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Large thermal reactors with low flux coupling between regions may experience spatial power oscillations because of the non-uniform presence of xenon-135. Xenon-induced spatial power oscillations occur as a result of rapid perturbations to power distribution that cause the xenon and iodine distribution to be out of phase with the perturbed power distribution. This results in a shift in xenon and iodine distributions that causes the power distribution to change in an opposite direction from the initial perturbation.
The instantaneous production rate of xenon-135 is dependent on the iodine-135 concentration and therefore on the local neutron flux history. On the other hand, the destruction rate of xenon-135 is dependent on the instantaneous local neutron flux.
The combination of delayed generation and high neutron-capture cross section produces a diversity of impacts on nuclear reactor operation. The mechanism is described in the following four steps.
# An initial lack of symmetry (for example, axial symmetry, in the case of axial oscillations) in the core power distribution (for example as a result of significant control rods movement) causes an imbalance in fission rates within the reactor core, and therefore, in the iodine-135 buildup and the xenon-135 absorption.
# In the high-flux region, xenon-135 burnout allows the flux to increase further, while in the low-flux region, the increase in xenon-135 causes a further reduction in flux. The iodine concentration increases where the flux is high and decreases where the flux is low. This shift in the xenon distribution is such as to increase (decrease) the multiplication properties of the region in which the flux has increased (decreased), thus enhancing the flux tilt.
# As soon as the iodine-135 levels build up sufficiently, decay to xenon reverses the initial situation. Flux decreases in this area, and the former low-flux region increases in power.
# Repetition of these patterns can lead to xenon oscillations moving about the core with periods on the order of about 24 hours.
With little change in overall power level, these oscillations can significantly change the local power levels. This oscillation may go unnoticed and reach dangerous local flux levels if only the total power of the core is monitored. Therefore, most PWRs use tandem power range excore neutron detectors to monitor upper and lower halves of the core separately. | 1 | Fission Products + Nuclear Fission |
Like biotic molecules, position specific isotope enrichments in abiotic molecules can reflect the source of chemical precursors and synthesis pathways. The energy for abiotic reactions can come from many different sources, which will affect fractionation. For instance, metal catalysts can speed up abiotic reactions. Reactions can be slowed down or sped up by different temperature and pressure conditions, which will affect the equilibrium constant or activation energy of reversible and irreversible reactions, respectively.
For example, carbon in the interstellar medium and solar nebula partition into distinct states based on thermodynamic favorability. Measuring site-specific isotope enrichments of carbon from organic molecules extracted from carbonaceous chondrites can elucidate where each carbon atom comes from, and how organic molecules can be synthesized abiotically. More broadly, these isotope enrichments can provide information about physical processes in the region where the molecular precursors were formed, and where the molecule formed in the solar system (i.e., nucleosynthetic heterogeneity, mass independent fractionation, self-shielding, etc.).
Another example of distinct site-specific fractionations in abiotic molecules is Fischer-Tropsch-type synthesis, which is thought to produce abiogenic hydrocarbon chains. Through this reaction mechanism, site enrichments of carbon would deplete as carbon chain length increases, and be distinct from site-specific enrichments of hydrocarbons of biological origins. | 0 | Isotopes |
Strontium-90 () is a radioactive isotope of strontium produced by nuclear fission, with a half-life of 28.8 years. It undergoes β decay into yttrium-90, with a decay energy of 0.546 MeV. Strontium-90 has applications in medicine and industry and is an isotope of concern in fallout from nuclear weapons, nuclear weapons testing, and nuclear accidents. | 1 | Fission Products + Nuclear Fission |
* Allègre C.J., 2008. Isotope Geology (Cambridge University Press).
* Faure G., Mensing T.M. (2004), Isotopes: Principles and Applications (John Wiley & Sons).
* Hoefs J., 2004. Stable Isotope Geochemistry (Springer Verlag).
* Sharp Z., 2006. Principles of Stable Isotope Geochemistry (Prentice Hall). | 0 | Isotopes |
Iodine-131, in higher doses than for thyrotoxicosis, is used for ablation of remnant thyroid tissue following a complete thyroidectomy to treat thyroid cancer. | 1 | Fission Products + Nuclear Fission |
While arsenic presents no radiological hazard, it is extremely chemically toxic. If it is desired to get rid of arsenic (no matter its origin), thermal neutron irradiation of the only stable isotope will yield short lived which quickly decays to stable . If Arsenic is irradiated with sufficient fast neutrons to cause notable "knockout" (n,2n) or even (n,3n) reactions, Isotopes of germanium will be produced instead. | 1 | Fission Products + Nuclear Fission |
Nuclear weapons use fission as either the partial or the main energy source. Depending on the weapon design and where it is exploded, the relative importance of the fission product radioactivity will vary compared to the activation product radioactivity in the total fallout radioactivity.
The immediate fission products from nuclear weapon fission are essentially the same as those from any other fission source, depending slightly on the particular nuclide that is fissioning. However, the very short time scale for the reaction makes a difference in the particular mix of isotopes produced from an atomic bomb.
For example, the Cs/Cs ratio provides an easy method of distinguishing between fallout from a bomb and the fission products from a power reactor. Almost no caesium-134 is formed by nuclear fission (because xenon-134 is stable). The Cs is formed by the neutron activation of the stable Cs which is formed by the decay of isotopes in the isobar (A = 133). So in a momentary criticality, by the time that the neutron flux becomes zero too little time will have passed for any Cs to be present. While in a power reactor plenty of time exists for the decay of the isotopes in the isobar to form Cs, the Cs thus formed can then be activated to form Cs only if the time between the start and the end of the criticality is long.
According to Jiri Hala's textbook, the radioactivity in the fission product mixture in an atom bomb is mostly caused by short-lived isotopes such as iodine-131 and barium-140. After about four months, cerium-141, zirconium-95/niobium-95, and strontium-89 represent the largest share of radioactive material. After two to three years, cerium-144/praseodymium-144, ruthenium-106/rhodium-106, and promethium-147 are responsible for the bulk of the radioactivity. After a few years, the radiation is dominated by strontium-90 and caesium-137, whereas in the period between 10,000 and a million years it is technetium-99 that dominates. | 1 | Fission Products + Nuclear Fission |
Plants can be characterised by the ratio of carbon isotopes they sequester, due to alterations in the evolution of photosynthetic biochemical pathways. So-called C3 plants fix CO into a 3-carbon molecule and have a greater proportion of C, whereas C4 plants fix it into a 4-carbon molecule, and have a carbon isotope signature with higher C. This signature translates across trophic levels and can be used to determine the diets of people and animals. Isotopic analysis has been used to illuminate the diets of the different species of the Paranthropus genus. It was determined that P. boisei had a reduced ratio of C3:C4, meaning they likely consumed a greater proportion of grasses and sedges than trees, shrubs and temperature grasses. P. aethiopicus showed a similar trend, whereas P. robustus was a generalist, with a broader dietary niche. Furthermore, carbon isotope analysis shows that around 2.37 million years ago, hominins displayed a widespread shift to favour C4 plants. | 0 | Isotopes |
In reactor fuel, the fission product xenon tends to migrate to form bubbles in the fuel. As caesium 133, 135, and 137 are formed by the beta particle decay of the corresponding xenon isotopes, this causes the caesium to become physically separated from the bulk of the uranium oxide fuel.
Because Xe is a potent nuclear poison with the largest cross section for thermal neutron absorption, the buildup of Xe in the fuel inside a power reactor can lower the reactivity greatly. If a power reactor is shut down or left running at a low power level, then large amounts of Xe can build up through decay of I. When the reactor is restarted or the low power level is increased significantly, Xe will be quickly consumed through neutron capture reactions and the reactivity of the core will increase. Under some circumstances, control systems may not be able to respond quickly enough to manage an abrupt reactivity increase as the built-up Xe burns off. It is thought that xenon poisoning was one of the factors which led to the power surge which damaged the Chernobyl reactor core. | 1 | Fission Products + Nuclear Fission |
NAIL-MS can also be applied to oligonucleotide analysis by mass spectrometry. This is useful when the sequence information is to be retained. | 0 | Isotopes |
Krypton-85, with a half-life 10.76 years, is formed by the fission process with
a fission yield of about 0.3%. Only 20% of the fission products of mass 85 become Kr itself; the rest passes through a short-lived nuclear isomer and then to stable Rb. If irradiated reactor fuel is reprocessed, this radioactive krypton may be released into the air. This krypton release can be detected and used as a means of detecting clandestine nuclear reprocessing. Strictly speaking, the stage which is detected is the dissolution of used nuclear fuel in nitric acid, as it is at this stage that the krypton and other fission gases like the more abundant xenon are released. Despite the industrial applications of Krypton-85 and the relatively high prices of both Krypton and Xenon, they are not currently extracted from spent fuel to any appreciable extent even though Krypton and Xenon both become solid at the temperature of liquid nitrogen and could thus be captured in a cold trap if the flue gas of a voloxidation process were cooled by liquid nitrogen.
Increase of fission gases above a certain limit can lead to fuel pin swelling and even puncture, so that fission gas measurement after discharging the fuel from the reactor is most important to make burn-up calculations, to study the nature of fuel inside the reactor, behaviour with pin materials, for effective utilization of fuel and also reactor safety. In addition to that, they are a nuisance in a nuclear reactor due to being neutron poisons, albeit not to the same extent as isotopes of xenon, another noble gas produced by fission. | 1 | Fission Products + Nuclear Fission |
Public health authorities in Western Australia issued an emergency alert for a stretch of road measuring about 1,400 km after a capsule containing caesium-137 was lost in transport on 25 January 2023. The 8 mm capsule contained a small quantity of the radioactive material when it disappeared from a truck. The State Government immediately launched a search, with the WA Department of Health's chief health officer Andrew Robertson warning an exposed person could expect to receive the equivalent of "about 10 X-rays an hour". Experts warned, if the capsule were found, the public should stay at least 5 metres away. The capsule was found on 1 February 2023. | 1 | Fission Products + Nuclear Fission |
The six factor formula effective neutron multiplication factor, k, is the average number of neutrons from one fission that cause another fission. The remaining neutrons either are absorbed in non-fission reactions or leave the system without being absorbed. The value of k determines how a nuclear chain reaction proceeds:
* k < 1 (subcriticality): The system cannot sustain a chain reaction, and any beginning of a chain reaction dies out over time. For every fission that is induced in the system, an average total of 1/(1 − k) fissions occur. Proposed subcritical reactors make use of the fact that a nuclear reaction sustained by an external neutron source can be "switched off" when the neutron source is removed. This provides a certain degree of inherent safety.
* k = 1 (criticality): Every fission causes an average of one more fission, leading to a fission (and power) level that is constant. Nuclear power plants operate with k = 1 unless the power level is being increased or decreased.
* k > 1 (supercriticality): For every fission in the material, it is likely that there will be "k" fissions after the next mean generation time (Λ). The result is that the number of fission reactions increases exponentially, according to the equation , where t is the elapsed time. Nuclear weapons are designed to operate under this state. There are two subdivisions of supercriticality: prompt and delayed.
When describing kinetics and dynamics of nuclear reactors, and also in the practice of reactor operation, the concept of reactivity is used, which characterizes the deflection of reactor from the critical state: ρ = (k − 1)/k. InHour (from inverse of an hour, sometimes abbreviated ih or inhr) is a unit of reactivity of a nuclear reactor.
In a nuclear reactor, k will actually oscillate from slightly less than 1 to slightly more than 1, due primarily to thermal effects (as more power is produced, the fuel rods warm and thus expand, lowering their capture ratio, and thus driving k lower). This leaves the average value of k at exactly 1. Delayed neutrons play an important role in the timing of these oscillations. | 1 | Fission Products + Nuclear Fission |
According to the Ronen Fissile rule, for a heavy element with 90 ≤ Z ≤ 100, its isotopes with , with few exceptions, are fissile (where N = number of neutrons and Z = number of protons).
The term fissile is distinct from fissionable. A nuclide capable of undergoing fission (even with a low probability) after capturing a neutron of high or low energy is referred to as fissionable. A fissionable nuclide that can be induced to fission with low-energy thermal neutrons with a high probability is referred to as fissile. Fissionable materials include also those (such as uranium-238) for which fission can be induced only by high-energy neutrons. As a result, fissile materials (such as uranium-235) are a subset of fissionable materials.
Uranium-235 fissions with low-energy thermal neutrons because the binding energy resulting from the absorption of a neutron is greater than the critical energy required for fission; therefore uranium-235 is fissile. By contrast, the binding energy released by uranium-238 absorbing a thermal neutron is less than the critical energy, so the neutron must possess additional energy for fission to be possible. Consequently, uranium-238 is fissionable but not fissile.
An alternative definition defines fissile nuclides as those nuclides that can be made to undergo nuclear fission (i.e., are fissionable) and also produce neutrons from such fission that can sustain a nuclear chain reaction in the correct setting. Under this definition, the only nuclides that are fissionable but not fissile are those nuclides that can be made to undergo nuclear fission but produce insufficient neutrons, in either energy or number, to sustain a nuclear chain reaction. As such, while all fissile isotopes are fissionable, not all fissionable isotopes are fissile. In the arms control context, particularly in proposals for a Fissile Material Cutoff Treaty, the term fissile is often used to describe materials that can be used in the fission primary of a nuclear weapon. These are materials that sustain an explosive fast neutron nuclear fission chain reaction.
Under all definitions above, uranium-238 () is fissionable, but not fissile. Neutrons produced by fission of have lower energies than the original neutron (they behave as in an inelastic scattering), usually below 1 MeV (i.e., a speed of about 14,000 km/s), the fission threshold to cause subsequent fission of , so fission of does not sustain a nuclear chain reaction.
Fast fission of in the secondary stage of a thermonuclear weapon, due to the production of high-energy neutrons from nuclear fusion, contributes greatly to the yield and to fallout of such weapons. Fast fission of tampers has also been evident in pure fission weapons. The fast fission of also makes a significant contribution to the power output of some fast-neutron reactors. | 1 | Fission Products + Nuclear Fission |
Analysis of the ratio of O to O in the shells of the Colorado Delta clam was used to assess the historical extent of the estuary in the Colorado River Delta prior to construction of upstream dams. | 0 | Isotopes |
A large fraction of the I contained in spent fuel is released into the gas phase, when spent fuel is first chopped and then dissolved in boiling nitric acid during reprocessing. At least for civil reprocessing plants, special scrubbers are supposed to withhold 99.5% (or more) of the Iodine by adsorption, before exhaust air is released into the environment. However, the Northeastern Radiological Health Laboratory (NERHL) found, during their measurements at the first US civil reprocessing plant, which was operated by Nuclear Fuel Services, Inc. (NFS) in Western New York, that "between 5 and 10% of the total I available from the dissolved fuel" was released into the exhaust stack. They further wrote that "these values are greater than predicted output (Table 1). This was expected since the iodine scrubbers were not operating during the dissolution cycles monitored."
The Northeastern Radiological Health Laboratory further states that, due to limitations of their measuring systems, the actual release of I may have even been higher, "since [I] losses [by adsorption] probably occurred in the piping and ductwork between the stack and the sampler". Furthermore, the sample taking system used by the NERHL had a bubbler trap for measuring the tritium content of the gas samples before the iodine trap. The NERHL found out only after taking the samples that "the bubbler trap retained 60 to 90% of the I sampled". They concluded: "The bubblers located upstream of the ion exchangers removed a major portion of the gaseous I before it reached the ion exchange sampler. The iodine removal ability of the bubbler was anticipated, but not in the magnitude that it occurred." The documented release of "between 5 and 10% of the total I available from the dissolved fuel" is not corrected for those two measurement deficiencies.
Military isolation of plutonium from spent fuel has also released I to the atmosphere: "More than 685,000 curies of iodine 131 spewed from the stacks of Hanford's separation plants in the first three years of operation." As I and I have very similar physical and chemical properties, and no isotope separation was performed at Hanford, I must have also been released there in large quantities during the Manhattan project. As Hanford reprocessed "hot" fuel, that had been irradiated in a reactor only a few months earlier, the activity of the released short-lived I, with a half-life time of just 8 days, was much higher than that of the long-lived I. However, while all of the I released during the times of the Manhattan project has decayed by now, over 99.999% of the I is still in the environment.
Ice borehole data obtained from the university of Bern at the Fiescherhorn glacier in the Alpian mountains at a height of 3950 m show a somewhat steady increase in the I deposit rate (shown in the image as a solid line) with time. In particular, the highest values obtained in 1983 and 1984 are about six times as high as the maximum that was measured during the period of the atmospheric bomb testing in 1961. This strong increase following the conclusion of the atmospheric bomb testing indicates that nuclear fuel reprocessing has been the primary source of atmospheric iodine-129 since then. These measurements lasted until 1986. | 1 | Fission Products + Nuclear Fission |
The sum of the atomic mass of the two atoms produced by the fission of one fissile atom is always less than the atomic mass of the original atom. This is because some of the mass is lost as free neutrons, and once kinetic energy of the fission products has been removed (i.e., the products have been cooled to extract the heat provided by the reaction), then the mass associated with this energy is lost to the system also, and thus appears to be "missing" from the cooled fission products.
Since the nuclei that can readily undergo fission are particularly neutron-rich (e.g. 61% of the nucleons in uranium-235 are neutrons), the initial fission products are often more neutron-rich than stable nuclei of the same mass as the fission product (e.g. stable zirconium-90 is 56% neutrons compared to unstable strontium-90 at 58%). The initial fission products therefore may be unstable and typically undergo beta decay to move towards a stable configuration, converting a neutron to a proton with each beta emission. (Fission products do not decay via alpha decay.)
A few neutron-rich and short-lived initial fission products decay by ordinary beta decay (this is the source of perceptible half life, typically a few tenths of a second to a few seconds), followed by immediate emission of a neutron by the excited daughter-product. This process is the source of so-called delayed neutrons, which play an important role in control of a nuclear reactor.
The first beta decays are rapid and may release high energy beta particles or gamma radiation. However, as the fission products approach stable nuclear conditions, the last one or two decays may have a long half-life and release less energy. | 1 | Fission Products + Nuclear Fission |
Natural isotopes must be either stable, have a half-life exceeding about 7 years (there are 35 isotopes in this category, see stable isotope for more details) or are generated in large amounts cosmogenically (such as C, which has a half-life of only 6000 years but is made by cosmic rays colliding with N). | 0 | Isotopes |
The original sulfur isotopic reference material was the Canyon Diablo Troilite (CDT), a meteorite recovered from Meteor Crater in Arizona. The Canyon Diablo Meteorite was chosen because it was thought to have a sulfur isotopic composition similar to the bulk Earth. However, the meteorite was later found to be isotopically heterogeneous with variations up to 0.4‰ (Beaudoin et al., 1994). This isotopic variability resulted in problems for the interlaboratory calibration of sulfur isotope measurements. A meeting of the IAEA in 1993 defined Vienna Canyon Diablo Troilite (VCDT) in an allusion to the earlier establishment of VSMOW. Like the original SMOW and VPDB, VCDT was never a physical material that could be measured but was still used as the definition of the sulfur isotopic scale. For the purposes of actually measuring S/S ratios, the IAEA defined the δS of IAEA-S-1 (originally called IAEA-NZ1) to be -0.30‰ relative to VCDT. These fairly recent changes to the sulfur isotope reference materials have greatly improved interlaboratory reproducibility (Coplen & Krouse, 1998). | 0 | Isotopes |
In isotope hydrology, stable isotopes of water (H and O) are used to estimate the source, age, and flow paths of water flowing through ecosystems. The main effects that change the stable isotope composition of water are evaporation and condensation. Variability in water isotopes is used to study sources of water to streams and rivers, evaporation rates, groundwater recharge, and other hydrological processes. | 0 | Isotopes |
A recent development in forensic science is the isotopic analysis of hair strands. Hair has a recognisable growth rate of 9-11mm per month or 15 cm per year. Human hair growth is primarily a function of diet, especially drinking water intake. The stable isotopic ratios of drinking water are a function of location, and the geology that the water percolates through. Sr, Sr and oxygen isotope variations are different all over the world. These differences in isotopic ratio are then biologically set in our hair as it grows and it has therefore become possible to identify recent geographic histories by the analysis of hair strands. For example, it could be possible to identify whether a terrorist suspect had recently been to a particular location from hair analysis. This hair analysis is a non-invasive method which is becoming very popular in cases that DNA or other traditional means are bringing no answers.
Isotope analysis can be used by forensic investigators to determine whether two or more samples of explosives are of a common origin. Most high explosives contain carbon, hydrogen, nitrogen and oxygen atoms and thus comparing their relative abundances of isotopes can reveal the existence of a common origin. Researchers have also shown that analysis of the C/C ratios can locate the country of origin for a given explosive.
Stable isotopic analysis has also been used in the identification of drug trafficking routes. Isotopic abundances are different in morphine grown from poppies in south-east Asia versus poppies grown in south-west Asia. The same is applied to cocaine that is derived from Bolivia and that from Colombia. | 0 | Isotopes |
Measurements of Δ47 can be used to constrain natural and synthetic sources of atmospheric CO, (e.g. respiration and combustion), as each of these processes are associated with different average Δ47 temperatures of formation. | 0 | Isotopes |
The boiling point of an element (or its compounds) is able to control the percentage of that element that a power reactor accident releases. The ability of an element to form a solid controls the rate it is deposited on the ground after having been injected into the atmosphere by a nuclear detonation or accident. | 1 | Fission Products + Nuclear Fission |
In conventional δO analysis, both the δO values in carbonates and water are needed to estimate paleoclimate. However, for many times and places, the δO in water can only be inferred, and also the O/O ratio between carbonate and water may vary with the change in temperature. Therefore, the accuracy of the thermometer may be compromised.
Whereas for the carbonate clumped-isotope thermometer, the equilibrium is independent of the isotope compositions of waters from which carbonates grew. Therefore, the only information needed is the abundance of bonds between rare, heavy isotopes within the carbonate mineral. | 0 | Isotopes |
A key premise of most clumped isotope analyses is that samples have retained their primary isotopic signatures. However, isotopic resetting or alteration, resulting from elevated temperature, can provide a different type of information about past climates. For example, when carbonate is isotopically reset by high temperatures, measurements of Δ47 can provide information about the duration and extent of metamorphic alteration. In one such study, Δ47 from late Neoproterozoic Doushantou cap carbonate is used to assess the temperature evolution of the lower crust in southern China. | 0 | Isotopes |
In 1961, Abelson and Hoering developed a technique for removing the carboxylic acid of amino acids using the ninhydrin reaction. This reaction converts the carboxylic acid to a molecule of CO which is measured via an Isotope Ratio Mass Spectrometer. | 0 | Isotopes |
The certification of isotopic reference materials is relatively complex. Like most aspects of reporting isotopic compositions it reflects a combination of historical artifacts and modern institutions. As a result, the details surrounding the certification of isotopic reference materials varies by element and chemical compound. As a general guideline, the isotopic composition of primary and original calibration reference materials were used to define the isotopic scales and so have no associated uncertainty. Updated calibration materials are generally certified by IAEA and important reference materials for two-point isotopic scales (SLAP, LSVEC) were reached through interlaboratory comparison. The isotopic composition of additional reference materials are either established through individual analytical facilities or through interlaboratory comparisons but often lack an official IAEA certification. There are certified values for most of the materials listed in Table 1, about half of the materials listed in Tables 2–7, and few of the materials in Table 8. | 0 | Isotopes |
The ratio of O to O in ice and deep sea cores is temperature dependent, and can be used as a proxy measure for reconstructing climate change. During colder periods of the Earth's history (glacials) such as during the ice ages, O is preferentially evaporated from the colder oceans, leaving the slightly heavier and more sluggish O behind. Organisms such as foraminifera which combine oxygen dissolved in the surrounding water with carbon and calcium to build their shells therefore incorporate the temperature-dependent O to O ratio. When these organisms die, they settle out on the sea bed, preserving a long and invaluable record of global climate change through much of the Quaternary. Similarly, ice cores on land are enriched in the heavier O relative to O during warmer climatic phases (interglacials) as more energy is available for the evaporation of the heavier O isotope. The oxygen isotope record preserved in the ice cores is therefore a "mirror" of the record contained in ocean sediments.
Oxygen isotopes preserve a record of the effects of the Milankovitch cycles on climate change during the Quaternary, revealing an approximately 100,000-year cyclicity in the Earth's climate. | 0 | Isotopes |
One would expect that enrichment of heavy isotopes leads to progressively slower reactions, but the IsoRes hypothesis suggests that there exist certain resonance compositions for which kinetics increases even for higher abundances of heavy stable isotopes. For example, at 9.5% C, 10.9% N and 6.6% O (when all three elements are 10-35 times enriched compared to their natural abundances) and normal deuterium composition (150 ppm or 0.015%), a very strong resonance (Fig. 1C) is predicted (“super-resonance”).
Yet another nontrivial prediction of the IsoRes hypothesis is that at ≈250-350 ppm deuterium content, the terrestrial resonance becomes “perfect”, and the rates of biochemical reactions and growth of terrestrial organisms further increase. This prediction seems to be matched by at least some experimental observations. | 0 | Isotopes |
The I-Xe system was first applied in 1975 to estimate the age of the Earth. For all Xe isotopes, the initial isotope composition of iodine in the Earth is given by
where is the isotopic ratios of iodine at the time that Earth primarily formed, is the isotopic ratio of iodine at the end of stellar nucleosynthesis, and is the time interval between the end of stellar nucleosynthesis and the formation of the Earth. The estimated iodine-127 concentration in the Bulk Silicate Earth (BSE) (= crust + mantle average) ranges from 7 to 10 parts per billion (ppb) by mass. If the BSE represents Earth's chemical composition, the total I in the BSE ranges from 2.26×10 to 3.23×10 moles. The meteorite Bjurböle is 4.56 billion years old with an initial I/I ratio of 1.1×10, so an equation can be derived as
where is the interval between the formation of the Earth and the formation of meteorite Bjurböle. Given the half life of I of 15.7 Myr, and assuming that all the initial I has decayed to Xe, the following equation can be derived:
Xe in the modern atmosphere is 3.63×10 grams. The iodine content for BSE lies between 10 and 12 ppb by mass. Consequently, should be 108 Myr, i.e., the Xe-closure age is 108 Myr younger than the age of meteorite Bjurböle. The estimated Xe closure time was ~4.45 billion years ago when the growing Earth started to retain Xe in its atmosphere, which is coincident with ages derived from other geochronology dating methods. | 0 | Isotopes |
Plenty of radioactive ruthenium-103, ruthenium-106, and stable ruthenium are formed by the fission process. The ruthenium in PUREX raffinate can become oxidized to form volatile ruthenium tetroxide which forms a purple vapour above the surface of the aqueous liquor. The ruthenium tetroxide is very similar to osmium tetroxide; the ruthenium compound is a stronger oxidant which enables it to form deposits by reacting with other substances. In this way the ruthenium in a reprocessing plant is very mobile, difficult to stabilize, and can be found in odd places. It has been called extremely troublesome and has a notorious reputation as an especially difficult product to handle during reprocessing. Voloxidation combined with cold trap collection of the flue gases could recover the volatile ruthenium tetroxide before it can become a nuisance in further processing. After the radioactive isotopes have had time to decay, recovered ruthenium could be sold at its relatively high market value.
In addition, the ruthenium in PUREX raffinate forms a large number of nitrosyl complexes which makes the chemistry of the ruthenium very complex. The ligand exchange rate at ruthenium and rhodium tends to be long, hence it can take a long time for a ruthenium or rhodium compound to react.
At Chernobyl, during the fire, the ruthenium became volatile and behaved differently from many of the other metallic fission products. Some of the particles which were emitted by the fire were very rich in ruthenium.
As the longest-lived radioactive isotope ruthenium-106 has a half-life of only 373.59 days, it has been suggested that the ruthenium and palladium in PUREX raffinate should be used as a source of the metals after allowing the radioactive isotopes to decay. After ten half life cycles have passed over 99.96% of any radioisotope is stable. For Ru-106 this is 3,735.9 days or about 10 years. | 1 | Fission Products + Nuclear Fission |
A comparative NAIL-MS experiment is quite similar to a SILAC experiment but for RNA instead of proteins. First, two populations of the respective cells are cultivated. One of the cell populations is fed with growth medium containing unlabeled nutrients, whereas the second population is fed with growth medium containing stable isotope labeled nutrients. The cells then incorporate the respective isotopologues into their RNA molecules. One of the cell populations serves as a control group whereas the other is subject to the associated research (e.g. KO strain, stress). Upon harvesting of the two cell populations they are mixed and co-processed together to exclude purification-bias. Due to the distinct masses of incorporated nutrients into the nucleosides a differentiation of the two cell populations is possible by mass spectrometry. | 0 | Isotopes |
* A technique similar to radioisotopic labeling is radiometric dating: using the known half-life of an unstable element, one can calculate the amount of time that has elapsed since a known concentration of isotope existed. The most widely known example is radiocarbon dating used to determine the age of carbonaceous materials.
* Several forms of spectroscopy rely on the unique nuclear properties of specific isotopes, both radioactive and stable. For example, nuclear magnetic resonance (NMR) spectroscopy can be used only for isotopes with a nonzero nuclear spin. The most common nuclides used with NMR spectroscopy are H, D, N, C, and P.
* Mössbauer spectroscopy also relies on the nuclear transitions of specific isotopes, such as Fe.
* Radionuclides also have important uses. Nuclear power and nuclear weapons development require relatively large quantities of specific isotopes. Nuclear medicine and radiation oncology utilize radioisotopes respectively for medical diagnosis and treatment. | 0 | Isotopes |
Substrates need to be prepared and analyzed in a specific way to elucidate site specific isotope enrichments. This requires clean separation of the compound of interest from the original sample, which can require a variety of different preparatory chemistries. Once isolated, position-specific isotope enrichments can be analyzed with a variety of instruments, which all have different advantages and provide varying degrees of precision. | 0 | Isotopes |
Tellurium-128 and -130 are essentially stable. They only decay by double beta decay, with half lives >10 years. They constitute the major fraction of natural occurring tellurium at 32 and 34% respectively.
Tellurium-132 and its daughter I are important in the first few days after a criticality. It was responsible for a large fraction of the dose inflicted on workers at Chernobyl in the first week.
The isobar forming Te/I is: Tin-132 (half-life 40 s) decaying to antimony-132 (half-life 2.8 minutes) decaying to tellurium-132 (half-life 3.2 days) decaying to iodine-132 (half-life 2.3 hours) which decays to stable xenon-132.
The creation of tellurium-126 is delayed by the long half-life (230 k years) of tin-126. | 1 | Fission Products + Nuclear Fission |
Jupiter's atmosphere has 2.5 ± 0.5 times the solar abundance values for Xenon and similarly elevated argon and krypton (2.1 ± 0.5 and 2.7 ± 0.5 times solar values separately). These signals of enrichment are due to these elements coming to Jupiter in very cold (T<30K) icy planetesimals. | 0 | Isotopes |
The signal of mass-independent fractionation of sulfur isotopes, known as MIF-S, correlates with the end of Xe isotope fractionation. During the Great Oxidation Event (GOE), the ozone layer formed when O rose, accounting for the end of the MIF-S signature. The disappearance of the MIF-S signal has been regarded as changing the redox ratio of Earth's surface reservoirs. However, potential memory effects of MIF-S due to oxidative weathering can lead to large uncertainty on the process and chronology of GOE. Compared to the MIF-S signals, hydrodynamic escape of Xe is not affected by the ozone formation and may be even more sensitive to O availability, promising to provide more details about the oxidation history of Earth. | 0 | Isotopes |
Founded in 1974, the International Atomic Energy Agency (IAEA) was created to set forth international standards for nuclear reactor safety. However, without a proper policing force, the guidelines set forth by the IAEA were often treated lightly or ignored completely. In 1986, the disaster at Chernobyl was evidence that international nuclear reactor safety was not to be taken lightly. Even in the midst of the Cold War, the Nuclear Regulatory Commission sought to improve the safety of Soviet nuclear reactors. As noted by IAEA Director General Hans Blix, "A radiation cloud doesn't know international boundaries." The NRC showed the Soviets the safety guidelines used in the US: capable regulation, safety-minded operations, and effective plant designs. The Soviets, however, had their own priority: keeping the plant running at all costs. In the end, the same shift between deterministic safety designs to probabilistic safety designs prevailed. In 1989, the World Association of Nuclear Operators (WANO) was formed to cooperate with the IAEA to ensure the same three pillars of reactor safety across international borders. In 1991, WANO concluded (using a probabilistic safety approach) that all former communist-controlled nuclear reactors could not be trusted, and should be closed. Compared to a "Nuclear Marshall Plan", efforts were taken throughout the 1990s and 2000s to ensure international standards of safety for all nuclear reactors. | 1 | Fission Products + Nuclear Fission |
Clumped isotopes are heavy isotopes that are bonded to other heavy isotopes. The relative abundance of clumped isotopes (and multiply-substituted isotopologues) in molecules such as methane, nitrous oxide, and carbonate is an area of active investigation. The carbonate clumped-isotope thermometer, or "C–O order/disorder carbonate thermometer", is a new approach for paleoclimate reconstruction, based on the temperature dependence of the clumping of C and O into bonds within the carbonate mineral lattice. This approach has the advantage that the O ratio in water is not necessary (different from the δO approach), but for precise paleotemperature estimation, it also needs very large and uncontaminated samples, long analytical runs, and extensive replication. Commonly used sample sources for paleoclimatological work include corals, otoliths, gastropods, tufa, bivalves, and foraminifera. Results are usually expressed as Δ47 (said as "cap 47"), which is the deviation of the ratio of isotopologues of CO with a molecular weight of 47 to those with a weight of 44 from the ratio expected if they were randomly distributed. | 0 | Isotopes |
Primary, calibration, and reference materials are only available in small quantities and purchase is often limited to once every few years. Depending on the specific isotope systems and instrumentation, a shortage of available reference materials can be problematic for daily instrument calibrations or for researchers attempting to measure isotope ratios in a large number of natural samples. Rather than using primary materials or reference materials, a laboratory measuring stable isotope ratios will typically purchase a small quantity of the relevant reference materials and measure the isotope ratio of an in-house material against the reference, making that material into a working standard specific to that analytical facility. Once this lab-specific working standard has been calibrated to the international scale the standard is used to measure the isotopic composition of unknown samples. After measurement of both sample and working standard against a third material (commonly called the working gas or the transfer gas) the recorded isotopic distributions are mathematically corrected back to the international scale. It is thus critical to measure the isotopic composition of the working standard with high precision and accuracy (as well as possible given the precision of the instrument and the accuracy of the purchased reference material) because the working standard forms the ultimate basis for accuracy of most mass spectrometric observations. Unlike reference materials, working standards are typically not calibrated across multiple analytical facilities and the accepted δ value measured in a given laboratory could reflect bias specific to a single instrument. However, within a single analytical facility this bias can be removed during data reduction. Because each laboratory defines unique working standards the primary, calibration, and reference materials are long-lived while still ensuring that the isotopic composition of unknown samples can be compared across laboratories. | 0 | Isotopes |
These case studies represent some potential applications for position specific isotope analysis, but certainly not all. The opportunities for samples to measure and processes to characterize are virtually unlimited, and new methodological developments will help make these measurements possible going forward. | 0 | Isotopes |
A bone seeker is an element, often a radioisotope, that tends to accumulate in the bones of humans and other animals when it is introduced into the body.
For example, strontium and radium are chemically similar to calcium and can replace the calcium in bones. Plutonium is also a bone seeker, though the mechanism by which it accumulates in bone tissue is unknown.
Radioactive bone seekers are particular health risks as they irradiate surrounding tissue, though this can be useful for radiotherapyradium-223 is used in this way. Stable bone seekers can also be harmful: excessive strontium absorption has been linked with increased levels of rickets. The salt strontium ranelate, however, is a bone seeker which is sometimes used to strengthen bones as a treatment for osteoporosis. Bone seekers have been proposed as a method of delivering antibiotics to infected bone tissue. | 0 | Isotopes |
As the nuclear energy sector continues to grow, the international rhetoric surrounding nuclear warfare intensifies, and the ever-present threat of radioactive materials falling into the hands of dangerous people persists, many scientists are working hard to find the best way to protect human organs from the harmful effects of high energy radiation. Acute radiation syndrome (ARS) is the most immediate risk to humans when exposed to ionizing radiation in dosages greater than around 0.1 Gy/hr. Radiation in the low energy spectrum (alpha and beta radiation) with minimal penetrating power is unlikely to cause significant damage to internal organs. The high penetrating power of gamma and neutron radiation, however, easily penetrates the skin and many thin shielding mechanisms to cause cellular degeneration in the stem cells found in bone marrow. While full body shielding in a secure fallout shelter as described above is the most optimal form of radiation protection, it requires being locked in a very thick bunker for a significant amount of time. In the event of a nuclear catastrophe of any kind, it is imperative to have mobile protection equipment for medical and security personnel to perform necessary containment, evacuation, and any number of other important public safety objectives. The mass of the shielding material required to properly protect the entire body from high energy radiation would make functional movement essentially impossible. This has led scientists to begin researching the idea of partial body protection: a strategy inspired by hematopoietic stem cell transplantation (HSCT). The idea is to use enough shielding material to sufficiently protect the high concentration of bone marrow in the pelvic region, which contains enough regenerative stem cells to repopulate the body with unaffected bone marrow. More information on bone marrow shielding can be found in the [https://journals.lww.com/health-physics/pages/default.aspx Health Physics Radiation Safety Journal] article [https://journals.lww.com/health-physics/Abstract/2017/09000/Selective_Shielding_of_Bone_Marrow___An_Approach.4.aspx Selective Shielding of Bone Marrow: An Approach to Protecting Humans from External Gamma Radiation], or in the Organisation for Economic Co-operation and Development (OECD) and the Nuclear Energy Agency (NEA)'s 2015 report: [https://www.oecd-nea.org/rp/docs/2014/crpph-r2014-5.pdf Occupational Radiation Protection in Severe Accident Management.] | 1 | Fission Products + Nuclear Fission |
A significant amount of zirconium is formed by the fission process; some of this consists of short-lived radionuclides (Zr and Zr which decay to molybdenum), while almost 10% of the fission products mixture after years of decay consists of five stable or nearly stable isotopes of zirconium plus Zr with a halflife of 1.53 million years which is one of the 7 major long-lived fission products. Zirconium is commonly used in cladding of fuel rods due to its low neutron cross section. However, a small share of this zirconium does capture neutrons and contributes to the overall inventory of radioactive zirconium isotopes. Zircalloy cladding is not commonly reused and neither is fission product zirconium, which could be used in cladding as its relatively weak radioactivity would be of no major concern inside a nuclear reactor. Despite its high yield and long live, Zr-93 is generally not deemed to be of major concern as it is not chemically mobile and emits little radiation.
In PUREX plants the zirconium (regardless of source or isotope) sometimes forms a third phase which can be a disturbance in the plant. The third phase is the term in solvent extraction given to a third layer (such as foam and/or emulsion) which forms from the two layers in the solvent extraction process. The zirconium forms the third phase by forming small particles which stabilise the emulsion which is the third phase.
Zirconium-90 mostly forms by successive beta decays out of Strontium-90. A nonradioactive Zirconium sample can be extracted from spent fuel by extracting Strontium-90 and allowing enough of it to decay (e.g. In an RTG). The Zirconium can then be separated from the remaining strontium leaving a very isotopically pure Zr-90 sample. | 1 | Fission Products + Nuclear Fission |
Sr finds extensive use in medicine as a radioactive source for superficial radiotherapy of some cancers. Controlled amounts of Sr and Sr can be used in treatment of bone cancer, and to treat coronary restenosis via vascular brachytherapy. It is also used as a radioactive tracer in medicine and agriculture. | 1 | Fission Products + Nuclear Fission |
The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isotopes of the same element. The relative abundance of such stable isotopes can be measured experimentally (isotope analysis), yielding an isotope ratio that can be used as a research tool. Theoretically, such stable isotopes could include the radiogenic daughter products of radioactive decay, used in radiometric dating. However, the expression stable-isotope ratio is preferably used to refer to isotopes whose relative abundances are affected by isotope fractionation in nature. This field is termed stable isotope geochemistry. | 0 | Isotopes |
The natural nuclear reactor at Oklo formed when a uranium-rich mineral deposit became inundated with groundwater, which could act as a moderator for the neutrons produced by nuclear fission. A chain reaction took place, producing heat that caused the groundwater to boil away; without a moderator that could slow the neutrons, however, the reaction slowed or stopped. The reactor thus had a negative void coefficient of reactivity, something employed as a safety mechanism in human-made light water reactors. After cooling of the mineral deposit, the water returned, and the reaction restarted, completing a full cycle every 3 hours. The fission reaction cycles continued for hundreds of thousands of years and ended when the ever-decreasing fissile materials, coupled with the build-up of neutron poisons, no longer could sustain a chain reaction.
Fission of uranium normally produces five known isotopes of the fission-product gas xenon; all five have been found trapped in the remnants of the natural reactor, in varying concentrations. The concentrations of xenon isotopes, found trapped in mineral formations 2 billion years later, make it possible to calculate the specific time intervals of reactor operation: approximately 30 minutes of criticality followed by 2 hours and 30 minutes of cooling down (exponentially decreasing residual decay heat) to complete a 3-hour cycle. Xenon-135 is the strongest known neutron poison. However, it is not produced directly in appreciable amounts but rather as a decay product of Iodine-135 (or one of its parent nuclides). Xenon-135 itself is unstable and decays to caesium-135 if not allowed to absorb neutrons. While caesium-135 is relatively long lived, all caesium-135 produced by the Oklo reactor has since decayed further to stable barium-135. Meanwhile, Xenon-136, the product of neutron capture in xenon-135 only decays extremely slowly via double beta decay and thus scientists were able to determine the neutronics of this reactor by calculations based on those isotope ratios almost two billion years after it stopped fissioning uranium.
A key factor that made the reaction possible was that, at the time the reactor went critical 1.7 billion years ago, the fissile isotope made up about 3.1% of the natural uranium, which is comparable to the amount used in some of today's reactors. (The remaining 96.9% was non-fissile and roughly 55 ppm .) Because has a shorter half-life than , and thus decays more rapidly, the current abundance of in natural uranium is only 0.72%. A natural nuclear reactor is therefore no longer possible on Earth without heavy water or graphite.
The Oklo uranium ore deposits are the only known sites in which natural nuclear reactors existed. Other rich uranium ore bodies would also have had sufficient uranium to support nuclear reactions at that time, but the combination of uranium, water and physical conditions needed to support the chain reaction was unique, as far as is currently known, to the Oklo ore bodies. It is also possible, that other natural nuclear fission reactors were once operating but have since been geologically disturbed so much as to be unrecognizable, possibly even "diluting" the uranium so far that the isotope ratio would no longer serve as a "fingerprint". Only a small part of the continental crust and no part of the oceanic crust reaches the age of the deposits at Oklo or an age during which isotope ratios of natural uranium would have allowed a self sustaining chain reaction with water as a moderator.
Another factor which probably contributed to the start of the Oklo natural nuclear reactor at 2 billion years, rather than earlier, was the increasing oxygen content in the Earth's atmosphere. Uranium is naturally present in the rocks of the earth, and the abundance of fissile was at least 3% or higher at all times prior to reactor startup. Uranium is soluble in water only in the presence of oxygen. Therefore, increasing oxygen levels during the aging of the Earth may have allowed uranium to be dissolved and transported with groundwater to places where a high enough concentration could accumulate to form rich uranium ore bodies. Without the new aerobic environment available on Earth at the time, these concentrations probably could not have taken place.
It is estimated that nuclear reactions in the uranium in centimeter- to meter-sized veins consumed about five tons of and elevated temperatures to a few hundred degrees Celsius. Most of the non-volatile fission products and actinides have only moved centimeters in the veins during the last 2 billion years. Studies have suggested this as a useful natural analogue for nuclear waste disposal. The overall mass defect from the fission of five tons of is about . Over its lifetime the reactor produced roughly in thermal energy, including neutrinos. If one ignores fission of plutonium (which makes up roughly a third of fission events over the course of normal burnup in modern human-made light water reactors), then fission product yields amount to roughly of technetium-99 (since decayed to ruthenium-99), of zirconium-93 (since decayed to niobium-93), of caesium-135 (since decayed to barium-135, but the real value is probably lower as its parent nuclide, xenon-135, is a strong neutron poison and will have absorbed neutrons before decaying to in some cases), of palladium-107 (since decayed to silver), of strontium-90 (long since decayed to zirconium), and of caesium-137 (long since decayed to barium). | 1 | Fission Products + Nuclear Fission |
The dose that would be lethal to 50% of a population is a common parameter used to compare the effects of various fallout types or circumstances. Usually, the term is defined for a specific time, and limited to studies of acute lethality. The common time periods used are 30 days or less for most small laboratory animals and to 60 days for large animals and humans. The LD figure assumes that the individuals did not receive other injuries or medical treatment.
In the 1950s, the LD for gamma rays was set at 3.5 Gy, while under more dire conditions of war (a bad diet, little medical care, poor nursing) the LD was 2.5 Gy (250 rad). There have been few documented cases of survival beyond 6 Gy. One person at Chernobyl survived a dose of more than 10 Gy, but many of the persons exposed there were not uniformly exposed over their entire body. If a person is exposed in a non-homogeneous manner then a given dose (averaged over the entire body) is less likely to be lethal. For instance, if a person gets a hand/low arm dose of 100 Gy, which gives them an overall dose of 4 Gy, they are more likely to survive than a person who gets a 4 Gy dose over their entire body. A hand dose of 10 Gy or more would likely result in loss of the hand. A British industrial radiographer who was estimated to have received a hand dose of 100 Gy over the course of his lifetime lost his hand because of radiation dermatitis. Most people become ill after an exposure to 1 Gy or more. Fetuses are often more vulnerable to radiation and may miscarry, especially in the first trimester.
One hour after a surface burst, the radiation from fallout in the crater region is 30 grays per hour (Gy/h). Civilian dose rates in peacetime range from 30 to 100 µGy per year.
Fallout radiation decays relatively quickly with time. Most areas become fairly safe for travel and decontamination after three to five weeks.
For yields of up to 10 kt, prompt radiation is the dominant producer of casualties on the battlefield. Humans receiving an acute incapacitating dose (30 Gy) have their performance degraded almost immediately and become ineffective within several hours. However, they do not die until five to six days after exposure, assuming they do not receive any other injuries. Individuals receiving less than a total of 1.5 Gy are not incapacitated. People receiving doses greater than 1.5 Gy become disabled, and some eventually die.
A dose of 5.3 Gy to 8.3 Gy is considered lethal but not immediately incapacitating. Personnel exposed to this amount of radiation have their cognitive performance degraded in two to three hours, depending on how physically demanding the tasks they must perform are, and remain in this disabled state at least two days. However, at that point they experience a recovery period and can perform non-demanding tasks for about six days, after which they relapse for about four weeks. At this time they begin exhibiting symptoms of radiation poisoning of sufficient severity to render them totally ineffective. Death follows at approximately six weeks after exposure, although outcomes may vary. | 1 | Fission Products + Nuclear Fission |
Theranostics, a treatment that combines therapy and diagnosis, is a new trend in precision medicine where the radioisotopes produced at MEDICIS already triggered research projects. The strategy the facility uses is to find an element that has two radioisotopes, used for imaging and therapy separately.
A promising element for use in theranostics is terbium as it has four different radioisotopes for use in therapy and PET or SPECT imaging. In 2021, Tb radioisotope production was successfully performed with the MELISSA laser ion source, with a 53% ionisation efficiency obtained by MEDICIS-Promed students. Since 2021, three other non-conventional isotopes of interest for PET imaging or therapeutic applications have been produced.
Exploration of mass separated Sm at MEDICIS using in vitro biological studies showed that the ability for tumors to absorb (uptake) and retain substances (retention) was improved compared to normal tissues. Animal SPECT-CT scans of mice were obtained post-injection and showed cleared activity after twenty-four hours. | 0 | Isotopes |
The natural reactor of Oklo has been used to check if the atomic fine-structure constant α might have changed over the past 2 billion years. That is because α influences the rate of various nuclear reactions. For example, captures a neutron to become , and since the rate of neutron capture depends on the value of α, the ratio of the two samarium isotopes in samples from Oklo can be used to calculate the value of α from 2 billion years ago.
Several studies have analysed the relative concentrations of radioactive isotopes left behind at Oklo, and most have concluded that nuclear reactions then were much the same as they are today, which implies α was the same too. | 1 | Fission Products + Nuclear Fission |
The atomic mass of different isotopes affect their chemical kinetic behavior, leading to natural isotope separation processes. | 0 | Isotopes |
The isotopic resonance hypothesis (IsoRes) postulates that certain isotopic compositions of chemical elements affect kinetics of chemical reactions involving molecules built of these elements. The isotopic compositions for which this effect is predicted are called resonance isotopic compositions.
Fundamentally, the IsoRes hypothesis relies on a postulate that less complex systems exhibit faster kinetics than equivalent but more complex systems. Furthermore, system's complexity is affected by its symmetry (more symmetric systems are simpler), and symmetry (in general meaning) of reactants may be affected by their isotopic composition.
The term “resonance” relates to the use of this term in nuclear physics, where peaks in the dependence of a reaction cross section upon energy are called “resonances”. Similarly, a sharp increase (or decrease) in the reaction kinetics as a function of the average isotopic mass of a certain element is called here a resonance. | 0 | Isotopes |
In the field of stable isotope geochemistry, isotopologues of simple molecules containing rare heavy isotopes of carbon, oxygen, hydrogen, nitrogen, and sulfur are used to trace equilibrium and kinetic processes in natural environments and in Earth's past. | 0 | Isotopes |
In geochemistry, geophysics and nuclear physics, primordial nuclides, also known as primordial isotopes, are nuclides found on Earth that have existed in their current form since before Earth was formed. Primordial nuclides were present in the interstellar medium from which the solar system was formed, and were formed in, or after, the Big Bang, by nucleosynthesis in stars and supernovae followed by mass ejection, by cosmic ray spallation, and potentially from other processes. They are the stable nuclides plus the long-lived fraction of radionuclides surviving in the primordial solar nebula through planet accretion until the present; 286 such nuclides are known. | 0 | Isotopes |
A caesium-137 capsule went missing from a steam power plant in Prachin Buri province, Thailand on 23 February 2023, triggering a search by officials from Thailand's Office of Atoms for Peace (OAP) and the Prachin Buri provincial administration. However, the Thai public was not notified until 14 March.
On 20 March, the Secretary-General of the OAP and the governor of Prachin Buri held a press conference stating that they had found caesium-137 contaminated furnace dust at a steel melting plant in Kabin Buri district. | 1 | Fission Products + Nuclear Fission |
The technique measures a subjects carbon dioxide production during the interval between first and last body water samples. The method depends on the details of carbon metabolism in our bodies. When cellular respiration breaks down carbon-containing molecules to release energy, carbon dioxide is released as a byproduct. Carbon dioxide contains two oxygen atoms and only one carbon atom, but food molecules such as carbohydrates do not contain enough oxygen to provide both oxygen atoms found in CO. It turns out, one of the two oxygen atoms in CO is derived from body water. If the oxygen in water is labeled with O, then CO produced by respiration will contain labeled oxygen. In addition, as CO travels from the site of respiration through the cytoplasm of a cell, through the interstitial fluids, into the bloodstream and then to the lungs some of it is reversibly converted to bicarbonate. So, after consuming water labeled with O, the O equilibrates with the bodys bicarbonate and dissolved carbon dioxide pool (through the action of the enzyme carbonic anhydrase). As carbon dioxide is exhaled, O is lost from the body. This was discovered by Lifson in 1949. However, O is also lost through body water loss (such as urine and evaporation of fluids). However, deuterium (the second label in the doubly labeled water) is lost only when body water is lost. Thus, the loss of deuterium in body water over time can be used to mathematically compensate for the loss of O by the water-loss route. This leaves only the remaining net loss of O in carbon dioxide. This measurement of the amount of carbon dioxide lost is an excellent estimate for total carbon dioxide production. Once this is known, the total metabolic rate may be estimated from simplifying assumptions regarding the ratio of oxygen used in metabolism (and therefore heat generated), to carbon dioxide eliminated (see respiratory quotient). This quotient can be measured in other ways, and almost always has a value between 0.7 and 1.0, and for a mixed diet is usually about 0.8.
In lay terms:
* Metabolism can be calculated from oxygen-in/CO-out.
* DLW (tagged) water is traceable hydrogen (deuterium), and traceable oxygen (O).
* The O leaves the body in two ways: (i) exhaled CO, and (ii) water loss in (mostly) urine, sweat, & breath.
* But the deuterium leaves only in the second way (water loss).
From deuterium loss, we know how much of the tagged water left the body as water. And, since the concentration of O in the bodys water is measured after the labeling dose is given, we also know how much of the tagged oxygen left the body in the water. (A simpler view is that the ratio of deuterium to O in body water is fixed, so total loss-rate of deuterium from the body multiplied by this ratio, immediately gives the loss rate of O in water.) Measurement of O dilution with time gives the total loss of this isotope by all routes (by water and respiration). Since the ratio of O to total water oxygen in the body is measured, we can convert O loss in respiration to total oxygen lost from the bodys water pool via conversion to carbon dioxide. How much oxygen left the body as CO is the same as the CO produced by metabolism, since the body only produces CO by this route. The CO loss tells us the energy produced, if we know or can estimate the respiratory quotient (ratio of CO produced to oxygen used). | 0 | Isotopes |
Lipids are of particular interest to stable isotope geochemists because they are preserved in rocks for millions of years. Monson & Hayes used ozonolysis to characterize the position-specific isotope abundances of unsaturated fatty acids, turning different carbon positions into carbon dioxide. Using this technique, they directly measured an isotopic pattern in fatty acids that had been predicted for years. | 0 | Isotopes |
Isotopic reference materials exist for non-traditional isotope systems (elements other than hydrogen, carbon, oxygen, nitrogen, and sulfur), including lithium, boron, magnesium, calcium, iron, and many others. Because the non-traditional systems were developed relatively recently, the reference materials for these systems are more straightforward and less numerous than for the traditional isotopic systems. The following table contains the material defining the δ=0 for each isotopic scale, the best measurement of the absolute isotopic fractions of an indicated material (which is often the same as the material defining the scale, but not always), the calculated absolute isotopic ratio, and links to lists of isotopic reference materials prepared by the Commission on Isotopic Abundances and Atomic Weight (part of the International Union of Pure and Applied Chemistry (IUPAC)). A summary list of non-traditional stable isotope systems is available [http://www.ciaaw.org/reference-materials.htm here], and much of this information is derived from Brand et al. (2014). In addition to the isotope systems listed in Table 8, ongoing research is focused on measuring the isotopic composition of barium (Allmen et al., 2010; Miyazaki et al., 2014; Nan et al., 2015) and vanadium (Nielson et al., 2011). Specpure Alfa Aesar is an isotopically well-characterized vanadium solution (Nielson et al., 2011). Furthermore, fractionation during chemical processing can be problematic for certain isotopic analyses, such as measuring heavy isotope ratios following column chromatography. In these cases reference materials can be calibrated for particular chemical procedures.
Table 8 gives the material and isotopic ratio defining the δ = 0 scale for each of the indicated elements. In addition, Table 8 lists the material with the best measurement as determined by Meija et al. (2016). "Material" gives chemical formula, "Type of ratio" is the isotopic ratio reported in "Isotope ratio", and "Citation" gives the article(s) reporting the isotopic abundances on which the isotope ratio is based. The isotopic ratios reflect the results from individual analyses of absolute mass fraction, reported in the cited studies, aggregated in Meija et al. (2016), and manipulated to reach the reported ratios. Error was calculated as the square root of the sum of the squares of fractional reported errors. | 0 | Isotopes |
At least three isotopes of iodine are important. I, I (radioiodine) and I. Open air nuclear testing and the Chernobyl disaster both released iodine-131.
The short-lived isotopes of iodine are particularly harmful because the thyroid collects and concentrates iodide – radioactive as well as stable. Absorption of radioiodine can lead to acute, chronic, and delayed effects. Acute effects from high doses include thyroiditis, while chronic and delayed effects include hypothyroidism, thyroid nodules, and thyroid cancer. It has been shown that the active iodine released from Chernobyl and Mayak has resulted in an increase in the incidence of thyroid cancer in the former Soviet Union.
One measure which protects against the risk from radio-iodine is taking a dose of potassium iodide (KI) before exposure to radioiodine. The non-radioactive iodide "saturates" the thyroid, causing less of the radioiodine to be stored in the body.
Administering potassium iodide reduces the effects of radio-iodine by 99% and is a prudent, inexpensive supplement to fallout shelters. A low-cost alternative to commercially available iodine pills is a saturated solution of potassium iodide. Long-term storage of KI is normally in the form of reagent-grade crystals.
The administration of known goitrogen substances can also be used as a prophylaxis in reducing the bio-uptake of iodine, (whether it be the nutritional non-radioactive iodine-127 or radioactive iodine, radioiodine - most commonly iodine-131, as the body cannot discern between different iodine isotopes).
Perchlorate ions, a common water contaminant in the USA due to the aerospace industry, has been shown to reduce iodine uptake and thus is classified as a goitrogen. Perchlorate ions are a competitive inhibitor of the process by which iodide is actively deposited into thyroid follicular cells. Studies involving healthy adult volunteers determined that at levels above 0.007 milligrams per kilogram per day (mg/(kg·d)), perchlorate begins to temporarily inhibit the thyroid gland's ability to absorb iodine from the bloodstream ("iodide uptake inhibition", thus perchlorate is a known goitrogen).
The reduction of the iodide pool by perchlorate has dual effects – reduction of excess hormone synthesis and hyperthyroidism, on the one hand, and reduction of thyroid inhibitor synthesis and hypothyroidism on the other. Perchlorate remains very useful as a single dose application in tests measuring the discharge of radioiodide accumulated in the thyroid as a result of many different disruptions in the further metabolism of iodide in the thyroid gland.
Treatment of thyrotoxicosis (including Graves' disease) with 600–2,000 mg potassium perchlorate (430-1,400 mg perchlorate) daily for periods of several months or longer was once common practice, particularly in Europe, and perchlorate use at lower doses to treat thyroid problems continues to this day. Although 400 mg of potassium perchlorate divided into four or five daily doses was used initially and found effective, higher doses were introduced when 400 mg/day was discovered not to control thyrotoxicosis in all subjects.
Current regimens for treatment of thyrotoxicosis (including Graves' disease), when a patient is exposed to additional sources of iodine, commonly include 500 mg potassium perchlorate twice per day for 18–40 days.
Prophylaxis with perchlorate-containing water at concentrations of 17 ppm, which corresponds to 0.5 mg/kg-day personal intake, if one is 70 kg and consumes 2 litres of water per day, was found to reduce baseline radioiodine uptake by 67% This is equivalent to ingesting a total of just 35 mg of perchlorate ions per day. In another related study where subjects drank just 1 litre of perchlorate-containing water per day at a concentration of 10 ppm, i.e. daily 10 mg of perchlorate ions were ingested, an average 38% reduction in the uptake of iodine was observed.
However, when the average perchlorate absorption in perchlorate plant workers subjected to the highest exposure has been estimated as approximately 0.5 mg/kg-day, as in the above paragraph, a 67% reduction of iodine uptake would be expected. Studies of chronically exposed workers though have thus far failed to detect any abnormalities of thyroid function, including the uptake of iodine. this may well be attributable to sufficient daily exposure or intake of healthy iodine-127 among the workers and the short 8 hr biological half life of perchlorate in the body.
To completely block the uptake of iodine-131 by the purposeful addition of perchlorate ions to a populaces water supply, aiming at dosages of 0.5 mg/kg-day, or a water concentration of 17 ppm, would therefore be grossly inadequate at truly reducing radioiodine uptake. Perchlorate ion concentrations in a regions water supply would need to be much higher, at least 7.15 mg/kg of body weight per day, or a water concentration of 250 ppm, assuming people drink 2 liters of water per day, to be truly beneficial to the population at preventing bioaccumulation when exposed to a radioiodine environment, independent of the availability of iodate or iodide drugs.
The continual distribution of perchlorate tablets or the addition of perchlorate to the water supply would need to continue for no less than 80–90 days, beginning immediately after the initial release of radioiodine was detected. After 80–90 days passed, released radioactive iodine-131 would have decayed to less than 0.1% of its initial quantity, at which time the danger from biouptake of iodine-131 is essentially over.
In the event of a radioiodine release, the ingestion of prophylaxis potassium iodide, if available, or even iodate, would rightly take precedence over perchlorate administration, and would be the first line of defense in protecting the population from a radioiodine release. However, in the event of a radioiodine release too massive and widespread to be controlled by the limited stock of iodide and iodate prophylaxis drugs, then the addition of perchlorate ions to the water supply, or distribution of perchlorate tablets would serve as a cheap, efficacious, second line of defense against carcinogenic radioiodine bioaccumulation.
The ingestion of goitrogen drugs is, much like potassium iodide also not without its dangers, such as hypothyroidism. In all these cases however, despite the risks, the prophylaxis benefits of intervention with iodide, iodate, or perchlorate outweigh the serious cancer risk from radioiodine bioaccumulation in regions where radioiodine has sufficiently contaminated the environment. | 1 | Fission Products + Nuclear Fission |
The agreed-upon isotopic composition of primary reference and the original calibration materials were generally not reached through interlaboratory comparison. In part this is simply because the original materials were used to the define the isotopic scales and so have no associated uncertainty. VSMOW serves as the primary reference and calibration material for the hydrogen isotope system and one of two possible scales for the oxygen isotope system, and was prepared by Harmon Craig. VSMOW2 is the replacement calibration standard and was calibrated by measurements at five selected laboratories. The isotopic composition of SLAP was reached through interlaboratory comparison. NBS-19 is the original calibration material for the carbon isotope scale made by I. Friedman, J. R. O’Neil and G. Cebula and is used to define the VPDB scale. IAEA-603 is the replacement calibration standard and was calibrated by measurements at three selected laboratories (GEOTOP-UQAM in Montreal, Canada; USGS in Reston, USA; MPI-BGC in Jena, Germany). The isotopic composition of LSVEC was reached through interlaboratory comparison. IAEA-S-1, the original calibration material for the sulfur isotope scale and still in use today, was prepared by B. W. Robinson. | 0 | Isotopes |
Nitrogen-15, or N, is often used in agricultural and medical research, for example in the Meselson–Stahl experiment to establish the nature of DNA replication. An extension of this research resulted in development of DNA-based stable-isotope probing, which allows examination of links between metabolic function and taxonomic identity of microorganisms in the environment, without the need for culture isolation. Proteins can be isotopically labelled by cultivating them in a medium containing N as the only source of nitrogen, e.g., in quantitative proteomics such as SILAC.
Nitrogen-15 is extensively used to trace mineral nitrogen compounds (particularly fertilizers) in the environment. When combined with the use of other isotopic labels, N is also a very important tracer for describing the fate of nitrogenous organic pollutants. Nitrogen-15 tracing is an important method used in biogeochemistry.
The ratio of stable nitrogen isotopes, N/N or δN, tends to increase with trophic level, such that herbivores have higher nitrogen isotope values than plants, and carnivores have higher nitrogen isotope values than herbivores. Depending on the tissue being examined, there tends to be an increase of 3-4 parts per thousand with each increase in trophic level. The tissues and hair of vegans therefore contain significantly lower δN than the bodies of people who eat mostly meat. Similarly, a terrestrial diet produces a different signature than a marine-based diet. Isotopic analysis of hair is an important source of information for archaeologists, providing clues about the ancient diets and differing cultural attitudes to food sources.
A number of other environmental and physiological factors can influence the nitrogen isotopic composition at the base of the food web (i.e. in plants) or at the level of individual animals. For example, in arid regions, the nitrogen cycle tends to be more open and prone to the loss of N, increasing δN in soils and plants. This leads to relatively high δN values in plants and animals in hot and arid ecosystems relative to cooler and moister ecosystems. Furthermore, elevated δN have been linked to the preferential excretion of 14N and reutilization of already enriched 15N tissues in the body under prolonged water stress conditions or insufficient protein intake.
δN also provides a diagnostic tool in planetary science as the ratio exhibited in atmospheres and surface materials "is closely tied to the conditions under which materials form". | 0 | Isotopes |
Of the 80 elements with a stable isotope, the largest number of stable isotopes observed for any element is ten (for the element tin). No element has nine or eight stable isotopes. Five elements have seven stable isotopes, eight have six stable isotopes, ten have five stable isotopes, nine have four stable isotopes, five have three stable isotopes, 16 have two stable isotopes (counting as stable), and 26 elements have only a single stable isotope (of these, 19 are so-called mononuclidic elements, having a single primordial stable isotope that dominates and fixes the atomic weight of the natural element to high precision; 3 radioactive mononuclidic elements occur as well). In total, there are 251 nuclides that have not been observed to decay. For the 80 elements that have one or more stable isotopes, the average number of stable isotopes is 251/80 ≈ 3.14 isotopes per element. | 0 | Isotopes |
Clumped isotopes analyses have traditionally been used in lieu of conventional δO analyses when the δO of seawater or source water is poorly constrained. While conventional δO analysis solves for temperature as a function of both carbonate and water δO, clumped isotope analyses can provide temperature estimates that are independent of the source water δO. Δ47-derived temperature can then be used in conjunction with carbonate δO to reconstruct δO of the source water, thus providing information on the water with which the carbonate was equilibrated.
Clumped isotope analyses thus allow for estimates of two key environmental variables: temperature and water δO. These variables are especially useful for reconstructing past climates, as they can provide information on a wide range of environmental properties. For example, temperature variability can imply changes in solar irradiance, greenhouse gas concentration, or albedo, while changes in water δO can be used to estimate changes in ice volume, sea level, or rainfall intensity and location.
Studies have used temperatures derived from clumped isotopes for varied and numerous paleoclimate applications — to constrain δO of past seawater, pinpoint the timing of icehouse-hothouse transitions, track changes in ice volume through an ice age, and to reconstruct temperature changes in ancient lake basins. | 0 | Isotopes |
Strontium-90 is classified as high-level waste. Its 29-year half-life means that it can take hundreds of years to decay to negligible levels. Exposure from contaminated water and food may increase the risk of leukemia and bone cancer. Reportedly, thousands of capsules of radioactive strontium containing millions of curies are stored at Hanford Site's Waste Encapsulation and Storage Facility. | 1 | Fission Products + Nuclear Fission |
The fission product mixture contains significant amounts of molybdenum. Molybdenum-99 is of enormous interest to nuclear medicine as the parent nuclide to but its short half life means it'll usually be decayed long before the spent fuel is reprocessed. can be produced both by fission followed by immediate reprocessing (usually only done in small scale research reactors) or in particle accelerators. As Molybdenum-100 only decays extremely slowly via double beta decay (half life longer than the age of the universe) the molybdenum content of spent fuel will be essentially stable after a few days have passed to allow the Molybdenum-99 to decay. | 1 | Fission Products + Nuclear Fission |
For introduction of radionuclides into organism, ingestion is the most important route. Insoluble compounds are not absorbed from the gut and cause only local irradiation before they are excreted. Soluble forms however show wide range of absorption percentages. | 1 | Fission Products + Nuclear Fission |
Since its original descriptions, the Urey–Bigeleisen–Mayer equation has taken many forms. Given an isotopic exchange reaction , such that designates a molecule containing an isotope of interest, the equation can be expressed by relating the equilibrium constant, , to the product of partition function ratios, namely the translational, rotational, vibrational, and sometimes electronic partition functions. Thus the equation can be written as: where and is each respective partition function of molecule or atom . It is typical to approximate the rotational partition function ratio as quantized rotational energies in a rigid rotor system. The Urey model also treats molecular vibrations as simplified harmonic oscillators and follows the Born–Oppenheimer approximation.
Isotope partitioning behavior is often reported as a reduced partition function ratio, a simplified form of the Bigeleisen–Mayer equation notated mathematically as or . The reduced partition function ratio can be derived from power series expansion of the function and allows the partition functions to be expressed in terms of frequency. It can be used to relate molecular vibrations and intermolecular forces to equilibrium isotope effects.
As the model is an approximation, many applications append corrections for improved accuracy. Some common, significant modifications to the equation include accounting for pressure effects, nuclear geometry, and corrections for anharmonicity and quantum mechanical effects. For example, hydrogen isotope exchange reactions have been shown to disagree with the requisite assumptions for the model but correction techniques using path integral methods have been suggested. | 0 | Isotopes |
Used for the first time in 1951 to localize leaks in a drinking water supply system of Munich, Germany, iodine-131 became one of the most commonly used gamma-emitting industrial radioactive tracers, with applications in isotope hydrology and leak detection.
Since the late 1940s, radioactive tracers have been used by the oil industry. Tagged at the surface, water is then tracked downhole, using the appropriated gamma detector, to determine flows and detect underground leaks. I-131 has been the most widely used tagging isotope in an aqueous solution of sodium iodide. It is used to characterize the hydraulic fracturing fluid to help determine the injection profile and location of fractures created by hydraulic fracturing. | 1 | Fission Products + Nuclear Fission |
The I isotope is also used as a radioactive label for certain radiopharmaceuticals that can be used for therapy, e.g. I-metaiodobenzylguanidine (I-MIBG) for imaging and treating pheochromocytoma and neuroblastoma. In all of these therapeutic uses, I destroys tissue by short-range beta radiation. About 90% of its radiation damage to tissue is via beta radiation, and the rest occurs via its gamma radiation (at a longer distance from the radioisotope). It can be seen in diagnostic scans after its use as therapy, because I is also a gamma-emitter. | 1 | Fission Products + Nuclear Fission |
Oxygen comes in three variants, but the O is so rare that it is very difficult to detect (~0.04% abundant). The ratio of O/O in water depends on the amount of evaporation the water experienced (as O is heavier and therefore less likely to vaporize). As the vapor tension depends on the concentration of dissolved salts, the O/O ratio shows correlation on the salinity and temperature of water. As oxygen gets built into the shells of calcium carbonate secreting organisms, such sediments provide a chronological record of temperature and salinity of the water in the area.
Oxygen isotope ratio in atmosphere varies predictably with time of year and geographic location; e.g. there is a 2% difference between O-rich precipitation in Montana and O-depleted precipitation in Florida Keys. This variability can be used for approximate determination of geographic location of origin of a material; e.g. it is possible to determine where a shipment of uranium oxide was produced. The rate of exchange of surface isotopes with the environment has to be taken in account.
The oxygen isotopic signatures of solid samples (organic and inorganic) are usually measured with pyrolysis and mass spectrometry. Researchers need to avoid improper or prolonged storage of the samples for accurate measurements. | 0 | Isotopes |
A primordial element is a chemical element with at least one primordial nuclide. There are 251 stable primordial nuclides and 35 radioactive primordial nuclides, but only 80 primordial stable elements—hydrogen through lead, atomic numbers 1 to 82, with the exceptions of technetium (43) and promethium (61)—and three radioactive primordial elements—bismuth (83), thorium (90), and uranium (92). If plutonium (94) turns out to be primordial (specifically, the long-lived isotope Pu), then it would be a fourth radioactive primordial, though practically speaking it would still be more convenient to produce synthetically. Bismuth's half-life is so long that it is often classed with the 80 primordial stable elements instead, since its radioactivity is not a cause for serious concern. The number of elements is smaller than the number of nuclides, because many of the primordial elements are represented by multiple isotopes. See chemical element for more information. | 0 | Isotopes |
In a typical nuclear reactor fueled with uranium-235, the presence of Xe as a fission product presents designers and operators with problems due to its large neutron cross section for absorption. Because absorbing neutrons can detrimentally affect a nuclear reactors ability to increase power, reactors are designed to mitigate this effect; operators are trained to properly anticipate and react to these transients. In fact, during World War II, Enrico Fermi suspected the effect of Xe , and followed the advice of Emilio Segrè in contacting his student Chien-Shiung Wu. Wus soon-to-be published paper on Xe-135 completely verified Fermi's guess that it absorbed neutrons and disrupted the B Reactor that was being used in their project.
During periods of steady state operation at a constant neutron flux level, the Xe concentration builds up to its equilibrium value for that reactor power in about 40 to 50 hours. When the reactor power is increased, Xe concentration initially decreases because the burn up is increased at the new higher power level. Because 95% of the Xe production is from decay of I , which has a 6.57 hour half-life, the production of Xe remains constant; at this point, the Xe concentration reaches a minimum. The concentration then increases to the new equilibrium level (more accurately steady state level) for the new power level in roughly 40 to 50 hours. During the initial 4 to 6 hours following the power change, the magnitude and the rate of change of concentration is dependent upon the initial power level and on the amount of change in power level; the Xe concentration change is greater for a larger change in power level. When reactor power is decreased, the process is reversed.
Iodine-135 is a fission product of uranium with a yield of about 6% (counting also the I produced almost immediately from decay of fission-produced tellurium-135). This I decays with a 6.57 hour half-life to Xe. Thus, in an operating nuclear reactor, Xe is being continuously produced. Xe has a very large neutron absorption cross-section, so in the high-neutron-flux environment of a nuclear reactor core, the Xe soon absorbs a neutron and becomes effectively stable . (The half life of is >10 years, and it is not treated as a radioisotope.) Thus, in about 50 hours, the Xe concentration reaches equilibrium where its creation by I decay is balanced with its destruction by neutron absorption.
When reactor power is decreased or shut down by inserting neutron-absorbing control rods, the reactor neutron flux is reduced and the equilibrium shifts initially towards higher Xe concentration. The Xe concentration peaks about 11.1 hours after reactor power is decreased. Since Xe has a 9.2 hour half-life, the Xe concentration gradually decays back to low levels over 72 hours.
The temporarily high level of Xe with its high neutron absorption cross-section makes it difficult to restart the reactor for several hours. The neutron-absorbing Xe acts like a control rod, reducing reactivity. The inability of a reactor to be started due to the effects of Xe is sometimes referred to as xenon-precluded start-up, and the reactor is said to be "poisoned out". The period of time that the reactor is unable to overcome the effects of Xe is called the "xenon dead time".
If sufficient reactivity control authority is available, the reactor can be restarted, but the xenon burn-out transient must be carefully managed. As the control rods are extracted and criticality is reached, neutron flux increases many orders of magnitude and the Xe begins to absorb neutrons and be transmuted to . The reactor burns off the nuclear poison. As this happens, the reactivity and neutron flux increases, and the control rods must be gradually reinserted to counter the loss of neutron absorption by the Xe. Otherwise, the reactor neutron flux will continue to increase, burning off even more xenon poison, on a path to runaway criticality. The time constant for this burn-off transient depends on the reactor design, power level history of the reactor for the past several days, and the new power setting. For a typical step up from 50% power to 100% power, Xe concentration falls for about 3 hours.
Xenon poisoning was a contributing factor to the Chernobyl disaster; during a run-down to a lower power, a combination of operator error and xenon poisoning caused the reactor thermal power to fall to near-shutdown levels. The crew's resulting efforts to restore power placed the reactor in a highly unsafe configuration. A flaw in the SCRAM system inserted positive reactivity, causing a thermal transient and a steam explosion that tore the reactor apart.
Reactors using continuous reprocessing like many molten salt reactor designs might be able to extract Xe from the fuel and avoid these effects. Fluid fuel reactors cannot develop xenon inhomogeneity because the fuel is free to mix. Also, the Molten Salt Reactor Experiment demonstrated that spraying the liquid fuel as droplets through a gas space during recirculation can allow xenon and krypton to leave the fuel salts. Removing Xe from neutron exposure improves neutron economy, but causes the reactor to produce more of the long-lived fission product Cs. The long lived (but 76000 times less radioactive) caesium-135 condenses in a separate tank after the decay of Xe, and is physically separate from the 30.05 year half life caesium-137 (Cs) produced in the fuel, and it is practical to handle them separately (fission yield is appr. 6% for both). | 1 | Fission Products + Nuclear Fission |
When working on the global annual average isotopic composition of oxygen-18 and deuterium (H) in meteoric water, geochemist Harmon Craig observed a correlation between these two isotopes, and subsequently developed and defined the equation for GMWL:
Where δO and δH (also known as δD) are the ratio of heavy to light isotopes (e.g. O/O, H/H).
The relationship of δO and δH in meteoric water is caused by mass dependent fractionation of oxygen and hydrogen isotopes between evaporation from ocean seawater and condensation from vapor. As oxygen isotopes (O and O) and hydrogen isotopes (H and H) have different masses, they behave differently in the evaporation and condensation processes, and thus result in the fractionation between O and O as well as H and H. Equilibrium fractionation causes the isotope ratios of δO and δH to vary between localities within the area. The fractionation processes can be influenced by a number of factors including: temperature, latitude, continentality, and most importantly, humidity. | 0 | Isotopes |
Elements are composed either of one nuclide (mononuclidic elements), or of more than one naturally occurring isotopes. The unstable (radioactive) isotopes are either primordial or postprimordial. Primordial isotopes were a product of stellar nucleosynthesis or another type of nucleosynthesis such as cosmic ray spallation, and have persisted down to the present because their rate of decay is so slow (e.g. uranium-238 and potassium-40). Post-primordial isotopes were created by cosmic ray bombardment as cosmogenic nuclides (e.g., tritium, carbon-14), or by the decay of a radioactive primordial isotope to a radioactive radiogenic nuclide daughter (e.g. uranium to radium). A few isotopes are naturally synthesized as nucleogenic nuclides, by some other natural nuclear reaction, such as when neutrons from natural nuclear fission are absorbed by another atom.
As discussed above, only 80 elements have any stable isotopes, and 26 of these have only one stable isotope. Thus, about two-thirds of stable elements occur naturally on Earth in multiple stable isotopes, with the largest number of stable isotopes for an element being ten, for tin (). There are about 94 elements found naturally on Earth (up to plutonium inclusive), though some are detected only in very tiny amounts, such as plutonium-244. Scientists estimate that the elements that occur naturally on Earth (some only as radioisotopes) occur as 339 isotopes (nuclides) in total. Only 251 of these naturally occurring nuclides are stable, in the sense of never having been observed to decay as of the present time. An additional 35 primordial nuclides (to a total of 286 primordial nuclides), are radioactive with known half-lives, but have half-lives longer than 100 million years, allowing them to exist from the beginning of the Solar System. See list of nuclides for details.
All the known stable nuclides occur naturally on Earth; the other naturally occurring nuclides are radioactive but occur on Earth due to their relatively long half-lives, or else due to other means of ongoing natural production. These include the afore-mentioned cosmogenic nuclides, the nucleogenic nuclides, and any radiogenic nuclides formed by ongoing decay of a primordial radioactive nuclide, such as radon and radium from uranium.
An additional ~3000 radioactive nuclides not found in nature have been created in nuclear reactors and in particle accelerators. Many short-lived nuclides not found naturally on Earth have also been observed by spectroscopic analysis, being naturally created in stars or supernovae. An example is aluminium-26, which is not naturally found on Earth but is found in abundance on an astronomical scale.
The tabulated atomic masses of elements are averages that account for the presence of multiple isotopes with different masses. Before the discovery of isotopes, empirically determined noninteger values of atomic mass confounded scientists. For example, a sample of chlorine contains 75.8% chlorine-35 and 24.2% chlorine-37, giving an average atomic mass of 35.5 atomic mass units.
According to generally accepted cosmology theory, only isotopes of hydrogen and helium, traces of some isotopes of lithium and beryllium, and perhaps some boron, were created at the Big Bang, while all other nuclides were synthesized later, in stars and supernovae, and in interactions between energetic particles such as cosmic rays, and previously produced nuclides. (See nucleosynthesis for details of the various processes thought responsible for isotope production.) The respective abundances of isotopes on Earth result from the quantities formed by these processes, their spread through the galaxy, and the rates of decay for isotopes that are unstable. After the initial coalescence of the Solar System, isotopes were redistributed according to mass, and the isotopic composition of elements varies slightly from planet to planet. This sometimes makes it possible to trace the origin of meteorites. | 0 | Isotopes |
Barium is formed in large amounts by the fission process. A short-lived barium isotope was confused with radium by some early workers. They were bombarding uranium with neutrons in an attempt to form a new element. But instead they caused fission which generated a large amount of radioactivity in the target. Because the chemistry of barium and radium the two elements could be coseparated by for instance a precipitation with sulfate anions. Because of this similarity of their chemistry the early workers thought that the very radioactive fraction which was separated into the "radium" fraction contained a new isotope of radium. Some of this early work was done by Otto Hahn and Fritz Strassmann. | 1 | Fission Products + Nuclear Fission |
Iodine in food is absorbed by the body and preferentially concentrated in the thyroid where it is needed for the functioning of that gland. When I is present in high levels in the environment from radioactive fallout, it can be absorbed through contaminated food, and will also accumulate in the thyroid. As it decays, it may cause damage to the thyroid. The primary risk from exposure to I is an increased risk of radiation-induced cancer in later life. Other risks include the possibility of non-cancerous growths and thyroiditis.
The risk of thyroid cancer in later life appears to diminish with increasing age at time of exposure. Most risk estimates are based on studies in which radiation exposures occurred in children or teenagers. When adults are exposed, it has been difficult for epidemiologists to detect a statistically significant difference in the rates of thyroid disease above that of a similar but otherwise-unexposed group.
The risk can be mitigated by taking iodine supplements, raising the total amount of iodine in the body and, therefore, reducing uptake and retention in the face and chest and lowering the relative proportion of radioactive iodine. However, such supplements were not consistently distributed to the population living nearest to the Chernobyl nuclear power plant after the disaster, though they were widely distributed to children in Poland.
Within the US, the highest I fallout doses occurred during the 1950s and early 1960s to children having consumed fresh milk from sources contaminated as the result of above-ground testing of nuclear weapons. The National Cancer Institute provides additional information on the health effects from exposure to I in fallout, as well as individualized estimates, for those born before 1971, for each of the 3070 counties in the USA. The calculations are taken from data collected regarding fallout from the nuclear weapons tests conducted at the Nevada Test Site.
On 27 March 2011, the Massachusetts Department of Public Health reported that I was detected in very low concentrations in rainwater from samples collected in Massachusetts, USA, and that this likely originated from the Fukushima power plant. Farmers near the plant dumped raw milk, while testing in the United States found 0.8 pico-curies per liter of iodine-131 in a milk sample, but the radiation levels were 5,000 times lower than the FDA's "defined intervention level".
The levels were expected to drop relatively quickly | 1 | Fission Products + Nuclear Fission |
Of the known chemical elements, 80 elements have at least one stable nuclide. These comprise the first 82 elements from hydrogen to lead, with the two exceptions, technetium (element 43) and promethium (element 61), that do not have any stable nuclides. As of 2023, there were a total of 251 known "stable" nuclides. In this definition, "stable" means a nuclide that has never been observed to decay against the natural background. Thus, these elements have half-lives too long to be measured by any means, direct or indirect.
Stable isotopes:
* 1 element (tin) has 10 stable isotopes
* 5 elements have 7 stable isotopes apiece
* 7 elements have 6 stable isotopes apiece
* 11 elements have 5 stable isotopes apiece
* 9 elements have 4 stable isotopes apiece
* 5 elements have 3 stable isotopes apiece
* 16 elements have 2 stable isotopes apiece
* 26 elements have 1 single stable isotope.
These last 26 are thus called monoisotopic elements. The mean number of stable isotopes for elements which have at least one stable isotope is 251/80 = 3.1375. | 0 | Isotopes |
Isotope biogeochemistry has been used to investigate the timeline surrounding life and its earliest iterations on Earth. Isotopic fingerprints typical of life, preserved in sediments, have been used to suggest, but do not necessarily prove, that life was already in existence on Earth by 3.85 billion years ago.
Sulfur isotope evidence has also been used to corroborate the timing of the Great Oxidation Event, during which the Earth's atmosphere experienced a measurable rise in oxygen (to about 9% of modern values) for the first time about 2.3-2.4 billion years ago. Mass-independent sulfur isotope fractionations are found to be widespread in the geologic record before about 2.45 billion years ago, and these isotopic signatures have since ceded to mass-dependent fractionation, providing strong evidence that the atmosphere shifted from anoxic to oxygenated at that threshold.
Modern sulfate-reducing bacteria are known to favorably reduce lighter S instead of S, and the presence of these microorganisms can measurably alter the sulfur isotope composition of the ocean. Because the δS values of sulfide minerals is primarily influenced by the presence of sulfate-reducing bacteria, the absence of sulfur isotope fractionations in sulfide minerals suggests the absence of these bacterial processes or the absence of freely available sulfate. Some have used this knowledge of microbial sulfur fractionation to suggest that minerals (namely pyrite) with large sulfur isotope fractionations relative to the inferred seawater composition may be evidence of life. This claim is not clear-cut, however, and is sometimes contested using geologic evidence from the ~3.49 Ga sulfide minerals found in the Dresser Formation of Western Australia, which are found to have δS values as negative as -22‰. Because it has not been proven that the sulfide and barite minerals formed in the absence of major hydrothermal input, it is not conclusive evidence of life or of the microbial sulfate reduction pathway in the Archean. | 0 | Isotopes |
Stable isotopes have become a popular method for understanding aquatic ecosystems because they can help scientists in understanding source links and process information in marine food webs. These analyses can also be used to a certain degree in terrestrial systems. Certain isotopes can signify distinct primary producers forming the bases of food webs and trophic level positioning. The stable isotope compositions are expressed in terms of delta values (δ) in permil (‰), i.e. parts per thousand differences from a standard. They express the proportion of an isotope that is in a sample. The values are expressed as:
: δX = [(R / R) – 1] × 10
where X represents the isotope of interest (e.g., C) and R represents the ratio of the isotope of interest and its natural form (e.g., C/C). Higher (or less negative) delta values indicate increases in a samples isotope of interest, relative to the standard, and lower (or more negative) values indicate decreases. The standard reference materials for carbon, nitrogen, and sulfur are Pee Dee Belamnite limestone, nitrogen gas in the atmosphere, and Cañon Diablo meteorite respectively. Analysis is usually done using a mass spectrometer, detecting small differences between gaseous elements. Analysis of a sample can cost anywhere from $30 to $100. Stable isotopes assist scientists in analyzing animal diets and food webs by examining the animal tissues that bear a fixed isotopic enrichment or depletion vs. the diet. Muscle or protein fractions have become the most common animal tissue used to examine the isotopes because they represent the assimilated nutrients in their diet. The main advantage to using stable isotope analysis as opposed to stomach content observations is that no matter what the status is of the animals stomach (empty or not), the isotope tracers in the tissues will give us an understanding of its trophic position and food source. The three major isotopes used in aquatic ecosystem food web analysis are C, N and S. While all three indicate information on trophic dynamics, it is common to perform analysis on at least two of the previously mentioned 3 isotopes for better understanding of marine trophic interactions and for stronger results. | 0 | Isotopes |
After Cs and Sr have decayed to low levels, the bulk of radioactivity from spent fuel come not from fission products but actinides, notably plutonium-239 (half-life 24 ka), plutonium-240 (6.56 ka), americium-241 (432 years), americium-243 (7.37 ka), curium-245 (8.50 ka), and curium-246 (4.73 ka). These can be recovered by nuclear reprocessing (either before or after most Cs and Sr decay) and fissioned, offering the possibility of greatly reducing waste radioactivity in the time scale of about 10 to 10 years. Pu is usable as fuel in existing thermal reactors, but some minor actinides like Am, as well as the non-fissile and less-fertile isotope plutonium-242, are better destroyed in fast reactors, accelerator-driven subcritical reactors, or fusion reactors. Americium-241 has some industrial applications and is used in smoke detectors and is thus often separated from waste as it fetches a price that makes such separation economic. | 1 | Fission Products + Nuclear Fission |
As an example of isotopic symmetry (in compositional, and not in geometrical sense) affecting the kinetics of physic-chemical processes, see mass independent isotope fractionation in ozone O. | 0 | Isotopes |
A wide range of biological changes may follow the irradiation of animals. These vary from rapid death following high doses of penetrating whole-body radiation, to essentially normal lives for a variable period of time until the development of delayed radiation effects, in a portion of the exposed population, following low dose exposures.
The unit of actual exposure is the röntgen, defined in ionisations per unit volume of air. All ionisation based instruments (including geiger counters and ionisation chambers) measure exposure. However, effects depend on the energy per unit mass, not the exposure measured in air. A deposit of 1 joule per kilogram has the unit of 1 gray (Gy). For 1 MeV energy gamma rays, an exposure of 1 röntgen in air produces a dose of about 0.01 gray (1 centigray, cGy) in water or surface tissue. Because of shielding by the tissue surrounding the bones, the bone marrow only receives about 0.67 cGy when the air exposure is 1 röntgen and the surface skin dose is 1 cGy. Some lower values reported for the amount of radiation that would kill 50% of personnel (the ) refer to bone marrow dose, which is only 67% of the air dose. | 1 | Fission Products + Nuclear Fission |
The International Nuclear and Radiological Event Scale (INES) is the primary form of categorizing the potential health and environmental effects of a nuclear or radiological event and communicating it to the public. The scale, which was developed in 1990 by the International Atomic Energy Agency and the Nuclear Energy Agency of the Organization for Economic Co-operation and Development, classifies these nuclear accidents based on the potential impact of the fallout:
* Defence-in-Depth: This is the lowest form of nuclear accidents and refers to events that have no direct impact on people or the environment but must be taken note of to improve future safety measures.
* Radiological Barriers and Control: This category refers to events that have no direct impact on people or the environment and only refer to the damage caused within major facilities.
* People and the Environment: This section of the scale consists of more serious nuclear accidents. Events in this category could potentially cause radiation to spread to people close to the location of the accident. This also includes an unplanned, widespread release of the radioactive material.
The INES scale is composed of seven steps that categorize the nuclear events, ranging from anomalies that must be recorded to improve upon safety measures to serious accidents that require immediate action.
Chernobyl
The 1986 nuclear reactor explosion at Chernobyl was categorized as a Level 7 accident, which is the highest possible ranking on the INES scale, due to widespread environmental and health effects and "external release of a significant fraction of reactor core inventory". The nuclear accident still stands as the only accident in commercial nuclear power that led to radiation-related deaths. The steam explosion and fires released approximately 5200 PBq, or at least 5 percent of the reactor core, into the atmosphere. The explosion itself resulted in the deaths of two plant workers, while 28 people died over the weeks that followed of severe radiation poisoning. Furthermore, young children and adolescents in the areas most contaminated by the radiation exposure showed an increase in the risk for thyroid cancer, although the United Nations Scientific Committee on the Effects of Atomic Radiation stated that "there is no evidence of a major public health impact" apart from that. The nuclear accident also took a heavy toll on the environment, including contamination in urban environments caused by the deposition of radionuclides and the contamination of "different crop types, in particular, green leafy vegetables ... depending on the deposition levels, and time of the growing season".
Three Mile Island
The nuclear meltdown at Three Mile Island in 1979 was categorized as a Level 5 accident on the INES scale because of the "severe damage to the reactor core" and the radiation leak caused by the incident. Three Mile Island was the most serious accident in the history of American commercial nuclear power plants, yet the effects were different from those of the Chernobyl accident. A study done by the Nuclear Regulatory Commission following the incident reveals that the nearly 2 million people surrounding the Three Mile Island plant "are estimated to have received an average radiation dose of only 1 millirem above the usual background dose". Furthermore, unlike those affected by radiation in the Chernobyl accident, the development of thyroid cancer in the people around Three Mile Island was "less aggressive and less advanced".
Fukushima
Like the Three Mile Island incident, the incident at Fukushima was initially categorized as a Level 5 accident on the INES scale after a tsunami disabled the power supply and cooling of three reactors, which then suffered significant melting in the days that followed. However, after combining the events at the three reactors rather than assessing them individually, the accident was upgraded to an INES Level 7. The radiation exposure from the incident caused a recommended evacuation for inhabitants up to 30 km away from the plant. However, it was also hard to track such exposure because 23 out of the 24 radioactive monitoring stations were also disabled by the tsunami. Removing contaminated water, both in the plant itself and run-off water that spread into the sea and nearby areas, became a huge challenge for the Japanese government and plant workers. During the containment period following the accident, thousands of cubic meters of slightly contaminated water were released in the sea to free up storage for more contaminated water in the reactor and turbine buildings. However, the fallout from the Fukushima accident had a minimal impact on the surrounding population. According to the Institut de Radioprotection et de Surêté Nucléaire, over 62 percent of assessed residents within the Fukushima prefecture received external doses of less than 1 mSv in the four months following the accident. In addition, comparing screening campaigns for children inside the Fukushima prefecture and in the rest of the country revealed no significant difference in the risk of thyroid cancer. | 1 | Fission Products + Nuclear Fission |
A great deal of the lighter lanthanides (lanthanum, cerium, neodymium, and samarium) are formed as fission products. In Africa, at Oklo where the natural nuclear fission reactor operated over a billion years ago, the isotopic mixture of neodymium is not the same as normal neodymium, it has an isotope pattern very similar to the neodymium formed by fission.
In the aftermath of criticality accidents, the level of La is often used to determine the fission yield (in terms of the number of nuclei which underwent fission).
Samarium-149 is the second most important neutron poison in nuclear reactor physics. Samarium-151, produced at lower yields, is the third most abundant medium-lived fission product but emits only weak beta radiation. Both have high neutron absorption cross sections, so that much of them produced in a reactor are later destroyed there by neutron absorption.
Lanthanides are a problem in nuclear reprocessing because they are chemically very similar to actinides and most reprocessing aims at separating some or all of the actinides from the fission products or at least the neutron poisons among them. | 1 | Fission Products + Nuclear Fission |
Isotope analysis is the identification of isotopic signature, abundance of certain stable isotopes of chemical elements within organic and inorganic compounds. Isotopic analysis can be used to understand the flow of energy through a food web, to reconstruct past environmental and climatic conditions, to investigate human and animal diets, for food authentification, and a variety of other physical, geological, palaeontological and chemical processes. Stable isotope ratios are measured using mass spectrometry, which separates the different isotopes of an element on the basis of their mass-to-charge ratio. | 0 | Isotopes |
Lead consists of four stable isotopes: Pb, Pb, Pb, and Pb. Local variations in uranium/thorium/lead content cause a wide location-specific variation of isotopic ratios for lead from different localities. Lead emitted to the atmosphere by industrial processes has an isotopic composition different from lead in minerals. Combustion of gasoline with tetraethyllead additive led to formation of ubiquitous micrometer-sized lead-rich particulates in car exhaust smoke; especially in urban areas the man-made lead particles are much more common than natural ones. The differences in isotopic content in particles found in objects can be used for approximate geolocation of the object's origin. | 0 | Isotopes |
Cold fission or cold nuclear fission is defined as involving fission events for which fission fragments have such low excitation energy that no neutrons or gammas are emitted.
Cold fission events have so low a probability of occurrence that it is necessary to use a high-flux nuclear reactor to study them.
According to research first published in 1981, the first observation of cold fission events was in experiments on fission induced by thermal neutrons of uranium 233, uranium 235, and plutonium 239 using the high-flux reactor at the Institut Laue-Langevin in Grenoble, France. Other experiments on cold fission were also done involving Cm and Cf. A unified approach of cluster decay, alpha decay and cold fission was developed by Dorin N. Poenaru et al. A phenomenological interpretation was proposed by Gönnenwein and Duarte et al.
The importance of cold fission phenomena lies in the fact that fragments reaching detectors have the same mass that they obtained at the "scission" configuration, just before the attractive but short-range nuclear force becomes null, and only Coulomb interaction acts between fragments. After this, Coulomb potential energy is converted into fragments of kinetic energies, which—added to pre-scission kinetic energies—is measured by detectors.
The fact that cold fission preserves nuclear mass until the fission fragments reach the detectors permits the experimenter to better determine the fission dynamics, especially the aspects related to Coulomb and shell effects in low energy fission and nucleon pair breaking. Adopting several theoretical assumptions about scission configuration one can calculate the maximal value of kinetic energy as a function of charge and mass of fragments and compare them to experimental results. | 1 | Fission Products + Nuclear Fission |
Unlike many other dating techniques, fission-track dating is uniquely suited for determining low-temperature thermal events using common accessory minerals over a very wide geological range (typically 0.1 Ma to 2000 Ma). Apatite, sphene, zircon, micas and volcanic glass typically contain enough uranium to be useful in dating samples of relatively young age (Mesozoic and Cenozoic) and are the materials most useful for this technique. Additionally low-uranium epidotes and garnets may be used for very old samples (Paleozoic to Precambrian). The fission-track dating technique is widely used in understanding the thermal evolution of the upper crust, especially in mountain belts. Fission tracks are preserved in a crystal when the ambient temperature of the rock falls below the annealing temperature. This annealing temperature varies from mineral to mineral and is the basis for determining low-temperature vs. time histories. While the details of closure temperatures are complicated, they are approximately 70 to 110 °C for typical apatite, c. 230 to 250 °C for zircon, and c. 300 °C for titanite.
Because heating of a sample above the annealing temperature causes the fission damage to heal or anneal, the technique is useful for dating the most recent cooling event in the history of the sample. This resetting of the clock can be used to investigate the thermal history of basin sediments, kilometer-scale exhumation caused by tectonism and erosion, low temperature metamorphic events, and geothermal vein formation. The fission track method has also been used to date archaeological sites and artifacts. It was used to confirm the potassium-argon dates for the deposits at Olduvai Gorge. | 1 | Fission Products + Nuclear Fission |
Krypton-85 (Kr) is a radioisotope of krypton.
Krypton-85 has a half-life of 10.756 years and a maximum decay energy of 687 keV. It decays into stable rubidium-85. Its most common decay (99.57%) is by beta particle emission with maximum energy of 687 keV and an average energy of 251 keV. The second most common decay (0.43%) is by beta particle emission (maximum energy of 173 keV) followed by gamma ray emission (energy of 514 keV). Other decay modes have very small probabilities and emit less energetic gamma rays. Krypton-85 is mostly synthetic, though it is produced naturally in trace quantities by cosmic ray spallation.
In terms of radiotoxicity, 440 Bq of Kr is equivalent to 1 Bq of radon-222, without considering the rest of the radon decay chain. | 1 | Fission Products + Nuclear Fission |
Niobium-95, with a half-life of 35 days, is initially present as a fission product. The only stable isotope of niobium has mass number 93, and fission products of mass 93 first decay to long-lived zirconium-93 (half-life 1.53 Ma). Niobium-95 will decay to molybdenum-95 which is stable. | 1 | Fission Products + Nuclear Fission |
Nuclear weapons employ high quality, highly enriched fuel exceeding the critical size and geometry (critical mass) necessary in order to obtain an explosive chain reaction. The fuel for energy purposes, such as in a nuclear fission reactor, is very different, usually consisting of a low-enriched oxide material (e.g. UO). There are two primary isotopes used for fission reactions inside of nuclear reactors. The first and most common is uranium-235. This is the fissile isotope of uranium and it makes up approximately 0.7% of all naturally occurring uranium. Because of the small amount of U that exists, it is considered a non-renewable energy source despite being found in rock formations around the world. Uranium-235 cannot be used as fuel in its base form for energy production. It must undergo a process known as refinement to produce the compound UO or uranium dioxide. The uranium dioxide is then pressed and formed into ceramic pellets, which can subsequently be placed into fuel rods. This is when the compound uranium dioxide can be used for nuclear power production. The second most common isotope used in nuclear fission is plutonium-239. This is due to its ability to become fissile with slow neutron interaction. This isotope is formed inside nuclear reactors through exposing U to the neutrons released during fission. As a result of neutron capture, uranium-239 is produced, which undergoes two beta decays to become plutonium-239. Plutonium once occurred as a primordial element in the earth's crust, but only trace amounts remain, so it is predominantly synthetic. Another proposed fuel for nuclear reactors, which however plays no commercial role as of 2021, is uranium-233, which is "bred" by neutron capture and subsequent beta decays from natural thorium, which is almost 100% composed of the isotope thorium-232. This is called the thorium fuel cycle. | 1 | Fission Products + Nuclear Fission |
Atomic nuclei consist of protons and neutrons bound together by the residual strong force. Because protons are positively charged, they repel each other. Neutrons, which are electrically neutral, stabilize the nucleus in two ways. Their copresence pushes protons slightly apart, reducing the electrostatic repulsion between the protons, and they exert the attractive nuclear force on each other and on protons. For this reason, one or more neutrons are necessary for two or more protons to bind into a nucleus. As the number of protons increases, so does the ratio of neutrons to protons necessary to ensure a stable nucleus (see graph at right). For example, although the neutron:proton ratio of is 1:2, the neutron:proton ratio of is greater than 3:2. A number of lighter elements have stable nuclides with the ratio 1:1 (Z = N). The nuclide (calcium-40) is observationally the heaviest stable nuclide with the same number of neutrons and protons. All stable nuclides heavier than calcium-40 contain more neutrons than protons. | 0 | Isotopes |
At branch points, two or more separate reactions compete for the same reactant. This affects the isotopic composition of all products downstream of the branch point. To illustrate this, consider the network below:
Here, the flux of material into pool B (φ) is balanced by two fluxes, one into pool C and the other into pool D (φ and φ respectively). The mass balance for the heavier isotope in this system is represented by
Define f = φ / (φ + φ) = φ/φ as the fractional yield of C. Dividing through by φ gives
Applying the approximation introduced in the previous section, δ ≈ δ + ε. Further, δ ≈ δ + ε and δ ≈ δ + ε. Substituting these relations into the mass balance and solving for δ gives
The isotopic composition of pool B is clearly dependent on the fractional yield of C. Since there are no fluxes out of pools C or D, δ = δ, δ = δ. Thus, the isotopic compositions of these pools are offset from δ by ε and ε respectively. The figure at right summarizes these results. | 0 | Isotopes |
The strontium radioisotopes are very important, as strontium is a calcium mimic which is incorporated in bone growth and therefore has a great ability to harm humans. On the other hand, this also allows Sr to be used in the open source radiotherapy of bone tumors. This tends to be used in palliative care to reduce the pain due to secondary tumors in the bones.
Strontium-90 is a strong beta emitter with a half-life of 28.8 years. Its fission product yield decreases as the mass of the fissile nuclide increases - fission of produces more than fission of with fission of in the middle. A map of Sr contamination around Chernobyl has been published by the IAEA. Due to its very small neutron absorption cross section, Strontium-90 is poorly suited for thermal neutron induced nuclear transmutation as a way of disposing of it.
Strontium-90 has been used in radioisotope thermoelectric generators (RTGs) in the past because of its relatively high power density (0.95 W/g for the metal, 0.46 W/g for the commonly used inert perovskite form Strontium titanate) and because it is easily extracted from spent fuel (both native Strontium metal and Strontium oxide react with water by forming soluble Strontium hydroxide). However, the increased availability of renewable energy for off-grid applications formerly served by RTGs as well as concern about orphan sources has led to a nigh-total abandonment of in RTGs. The few (largely space based) applications for RTGs that still exist are largely supplied by despite its higher cost, as it has a higher power density, longer half life and is easier shielded since it is an alpha emitter while Strontium-90 is a beta emitter. | 1 | Fission Products + Nuclear Fission |
The idea of boosting was originally developed between late 1947 and late 1949 at Los Alamos. The primary benefit of boosting is further miniaturization of nuclear weapons as it reduces the minimum inertial confinement time required for a supercritical nuclear explosion by providing a sudden influx of fast neutrons before the critical mass would blow itself apart. This would eliminate the need for an aluminum pusher and uranium tamper and the explosives needed to push them and the fissile material into a supercritical state. While the bulky Fat Man had a diameter of and required 3 tons of high explosives for implosion, a boosted fission primary can be fitted on a small nuclear warhead (such as the W88) to ignite the thermonuclear secondary. | 1 | Fission Products + Nuclear Fission |
Rubidium-87 has such a long half life as to be essentially stable (longer than the age of the Earth). Rubidium-86 quickly decays to stable Strontium-86 if produced either directly, via (n,2n) reactions in Rubidium-87 or via neutron capture in Rubidium-85. | 1 | Fission Products + Nuclear Fission |
The Facility for Rare Isotope Beams (FRIB) is a scientific user facility for nuclear science, funded by the U.S. Department of Energy Office of Science (DOE-SC), Michigan State University (MSU), and the State of Michigan. Michigan State University contributed an additional $212 million in various ways, including the land. MSU established and operates FRIB as a user facility for the Office of Nuclear Physics in the U.S. Department of Energy Office of Science. At FRIB, scientists research the properties of rare isotopes to advance knowledge in the areas of nuclear physics, nuclear astrophysics, fundamental interactions of nuclei, and real-world applications of rare isotopes. Construction of the FRIB conventional facilities began in spring 2014 and was completed in 2017. Technical construction started in the fall of 2014 and was completed in January 2022. The total project cost was $730M with project completion in June 2022.
FRIB will provide researchers with the technical capabilities to study the properties of rare isotopes (that is, short-lived atomic nuclei not normally found on Earth). Real-world applications of the research include materials science, nuclear medicine, and the fundamental understanding of nuclear material important to nuclear weapons stockpile stewardship. More than 20 working groups specializing in experimental equipment and scientific topics have been organized through the FRIB Users Organization.
The FRIB will be capable of expanding the known Chart of the Nuclides from some approximately 3000 identified isotopes to over 6000 potentially identifiable isotopes. It will accelerate beams of known isotopes through a matrix which will disrupt the nuclei, forming a variety of unusual isotopes of short half-life. These will be filtered by directing away the undesired charge/mass isotopes by a magnetic field, leaving a small beam of the desired novel isotope for study. Such beam can also target other known isotopes, fusing with the target, to create still further unknown isotopes, for further study. This will allow expansion of the Chart of the Nuclides towards its outer sides, the so-called Nuclear drip line. It will also allow expansion of the Chart towards heavier isotopes, towards the Island of stability and beyond.
The establishment of a Facility for Rare Isotope Beams (FRIB) is the first recommendation in the 2012 National Academies Decadal Study of Nuclear Physics: Nuclear Physics: Exploring the Heart of the Matter. The priority for completion is listed in the 2015 Long Range Plan for Nuclear Science: Implementing Reaching for the Horizon by the DOE/NSF Nuclear Science Advisory Committee.
The facility has a robust Health Physics program under the umbrella of the university's Environmental Health and Safety department. | 0 | Isotopes |
One aim of the Manhattan Project was increasing the availability of concentrated radioactive and stable isotopes, in particular C, S, P, and deuterium for heavy water. Harold Urey, Nobel laureate physical chemist known for his discovery of deuterium, became its head of isotope separation research while a professor at Columbia University. In 1945, he joined The Institute for Nuclear Studies at the University of Chicago, where he continued to work with chemist Jacob Bigeleisen and physicist Maria Mayer, both also veterans of isotopic research in the Manhattan Project. In 1946, Urey delivered the Liversidge lecture at the then-Royal Institute of Chemistry, where he outlined his proposed model of stable isotope fractionation. Bigeleisen and Mayer had been working on similar work since at least 1944 and, in 1947, published their model independently from Urey. Their calculations were mathematically equivalent to a 1943 derivation of the reduced partition function by German physicist Ludwig Waldmann. | 0 | Isotopes |
While the radioactive silver isotopes that are produced quickly decay away leaving only stable silver, extracting it for use is not economical, unless as byproduct of platinum group metal extraction. | 1 | Fission Products + Nuclear Fission |
Harriet Hall investigated health claims being attributed to drinking DDW, which has been sold for as much as $20 per liter. In a July 2020 article published at Skeptical Inquirer online, she reported that the overwhelming majority of DDW studies, despite showing positive outcomes, did not involve humans, and the few that did, did not verify any human efficacy. | 0 | Isotopes |