aquatic plants like ditch grass reflect the C levels in their environment when living, if C was deficient in the habitat, this could imply a false date. | 0 | Isotopes |
Selenium-79 is a radioisotope of selenium present in spent nuclear fuel and the wastes resulting from reprocessing this fuel. It is one of only 7 long-lived fission products. Its fission yield is low (about 0.04%), as it is near the lower end of the mass range for fission products. Its half-life has been variously reported as 650,000 years, 65,000 years, 1.13 million years, 480,000 years, 295,000 years, 377,000 years and most recently with best current precision, 327,000 years.
Se decays to Br by emitting a beta particle with no attendant gamma radiation (i.e., 100% β decay). This complicates its detection and liquid scintillation counting (LSC) is required for measuring it in environmental samples. The low specific activity (5.1 × 10 Bq/g) and relatively low energy (151 keV) of its beta particles have been said to limit the radioactive hazards of this isotope.
Performance assessment calculations for the Belgian deep geological repository estimated Se may be the major contributor to activity release in terms of becquerels (decays per second), "attributable partly to the uncertainties about its migration behaviour in the Boom Clay and partly to its conversion factor in the biosphere." (p. 169). However, "calculations for the Belgian safety assessments use a half-life of 65 000 years" (p. 177), much less than the currently estimated half-life, and "the migration parameters ... have been estimated very cautiously for Se." (p. 179)
Neutron absorption cross sections for Se have been estimated at 50 barns for thermal neutrons and 60.9 barns for resonance integral.
Selenium-80 and selenium-82 have higher fission yields, about 20 times the yield of Se in the case of uranium-235, 6 times in the case of plutonium-239 or uranium-233, and 14 times in the case of plutonium-241. | 1 | Fission Products + Nuclear Fission |
Iodine-131 (I, I-131) is an important radioisotope of iodine discovered by Glenn Seaborg and John Livingood in 1938 at the University of California, Berkeley. It has a radioactive decay half-life of about eight days. It is associated with nuclear energy, medical diagnostic and treatment procedures, and natural gas production. It also plays a major role as a radioactive isotope present in nuclear fission products, and was a significant contributor to the health hazards from open-air atomic bomb testing in the 1950s, and from the Chernobyl disaster, as well as being a large fraction of the contamination hazard in the first weeks in the Fukushima nuclear crisis. This is because I is a major fission product of uranium and plutonium, comprising nearly 3% of the total products of fission (by weight). See fission product yield for a comparison with other radioactive fission products. I is also a major fission product of uranium-233, produced from thorium.
Due to its mode of beta decay, iodine-131 causes mutation and death in cells that it penetrates, and other cells up to several millimeters away. For this reason, high doses of the isotope are sometimes less dangerous than low doses, since they tend to kill thyroid tissues that would otherwise become cancerous as a result of the radiation. For example, children treated with moderate dose of I for thyroid adenomas had a detectable increase in thyroid cancer, but children treated with a much higher dose did not. Likewise, most studies of very-high-dose I for treatment of Graves' disease have failed to find any increase in thyroid cancer, even though there is linear increase in thyroid cancer risk with I absorption at moderate doses. Thus, iodine-131 is increasingly less employed in small doses in medical use (especially in children), but increasingly is used only in large and maximal treatment doses, as a way of killing targeted tissues. This is known as "therapeutic use".
Iodine-131 can be "seen" by nuclear medicine imaging techniques (e.g., gamma cameras) whenever it is given for therapeutic use, since about 10% of its energy and radiation dose is via gamma radiation. However, since the other 90% of radiation (beta radiation) causes tissue damage without contributing to any ability to see or "image" the isotope, other less-damaging radioisotopes of iodine such as iodine-123 (see isotopes of iodine) are preferred in situations when only nuclear imaging is required. The isotope I is still occasionally used for purely diagnostic (i.e., imaging) work, due to its low expense compared to other iodine radioisotopes. Very small medical imaging doses of I have not shown any increase in thyroid cancer. The low-cost availability of I, in turn, is due to the relative ease of creating I by neutron bombardment of natural tellurium in a nuclear reactor, then separating I out by various simple methods (i.e., heating to drive off the volatile iodine). By contrast, other iodine radioisotopes are usually created by far more expensive techniques, starting with cyclotron radiation of capsules of pressurized xenon gas.
Iodine-131 is also one of the most commonly used gamma-emitting radioactive industrial tracer. Radioactive tracer isotopes are injected with hydraulic fracturing fluid to determine the injection profile and location of fractures created by hydraulic fracturing.
Much smaller incidental doses of iodine-131 than those used in medical therapeutic procedures, are supposed by some studies to be the major cause of increased thyroid cancers after accidental nuclear contamination. These studies suppose that cancers happen from residual tissue radiation damage caused by the I, and should appear mostly years after exposure, long after the I has decayed. Other studies did not find a correlation. | 1 | Fission Products + Nuclear Fission |
It is now known from study of the Sun and primitive meteorites that the solar system was initially almost homogeneous in isotopic composition. Deviations from the (evolving) galactic average, locally sampled around the time that the Sun's nuclear burning began, can generally be accounted for by mass fractionation (see the article on mass-independent fractionation) plus a limited number of nuclear decay and transmutation processes. There is also evidence for injection of short-lived (now-extinct) isotopes from a nearby supernova explosion that may have triggered solar nebula collapse. Hence deviations from natural abundance on Earth are often measured in parts per thousand (per mille or ‰) because they are less than one percent (%).
An exception to this lies with the presolar grains found in primitive meteorites. These small grains condensed in the outflows of evolved ("dying") stars and escaped the mixing and homogenization processes in the interstellar medium and the solar accretion disk (also known as the solar nebula or protoplanetary disk). As stellar condensates ("stardust"), these grains carry the isotopic signatures of specific nucleosynthesis processes in which their elements were made. In these materials, deviations from "natural abundance" are sometimes measured in factors of 100. | 0 | Isotopes |
In general, most actinide isotopes with an odd neutron number are fissile. Most nuclear fuels have an odd atomic mass number ( = the total number of nucleons), and an even atomic number Z. This implies an odd number of neutrons. Isotopes with an odd number of neutrons gain an extra 1 to 2 MeV of energy from absorbing an extra neutron, from the pairing effect which favors even numbers of both neutrons and protons. This energy is enough to supply the needed extra energy for fission by slower neutrons, which is important for making fissionable isotopes also fissile.
More generally, nuclides with an even number of protons and an even number of neutrons, and located near a well-known curve in nuclear physics of atomic number vs. atomic mass number are more stable than others; hence, they are less likely to undergo fission. They are more likely to "ignore" the neutron and let it go on its way, or else to absorb the neutron but without gaining enough energy from the process to deform the nucleus enough for it to fission. These "even-even" isotopes are also less likely to undergo spontaneous fission, and they also have relatively much longer partial half-lives for alpha or beta decay. Examples of these isotopes are uranium-238 and thorium-232. On the other hand, other than the lightest nuclides, nuclides with an odd number of protons and an odd number of neutrons (odd Z, odd N) are usually short-lived (a notable exception is neptunium-236 with a half-life of 154,000 years) because they readily decay by beta-particle emission to their isobars with an even number of protons and an even number of neutrons (even Z, even N) becoming much more stable. The physical basis for this phenomenon also comes from the pairing effect in nuclear binding energy, but this time from both proton–proton and neutron–neutron pairing. The relatively short half-life of such odd-odd heavy isotopes means that they are not available in quantity and are highly radioactive. | 1 | Fission Products + Nuclear Fission |
After the detonation of a weapon at or above the fallout-free altitude (an air burst), fission products, un-fissioned nuclear material, and weapon residues vaporized by the heat of the fireball condense into a suspension of particles 10 nm to 20 µm in diameter. This size of particulate matter, lifted to the stratosphere, may take months or years to settle, and may do so anywhere in the world. Its radioactive characteristics increase the statistical cancer risk. Elevated atmospheric radioactivity remains measurable after the widespread nuclear testing of the 1950s.
Radioactive fallout has occurred around the world; for example, people have been exposed to iodine-131 from atmospheric nuclear testing. Fallout accumulates on vegetation, including fruits and vegetables. Starting from 1951 people may have gotten exposure, depending on whether they were outside, the weather, and whether they consumed contaminated milk, vegetables or fruit. Exposure can be on an intermediate time scale or long term. The intermediate time scale results from fallout that has been put into the troposphere and ejected by precipitation during the first month. Long-term fallout can sometimes occur from deposition of tiny particles carried in the stratosphere. By the time that stratospheric fallout has begun to reach the earth, the radioactivity is very much decreased. Also, after a year it is estimated that a sizable quantity of fission products move from the northern to the southern stratosphere. The intermediate time scale is between 1 and 30 days, with long term fallout occurring after that.
Examples of both intermediate and long term fallout occurred after the 1986 Chernobyl accident, which contaminated over of land in Ukraine and Belarus. The main fuel of the reactor was uranium, and surrounding this was graphite, both of which were vaporized by the hydrogen explosion that destroyed the reactor and breached its containment. An estimated 31 people died within a few weeks after this happened, including two plant workers killed at the scene. Although residents were evacuated within 36 hours, people started to complain of vomiting, migraines and other major signs of radiation sickness. The officials of Ukraine had to close off an area. Long term effects included at least 6,000 cases of thyroid cancer, mainly among children. Fallout spread throughout Western Europe, with Northern Scandinavia receiving a heavy dose, contaminating reindeer herds in Lapland, and salad greens becoming almost unavailable in France. Some sheep farms in North Wales and the North Of England were required to monitor radioactivity levels in their flocks until the control was lifted in 2012. | 1 | Fission Products + Nuclear Fission |
Isotope analysis has many applications in archaeology, from dating sites and artefacts, determination of past diets and migration patterns and for environmental reconstruction.
Information is determined by assessing the ratio of different isotopes of a particular element in a sample. The most widely studied and used isotopes in archaeology are carbon, oxygen, nitrogen, strontium and calcium.
An isotope is an atom of an element with an abnormal number of neutrons, changing their atomic mass. Isotopes can be subdivided into stable and unstable or radioactive. Unstable isotopes decay at a predictable rate over time. The first stable isotope was discovered in 1913, and most were identified by the 1930s. Archaeology was relatively slow to adopt the study of isotopes. Whereas chemistry, biology and physics, saw a rapid uptake in applications of isotope analysis in the 1950s and 1960s, following the commercialisation of the mass spectrometer. It wasn't until the 1970s, with the publication of works by Vogel and Van Der Merwe (1977) and DeNiro and Epstein (1978; 1981) that isotopic analysis became a mainstay of archaeological study. | 0 | Isotopes |
Hot particles, radioactive particles of nuclear fallout and radioactive waste, also exhibit distinct isotopic signatures. Their radionuclide composition (and thus their age and origin) can be determined by mass spectrometry or by gamma spectrometry. For example, particles generated by a nuclear blast contain detectable amounts of Co and Eu. The Chernobyl accident did not release these particles but did release Sb and Ce. Particles from underwater bursts will consist mostly of irradiated sea salts. Ratios of Eu/Eu, Eu/Eu, and Pu/Pu are also different for fusion and fission nuclear weapons, which allows identification of hot particles of unknown origin.
Uranium has a relatively constant isotope ratio in all natural samples with ~0.72% some 55 ppm (in secular equilibrium with its parent nuclide ) and the balance made up by . Isotopic compositions that diverge significantly from those values are evidence for the uranium having been subject to depletion or enrichment in some fashion or of (part of it) having participated in a nuclear fission reaction. While the latter is almost as universally due to human influence as the former two, the natural nuclear fission reactor at Oklo, Gabon was detected through a significant diversion of concentration in samples from Oklo compared to those of all other known deposits on earth. Given that is a material of proliferation concern then as now every IAEA-approved supplier of Uranium fuel keeps track of the isotopic composition of uranium to ensure none is diverted for nefarious purposes. It would thus become apparent quickly if another Uranium deposit besides Oklo proves to have once been a natural nuclear fission reactor. | 0 | Isotopes |
Initial measurements of position specific isotope enrichments were measured using isotope ratio mass spectrometry in which sites on a molecule were first degraded to , the was captured and purified, and then the CO was measured for its isotope composition on an Isotope Ratio Mass Spectrometer (IRMS). Py-GC-MS was also used in these experiments to degrade molecules even further and characterize their intramolecular isotopic distributions. Both GC-MS and LC-MS are capable of characterizing position specific isotope enrichments in isotopically labelled molecules. In these molecules, C is so abundant that it can be seen on a mass spectrometer with low sensitivity. The resolution of these instruments can distinguish two molecules with a 1 Dalton difference in their molecular masses; however, this difference could arise from the addition of many rare isotopes (O, C, H, etc.). For this reason, mass spectrometers using quadrupoles or time-of-flight detection techniques cannot be used for measuring position-specific enrichments at natural abundances. | 0 | Isotopes |
Isotopic oxygen is incorporated into the body primarily through ingestion at which point it is used in the formation of, for archaeological purposes, bones and teeth. The oxygen is incorporated into the hydroxylcarbonic apatite of bone and tooth enamel.
Bone is continually remodelled throughout the lifetime of an individual. Although the rate of turnover of isotopic oxygen in hydroxyapatite is not fully known, it is assumed to be similar to that of collagen; approximately 10 years. Consequently, should an individual remain in a region for 10 years or longer, the isotopic oxygen ratios in the bone hydroxyapatite would reflect the oxygen ratios present in that region.
Teeth are not subject to continual remodelling and so their isotopic oxygen ratios remain constant from the time of formation. The isotopic oxygen ratios, then, of teeth represent the ratios of the region in which the individual was born and raised. Where deciduous teeth are present, it is also possible to determine the age at which a child was weaned. Breast milk production draws upon the body water of the mother, which has higher levels of O due to the preferential loss of O through sweat, urine, and expired water vapour.
While teeth are more resistant to chemical and physical changes over time, both are subject to post-depositional diagenesis. As such, isotopic analysis makes use of the more resistant phosphate groups, rather than the less abundant hydroxyl group or the more likely diagenetic carbonate groups present. | 0 | Isotopes |
An isotopic signature (also isotopic fingerprint) is a ratio of non-radiogenic stable isotopes, stable radiogenic isotopes, or unstable radioactive isotopes of particular elements in an investigated material. The ratios of isotopes in a sample material are measured by isotope-ratio mass spectrometry against an isotopic reference material. This process is called isotope analysis. | 0 | Isotopes |
The high short-term radioactivity of spent nuclear fuel is primarily from fission products with short half-life.
The radioactivity in the fission product mixture is mostly due to short-lived isotopes such as I and Ba, after about four months Ce, Zr/Nb and Sr constitute the largest contributors, while after about two or three years the largest share is taken by Ce/Pr, Ru/Rh and Pm.
Note that in the case of a release of radioactivity from a power reactor or used fuel, only some elements are released. As a result, the isotopic signature of the radioactivity is very different from an open air nuclear detonation where all the fission products are dispersed. | 1 | Fission Products + Nuclear Fission |
The first paper on site-specific enrichment used the ninhydrin reaction to cleave the carboxyl site off alpha-amino acids in photosynthetic organisms. The authors demonstrated an enriched carboxyl site relative to the bulk δC of the molecules, which they attribute to uptake of heavier CO through the Calvin cycle. A recent study applied similar theory to understand enrichments in methionine, which they suggested would be powerful in origin and synthesis studies. | 0 | Isotopes |
Many units of measurement were historically, or are still, defined with reference to the properties of specific substances that, in many cases, occurred in nature as mixes of multiple isotopes, for example:
Since samples taken from different natural sources can have subtly different isotopic ratios, the relevant properties can differ between samples. If the definition simply refers to a substance without addressing the isotopic composition, this can lead to some level of ambiguity in the definition and variation in practical realizations of the unit by different laboratories, as was observed with the kelvin before 2007. If the definition refers only to one isotope (as that of the dalton does) or to a specific isotope ratio, e.g. Vienna Standard Mean Ocean Water, this removes a source of ambiguity and variation, but adds layers of technical difficulty (preparing samples of a desired isotopic ratio) and uncertainty (regarding how much an actual reference sample differs from the nominal ratio). The use of mononuclidic elements as reference material sidesteps these issues and notably the only substance referenced in the most recent iteration of the SI is caesium, a mononuclidic element.
Mononuclidic elements are also of scientific importance because their atomic weights can be measured to high accuracy, since there is minimal uncertainty associated with the isotopic abundances present in a given sample. Another way of stating this, is that, for these elements, the standard atomic weight and atomic mass are the same.
In practice, only 11 of the mononuclidic elements are used in standard atomic weight metrology. These are aluminium, bismuth, caesium, cobalt, gold, manganese, phosphorus, scandium, sodium, terbium, and thorium.
In nuclear magnetic resonance spectroscopy (NMR), the three most sensitive stable nuclei are hydrogen-1 (H), fluorine-19 (F) and phosphorus-31 (P). Fluorine and phosphorus are monoisotopic, with hydrogen nearly so. H NMR, F NMR and P NMR allow for identification and study of compounds containing these elements. | 0 | Isotopes |
The purpose of radiological emergency preparedness is to protect people from the effects of radiation exposure after a nuclear accident or bomb. Evacuation is the most effective protective measure. However, if evacuation is impossible or even uncertain, then local fallout shelters and other measures provide the best protection.
Zr) and/or involatiles is less for accident fallout than it is bomb fallout. A definitive report on Chernobyl is at [http://www.nea.fr/html/rp/chernobyl/allchernobyl.html] - Chapter 2, Table 1 lists the radioisotopes released in the fire. The percentage of the inventory which was released was controlled largely by how volatile the fission product is. Hence a greater proportion of xenon and iodine were released than of cerium and plutonium.
For the longer term response, a review of the methods that can be used to decontaminate an urban environment is provided in the scope report [http://www.icsu-scope.org/downloadpubs/scope50/chapter06.html Behaviour and Decontamination of Artificial Radionuclides in the Urban Environment]. Also see chapter four of the NEA reports [http://citeseer.ist.psu.edu/cache/papers/cs/28102/http:zSzzSzwww.nea.frzSzhtmlzSzrpzSzchernobylzSzchernobyl-1995.pdf/chernobyl-ten-years-on.pdf Chernobyl ten years on] and [http://www.nea.fr/html/rp/reports/2003/nea3508-chernobyl.pdf Chernobyl twenty years on] for details of how farming methods can be changed to reduce the impact of accident fallout.--> | 1 | Fission Products + Nuclear Fission |
Not all neutrons are emitted as a direct product of fission; some are instead due to the radioactive decay of some of the fission fragments. The neutrons that occur directly from fission are called "prompt neutrons", and the ones that are a result of radioactive decay of fission fragments are called "delayed neutrons". The fraction of neutrons that are delayed is called β, and this fraction is typically less than 1% of all the neutrons in the chain reaction.
The delayed neutrons allow a nuclear reactor to respond several orders of magnitude more slowly than just prompt neutrons would alone. Without delayed neutrons, changes in reaction rates in nuclear reactors would occur at speeds that are too fast for humans to control.
The region of supercriticality between k = 1 and k = 1/(1 − β) is known as delayed supercriticality (or delayed criticality). It is in this region that all nuclear power reactors operate. The region of supercriticality for k > 1/(1 − β) is known as prompt supercriticality (or prompt criticality), which is the region in which nuclear weapons operate.
The change in k needed to go from critical to prompt critical is defined as a dollar. | 1 | Fission Products + Nuclear Fission |
For technologically advanced states the gun-type method is now essentially obsolete, for reasons of efficiency and safety (discussed above).
The gun type method was largely abandoned by the United States as soon as the implosion technique was perfected, though it was retained in the specialised role of nuclear artillery for a time. Other nuclear powers, such as the United Kingdom, and the Soviet Union never built an example of this type of weapon. Besides requiring the use of highly enriched U-235, the technique has other severe limitations. The implosion technique is much better suited to the various methods employed to reduce the weight of the weapon and increase the proportion of material which fissions. South Africa built around five gun-type weapons, and no implosion-type weapons. They later abandoned their nuclear weapon program altogether. They were unique in their abandonment of nuclear weapons, and probably also by building gun-type weapons rather than implosion-type weapons.
There are also safety problems with gun-type weapons. For example, it is inherently dangerous to have a weapon containing a quantity and shape of fissile material that can form a critical mass through a relatively simple accident. Furthermore, if the weapon is dropped from an aircraft into the sea, then the moderating effect of the seawater can also cause a criticality accident without the weapon even being physically damaged. Neither can happen with an implosion-type weapon, since there is normally insufficient fissile material to form a critical mass without the correct detonation of the explosive lenses. | 1 | Fission Products + Nuclear Fission |
In the Acerinox accident of 1998, the Spanish recycling company Acerinox accidentally melted down a mass of radioactive caesium-137 that came from a gamma-ray generator. | 1 | Fission Products + Nuclear Fission |
This is a summary table from List of nuclides. Note that numbers are not exact and may change slightly in the future, as nuclides are observed to be radioactive, or new half-lives are determined to some precision. | 0 | Isotopes |
The "gun" method is roughly how the Little Boy weapon, which was detonated over Hiroshima, worked, using uranium-235 as its fissile material. In the Little Boy design, the U-235 "bullet" had a mass of around , and it was long, with a diameter of . The hollow cylindrical shape made it subcritical. It was powered by a cordite charge. The uranium target spike was about . Both the bullet and the target consisted of multiple rings stacked together.
The use of "rings" had two advantages: it allowed the larger bullet to confidently remain subcritical (the hollow column served to keep the material from having too much contact with other material), and it allowed sub-critical assemblies to be tested using the same bullet but with just one ring.
The barrel had an inside diameter of . Its length was , which allowed the bullet to accelerate to its final speed of about before coming into contact with the target.
When the bullet is at a distance of , the combination becomes critical. This means that some free neutrons may cause the chain reaction to take place before the material could be fully joined (see nuclear chain reaction).
Typically the chain reaction takes less than 1 μs (100 shakes), during which time the bullet travels only 0.3 mm. Although the chain reaction is slower when the supercriticality is low, it still happens in a time so short that the bullet hardly moves in that time.
This could cause a fizzle, a predetonation which would blow the material apart before creating much of an explosion. Thus, it is important that the frequency at which free neutrons occur is kept low, compared with the assembly time from this point. This also means that the speed of the projectile must be sufficiently high; its speed can be increased but this requires a longer and heavier barrel, or a higher pressure of the propellant gas for greater acceleration of the bullet subcritical mass.
In the case of Little Boy, the 20% U-238 in the uranium had 70 spontaneous fissions per second. With the fissionable material in a supercritical state, each gave a large probability of detonation: each fission creates on average 2.52 neutrons, which each have a probability of more than 1:2.52 of creating another fission. During the 1.35 ms of supercriticality prior to full assembly, there was a 10% probability of a fission, with somewhat less probability of pre-detonation.
Initially the Manhattan Project gun-type effort was directed at making a gun weapon that used plutonium as its source of fissile material, known as the "Thin Man" because of its extreme length. It was thought that if a plutonium gun-type bomb could be created, then the uranium gun-type bomb would be very easy to make by comparison. However, it was discovered in April 1944 that reactor-bred plutonium (Pu-239) is contaminated with another isotope of plutonium, Pu-240, which increases the material's spontaneous neutron-release rate, making pre-detonation inevitable. For this reason, a gun-type bomb is thought to only be usable with enriched-uranium fuel. It is unknown though possible to make a composite design using high grade plutonium in the bullet only.
After it was discovered that the "Thin Man" program would not be successful, Los Alamos redirected its efforts into creating the implosion-type plutonium weapon: "Fat Man". The gun program switched completely over to developing a uranium bomb.
Although in Little Boy of 80%-grade U-235 was used (hence ), the minimum is about 44 to 55 pounds (20 to 25 kg), versus for the implosion method.
Little Boy's target subcritical mass was enclosed in a neutron reflector made of tungsten carbide (WC). The presence of a neutron reflector reduced neutron losses during the chain reaction, and so reduced the quantity of uranium fuel needed. A more effective reflector material would be metallic beryllium, but this was not known until the postwar years when Ted Taylor developed an implosion design known as "Scorpion".
The scientists who designed the "Little Boy" weapon were confident enough of its success that they did not field-test a design before using it in war (though scientists such as Louis Slotin did perform non-destructive tests with sub-critical assemblies, dangerous experiments nicknamed tickling the dragon's tail). In any event, it could not be tested before being deployed, as there was only sufficient U-235 available for one device. Even though the design was never proof-tested, there was thought to be no risk of the device being captured by an enemy if it malfunctioned.
Even a "fizzle" would have completely disintegrated the device, while the multiple redundancies built into the "Little Boy" design meant there was negligible if any potential for the device to strike the ground without detonating at all.
For a quick start of the chain reaction at the right moment a neutron trigger/initiator is used. An initiator is not strictly necessary for an effective gun design, as long as the design uses "target capture" (in essence, ensuring that the two subcritical masses, once fired together, cannot come apart until they explode). Considering the 70 spontaneous fissions per second, this only causes a delay of a few times 1/70 second, which in this case does not matter. Initiators were only added to Little Boy late in its design. | 1 | Fission Products + Nuclear Fission |
A boosted fission weapon usually refers to a type of nuclear bomb that uses a small amount of fusion fuel to increase the rate, and thus yield, of a fission reaction. The neutrons released by the fusion reactions add to the neutrons released due to fission, allowing for more neutron-induced fission reactions to take place. The rate of fission is thereby greatly increased such that much more of the fissile material is able to undergo fission before the core explosively disassembles. The fusion process itself adds only a small amount of energy to the process, perhaps 1%.
The alternative meaning is an obsolete type of single-stage nuclear bomb that uses thermonuclear fusion on a large scale to create fast neutrons that can cause fission in depleted uranium, but which is not a two-stage hydrogen bomb. This type of bomb was referred to by Edward Teller as "Alarm Clock", and by Andrei Sakharov as "Sloika" or "Layer Cake" (Teller and Sakharov developed the idea independently, as far as is known). | 1 | Fission Products + Nuclear Fission |
Long-lived fission products (LLFPs) are radioactive materials with a long half-life (more than 200,000 years) produced by nuclear fission of uranium and plutonium. Because of their persistent radiotoxicity, it is necessary to isolate them from humans and the biosphere and to confine them in nuclear waste repositories for geological periods of time. The focus of this article is radioisotopes (radionuclides) generated by fission reactors. | 1 | Fission Products + Nuclear Fission |
Tritium is a radioactive isotope with a half-life of 12.355 years. Its main decay product is helium-3, which is among the nuclides with the largest cross-section for neutron capture. Therefore, periodically the weapon must have its helium waste flushed out and its tritium supply recharged. This is because any helium-3 in the weapons tritium supply would act as a poison during the weapons detonation, absorbing neutrons meant to collide with the nuclei of its fission fuel.
Tritium is relatively expensive to produce because each triton - the tritium nucleus - produced requires production of at least one free neutron which is used to bombard a feedstock material (lithium-6, deuterium, or helium-3). Actually, because of losses and inefficiencies, the number of free neutrons needed is closer to two for each triton produced (and tritium begins decaying immediately, so there are losses during collection, storage, and transport from the production facility to the weapons in the field.) The production of free neutrons demands the operation of either a breeder reactor or a particle accelerator (with a spallation target) dedicated to the tritium production facility. | 1 | Fission Products + Nuclear Fission |
Carbon is present in all biological material including skeletal remains, charcoal and food residues and plays an integral role in the dating of materials, through radiocarbon dating. The ratio of different carbon isotopes naturally fluctuates over time, and, by analysing the composition of carbon dioxide (CO) in ancient air bubbles trapped in ice cores, a chronological record of these fluctuations can be constructed. Primary producers (such as grasses) absorb and sequester CO during photosynthesis, these plants are then eaten by consumers (such as cows, and later humans) which inherit this same CO signature. Therefore, by matching the carbon isotope ratios from a sample to ratios from the ice core record, the sample can be assigned to a broad period. After death, an organism no longer absorbs CO, Cs instability causes its concentration to decrease over time The predictable rate at which this occurs is known as an elements decay rate. | 0 | Isotopes |
To be a useful fuel for nuclear fission chain reactions, the material must:
* Be in the region of the binding energy curve where a fission chain reaction is possible (i.e., above radium)
* Have a high probability of fission on neutron capture
* Release more than one neutron on average per neutron capture. (Enough of them on each fission, to compensate for non-fissions and absorptions in non-fuel material)
* Have a reasonably long half-life
* Be available in suitable quantities
Fissile nuclides in nuclear fuels include:
* Uranium-233, bred from thorium-232 by neutron capture with intermediate decays steps omitted.
* Uranium-235, which occurs in natural uranium and enriched uranium
* Plutonium-239, bred from uranium-238 by neutron capture with intermediate decays steps omitted.
* Plutonium-241, bred from plutonium-240 directly by neutron capture.
Fissile nuclides do not have a 100% chance of undergoing fission on absorption of a neutron. The chance is dependent on the nuclide as well as neutron energy. For low and medium-energy neutrons, the neutron capture cross sections for fission (σ), the cross section for neutron capture with emission of a gamma ray (σ), and the percentage of non-fissions are in the table at right.
Fertile nuclides in nuclear fuels include:
* Thorium-232, which breeds uranium-233 by neutron capture with intermediate decays steps omitted.
* Uranium-238, which breeds plutonium-239 by neutron capture with intermediate decays steps omitted.
* Plutonium-240, bred from plutonium-239 directly by neutron capture. | 1 | Fission Products + Nuclear Fission |
Unlike other isotopic dating methods, the "daughter" in fission track dating is an effect in the crystal rather than a daughter isotope. Uranium-238 undergoes spontaneous fission decay at a known rate, and it is the only isotope with a decay rate that is relevant to the significant production of natural fission tracks; other isotopes have fission decay rates too slow to be of consequence. The fragments emitted by this fission process
leave trails of damage (fossil tracks or ion tracks) in the crystal structure of the mineral that contains the uranium. The process of track production is essentially the same by which swift heavy ions produce ion tracks.
Chemical etching of polished internal surfaces of these minerals reveals spontaneous fission tracks, and the track density can be determined. Because etched tracks are relatively large (in the range 1 to 15 micrometres), counting can be done by optical microscopy, although other imaging techniques are used. The density of fossil tracks correlates with the cooling age of the sample and with uranium content, which needs to be determined independently.
To determine the uranium content, several methods have been used. One method is by neutron irradiation, where the sample is irradiated with thermal neutrons in a nuclear reactor, with an external detector, such as mica, affixed to the grain surface. The neutron irradiation induces fission of uranium-235 in the sample, and the resulting induced tracks are used to determine the uranium content of the sample because the U:U ratio is well known and assumed constant in nature. However, it is not always constant. To determine the number of induced fission events that occurred during neutron irradiation an external detector is attached to the sample and both sample and detector are simultaneously irradiated by thermal neutrons. The external detector is typically a low-uranium mica flake, but plastics such as CR-39 have also been used. The resulting induced fission of the uranium-235 in the sample creates induced tracks in the overlying external detector, which are later revealed by chemical etching. The ratio of spontaneous to induced tracks is proportional to the age.
Another method of determining uranium concentration is through LA-ICPMS, a technique where the crystal is hit with a laser beam and ablated, and then the material is passed through a mass spectrometer. | 1 | Fission Products + Nuclear Fission |
Alongside strontium, dietary calcium is deposited in bones teeth, however Ca is more readily deposited than Sr in humans and animals who consume primarily or exclusively plants. Therefore, the greater the Ca:Sr ratio in sample, the more herbivorous the animal was likely to be. | 0 | Isotopes |
If Germanium-75 is produced, it quickly decays to Arsenic. Germanium-76 is essentially stable, only decaying via extremely slow double beta decay to . | 1 | Fission Products + Nuclear Fission |
The 146 even-proton, even-neutron (EE) nuclides comprise ~58% of all stable nuclides and all have spin 0 because of pairing. There are also 24 primordial long-lived even-even nuclides. As a result, each of the 41 even-numbered elements from 2 to 82 has at least one stable isotope, and most of these elements have several primordial isotopes. Half of these even-numbered elements have six or more stable isotopes. The extreme stability of helium-4 due to a double pairing of 2 protons and 2 neutrons prevents any nuclides containing five (, ) or eight () nucleons from existing long enough to serve as platforms for the buildup of heavier elements via nuclear fusion in stars (see triple alpha process).
Only five stable nuclides contain both an odd number of protons and an odd number of neutrons. The first four "odd-odd" nuclides occur in low mass nuclides, for which changing a proton to a neutron or vice versa would lead to a very lopsided proton-neutron ratio (, , , and ; spins 1, 1, 3, 1). The only other entirely "stable" odd-odd nuclide, (spin 9), is thought to be the rarest of the 251 stable nuclides, and is the only primordial nuclear isomer, which has not yet been observed to decay despite experimental attempts.
Many odd-odd radionuclides (such as the ground state of tantalum-180) with comparatively short half-lives are known. Usually, they beta-decay to their nearby even-even isobars that have paired protons and paired neutrons. Of the nine primordial odd-odd nuclides (five stable and four radioactive with long half-lives), only is the most common isotope of a common element. This is the case because it is a part of the CNO cycle. The nuclides and are minority isotopes of elements that are themselves rare compared to other light elements, whereas the other six isotopes make up only a tiny percentage of the natural abundance of their elements. | 0 | Isotopes |
The United States government, often the Office of Civil Defense in the Department of Defense, provided guides to fallout protection in the 1960s, frequently in the form of booklets. These booklets provided information on how to best survive nuclear fallout. They also included instructions for various fallout shelters, whether for a family, a hospital, or a school shelter were provided. There were also instructions for how to create an improvised fallout shelter, and what to do to best increase a person's chances for survival if they were unprepared.
The central idea in these guides is that materials like concrete, dirt, and sand are necessary to shield a person from fallout particles and radiation. A significant amount of materials of this type are necessary to protect a person from fallout radiation, so safety clothing cannot protect a person from fallout radiation. However, protective clothing can keep fallout particles off a person's body, but the radiation from these particles will still permeate through the clothing. For safety clothing to be able to block the fallout radiation, it would have to be so thick and heavy that a person could not function.
These guides indicated that fallout shelters should contain enough resources to keep its occupants alive for up to two weeks. Community shelters were preferred over single-family shelters. The more people in a shelter, the greater quantity and variety of resources that shelter would be equipped with. These communities’ shelters would also help facilitate efforts to recuperate the community in the future. Single family shelters should be built below ground if possible. Many different types of fallout shelters could be made for a relatively small amount of money. A common format for fallout shelters was to build the shelter underground, with solid concrete blocks to act as the roof. If a shelter could only be partially underground, it was recommended to mound over that shelter with as much dirt as possible. If a house had a basement, it is best for a fallout shelter to be constructed in a corner of the basement. The center of a basement is where the most radiation will be because the easiest way for radiation to enter a basement is from the floor above. The two of the walls of the shelter in a basement corner will be the basement walls that are surrounded by dirt outside. Cinder blocks filled with sand or dirt were highly recommended for the other two walls. Concrete blocks, or some other dense material, should be used as a roof for a basement fallout shelter because the floor of a house is not an adequate roof for a fallout shelter. These shelters should contain water, food, tools, and a method for dealing with human waste.
If a person did not have a shelter previously built, these guides recommended trying to get underground. If a person had a basement but no shelter, they should put food, water, and a waste container in the corner of the basement. Then items such as furniture should be piled up to create walls around the person in the corner. If the underground cannot be reached, a tall apartment building at least ten miles from the blast was recommended as a good fallout shelter. People in these buildings should get as close to the center of the building as possible and avoid the top and ground floors.
Schools were preferred fallout shelters according to the Office of Civil Defense. Schools, not including universities, contained one-quarter of the population of the United States when they were in session at that time. Schools distribution across the nation reflected the density of the population and were often a best building in a community to act as a fallout shelter. Schools also already had organization with leaders set in place. The Office of Civil Defense recommended altering current schools and the construction of future schools to include thicker walls and roofs, better protected electrical systems, a purifying ventilation system, and a protected water pump. The Office of Civil Defense determined 10 square feet of net area per person were necessary in schools that were to function as a fallout shelter. A normal classroom could provide 180 people with area to sleep. If an attack were to happen, all the unnecessary furniture was to be moved out of the classrooms to make more room for people. It was recommended to keep one or two tables in the room if possible to use as a food-serving station.
The Office of Civil Defense conducted four case studies to find the cost of turning four standing schools into fallout shelters and what their capacity would be. The cost of the schools per occupant in the 1960s were $66.00, $127.00, $50.00, and $180.00. The capacity of people these schools could house as shelters were 735, 511, 484, and 460 respectively.
The US Department of Homeland Security and the Federal Emergency Management Agency in coordination with other agencies concerned with public protection in the aftermath of a nuclear detonation have developed more recent guidance documents that build on the older Civil Defense frameworks. Planning Guidance for Response to a Nuclear Detonation was published in 2022 and provided in-depth analysis and response planning for local government jurisdictions. | 1 | Fission Products + Nuclear Fission |
IAEA issues official certificates of isotopic composition for most new calibration materials. The IAEA has certified isotopic values for [https://nucleus.iaea.org/rpst/Documents/VSMOW2_SLAP2.pdf VSMOW2/SLAP2] and [https://nucleus.iaea.org/rpst/referenceproducts/ReferenceMaterials/Stable_Isotopes/13C18and7Li/IAEA-603/RM603_Reference_Sheet_2016-08-16.pdf IAEA-603] (the replacement for the NBS-19 CaCO standard). However, the isotopic composition of most reference materials distributed by IAEA are established in the scientific literature. For example, IAEA distributes the N isotope reference materials USGS34 (KNO) and USGS35 (NaNO), produced by a group of scientists at the USGS and reported in Böhlke et al. (2003), but has not certified the isotopic composition of these references. Moreover, the cited δN and δO values of these references were not reached through interlaboratory comparison. A second example is IAEA-SO-5, a BaSO reference material produced by R. Krouse and S. Halas and described in Halas & Szaran (2001). The value of this reference was reached through interlaboratory comparison but lacks IAEA certification. Other reference materials (LSVEV, IAEA-N3) were reached through interlaboratory comparison and are described by the IAEA but the status of their certification is unclear. | 0 | Isotopes |
The count of 251 known stable nuclides includes tantalum-180m, since even though its decay and instability is automatically implied by its notation of "metastable", this has still not yet been observed. All "stable" isotopes (stable by observation, not theory) are the ground states of nuclei, with the exception of tantalum-180m, which is a nuclear isomer or excited state. The ground state of this particular nucleus, tantalum-180, is radioactive with a comparatively short half-life of 8 hours; in contrast, the decay of the excited nuclear isomer is extremely strongly forbidden by spin-parity selection rules. It has been reported experimentally by direct observation that the half-life of Ta to gamma decay must be more than 10 years. Other possible modes of Ta decay (beta decay, electron capture, and alpha decay) have also never been observed. | 0 | Isotopes |
Doubly labeled water may be administered by injection, or orally (the usual route in humans). Since the isotopes will be diluted in body water, there is no need to administer them in a state of high isotopic purity, no need to employ water in which all or even most atoms are heavy atoms, or even to begin with water which is doubly labeled. It is also unnecessary to administer exactly one atom of O for every two atoms of deuterium. This matter in practice is governed by the economics of buying O enriched water, and the sensitivity of the mass-spectrographic equipment available.
In practice, doses of doubly labeled water for metabolic work are prepared by simply mixing a dose of deuterium oxide (heavy water) (90 to 99%) with a second dose of HO, which is water which has been separately enriched with O (though usually not to a high level, since doing this would be expensive, and unnecessary for this use), but otherwise contains normal hydrogen. The mixed water sample then contains both types of heavy atoms, in a far higher degree than normal water, and is now "doubly labeled." The free interchange of hydrogens between water molecules (via normal ionization) in liquid water ensures that the pools of oxygen and hydrogen in any sample of water (including the body's pool of water) will be separately equilibrated in a short time with any dose of added heavy isotope(s). | 0 | Isotopes |
Caesium-137, along with other radioactive isotopes caesium-134, iodine-131, xenon-133, and strontium-90, were released into the environment during nearly all nuclear weapon tests and some nuclear accidents, most notably the Chernobyl disaster and the Fukushima Daiichi disaster.
Caesium-137 in the environment is substantially anthropogenic (human-made). Caesium-137 is produced from the nuclear fission of plutonium and uranium, and decays into barium-137. By observing the characteristic gamma rays emitted by this isotope, one can determine whether the contents of a given sealed container were made before or after the first atomic bomb explosion (Trinity test, 16 July 1945), which spread some of it into the atmosphere, quickly distributing trace amounts of it around the globe. This procedure has been used by researchers to check the authenticity of certain rare wines, most notably the purported "Jefferson bottles". Surface soils and sediments are also dated by measuring the activity of Cs. | 1 | Fission Products + Nuclear Fission |
The concept of isotopes developed from radioactivity. The pioneering work on radioactivity by Henri Becquerel, Marie Curie and Pierre Curie was awarded the [https://www.nobelprize.org/nobel_prizes/physics/laureates/1903/ Nobel Prize in Physics in 1903]. Later Frederick Soddy would take radioactivity from physics to chemistry and shed light on the nature of isotopes, something with rendered him the [https://www.nobelprize.org/nobel_prizes/chemistry/laureates/1921/ Nobel Prize in Chemistry in 1921] (awarded in 1922).
The question of stable, non-radioactive isotopes was more difficult and required the development by Francis Aston of a high-resolution mass spectrograph, which allowed the separation of different stable isotopes of one and the same element. Francis Aston was awarded the [https://www.nobelprize.org/nobel_prizes/chemistry/laureates/1922/ 1922 Nobel Prize in Chemistry] for this achievement. With his enunciation of the whole-number rule, Aston solved a problem that had riddled chemistry for a hundred years. The understanding was that different isotopes of a given element would be chemically identical.
It was discovered in the 1930s by Harold Urey in 1932 (awarded the Nobel Prize in Chemistry in 1934). It was early on found that the deuterium content had a profound effect on chemistry and biochemistry.
In the linear approximation, the effect of isotopic substitution is proportional to the mass ratio of the heavy and light isotope. Thus chemical and biological effects of heavier isotopes of the “biological” atoms C, N and O are expected to be much smaller since the mass ratios for the normal to heavier isotopes are much closer to unity than the factor two for hydrogen to deuterium. However, it has been reported in 1930s, and then again in 1970s and 1990s, as well as recently, that relatively small changes in the content of the heavy isotope of hydrogen, deuterium, has profound effects on biological systems. These strong nonlinear effects could not be fully rationalized based on the known concepts of the isotopic effects. These and other observations make it possible that isotopes have a much more profound importance than could ever have been imagined by the pioneers.
In 2011 [http://chem1.mbb.ki.se/?page_id=10 Roman Zubarev] formulated the isotope resonance hypothesis. It originated in the following, unexpected observation. Define ΔM = M - M, where M is the monoisotopic mass (e.g. O = 15.994915 Da) and M is the nominal (integer) mass, i.e., the number of nucleons (e.g. O = 16). ΔM is a constant in the whole Universe. Define ΔM = M - M, where M is the average isotopic mass (e.g. O = 15.999 Da on Earth). Obviously ΔM depends on the precise isotopic composition for a given molecule. Finally define NMD = 1000ΔM/M and NIS = 1000ΔM/M, where NMD [in units of ‰] and NIS [in units of ‰] are the normalized isotopic defect and shift, respectively. If NIS is plotted as a function of NMD for a large number of terrestrial peptides, one would anticipate a homogenous distribution of data points (as in Fig. 1B). This is not what was found by Zubarev's team, instead they found band gap in the distribution with a narrow line in the middle (Fig. 1A).
This serendipitous discovery led Zubarev to formulate the isotope resonance hypothesis. | 0 | Isotopes |
After several years of cooling, most radioactivity is from the fission products caesium-137 and strontium-90, which are each produced in about 6% of fissions, and have half-lives of about 30 years. Other fission products with similar half-lives have much lower fission product yields, lower decay energy, and several (Sm, Eu, Cd) are also quickly destroyed by neutron capture while still in the reactor, so are not responsible for more than a tiny fraction of the radiation production at any time. Therefore, in the period from several years to several hundred years after use, radioactivity of spent fuel can be modeled simply as exponential decay of the Cs and Sr. These are sometimes known as medium-lived fission products.
Krypton-85, the 3rd most active MLFP, is a noble gas which is allowed to escape during current nuclear reprocessing; however, its inertness means that it does not concentrate in the environment, but diffuses to a uniform low concentration in the atmosphere. Spent fuel in the U.S. and some other countries is not likely to be reprocessed until decades after use, and by that time most of the Kr will have decayed. | 1 | Fission Products + Nuclear Fission |
Position-specific isotope analysis, also called site-specific isotope analysis, is a branch of isotope analysis aimed at determining the isotopic composition of a particular atom position in a molecule. Isotopes are elemental variants with different numbers of neutrons in their nuclei, thereby having different atomic masses. Isotopes are found in varying natural abundances depending on the element; their abundances in specific compounds can vary from random distributions (i.e., stochastic distribution) due to environmental conditions that act on the mass variations differently. These differences in abundances are called "fractionations," which are characterized via stable isotope analysis.
Isotope abundances can vary across an entire substrate (i.e., “bulk” isotope variation), specific compounds within a substrate (i.e., compound-specific isotope variation), or across positions within specific molecules (i.e., position specific isotope variation). Isotope abundances can be measured in a variety of ways (e.g., isotope ratio mass spectrometry, laser spectrometry, NMR, ESI-MS). Early analyses varied in technique, but were commonly limited by their ability to only measure average isotope compositions over molecules or samples. While this allows isotope analysis of the bulk substrate, it eliminates the ability to distinguish variation between different sites of the same element within the molecule. The field of position-specific isotope biogeochemistry studies these intramolecular variations, known as “position-specific isotope” and “site-specific isotope” enrichments. It focuses on position-specific isotope fractionations in many contexts, development of technologies to measure these fractionations and the application of position-specific isotope enrichments to questions surrounding biogeochemistry, microbiology, enzymology, medicinal chemistry, and earth history.
Position-specific isotope enrichments can retain critical information about synthesis and source of the atoms in the molecule. Indeed, bulk isotope analysis averages site-specific isotope effects across the molecule, and so while all those values have an influence on the bulk value, signatures of specific processes may be diluted or indistinguishable. While the theory of position-specific isotope analysis has existed for decades, new technologies exist now to allow these methods to be much more common. The potential applications of this approach are widespread, such as understanding metabolism in biomolecules, environmental pollutants in air, inorganic reaction mechanisms, etc. Clumped isotope analysis, a subset of position-specific isotope analysis, has already proven useful in characterizing sources of methane, paleoenvironment, paleoaltimetry, among many other applications. More specific case studies of position-specific isotope fractionation are detailed below. | 0 | Isotopes |
Carbon label is a form of isotopic labeling where a carbon-12 atom is replaced with either a stable carbon-13 atom or radioactive carbon-11 or carbon-14 atoms in a chemical compound so as to tag (i.e. label) that position of the compound to assist in determining the way a chemical reaction proceeds i.e. the reaction mechanism. | 0 | Isotopes |
Iodine-129 (I) is a long-lived radioisotope of iodine that occurs naturally but is also of special interest in the monitoring and effects of man-made nuclear fission products, where it serves as both a tracer and a potential radiological contaminant. | 1 | Fission Products + Nuclear Fission |
Antimony-125 decays with a half life of over two years to which itself decays with a half life of almost two months via isomeric transition to the ground state. While its relatively short half life and the significant gamma emissions (144.77 keV) of its daughter nuclide make usage in an RTG less attractive, Sb-125 could deliver a relatively high power density of 3.4 W/g.
Fluoride volatility can recover antimony as the mildly volatile (solid at room temperature) Antimony trifluoride or the more volatile (boiling point ) Antimony pentafluoride. | 1 | Fission Products + Nuclear Fission |
Human domination of the biosphere has threatened global biodiversity, with uncertain consequences for ecosystems that provide food, clean air and water, and other valuable ecosystem services. Understanding the impacts of biodiversity loss on ecosystem function requires knowledge of the interactions between organisms within both the same and different positions in a food web (i.e. trophic levels). Food webs can have very complex structures. In many ecosystems, organisms at trophic levels higher than herbivores consume a variable combination of prey and producers, exhibiting different forms of omnivory. The loss of predator species can have a cascading effect on all organisms at lower trophic levels. Networks with more omnivores that consume species at multiple trophic levels may be more resilient to these top-down effects. Together, these factors demonstrate that a food web's structure affects its sensitivity to reductions in biodiversity, highlighting the importance of food web studies. Amino acid isotopes are an important tool used in this field.
The abundance of N in some amino acids reflects an organisms position in a food web. This is due to the ways organisms metabolize different amino acids when they are consumed. Trophic amino acids (TrAAs) are first deaminated, meaning that the amino group is removed to produce an alpha-keto acid carbon skeleton. This reaction breaks a C-N bond, causing the amino acid to become more enriched in N due to a kinetic isotope effect. For instance, glutamate, a representative TrAA, has a δN value that increases by 8‰ with each trophic level. In contrast, the first reaction in the metabolism of source amino acids (SrcAAs) is not deamination. An example is phenylalanine, with is first converted to tyrosine in a reaction that breaks no C-N bonds. Thus, there is little variation in the δN values of SrcAAs between trophic levels. Their isotopic composition instead resembles that of the species at the base of the food web. Though these trends are conflated by some environmental effects, they have been used to infer an organisms trophic position. | 0 | Isotopes |
The most notable examples of mass-independent fractionation in nature are found in the isotopes of oxygen and sulfur. The first example was discovered by Robert N. Clayton, Toshiko Mayeda, and Lawrence Grossman in 1973, in the oxygen isotopic composition of refractory calcium–aluminium-rich inclusions in the Allende meteorite. The inclusions, thought to be among the oldest solid materials in the Solar System, show a pattern of low O/O and O/O relative to samples from the Earth and Moon. Both ratios vary by the same amount in the inclusions, although the mass difference between O and O is almost twice as large as the difference between O and O. Originally this was interpreted as evidence of incomplete mixing of O-rich material (created and distributed by a large star in a supernova) into the Solar nebula. However, recent measurement of the oxygen-isotope composition of the Solar wind, using samples collected by the Genesis spacecraft, shows that the most O-rich inclusions are close to the bulk composition of the solar system. This implies that Earth, the Moon, Mars, and asteroids all formed from O- and O-enriched material. Photodissociation of carbon monoxide in the Solar nebula has been proposed to explain this isotope fractionation.
Mass-independent fractionation also has been observed in ozone. Large, 1:1 enrichments of O/O and O/O in ozone were discovered in laboratory synthesis experiments by Mark Thiemens and John Heidenreich in 1983, and later found in stratospheric air samples measured by Konrad Mauersberger. These enrichments were eventually traced to the three-body ozone formation reaction.
:O + O → O* + M → O + M*
Theoretical calculations by Rudolph Marcus and others suggest that the enrichments are the result of a combination of mass-dependent and mass-independent kinetic isotope effects (KIE) involving the excited state O* intermediate related to some unusual symmetry properties. The mass-dependent isotope effect occurs in asymmetric species, and arises from the difference in zero-point energy of the two formation channels available (e.g., OO + O vs O + OO for formation of OOO.) These mass-dependent zero-point energy effects cancel one another out and do not affect the enrichment in heavy isotopes observed in ozone. The mass-independent enrichment in ozone is still not fully understood, but may be due to isotopically symmetric O* having a shorter lifetime than asymmetric O*, thus not allowing a statistical distribution of energy throughout all the degrees of freedom, resulting in a mass-independent distribution of isotopes. | 0 | Isotopes |
In 2012, a team of scientists used NMR spectroscopy to measure all of the position-specific carbon isotope abundances of glucose and other sugars. It was shown that the isotope abundances are heterogeneous. Different portions of the sugar molecules are used for biosynthesis based on the metabolic pathway an organism uses. Therefore, any interpretations of position-specific isotopes of molecules downstream of glucose have to consider this intramolecular heterogeneity.
Glucose is the monomer of cellulose, the polymer that makes plants and trees rigid. After the advent of position-specific analyses of glucose, biogeochemists from Sweden looked the concentric tree rings of a Pinus nigra that recorded yearly growth between 1961 and 1995. They digested the cellulose down to its glucose units and used NMR spectroscopy to analyze its intramolecular isotopic patterns. They found correlations with position-specific isotope enrichments that were not apparent with whole molecule carbon isotope analysis of glucose. By measuring position-specific enrichments in the 6-carbon glucose molecule, they gathered six times more information from the same sample. | 0 | Isotopes |
The proton:neutron ratio is not the only factor affecting nuclear stability. It depends also on evenness or oddness of its atomic number Z, neutron number N and, consequently, of their sum, the mass number A. Oddness of both Z and N tends to lower the nuclear binding energy, making odd nuclei, generally, less stable. This remarkable difference of nuclear binding energy between neighbouring nuclei, especially of odd-A isobars, has important consequences: unstable isotopes with a nonoptimal number of neutrons or protons decay by beta decay (including positron emission), electron capture, or other less common decay modes such as spontaneous fission and cluster decay.
Most stable nuclides are even-proton-even-neutron, where all numbers Z, N, and A are even. The odd-A stable nuclides are divided (roughly evenly) into odd-proton-even-neutron, and even-proton-odd-neutron nuclides. Stable odd-proton-odd-neutron nuclides are the least common. | 0 | Isotopes |
Ötzi is a Neolithic man who, in 1991, was found in an Alpine glacier between Austria and Italy. Ötzi is exceptionally well preserved since his body was dehydrated and encapsulated in glacial ice. Radiocarbon dating gave an age of approximately 5,200 years old. TIMS, ICP-MS and gas mass spectrometry have all been applied to the strontium, lead, and oxygen isotopes in Ötzis bones and teeth. His teeth indicated a likely birth and early childhood near to where the Eisack and Rienz rivers confluence. In his adulthood, however, Ötzis bones suggest that he moved to the lower Vinschgau and Etsch valley. More recent isotopic data, gathered from his gut contents, provides yet another timescale and hint that Ötzi's movement could be attributable to seasonal migration. | 0 | Isotopes |
I decays with a half-life of 8.02 days with beta minus and gamma emissions. This isotope of iodine has 78 neutrons in its nucleus, while the only stable nuclide, I, has 74. On decaying, I most often (89% of the time) expends its 971 keV of decay energy by transforming into stable xenon-131 in two steps, with gamma decay following rapidly after beta decay:
The primary emissions of I decay are thus electrons with a maximal energy of 606 keV (89% abundance, others 248–807 keV) and 364 keV gamma rays (81% abundance, others 723 keV). Beta decay also produces an antineutrino, which carries off variable amounts of the beta decay energy. The electrons, due to their high mean energy (190 keV, with typical beta-decay spectra present) have a tissue penetration of . | 1 | Fission Products + Nuclear Fission |
Non-mononuclidic elements are marked with an asterisk, and the long-lived primordial radioisotope given. In two cases (indium and rhenium), the most abundant naturally occurring isotope is the mildly radioactive one, and in the case of europium, nearly half of it is.
# Beryllium-9
# Fluorine-19
# Sodium-23
# Aluminium-27
# Phosphorus-31
# Scandium-45
# Vanadium-51* naturally occurs with 0.25% of radioactive vanadium-50
# Manganese-55
# Cobalt-59
# Arsenic-75
# Rubidium-85* naturally occurs with 27.835% of radioactive rubidium-87
# Yttrium-89
# Niobium-93
# Rhodium-103
# Indium-113* naturally occurs with majority (95.7%) radioactive isotope indium-115
# Iodine-127
# Caesium-133
# Lanthanum-139* naturally occurs with 0.09% radioactive lanthanum-138
# Praseodymium-141
# Europium-153* naturally occurs with 47.8% radioactive europium-151
# Terbium-159
# Holmium-165
# Thulium-169
# Lutetium-175* naturally occurs with 2.59% radioactive lutetium-176
# Rhenium-185* naturally occurs with majority (62.6%) radioactive isotope rhenium-187
# Gold-197 | 0 | Isotopes |
Before the isotopes can be separated and a ratio can be determined, the desired component of the tissue must be isolated. Such components include collagen, carbonate and apatite. Each component requires different means of isolation, and methods must be further specialised to account for the varied levels of decay and contamination which may occur as a result of taphonomy.
In the case of collagen, there are three main modes of isolation:
* Decalcification of small bone chunks in a 1-5% hydrochloric acid solution. If further decayed organic matter remains, a soak in 0.1 molar sodium hydroxide may be required. The isolated collagen is then freeze dried.
* Demineralisation of small bone chunks in sodium salt to separate collagen, which is then freeze-dried
* Demineralisation of powdered bone in 8% hydrochloric acid, slow hydrolysis in pH 3. If required, a further soak in 0.1 molar sodium hydroxide.
The latter is most effective in the instance of very poorly preserved bone, although it also faces an increased risk of contamination by other organic matter. Consequently, the supposedly isolated sample should be analysed and only tested if the readings fall within an acceptable range; most mass spectrometers now include a gas analyser as well as a combustion chamber to streamline this process. | 0 | Isotopes |
Meteorological conditions greatly influence fallout, particularly local fallout. Atmospheric winds are able to bring fallout over large areas. For example, as a result of a Castle Bravo surface burst of a 15 Mt thermonuclear device at Bikini Atoll on March 1, 1954, a roughly cigar-shaped area of the Pacific extending over 500 km downwind and varying in width to a maximum of 100 km was severely contaminated. There are three very different versions of the fallout pattern from this test, because the fallout was measured only on a small number of widely spaced Pacific Atolls. The two alternative versions both ascribe the high radiation levels at north Rongelap to a downwind hot spot caused by the large amount of radioactivity carried on fallout particles of about 50–100 micrometres size.
After Bravo, it was discovered that fallout landing on the ocean disperses in the top water layer (above the thermocline at 100 m depth), and the land equivalent dose rate can be calculated by multiplying the ocean dose rate at two days after burst by a factor of about 530. In other 1954 tests, including Yankee and Nectar, hot spots were mapped out by ships with submersible probes, and similar hot spots occurred in 1956 tests such as Zuni and Tewa.
However, the major U.S. "DELFIC" (Defence Land Fallout Interpretive Code) computer calculations use the natural size distributions of particles in soil instead of the afterwind sweep-up spectrum, and this results in more straightforward fallout patterns lacking the downwind hot spot.
Snow and rain, especially if they come from considerable heights, accelerate local fallout. Under special meteorological conditions, such as a local rain shower that originates above the radioactive cloud, limited areas of heavy contamination just downwind of a nuclear blast may be formed. | 1 | Fission Products + Nuclear Fission |
The effective neutron multiplication factor can be described using the product of six probability factors that describe a nuclear system. These factors, traditionally arranged chronologically with regards to the life of a neutron in a thermal reactor, include the probability of fast non-leakage , the fast fission factor , the resonance escape probability , the probability of thermal non-leakage , the thermal utilization factor , and the neutron reproduction factor (also called the neutron efficiency factor). The six-factor formula is traditionally written as follows:</blockquote>The factors are described as follows
* describes the probability that a fast neutron will not escape the system without interacting.
** The bounds of this factor are 0 and 1, with a value of 1 describing a system for which fast neutrons will never escape without interacting, i.e. an infinite system.
** Also written as
* is the ratio of total fissions to fissions caused only by thermal neutrons
** Fast neutrons have a small probability to cause fissions in uranium, specifically Uranium-238.
** The fast fission factor describes the contribution of fast fissions to the effective neutron multiplication factor
** The bounds of this factor are 1 and infinity, with a value of 1 describing a system for which only thermal neutrons are causing fissions. A value of 2 would denote a system in which thermal and fast neutrons are causing equal amounts of fissions.
* is the ratio of the number of neutrons that begin thermalization to the number of neutrons that reach thermal energies.
** Many isotopes have "resonances" in their capture cross-section curves that occur in energies between fast and thermal.
** If a neutron begins thermalization (i.e. begins to slow down), there is a possibility it will be absorbed by a non-multiplying material before it reaches thermal energy.
** The bounds of this factor are 0 and 1, with a value of 1 describing a system for which all fast neutrons that do not leak out and do not cause fast fissions eventually reach thermal energies.
* describes the probability that a thermal neutron will not escape the system without interacting.
** The bounds of this factor are 0 and 1, with a value of 1 describing a system for which thermal neutrons will never escape without interacting, i.e. an infinite system.
** Also written as
* is the ratio of number of thermal neutrons absorbed in by fissile nuclei versus the number of neutrons absorbed in all materials in the system.
** This factor describes the efficiency of thermal neutron utilization in the system, hence the name thermal utilization factor.
** The bounds of this factor are 0 and 1, with a value of 1 describing a system for which the entire system is made of fissile nuclei (i.e. thermal neutrons can only react with fissile materials). Similarly, a value of 0.5 describes a system for which reactions with fissile and non-fissile nuclei are equal.
** For a conventional nuclear power reactor, this factor is the only one that can be directly controlled by the operator. With manipulations to the control rods, you can increase the amount of neutrons being absorbed in non-fissile nuclei while simultaneously decreasing the amount of neutrons absorbed in fissile nuclei.
* describes the probability that a neutron absorbed will cause a fission reaction.
** This factor describes the behavior of the fissile material, specifically if a neutron is absorbed, how likely is it to cause a fission, and how many neutrons does the fission produce.
In an infinite medium, the multiplication factor may be described by the four factor formula, which is the same as described above with and both equal to 1. | 1 | Fission Products + Nuclear Fission |
Strontium-90 is a "bone seeker" that exhibits biochemical behavior similar to calcium, the next lighter group 2 element. After entering the organism, most often by ingestion with contaminated food or water, about 70–80% of the dose gets excreted. Virtually all remaining strontium-90 is deposited in bones and bone marrow, with the remaining 1% remaining in blood and soft tissues. Its presence in bones can cause bone cancer, cancer of nearby tissues, and leukemia. Exposure to Sr can be tested by a bioassay, most commonly by urinalysis.
The biological half-life of strontium-90 in humans has variously been reported as from 14 to 600 days, 1000 days, 18 years, 30 years and, at an upper limit, 49 years. The wide-ranging published biological half life figures are explained by strontium's complex metabolism within the body. However, by averaging all excretion paths, the overall biological half life is estimated to be about 18 years.
The elimination rate of strontium-90 is strongly affected by age and sex, due to differences in bone metabolism.
Together with the caesium isotopes Cs and Cs, and the iodine isotope I, it was among the most important isotopes regarding health impacts after the Chernobyl disaster.
As strontium has an affinity to the calcium-sensing receptor of parathyroid cells that is similar to that of calcium, the increased risk of liquidators of the Chernobyl power plant to suffer from primary hyperparathyroidism could be explained by binding of strontium-90. | 1 | Fission Products + Nuclear Fission |
The next table gives the terrestrial isotope distributions for some elements. Some elements, such as phosphorus and fluorine, only exist as a single isotope, with a natural abundance of 100%. | 0 | Isotopes |
The abundances of multiply substituted isotopologues can also be affected by kinetic processes. As for singly substituted isotopologues, departures from thermodynamic equilibrium in a doubly-substituted species can implicate the presence of a particular reaction taking place. Photochemistry occurring in the atmosphere has been shown to alter the abundance of O from equilibrium, as has photosynthesis. Measurements of CHD and CHD can identify microbial processing of methane and have been used to demonstrate the significance of quantum tunneling in the formation of methane, as well as mixing and equilibration of multiple methane reservoirs. Variations in the relative abundances of the two NO isotopologues NNO and NNO can distinguish whether NO has been produced by bacterial denitrification or by bacterial nitrification. | 0 | Isotopes |
Isotopic mass data from [http://physics.nist.gov/PhysRefData/Compositions/ Atomic Weights and Isotopic Compositions] ed. J. S. Coursey, D. J. Schwab and R. A. Dragoset, National Institute of Standards and Technology (2005). | 0 | Isotopes |
A common treatment method for preventing iodine-131 exposure is by saturating the thyroid with regular, stable iodine-127, as an iodide or iodate salt. | 1 | Fission Products + Nuclear Fission |
Nuclear fission weapons require a mass of fissile fuel that is prompt supercritical.
For a given mass of fissile material the value of k can be increased by increasing the density. Since the probability per distance travelled for a neutron to collide with a nucleus is proportional to the material density, increasing the density of a fissile material can increase k. This concept is utilized in the implosion method for nuclear weapons. In these devices, the nuclear chain reaction begins after increasing the density of the fissile material with a conventional explosive.
In the gun-type fission weapon, two subcritical pieces of fuel are rapidly brought together. The value of k for a combination of two masses is always greater than that of its components. The magnitude of the difference depends on distance, as well as the physical orientation.
The value of k can also be increased by using a neutron reflector surrounding the fissile material
Once the mass of fuel is prompt supercritical, the power increases exponentially. However, the exponential power increase cannot continue for long since k decreases when the amount of fission material that is left decreases (i.e. it is consumed by fissions). Also, the geometry and density are expected to change during detonation since the remaining fission material is torn apart from the explosion. | 1 | Fission Products + Nuclear Fission |
Caesium-137 reacts with water, producing a water-soluble compound (caesium hydroxide). The biological behaviour of caesium is similar to that of potassium and rubidium. After entering the body, caesium gets more or less uniformly distributed throughout the body, with the highest concentrations in soft tissue. However, unlike group 2 radionuclides like radium and strontium-90, caesium does not bioaccumulate and is excreted relatively quickly. The biological half-life of caesium is about 70 days.
A 1961 experiment showed that mice dosed with 21.5 μCi/g had a 50% fatality within 30 days (implying an LD of 245 μg/kg). A similar experiment in 1972 showed that when dogs are subjected to a whole body burden of 3800 μCi/kg (140 MBq/kg, or approximately 44 μg/kg) of caesium-137 (and 950 to 1400 rads), they die within 33 days, while animals with half of that burden all survived for a year. Important researches have shown a remarkable concentration of Cs in the exocrine cells of the pancreas, which are those most affected by cancer. In 2003, in autopsies performed on 6 children who died in the polluted area near Chernobyl (of reasons not directly linked to the Chernobyl disaster; mostly sepsis), where they also reported a higher incidence of pancreatic tumors, Bandazhevsky found a concentration of Cs 3.9 times higher than in their livers (1359 vs 347 Bq/kg, equivalent to 36 and 9.3 nCi/kg in these organs, 600 Bq/kg = 16 nCi/kg in the body according to measurements), thus demonstrating that pancreatic tissue is a strong accumulator and secretor in the intestine of radioactive cesium.
Accidental ingestion of caesium-137 can be treated with Prussian blue (Fe[Fe(CN)]), which binds to it chemically and reduces the biological half-life to 30 days. | 1 | Fission Products + Nuclear Fission |
Photodisintegration (also called phototransmutation) is a similar but different physical process, in which an extremely high energy gamma ray interacts with an atomic nucleus and causes it to enter an excited state, which immediately decays by emitting a subatomic particle. | 1 | Fission Products + Nuclear Fission |
A graph of fission product yield against the mass number of the fission fragments has two pronounced but fairly flat peaks, at around 90 to 100, and 130 to 140. With thermal neutrons, yields of fission products with mass between the peaks, such as Cd, Sn, Sn, Sn, Sb, Sn, and Sb are very low.
The higher the energy of the state that undergoes nuclear fission, the more likely a symmetric fission is, hence as the neutron energy increases and/or the energy of the fissioning atom increases, the valley between the two peaks becomes more shallow; for instance, the curve of yield against mass for Pu has a more shallow valley than that observed for U, when the neutrons are thermal neutrons. The curves for the fission of the later actinides tend to make even more shallow valleys. In extreme cases such as Fm, only one peak is seen. | 1 | Fission Products + Nuclear Fission |
Archaeological materials, such as bone, organic residues, hair, or sea shells, can serve as substrates for isotopic analysis. Carbon, nitrogen and zinc isotope ratios are used to investigate the diets of past people; these isotopic systems can be used with others, such as strontium or oxygen, to answer questions about population movements and cultural interactions, such as trade.
Carbon isotopes are analysed in archaeology to determine the source of carbon at the base of the foodchain. Examining the C/C isotope ratio, it is possible to determine whether animals and humans ate predominantly C3 or C4 plants. Potential C3 food sources include wheat, rice, tubers, fruits, nuts and many vegetables, while C4 food sources include millet and sugar cane. Carbon isotope ratios can also be used to distinguish between marine, freshwater, and terrestrial food sources.
Carbon isotope ratios can be measured in bone collagen or bone mineral (hydroxylapatite), and each of these fractions of bone can be analysed to shed light on different components of diet. The carbon in bone collagen is predominantly sourced from dietary protein, while the carbon found in bone mineral is sourced from all consumed dietary carbon, included carbohydrates, lipids, and protein.
Nitrogen isotopes can be used to infer soil conditions, with enriched δ15N used to infer the addition of manure. A complication is that enrichment also occurs as a result of environmental factors, such as wetland denitrification, salinity, aridity, microbes, and clearance.
To obtain an accurate picture of palaeodiets, it is important to understand processes of diagenesis that may affect the original isotopic signal. It is also important for the researcher to know the variations of isotopes within individuals, between individuals, and over time. | 0 | Isotopes |
The original carbon isotope reference material was a Belemnite fossil from the PeeDee Formation in South Carolina, known as the Pee Dee Belemnite (PDB). This PDB standard was rapidly consumed and subsequently researchers used replacement standards such as PDB II and PDB III. The carbon isotope reference frame was later established in Vienna against a hypothetical material called the Vienna Pee Dee Belemnite (VPDB). As with the original SMOW, VPDB never existed as a physical solution or solid. In order to make measurements researchers use the reference material NBS-19, colloquially known as the Toilet Seat Limestone, which has an isotopic ratio defined relative to the hypothetical VPDB. The exact origin of NBS-19 is unknown but it was a white marble slab and has a grain size of 200-300 micrometers. To improve the accuracy of carbon isotope measurements, in 2006 the δC scale was shifted from a one-point calibration against NBS-19 to a two point-calibration. In the new system the VPDB scale is pinned to both the LSVEC LiCO reference material and to the NBS-19 limestone (Coplen et al., 2006a; Coplen et al., 2006b). NBS-19 is now also exhausted and has been replaced with IAEA-603. | 0 | Isotopes |
While less rhodium than ruthenium and palladium is formed (around 3.6% yield), the mixture of fission products still contains a significant amount of this metal. Due to the high prices of ruthenium, rhodium, and palladium, some work has been done on the separation of these metals to enable them to be used at a later date. Because of the possibility of the metals being contaminated by radioactive isotopes, they are not suitable for making consumer products such as jewellery. However, this source of the metals could be used for catalysts in industrial plants such as petrochemical plants.
A dire example of people being exposed to radiation from contaminated jewellery occurred in the United States. It is thought that gold seeds used to contain radon were recycled into jewellery. The gold indeed did contain radioactive decay products of Rn.
Some other rhodium isotopes exist as "transitory states" of ruthenium decaying before further decaying towards stable isotopes of Palladium. If the low level radioactivity of Palladium (see below) is deemed excessive - for example for use as an investment or jewelry - either of its predecessors can be extracted from relatively "young" spent fuel and allowed to decay before extracting the stable end-product of the decay series. | 1 | Fission Products + Nuclear Fission |
Typical therapeutic doses of I-131 are between 2220 and 7400 megabecquerels (MBq). Because of this high radioactivity and because the exposure of stomach tissue to beta radiation would be high near an undissolved capsule, I-131 is sometimes administered to human patients in a small amount of liquid. Administration of this liquid form is usually by straw which is used to slowly and carefully suck up the liquid from a shielded container. For administration to animals (for example, cats with hyperthyroidism), for practical reasons the isotope must be administered by injection. European guidelines recommend administration of a capsule, due to "greater ease to the patient and the superior radiation protection for caregivers". | 1 | Fission Products + Nuclear Fission |
Isotope effects are recurring patterns in the partitioning of heavy and light isotopes across different chemical species or compounds, or between atomic sites within a molecule. These isotope effects can come about from a near infinite number of processes, but most of them can be narrowed down into two main categories, based on the nature of the chemical reaction creating or destroying the compound of interest:
(1) Kinetic isotope effects manifest in irreversible reactions, when one isotopologue is preferred in the transition state due to the lowest energy state. The preferred isotopologue will depend on whether the transition state of the molecule during a chemical reaction is more like the reactant or the product. Normal isotope effects are defined as those which partition the lighter isotope into the products of the reaction. Inverse isotope effects are less common as they preferentially partition the heavier isotope into the products.
(2) Equilibrium isotope effects manifest in reversible reactions, when molecules can exchange freely to reach the lowest possible energy state.
These variations can occur on a compound-specific level, but also on a position-specific level within a molecule. For instance, the carboxyl site of amino acids is exchangeable and therefore its carbon isotope signature can change over time and may not represent the original carbon source of the molecule. | 0 | Isotopes |
Photofission is a process in which a nucleus, after absorbing a gamma ray, undergoes nuclear fission and splits into two or more fragments.
The reaction was discovered in 1940 by a small team of engineers and scientists operating the Westinghouse Atom Smasher at the company's Research Laboratories in Forest Hills, Pennsylvania. They used a 5 MeV proton beam to bombard fluorine and generate high-energy photons, which then irradiated samples of uranium and thorium.
Gamma radiation of modest energies, in the low tens of MeV, can induce fission in traditionally fissile elements such as the actinides thorium, uranium, plutonium, and neptunium. Experiments have been conducted with much higher energy gamma rays, finding that the photofission cross section varies little within ranges in the low GeV range.
Baldwin et al made measurements of the yields of photo-fission in uranium and thorium together with a search for photo-fission in other heavy elements, using continuous x-rays from a 100-MeV betatron. Fission was detected in the presence of an intense background of x-rays by a differential ionization chamber and linear amplifier, the substance investigated being coated on an electrode of one chamber. They deduced the maximum cross section being of the order of 5×10 cm for uranium and half that for thorium. In the other elements studied, the cross section must be below 10 cm. | 1 | Fission Products + Nuclear Fission |
The danger of radiation from fallout also decreases rapidly with time due in large part to the exponential decay of the individual radionuclides. A book by Cresson H. Kearny presents data showing that for the first few days after the explosion, the radiation dose rate is reduced by a factor of ten for every seven-fold increase in the number of hours since the explosion. He presents data showing that "it takes about seven times as long for the dose rate to decay from 1000 roentgens per hour (1000 R/hr) to 10 R/hr (48 hours) as to decay from 1000 R/hr to 100 R/hr (7 hours)." This is a rule of thumb based on observed data, not a precise relation. | 1 | Fission Products + Nuclear Fission |
Due to redox-disequilibrium, selenium could be very reluctant to abiotic chemical reduction and would be released from the waste (spent fuel or vitrified waste) as selenate (), a soluble Se(VI) species, not sorbed onto clay minerals. Without solubility limit and retardation for aqueous selenium, the dose of Se is comparable to that of I. Moreover, selenium is an essential micronutrient as it is present in the catalytic centers in the glutathione peroxidase, an enzyme needed by many organisms for the protection of their cell membrane against oxidative stress damages; therefore, radioactive Se can be easily bioconcentrated in the food web. In the presence of nitrate () released in deep geological clay formations by bituminized waste issued from the spent fuel dissolution step during their reprocessing, even reduced forms of selenium could be easily oxidised and mobilised. | 1 | Fission Products + Nuclear Fission |
During detonations of devices at ground level (surface burst), below the fallout-free altitude, or in shallow water, heat vaporizes large amounts of earth or water, which is drawn up into the radioactive cloud. This material becomes radioactive when it combines with fission products or other radio-contaminants, or when it is neutron-activated.
The table below summarizes the abilities of common isotopes to form fallout. Some radiation taints large amounts of land and drinking water causing formal mutations throughout animal and human life.
A surface burst generates large amounts of particulate matter, composed of particles from less than 100 nm to several millimeters in diameter—in addition to very fine particles that contribute to worldwide fallout. The larger particles spill out of the stem and cascade down the outside of the fireball in a downdraft even as the cloud rises, so fallout begins to arrive near ground zero within an hour. More than half the total bomb debris lands on the ground within about 24 hours as local fallout. Chemical properties of the elements in the fallout control the rate at which they are deposited on the ground. Less volatile elements deposit first.
Severe local fallout contamination can extend far beyond the blast and thermal effects, particularly in the case of high yield surface detonations. The ground track of fallout from an explosion depends on the weather from the time of detonation onward. In stronger winds, fallout travels faster but takes the same time to descend, so although it covers a larger path, it is more spread out or diluted. Thus, the width of the fallout pattern for any given dose rate is reduced where the downwind distance is increased by higher winds. The total amount of activity deposited up to any given time is the same irrespective of the wind pattern, so overall casualty figures from fallout are generally independent of winds. But thunderstorms can bring down activity as rain allows fallout to drop more rapidly, particularly if the mushroom cloud is low enough to be below ("washout"), or mixed with ("rainout"), the thunderstorm.
Whenever individuals remain in a radiologically contaminated area, such contamination leads to an immediate external radiation exposure as well as a possible later internal hazard from inhalation and ingestion of radiocontaminants, such as the rather short-lived iodine-131, which is accumulated in the thyroid. | 1 | Fission Products + Nuclear Fission |
The position-specific isotope effect of an enzymatic reaction is expressed as the ratio of rate constants for a monoisotopic substrate and a substrate substituted with one rare isotope. For example, enzyme formate dehydrogenase catalyzes the reaction of formate and NAD+ to carbon dioxide and NADH. The hydrogen of formate is directly transferred to NAD+. This step has an isotope effect, because the rate of protium transfer from formate to NAD+ is nearly three times faster than the rate of the same reaction with a deuterium transfer. This is also an example of a primary isotope effect. A primary isotope effect is one in which the rare isotope is substituted where a bond is broken or formed. Secondary isotope effects occur on other positions in the molecule and are controlled by the molecular geometry of the transition state. These are generally considered to be negligible but do arise in certain cases, especially for hydrogen isotopes.
Unlike abiotic reactions, enzymatic reactions occur through a series of steps, including substrate-enzyme binding, conversion of substrate to product, and dissociation of enzyme-product complex. The observed isotope effect of an enzyme will be controlled by the rate limiting step in this mechanism. If the step that converts substrate to product is rate limiting, the enzyme will express its intrinsic isotope effect, that of the bond forming or breaking reaction. | 0 | Isotopes |
On scales greater than 10 years, fission products, chiefly Tc, again represent a significant proportion of the remaining, though lower radioactivity, along with longer-lived actinides like neptunium-237 and plutonium-242, if those have not been destroyed.
The most abundant long-lived fission products have total decay energy around 100–300 keV, only part of which appears in the beta particle; the rest is lost to a neutrino that has no effect. In contrast, actinides undergo multiple alpha decays, each with decay energy around 4–5 MeV.
Only seven fission products have long half-lives, and these are much longer than 30 years, in the range of 200,000 to 16 million years. These are known as long-lived fission products (LLFP). Three have relatively high yields of about 6%, while the rest appear at much lower yields. (This list of seven excludes isotopes with very slow decay and half-lives longer than the age of the universe, which are effectively stable and already found in nature, as well as a few nuclides like technetium-98 and samarium-146 that are "shadowed" from beta decay and can only occur as direct fission products, not as beta decay products of more neutron-rich initial fission products. The shadowed fission products have yields on the order of one millionth as much as iodine-129.) | 1 | Fission Products + Nuclear Fission |
Krypton-85 is produced in small quantities by the interaction of cosmic rays with stable krypton-84 in the atmosphere. Natural sources maintain an equilibrium inventory of about 0.09 PBq in the atmosphere. | 1 | Fission Products + Nuclear Fission |
If a graph of the mass or mole yield of fission products against the atomic number of the fragments is drawn then it has two peaks, one in the area zirconium through to palladium and one at xenon through to neodymium. This is because the fission event causes the nucleus to split in an asymmetric manner, as nuclei closer to magic numbers are more stable.
Yield vs. Z - This is a typical distribution for the fission of uranium. Note that in the calculations used to make this graph the activation of fission products was ignored and the fission was assumed to occur in a single moment rather than a length of time. In this bar chart results are shown for different cooling times (time after fission).
Because of the stability of nuclei with even numbers of protons and/or neutrons the curve of yield against element is not a smooth curve. It tends to alternate.
In general, the higher the energy of the state that undergoes nuclear fission, the more likely a symmetric fission is, hence as the neutron energy increases and/or the energy of the fissile atom increases, the valley between the two peaks becomes more shallow; for instance, the curve of yield against mass for Pu-239 has a more shallow valley than that observed for U-235, when the neutrons are thermal neutrons. The curves for the fission of the later actinides tend to make even more shallow valleys. In extreme cases such as Fm, only one peak is seen.
Yield is usually expressed relative to number of fissioning nuclei, not the number of fission product nuclei, that is, yields should sum to 200%.
The table in the next section ("Ordered by yield") gives yields for notable radioactive (with half-lives greater than one year, plus iodine-131) fission products, and (the few most absorptive) neutron poison fission products, from thermal neutron fission of U-235 (typical of nuclear power reactors), computed from [http://books.elsevier.com/companions/075067136X/pdfs/Yield.bas?mscssid=HAX80JCKT7RB8LS6F675GU2LM83N1CL6].
The yields in the table sum to only 45.5522%, including 34.8401% which have half-lives greater than one year:
The remainder and the unlisted 54.4478% decay with half-lives less than one year into nonradioactive nuclei.
This is before accounting for the effects of any subsequent neutron capture; e.g.:
* Xe capturing a neutron and becoming nearly stable Xe, rather than decaying to Cs which is radioactive with a half-life of 2.3 million years
* Nonradioactive Cs capturing a neutron and becoming Cs, which is radioactive with a half-life of 2 years
* Many of the fission products with mass 147 or greater such as Pm, Sm, Sm, and Eu have significant cross sections for neutron capture, so that one heavy fission product atom can undergo multiple successive neutron captures.
Besides fission products, the other types of radioactive products are
* plutonium containing Pu, Pu, Pu, Pu, and Pu,
* minor actinides including Np, Am, Am, curium isotopes, and perhaps californium
* reprocessed uranium containing U and other isotopes
* tritium
* activation products of neutron capture by the reactor or bomb structure or the environment | 1 | Fission Products + Nuclear Fission |
There are two main considerations for the location of an explosion: height and surface composition. A nuclear weapon detonated in the air, called an air burst, produces less fallout than a comparable explosion near the ground. A nuclear explosion in which the fireball touches the ground pulls soil and other materials into the cloud and neutron activates it before it falls back to the ground. An air burst produces a relatively small amount of the highly radioactive heavy metal components of the device itself.
In case of water surface bursts, the particles tend to be rather lighter and smaller, producing less local fallout but extending over a greater area. The particles contain mostly sea salts with some water; these can have a cloud seeding effect causing local rainout and areas of high local fallout. Fallout from a seawater burst is difficult to remove once it has soaked into porous surfaces because the fission products are present as metallic ions that chemically bond to many surfaces. Water and detergent washing effectively removes less than 50% of this chemically bonded activity from concrete or steel. Complete decontamination requires aggressive treatment like sandblasting, or acidic treatment. After the Crossroads underwater test, it was found that wet fallout must be immediately removed from ships by continuous water washdown (such as from the fire sprinkler system on the decks).
Parts of the sea bottom may become fallout. After the Castle Bravo test, white dust—contaminated calcium oxide particles originating from pulverized and calcined corals—fell for several hours, causing beta burns and radiation exposure to the inhabitants of the nearby atolls and the crew of the Daigo Fukuryū Maru fishing boat. The scientists called the fallout Bikini snow.
For subsurface bursts, there is an additional phenomenon present called "base surge". The base surge is a cloud that rolls outward from the bottom of the subsiding column, which is caused by an excessive density of dust or water droplets in the air. For underwater bursts, the visible surge is, in effect, a cloud of liquid (usually water) droplets with the property of flowing almost as if it were a homogeneous fluid. After the water evaporates, an invisible base surge of small radioactive particles may persist.
For subsurface land bursts, the surge is made up of small solid particles, but it still behaves like a fluid. A soil earth medium favors base surge formation in an underground burst. Although the base surge typically contains only about 10% of the total bomb debris in a subsurface burst, it can create larger radiation doses than fallout near the detonation, because it arrives sooner than fallout, before much radioactive decay has occurred. | 1 | Fission Products + Nuclear Fission |
Each fission of a parent atom produces a different set of fission product atoms. However, while an individual fission is not predictable, the fission products are statistically predictable. The amount of any particular isotope produced per fission is called its yield, typically expressed as percent per parent fission; therefore, yields total to 200%, not 100%. (The true total is in fact slightly greater than 200%, owing to rare cases of ternary fission.)
While fission products include every element from zinc through the lanthanides, the majority of the fission products occur in two peaks. One peak occurs at about (expressed by atomic masses 85 through 105) strontium to ruthenium while the other peak is at about tellurium to neodymium (expressed by atomic masses 130 through 145). The yield is somewhat dependent on the parent atom and also on the energy of the initiating neutron.
In general the higher the energy of the state that undergoes nuclear fission, the more likely that the two fission products have similar mass. Hence, as the neutron energy increases and/or the energy of the fissile atom increases, the valley between the two peaks becomes more shallow.
For instance, the curve of yield against mass for Pu has a more shallow valley than that observed for U when the neutrons are thermal neutrons. The curves for the fission of the later actinides tend to make even more shallow valleys. In extreme cases such as Fm, only one peak is seen; this is a consequence of symmetric fission becoming dominant due to shell effects.
The adjacent figure shows a typical fission product distribution from the fission of uranium. Note that in the calculations used to make this graph, the activation of fission products was ignored and the fission was assumed to occur in a single moment rather than a length of time. In this bar chart results are shown for different cooling times (time after fission).
Because of the stability of nuclei with even numbers of protons and/or neutrons, the curve of yield against element is not a smooth curve but tends to alternate. Note that the curve against mass number is smooth. | 1 | Fission Products + Nuclear Fission |
Xenon-135 (Xe) is an unstable isotope of xenon with a half-life of about 9.2 hours. Xe is a fission product of uranium and it is the most powerful known neutron-absorbing nuclear poison (2 million barns; up to 3 million barns under reactor conditions), with a significant effect on nuclear reactor operation. The ultimate yield of xenon-135 from fission is 6.3%, though most of this is from fission-produced tellurium-135 and iodine-135. | 1 | Fission Products + Nuclear Fission |
Krypton-85 is used in arc discharge lamps commonly used in the entertainment industry for large HMI film lights as well as high-intensity discharge lamps. The presence of krypton-85 in discharge tube of the lamps can make the lamps easy to ignite. Early experimental krypton-85 lighting developments included a railroad signal light designed in 1957 and an illuminated highway sign erected in Arizona in 1969. A 60 μCi (2.22 MBq) capsule of krypton-85 was used by the random number server HotBits (an allusion to the radioactive element being a quantum mechanical source of entropy), but was replaced with a 5 μCi (185 kBq) Cs-137 source in 1998.
Krypton-85 is also used to inspect aircraft components for small defects. Krypton-85 is allowed to penetrate small cracks, and then its presence is detected by autoradiography. The method is called "krypton gas penetrant imaging". The gas penetrates smaller openings than the liquids used in dye penetrant inspection and fluorescent penetrant inspection.
Krypton-85 was used in cold-cathode voltage regulator electron tubes, such as the type 5651.
Krypton-85 is also used for Industrial Process Control mainly for thickness and density measurements as an alternative to Sr-90 or Cs-137.
Krypton-85 is also used as a charge neutralizer in aerosol sampling systems. | 1 | Fission Products + Nuclear Fission |
Because many isotopic reference materials are defined relative to one another using the δ notation, there are few constraints on the absolute isotopic ratios of reference materials. For dual-inlet and continuous flow mass spectrometry uncertainty in the raw isotopic ratio is acceptable because samples are often measured through multi-collection and then compared directly with standards, with data in the published literature reported relative to the primary reference materials. In this case the actual measurement is of an isotope ratio and is rapidly converted to a ratio or ratios so the absolute isotope ratio is only minimally important for attaining high-accuracy measurements. However, the uncertainty in the raw isotopic ratio of reference materials is problematic for applications that do not directly measure mass-resolved ion beams. Measurements of isotope ratios through laser spectroscopy or nuclear magnetic resonance are sensitive to the absolute abundance of isotopes and uncertainty in the absolute isotopic ratio of a standard can limit measurement accuracy. It is possible that these techniques will ultimately be used to refine the isotope ratios of reference materials. | 0 | Isotopes |
Most naturally occurring nuclides are stable (about 251; see list at the end of this article), and about 35 more (total of 286) are known to be radioactive with sufficiently long half-lives (also known) to occur primordially. If the half-life of a nuclide is comparable to, or greater than, the Earth's age (4.5 billion years), a significant amount will have survived since the formation of the Solar System, and then is said to be primordial. It will then contribute in that way to the natural isotopic composition of a chemical element. Primordially present radioisotopes are easily detected with half-lives as short as 700 million years (e.g., U). This is the present limit of detection, as shorter-lived nuclides have not yet been detected undisputedly in nature except when recently produced, such as decay products or cosmic ray spallation.
Many naturally occurring radioisotopes (another 53 or so, for a total of about 339) exhibit still shorter half-lives than 700 million years, but they are made freshly, as daughter products of decay processes of primordial nuclides (for example, radium from uranium) or from ongoing energetic reactions, such as cosmogenic nuclides produced by present bombardment of Earth by cosmic rays (for example, C made from nitrogen).
Some isotopes that are classed as stable (i.e. no radioactivity has been observed for them) are predicted to have extremely long half-lives (sometimes as high as 10 years or more). If the predicted half-life falls into an experimentally accessible range, such isotopes have a chance to move from the list of stable nuclides to the radioactive category, once their activity is observed. For example, Bi and W were formerly classed as stable, but were found to be alpha-active in 2003. However, such nuclides do not change their status as primordial when they are found to be radioactive.
Most stable isotopes on Earth are believed to have been formed in processes of nucleosynthesis, either in the Big Bang, or in generations of stars that preceded the formation of the Solar System. However, some stable isotopes also show abundance variations in the earth as a result of decay from long-lived radioactive nuclides. These decay-products are termed radiogenic isotopes, in order to distinguish them from the much larger group of non-radiogenic isotopes. | 0 | Isotopes |
On Friday, April 5 an emergency regime was introduced in the Russian city of Khabarovsk after a local resident accidentally discovered that radiation levels had jumped sharply in one of the industrial areas of the city. According to volunteers of the dosimetric control group, the dosimeter at the NP site showed up to 800 microsieverts, which is 1600 times the safe value.
Employees of the Ministry of Emergency Situations fenced of the area of 30 by 30 meters, where they found a capsule with cesium from a defectoscope. The find was placed in a protective container and taken away for disposal. This was first reported by the Novaya Gazeta. [https://tsn.ua/svit/nadzvichayna-situaciya-u-habarovsku-radiaciyniy-fon-u-1600-raziv-perevischiv-normu-2551414.html Source] | 1 | Fission Products + Nuclear Fission |
Craig observed that δO and δH isotopic composition of cold meteoric water from sea ice in the Arctic and Antarctica are much more negative than that in warm meteoric water from the tropic. A correlation between temperature (T) and δO was proposed later in the 1970s. Such correlation is then applied to study surface temperature change over time. The δO composition in ancient meteoric water, preserved in ice cores, can also be collected and applied to reconstruct paleoclimate.
A meteoric water line can be calculated for a given area, named as local meteoric water line (LMWL), and used as a baseline within that area. Local meteoric water line can differ from the global meteoric water line in slope and intercept. Such deviated slope and intercept is a result largely from humidity. In 1964, the concept of deuterium excess d (d=δH - 8δO) was proposed. Later, a parameter of deuterium excess as a function of humidity has been established, as such the isotopic composition in local meteoric water can be applied to trace local relative humidity, study local climate and used as a tracer of climate change.
In hydrogeology, the δO and δH composition in groundwater are often used to study the origin of groundwater and groundwater recharge.
Recently it has been shown that, even taking into account the standard deviation related to instrumental errors and the natural variability of the amount-weighted precipitations, the LMWL calculated with the EIV (error in variable regression) method has no differences on the slope compared to classic OLSR (ordinary least square regression) or other regression methods. However, for certain purposes such as the evaluation of the shifts from the line of the geothermal waters, it would be more appropriate to calculate the so-called "prediction interval" or "error wings" related to LMWL. | 0 | Isotopes |
When a light isotope is replaced with a heavy isotope (e.g., C for C), the bond between the two atoms will vibrate more slowly, thereby lowering the zero-point energy of the bond and acting to stabilize the molecule. An isotopologue with a doubly substituted bond is therefore slightly more thermodynamically stable, which will tend to produce a higher abundance of the doubly substituted (or “clumped”) species than predicted by the statistical abundance of each heavy isotope (known as a stochastic distribution of isotopes). This effect increases in magnitude with decreasing temperature, so the abundance of the clumped species is related to the temperature at which the gas was formed or equilibrated. By measuring the abundance of the clumped species in standard gases formed in equilibrium at known temperatures, the thermometer can be calibrated and applied to samples with unknown abundances. | 0 | Isotopes |
The Orbitrap is a high-resolution Fourier transform mass spectrometer that has recently been adapted to allow for site-specific analyses. Molecules introduced into the Orbitrap are fragmented, accelerated, and analyzed. Because the Orbitrap characterizes molecular masses by measuring oscillations at radio frequencies, it is able to reach very high levels of precision, depending on measurement method (i.e., down to 0.1 per mille for long integration times). It is significantly faster than site-specific isotope measurements that can be performed using NMR, and can measure molecules with different rare isotopes but the same nominal mass at natural abundances (unlike GC and LCMS). It is also widely generalizable to molecules that can be introduced via gas or liquid solvent. Resolution of the Orbitrap is such that nominal isobars (e.g., H versus N versus C enrichments) can be distinguished from one another, and so molecules do not need to be converted into a homogeneous substrate to facilitate isotope analysis. Like other isotope measurements, measurements of site-specific enrichments on the Orbitrap should be compared to a standard of known composition. | 0 | Isotopes |
Actinides with odd neutron number are generally fissile (with thermal neutrons), whereas those with even neutron number are generally not, though they are fissionable with fast neutrons. All observationally stable odd-odd nuclides have nonzero integer spin. This is because the single unpaired neutron and unpaired proton have a larger nuclear force attraction to each other if their spins are aligned (producing a total spin of at least 1 unit), instead of anti-aligned. See deuterium for the simplest case of this nuclear behavior.
Only , , and have odd neutron number and are the most naturally abundant isotope of their element. | 0 | Isotopes |
Xe isotopes are also promising in tracing mantle dynamics in Earths evolution. The first explicit recognition of non-atmospheric Xe in terrestrial samples came from the analysis of CO-well gas in New Mexico, displaying an excess of I-derived or primitive source Xe and high content in Xe due to the decay of U. At present, the excess of Xe and Xe has been widely observed in mid-ocean ridge basalt (MORBs) and Oceanic island basalt (OIBs). Because Xe receives more fissiogenic contribution than other heavy Xe isotopes, Xe (decay of I) and Xe are usually normalized to Xe when discussing Xe isotope trends of different mantle sources. MORBs Xe/Xe and Xe/Xe ratios lie on a trend from atmospheric ratios to higher values and seemingly contaminated by the air. Oceanic island basalt (OIBs) data lies lower than those in MORBs, implying different Xe sources for OIBs and MORBs.
The deviations in Xe/Xe ratio between air and MORBs show that mantle degassing occurred before I was extinct, otherwise Xe/Xe in the air would be the same as in the mantle. The differences in the Xe/Xe ratio between MORBs and OIBs may indicate that the mantle reservoirs are still not thoroughly mixed. The chemical differences between OIBs and MORBs still await discovery.
To obtain mantle Xe isotope ratios, it is necessary to remove contamination by atmospheric Xe, which could start before 2.5 billion years ago. Theoretically, the many non-radiogenic isotopic ratios (Xe/Xe, Xe/Xe, and Xe/Xe) can be used to accurately correct for atmospheric contamination if slight differences between air and mantle can be precisely measured. Still, we cannot reach such precision with current techniques. | 0 | Isotopes |
Several applications exist that capitalize on the properties of the various isotopes of a given element. Isotope separation is a significant technological challenge, particularly with heavy elements such as uranium or plutonium. Lighter elements such as lithium, carbon, nitrogen, and oxygen are commonly separated by gas diffusion of their compounds such as CO and NO. The separation of hydrogen and deuterium is unusual because it is based on chemical rather than physical properties, for example in the Girdler sulfide process. Uranium isotopes have been separated in bulk by gas diffusion, gas centrifugation, laser ionization separation, and (in the Manhattan Project) by a type of production mass spectrometry. | 0 | Isotopes |
The doubly labeled water method is particularly useful for measuring average metabolic rate (field metabolic rate) over relatively long periods of time (a few days or weeks), in subjects for which other types of direct or indirect calorimetric measurements of metabolic rate would be difficult or impossible. For example, the technique can measure the metabolism of animals in the wild state, with the technical problems being related mainly to how to administer the dose of isotope, and collect several samples of body water at later times to check for differential isotope elimination.
Most animal studies involve capturing the subject animals and injecting them, then holding them for a variable period before the first blood sample has been collected. This period depends on the size of the animal involved and varies between 30 minutes for very small animals to 6 hours for much larger animals. In both animals and humans, the test is made more accurate if a single determination of respiratory quotient has been made for the organism eating the standard diet at the time of measurement, since this value changes relatively little (and more slowly) compared with the much larger metabolic rate changes related to thermoregulation and activity.
Because the heavy hydrogen and oxygen isotopes used in the standard doubly labeled water measurement are non-radioactive, and also non-toxic in the doses used (see heavy water), the doubly labeled water measurement of mean metabolic rate has been used extensively in human volunteers, and even in infants and pregnant women. The technique has been used on over 200 species of wild animals (mostly birds, mammals and some reptiles). Applications of the method to animals have been reviewed. A paper by Pontzer, Yamada, Sagayama and colleagues in 2021 summarized the results of over 6400 measurements using the technique in humans aged between 8 days and 96 years old.
Doubly labeled water (HO) can also be used for unusually warm ice and unusually dense water, as it has a higher melting point than and is denser than either light water or what is normally meant by "heavy water" (HO). HO melts at 4.00~4.04 °C (39.2 °F~39.27 °F) and the liquid reaches its maximum density of 1.21684~1.21699 g/cm at 11.43~11.49 °C (52.57 °F~52.68 °F). | 0 | Isotopes |
Nuclear fission produces fission products, as well as actinides from nuclear fuel nuclei that capture neutrons but fail to fission, and activation products from neutron activation of reactor or environmental materials. | 1 | Fission Products + Nuclear Fission |
A monoisotopic element is an element which has only a single stable isotope (nuclide). There are 26 such elements, as listed.
Stability is experimentally defined for chemical elements, as there are a number of stable nuclides with atomic numbers over ~40 which are theoretically unstable, but apparently have half-lives so long that they have not been observed either directly or indirectly (from measurement of products) to decay.
Monoisotopic elements are characterized, except in one case, by odd numbers of protons (odd Z), and even numbers of neutrons. Because of the energy gain from nuclear pairing, the odd number of protons imparts instability to isotopes of an odd Z, which in heavier elements requires a completely paired set of neutrons to offset this tendency into stability. (The five stable nuclides with odd Z and odd neutron numbers are hydrogen-2, lithium-6, boron-10, nitrogen-14, and tantalum-180m1.)
The single monoisotopic exception to the odd Z rule is beryllium; its single stable, primordial isotope, beryllium-9, has 4 protons and 5 neutrons. This element is prevented from having a stable isotope with equal numbers of neutrons and protons (beryllium-8, with 4 of each) by its instability toward alpha decay, which is favored due to the extremely tight binding of helium-4 nuclei. It is prevented from having a stable isotope with 4 protons and 6 neutrons by the very large mismatch in proton/neutron ratio for such a light element. (Nevertheless, beryllium-10 has a half-life of 1.36 million years, which is too short to be primordial, but still indicates unusual stability for a light isotope with such an imbalance.) | 0 | Isotopes |
Some fission products decay with the release of delayed neutrons, important to nuclear reactor control.
Other fission products, such as xenon-135 and samarium-149, have a high neutron absorption cross section. Since a nuclear reactor must balance neutron production and absorption rates, fission products that absorb neutrons tend to "poison" or shut the reactor down; this is controlled with burnable poisons and control rods. Build-up of xenon-135 during shutdown or low-power operation may poison the reactor enough to impede restart or interfere with normal control of the reaction during restart or restoration of full power. This played a major role in the Chernobyl disaster. | 1 | Fission Products + Nuclear Fission |
On December 11, 2008, the DOE-SC announced the selection of Michigan State University to design and establish FRIB.
The project earned Critical Decision 1 (CD-1) approval in September 2010 which established a preferred alternative and the associated established cost and schedule ranges.
On August 1, 2013, DOE-SC approved the project baseline (CD-2) and the start of civil construction (CD-3a), pending a notice to proceed. Civil construction could not start under the continuing appropriations resolution, which disallowed new construction starts.
On February 25, 2014, the board of the Michigan Strategic Fund met at Michigan State University and approved nearly $91 million to support the construction of FRIB.
The FRIB marked the official start of civil construction with a groundbreaking ceremony March 17, 2014. In attendance were representatives from the Michigan delegation, State of Michigan, Michigan State University, and the U.S. Department of Energy Office of Science. Technical construction started in October 2014, following a CD-3b approval by DOE-SC.
In March 2017, FRIB achieved beneficial occupancy of civil construction, and technical installation activities escalated as a result.
In February 2019, FRIB accelerated beams through the first 15 (of 46 total) cryomodules to 10 percent of FRIB's final beam energy. In August 2019, the radio-frequency quadrupole (RFQ) was conditioned above 100 kW, the CW power needed to achieve the FRIB mission goal of accelerating uranium beams. The RFQ prepares the beam for further acceleration in the linac.
Construction on two MSU-funded building additions was substantially completed in January 2020. The Cryogenic Assembly Building will be used for cryomodule maintenance and to perform cryogenic-engineering research. The High Rigidity Spectrometer and Isotope Harvesting Vault will house isotope-harvesting research equipment and provide space for experiments.
In March 2020, FRIB accelerated an argon-36 beam through 37 of 46 superconducting cryomodules to 204 MeV/nucleon or 57 percent of the speed of light.
In September 2020, DOE designated FRIB as a DOE-SC User Facility. U.S. Secretary of Energy Dan Brouillette announced the designation at a special ceremony held outdoors at MSU, under a tent adjacent to FRIB.
On February 24, 2021, the FRIB announced that 82 proposals requesting 9,784 hours of beam time and six letters of intent were submitted, covering 16 of the 17 National Academies benchmarks for FRIB, in response to their first call for proposals. These proposals represent FRIB's international user community of more than 1,500 scientists. Respondents include 597 individual scientists, 354 of whom are from the United States. They represent 130 institutions in 30 countries and 26 U.S. states.
On January 25, 2022, the FRIB project team delivered the first heavy-ion beam to the focal plane of the FRIB fragment separator, marking technical completion of the FRIB project.
On February 1–2, 2022, a review by the DOE-SC Office of Project Assessment reviewed FRIB's readiness for project completion and recommended that FRIB is ready for Critical Decision 4 (Approve Project Completion).
Michigan State University announced a ribbon-cutting ceremony for May 2, 2022.
On June 22, 2022, the first experiment at FRIB, which studied the beta decay of calcium-48 fragments that are so unstable that they only exist for mere fractions of a second, concluded successfully. FRIB's first scientific user experiment had participation from Argonne National Laboratory, Brookhaven National Laboratory, Florida State University, FRIB, Lawrence Berkeley National Laboratory, Lawrence Livermore National Laboratory, Louisiana State University, Los Alamos National Laboratory, Mississippi State University, Oak Ridge National Laboratory, and the University of Tennessee. On November 14, 2022, the results of the first experiment were published in Physical Review Letters. | 0 | Isotopes |
When a fissile atom undergoes nuclear fission, it breaks into two or more fission fragments. Also, several free neutrons, gamma rays, and neutrinos are emitted, and a large amount of energy is released. The sum of the rest masses of the fission fragments and ejected neutrons is less than the sum of the rest masses of the original atom and incident neutron (of course the fission fragments are not at rest). The mass difference is accounted for in the release of energy according to the equation E=Δmc:
:mass of released energy =
Due to the extremely large value of the speed of light, c, a small decrease in mass is associated with a tremendous release of active energy (for example, the kinetic energy of the fission fragments). This energy (in the form of radiation and heat) carries the missing mass, when it leaves the reaction system (total mass, like total energy, is always conserved). While typical chemical reactions release energies on the order of a few eVs (e.g. the binding energy of the electron to hydrogen is 13.6 eV), nuclear fission reactions typically release energies on the order of hundreds of millions of eVs.
Two typical fission reactions are shown below with average values of energy released and number of neutrons ejected:
Note that these equations are for fissions caused by slow-moving (thermal) neutrons. The average energy released and number of neutrons ejected is a function of the incident neutron speed. Also, note that these equations exclude energy from neutrinos since these subatomic particles are extremely non-reactive and, therefore, rarely deposit their energy in the system. | 1 | Fission Products + Nuclear Fission |