ChemTEB Classification Datasets
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Chemical Classification Datasets for Evaluating Text Embedding Models
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In 2009, a Chinese cement company (in Tongchuan, Shaanxi Province) was demolishing an old, unused cement plant and did not follow standards for handling radioactive materials. This caused some caesium-137 from a measuring instrument to be included with eight truckloads of scrap metal on its way to a steel mill, where the radioactive caesium was melted down into the steel. | 1 | Fission Products + Nuclear Fission |
In nuclear physics, a nuclear chain reaction occurs when one single nuclear reaction causes an average of one or more subsequent nuclear reactions, thus leading to the possibility of a self-propagating series or "positive feedback loop" of these reactions. The specific nuclear reaction may be the fission of heavy isotopes (e.g., uranium-235, U). A nuclear chain reaction releases several million times more energy per reaction than any chemical reaction. | 1 | Fission Products + Nuclear Fission |
Mass-independent isotope fractionation or Non-mass-dependent fractionation (NMD), refers to any chemical or physical process that acts to separate isotopes, where the amount of separation does not scale in proportion with the difference in the masses of the isotopes. Most isotopic fractionations (including typical kinetic fractionations and equilibrium fractionations) are caused by the effects of the mass of an isotope on atomic or molecular velocities, diffusivities or bond strengths. Mass-independent fractionation processes are less common, occurring mainly in photochemical and spin-forbidden reactions. Observation of mass-independently fractionated materials can therefore be used to trace these types of reactions in nature and in laboratory experiments. | 0 | Isotopes |
Some fission products (such as Cs) are used in medical and industrial radioactive sources.
TcO (pertechnetate) ion can react with steel surfaces to form a corrosion resistant layer. In this way these metaloxo anions act as anodic corrosion inhibitors - it renders the steel surface passive. The formation of TcO on steel surfaces is one effect which will retard the release of Tc from nuclear waste drums and nuclear equipment which has become lost prior to decontamination (e.g. nuclear submarine reactors which have been lost at sea).
In a similar way the release of radio-iodine in a serious power reactor accident could be retarded by adsorption on metal surfaces within the nuclear plant. Much of the other work on the iodine chemistry which would occur during a bad accident has been done. | 1 | Fission Products + Nuclear Fission |
The mass-independent distribution of isotopes in stratospheric ozone can be transferred to carbon dioxide (CO). This anomalous isotopic composition in CO can be used to quantify gross primary production, the uptake of CO by vegetation through photosynthesis. This effect of terrestrial vegetation on the isotopic signature of atmospheric CO was simulated with a global model and confirmed experimentally. | 0 | Isotopes |
In physics, natural abundance (NA) refers to the abundance of isotopes of a chemical element as naturally found on a planet. The relative atomic mass (a weighted average, weighted by mole-fraction abundance figures) of these isotopes is the atomic weight listed for the element in the periodic table. The abundance of an isotope varies from planet to planet, and even from place to place on the Earth, but remains relatively constant in time (on a short-term scale).
As an example, uranium has three naturally occurring isotopes: U, U, and U. Their respective natural mole-fraction abundances are 99.2739–99.2752%, 0.7198–0.7202%, and 0.0050–0.0059%. For example, if 100,000 uranium atoms were analyzed, one would expect to find approximately 99,274 U atoms, approximately 720 U atoms, and very few (most likely 5 or 6) U atoms. This is because U is much more stable than U or U, as the half-life of each isotope reveals: 4.468 × 10 years for U compared with 7.038 × 10 years for U and 245,500 years for U.
Exactly because the different uranium isotopes have different half-lives, when the Earth was younger, the isotopic composition of uranium was different. As an example, 1.7×10 years ago the NA of U was 3.1% compared with today's 0.7%, and that allowed a natural nuclear fission reactor to form, something that cannot happen today.
However, the natural abundance of a given isotope is also affected by the probability of its creation in nucleosynthesis (as in the case of samarium; radioactive Sm and Sm are much more abundant than stable Sm) and by production of a given isotope as a daughter of natural radioactive isotopes (as in the case of radiogenic isotopes of lead). | 0 | Isotopes |
Deuterium-depleted water can be produced in laboratories and factories. Various technologies are used for its production, such as electrolysis, distillation (low-temperature vacuum rectification), desalination from seawater, Girdler sulfide process, and catalytic exchange. | 0 | Isotopes |
Sr is used as a blade inspection method in some helicopters with hollow blade spars to indicate if a crack has formed. | 1 | Fission Products + Nuclear Fission |
Singly substituted isotopologues may be used for nuclear magnetic resonance experiments, where deuterated solvents such as deuterated chloroform (CDCl) do not interfere with the solutes' H signals, and in investigations of the kinetic isotope effect. | 0 | Isotopes |
Gilbert N. Lewis was the first to discover that heavy water inhibits (retards) seed growth (1933). His experiments with tobacco seeds showed that cultivation of cells on heavy water dramatically accelerates the aging process and leads to lethal results. | 0 | Isotopes |
A number of datable minerals occur as common detrital grains in sandstones, and if the strata have not been buried too deeply, these minerals grains retain information about the source rock. Fission track analysis of these minerals provides information about the thermal evolution of the source rocks and therefore can be used to understand provenance and the evolution of mountain belts that shed the sediment. This technique of detrital analysis is most commonly applied to zircon because it is very common and robust in the sedimentary system, and in addition it has a relatively high annealing temperature so that in many sedimentary basins the crystals are not reset by later heating.
Fission-track dating of detrital zircon is a widely applied analytical tool used to understand the tectonic evolution of source terrains that have left a long and continuous erosional record in adjacent basin strata. Early studies focused on using the cooling ages in detrital zircon from stratigraphic sequences to document the timing and rate of erosion of rocks in adjacent orogenic belts (mountain ranges). A number of recent studies have combined U/Pb and/or Helium dating (U+Th/He) on single crystals to document the specific history of individual crystals. This double-dating approach is an extremely powerful provenance tool because a nearly complete crystal history can be obtained, and therefore researchers can pinpoint specific source areas with distinct geologic histories with relative certainty. Fission-track ages on detrital zircon can be as young as 1 Ma to as old as 2000 Ma. | 1 | Fission Products + Nuclear Fission |
In order to get more reasonable values for the nuclear masses in the liquid drop model, it is necessary to include shell effects. Soviet physicist Vilen Strutinsky proposed such a method using "shell correction" and corrections for nuclear pairing to the liquid drop model. In this method, the total energy of the nucleus is taken as the sum of the liquid drop model energy, , the shell, , and pairing, , corrections to this energy as:
The shell corrections, just like the liquid drop energy, are functions of the nuclear deformation. The shell corrections tend to lower the ground state masses of spherical nuclei with magic or near-magic numbers of neutrons and protons. They also tend to lower the ground state mass of mid shell nuclei at some finite deformation thus accounting for the deformed nature of the actinides. Without these shell effects, the heaviest nuclei could not be observed, as they would decay by spontaneous fission on a time scale much shorter than we can observe.
This combination of macroscopic liquid drop and microscopic shell effects predicts that for nuclei in the U-Pu region, a double-humped fission barrier with equal barrier heights and a deep secondary minimum will occur. For heavier nuclei, like californium, the first barrier is predicted to be much larger than the second barrier and passage over the first barrier is rate determining. In general, there is ample experimental and theoretical evidence that the lowest energy path in the fission process corresponds to having the nucleus, initially in an axially symmetric and mass (reflection) symmetric shape pass over the first maximum in the fission barrier with an axially asymmetric but mass symmetric shape and then to pass over the second maximum in the barrier with an axially symmetric but mass (reflection) asymmetric shape. Because of the complicated multidimensional character of the fission process, there are no simple formulas for the fission barrier heights. However, there are extensive tabulations of experimental characterizations of the fission barrier heights for various nuclei. | 1 | Fission Products + Nuclear Fission |
An emerging body of work highlights the application potential for clumped isotopes to reconstruct temperature and fluid properties in hydrothermal ore deposits. In mineral exploration, delineation of the heat footprint around an ore body provides critical insight into the processes that drive transport and deposition of metals. During proof of concept studies, clumped isotopes were used to provide accurate temperature reconstructions in epithermal, sediment hosted, and Mississippi Valley Type (MVT) deposits. These case studies are supported by measurement of carbonates in active geothermal settings. | 0 | Isotopes |
Fission track dating is a radiometric dating technique based on analyses of the damage trails, or tracks, left by fission fragments in certain uranium-bearing minerals and glasses. Fission-track dating is a relatively simple method of radiometric dating that has made a significant impact on understanding the thermal history of continental crust, the timing of volcanic events, and the source and age of different archeological artifacts. The method involves using the number of fission events produced from the spontaneous decay of uranium-238 in common accessory minerals to date the time of rock cooling below closure temperature. Fission tracks are sensitive to heat, and therefore the technique is useful at unraveling the thermal evolution of rocks and minerals. Most current research using fission tracks is aimed at: a) understanding the evolution of mountain belts; b) determining the source or provenance of sediments; c) studying the thermal evolution of basins; d) determining the age of poorly dated strata; and e) dating and provenance determination of archeological artifacts.
In the 1930s it was discovered that uranium (specifically U-235) would undergo fission when struck by neutrons. This caused damage tracks in solids which could be revealed by chemical etching. | 1 | Fission Products + Nuclear Fission |
The ratio of H, also known as deuterium, to H has been studied in both plant and animal tissue. Hydrogen isotopes in plant tissue are correlated with local water values but vary based on fractionation during photosynthesis, transpiration, and other processes in the formation of cellulose. A study on the isotope ratios of tissues from plants growing within a small area in Texas found tissues from CAM plants were enriched in deuterium relative to C4 plants. Hydrogen isotope ratios in animal tissue reflect diet, including drinking water, and have been used to study bird migration and aquatic food webs. | 0 | Isotopes |
# Extract from carbonates by reaction with anhydrous phosphoric acid. (there is no direct way to measure the abundance of COs in with high enough precision). The phosphoric acid temperature is often held between 25° and 90 °C and can be as high as 110 °C.
# Purify the that has been extracted. This step removes contaminant gases like hydrocarbons and halocarbons which can be removed by gas chromatography.
# Mass spectrometric analyses of purified , to obtain δC, δO, and Δ47 (abundance of mass-47 ) values. (Precision needs to be as high as ≈10, for the isotope signals of interest are often less than ≈10) | 0 | Isotopes |
Similar investigations into the isotopic ratios of ruthenium at Oklo found a much higher concentration than otherwise naturally occurring (27–30% vs. 12.7%). This anomaly could be explained by the decay of to . In the bar chart the normal natural isotope signature of ruthenium is compared with that for fission product ruthenium which is the result of the fission of with thermal neutrons. It is clear that the fission ruthenium has a different isotope signature. The level of in the fission product mixture is low because fission produces neutron rich isotopes which subsequently beta decay and would only be produced in appreciable quantities by double beta decay of the very long-lived (half life years) molybdenum isotope . On the timescale of when the reactors were in operation, very little (about 0.17 ppb) decay to will have occurred. Other pathways of production like neutron capture in or (quickly followed by beta decay) can only have occurred during high neutron flux and thus ceased when the fission chain reaction stopped. | 1 | Fission Products + Nuclear Fission |
Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the release of heat energy (kinetic energy of the nuclei), and gamma rays. The two smaller nuclei are the fission products. (See also Fission products (by element)).
About 0.2% to 0.4% of fissions are ternary fissions, producing a third light nucleus such as helium-4 (90%) or tritium (7%).
The fission products themselves are usually unstable and therefore radioactive. Due to being relatively neutron-rich for their atomic number, many of them quickly undergo beta decay. This releases additional energy in the form of beta particles, antineutrinos, and gamma rays. Thus, fission events normally result in beta and additional gamma radiation that begins immediately after, even though this radiation is not produced directly by the fission event itself.
The produced radionuclides have varying half-lives, and therefore vary in radioactivity. For instance, strontium-89 and strontium-90 are produced in similar quantities in fission, and each nucleus decays by beta emission. But Sr has a 30-year half-life, and Sr a 50.5-day half-life. Thus in the 50.5 days it takes half the Sr atoms to decay, emitting the same number of beta particles as there were decays, less than 0.4% of the Sr atoms have decayed, emitting only 0.4% of the betas. The radioactive emission rate is highest for the shortest lived radionuclides, although they also decay the fastest. Additionally, less stable fission products are less likely to decay to stable nuclides, instead decaying to other radionuclides, which undergo further decay and radiation emission, adding to the radiation output. It is these short lived fission products that are the immediate hazard of spent fuel, and the energy output of the radiation also generates significant heat which must be considered when storing spent fuel. As there are hundreds of different radionuclides created, the initial radioactivity level fades quickly as short lived radionuclides decay, but never ceases completely as longer lived radionuclides make up more and more of the remaining unstable atoms. In fact the short lived products are so predominant that 87 percent decay to stable isotopes within the first month after removal from the reactor core. | 1 | Fission Products + Nuclear Fission |
The terminology of isotopic reference materials is not applied consistently across subfields of isotope geochemistry or even between individual laboratories. The terminology defined below comes from Gröening et al. (1999) and Gröening (2004). Reference materials are the basis for accuracy across many different types of measurement, not only the mass spectrometry, and there is a large body of literature concerned with the certification and testing of reference materials. | 0 | Isotopes |
It is expected that some continual improvement of experimental sensitivity will allow discovery of very mild radioactivity (instability) of some isotopes that are considered to be stable today. For example, in 2003 it was reported that bismuth-209 (the only primordial isotope of bismuth) is very mildly radioactive, with the half-life time of (1.9 ± 0.2) × 10 yr, confirming earlier theoretical predictions from nuclear physics that bismuth-209 would decay very slowly by alpha emission.
Isotopes that are theoretically believed to be unstable but have not been observed to decay are termed as observationally stable. Currently there are 105 "stable" isotopes which are theoretically unstable, 40 of which have been observed in detail with no sign of decay, the lightest in any case being Ar. Many "stable" nuclides are "metastable" inasmuch as they would release energy if a radioactive decay were to occur, and are, in fact, expected to undergo very rare kinds of radioactive decay, including double-beta emission.
146 nuclides from 62 elements with atomic numbers from 1 (hydrogen) through 66 (dysprosium) except 43 (technetium), 61 (promethium), 62 (samarium), and 63 (europium) are theoretically stable to any kind of nuclear decay—except for the theoretical possibility of proton decay, which has never been observed despite extensive searches for it—and spontaneous fission, which is theoretically possible for the nuclides with atomic mass numbers ≥ 93.
For processes other than spontaneous fission, other theoretical decay routes for heavier elements include:
* alpha decay – 70 heavy nuclides (the lightest two are cerium-142 and neodymium-143)
* double beta decay – 55 nuclides
* beta decay – tantalum-180m
* electron capture – tellurium-123, tantalum-180m
* double electron capture
* isomeric transition – tantalum-180m
These include all nuclides of mass 165 and greater. Argon-36 is presently the lightest known "stable" nuclide which is theoretically unstable.
The positivity of energy release in these processes means that they are allowed kinematically (they do not violate the conservation of energy) and, thus, in principle, can occur. They are not observed due to strong but not absolute suppression, by spin-parity selection rules (for beta decays and isomeric transitions) or by the thickness of the potential barrier (for alpha and cluster decays and spontaneous fission). | 0 | Isotopes |
Deuterium-depleted water (DDW) is water which has a lower concentration of deuterium than occurs naturally at sea level on Earth.
DDW is sometimes known as light water or protium water, although "light water" has long referred to ordinary water, specifically in nuclear reactors. | 0 | Isotopes |
Sulfur has four stable isotopes, S, S, S, and S, of which S is the most abundant by a large margin due to the fact it is created by the very common C in supernovas. Sulfur isotope ratios are almost always expressed as ratios relative to S due to this major relative abundance (95.0%). Sulfur isotope fractionations are usually measured in terms of δS due to its higher abundance (4.25%) compared to the other stable isotopes of sulfur, though δS is also sometimes measured. Differences in sulfur isotope ratios are thought to exist primarily due to kinetic fractionation during reactions and transformations.
Sulfur isotopes are generally measured against standards; prior to 1993, the Canyon Diablo troilite standard (abbreviated to CDT), which has a S:S equal to 22.220, was used as both a reference material and the zero point for the isotopic scale. Since 1993, the Vienna-CDT standard has been used as a zero point, and there are several materials used as reference materials for sulfur isotope measurements. Sulfur fractionations by natural processes measured against these standards have been shown to exist between -72‰ and +147‰, as calculated by the following equation:
As a very redox-active element, sulfur can be useful for recording major chemistry-altering events throughout Earths history, such as marine evaporites which reflect the change in the atmospheres redox state brought about by the Oxygen Crisis. | 0 | Isotopes |
*The use of Iodine-131 as a poison – used in small doses over a period of time to disrupt a persons ability to think and tell right from wrong – played a central role in the episode "The Case of the Melancholy Marksman" of the long-running CBS TV series Perry Mason' (season 5, episode 24, first broadcast March 24, 1962). | 1 | Fission Products + Nuclear Fission |
Amino acids are a key nutrient in ecosystems. Some are essential to animals, meaning that these organisms cannot synthesize them de novo. Instead, animals rely on their diet to acquire these molecules, creating strong interdependencies between animals and organisms with complete amino acid synthesis capabilities. In a study of bacteria and archaea at Antarctica's McMurdo Dry Valleys, the distribution of C between their amino acids reflected the biosynthetic pathways employed by these organisms. Autotrophs and heterotrophs had distinct isotopic fingerprints, as did organisms that employed alternatives to the citric acid cycle to ferment or produce acetate. Plants, fungi, and bacteria are also distinguishable by their amino acid carbon isotopes. The compositions of the essential amino acids, which have more complex biosynthetic pathways, are particularly informative. Lysine, isoleucine, leucine, threonine, and valine all had significantly different δC values between at least two of these groups. It is important to note that the fungi and bacteria in this study were grown on amino acid-free media to ensure that all the amino acids were synthesized by the organisms of interest. Bacteria and fungi can also scavenge amino acids from the environment, complicating the interpretation of data from field samples. Nevertheless, researchers have successfully used these differences to identify the sources of amino acids in food webs. Terrestrial and marine producers in a mangrove forest had different patterns of C enrichment in their amino acids. Fishes from a coral reef with diets containing different carbon sources also had variable amino acid δC values. Furthermore, one study observed distinct amino acid isotopic compositions for desert C, C, and CAM plants. These applications in diverse ecosystems highlight the versatility of compound-specific amino acid isotope analysis. | 0 | Isotopes |
Some unstable isotopes which occur naturally (such as , , and ) are not primordial, as they must be constantly regenerated. This occurs by cosmic radiation (in the case of cosmogenic nuclides such as and ), or (rarely) by such processes as geonuclear transmutation (neutron capture of uranium in the case of and ). Other examples of common naturally occurring but non-primordial nuclides are isotopes of radon, polonium, and radium, which are all radiogenic nuclide daughters of uranium decay and are found in uranium ores. The stable argon isotope Ar is actually more common as a radiogenic nuclide than as a primordial nuclide, forming almost 1% of the Earths atmosphere, which is regenerated by the beta decay of the extremely long-lived radioactive primordial isotope K, whose half-life is on the order of a billion years and thus has been generating argon since early in the Earths existence. (Primordial argon was dominated by the alpha process nuclide Ar, which is significantly rarer than Ar on Earth.)
A similar radiogenic series is derived from the long-lived radioactive primordial nuclide Th. These nuclides are described as geogenic, meaning that they are decay or fission products of uranium or other actinides in subsurface rocks. All such nuclides have shorter half-lives than their parent radioactive primordial nuclides. Some other geogenic nuclides do not occur in the decay chains of Th, U, or U but can still fleetingly occur naturally as products of the spontaneous fission of one of these three long-lived nuclides, such as Sn, which makes up about 10 of all natural tin. Another, Tc, has also been detected. There are five other long-lived fission products known. | 0 | Isotopes |
The prompt neutron lifetime, , is the average time between the emission of neutrons and either their absorption in the system or their escape from the system. The neutrons that occur directly from fission are called "prompt neutrons", and the ones that are a result of radioactive decay of fission fragments are called "delayed neutrons". The term lifetime is used because the emission of a neutron is often considered its "birth", and the subsequent absorption is considered its "death". For thermal (slow-neutron) fission reactors, the typical prompt neutron lifetime is on the order of 10 seconds, and for fast fission reactors, the prompt neutron lifetime is on the order of 10 seconds. These extremely short lifetimes mean that in 1 second, 10,000 to 10,000,000 neutron lifetimes can pass. The average (also referred to as the adjoint unweighted) prompt neutron lifetime takes into account all prompt neutrons regardless of their importance in the reactor core; the effective prompt neutron lifetime (referred to as the adjoint weighted over space, energy, and angle) refers to a neutron with average importance. | 1 | Fission Products + Nuclear Fission |
I, with a half-life of 8 days, is a hazard from nuclear fallout because iodine concentrates in the thyroid gland. See also Radiation effects from Fukushima Daiichi nuclear disaster#Iodine-131 and
Downwinders#Nevada.
In common with Sr, I is used for the treatment of cancer. A small dose of I can be used in a thyroid function test while a large dose can be used to destroy the thyroid cancer. This treatment will also normally seek out and destroy any secondary tumor which arose from a thyroid cancer. Much of the energy from the beta emission from the I will be absorbed in the thyroid, while the gamma rays are likely to be able to escape from the thyroid to irradiate other parts of the body.
Large amounts of I was released during an experiment named the Green Run in which fuel which had only been allowed to cool for a short time after irradiation was reprocessed in a plant which had no iodine scrubber in operation.
I, with a half-life almost a billion times as long, is a long-lived fission product. It is among the most troublesome because it accumulates in a relatively small organ (the thyroid) where even its comparatively low radiation dose can cause great damage as it has a long biological half life. For this reason, Iodine is often considered for transmutation despite the presence of stable in spent fuel. In the thermal neutron spectrum, more Iodine-129 is destroyed than newly created since Iodine-128 is short lived and the isotope ratio is in favor of . Depending on the design of the transmutation apparatus, care must be taken as Xenon, the product of Iodine's beta decay, is both a strong neutron poison and a gas that is nigh impossible to chemically "fix" in solid compounds, so it will either escape to the outside air or put pressure on the vessel containing the transmutation target.
I is stable, the only one of the isotopes of iodine that is nonradioactive. It makes up only about of the iodine in spent fuel, with I-129 about . | 1 | Fission Products + Nuclear Fission |
Some isotopes/nuclides are radioactive, and are therefore referred to as radioisotopes or radionuclides, whereas others have never been observed to decay radioactively and are referred to as stable isotopes or stable nuclides. For example, is a radioactive form of carbon, whereas and are stable isotopes. There are about 339 naturally occurring nuclides on Earth, of which 286 are primordial nuclides, meaning that they have existed since the Solar System's formation.
Primordial nuclides include 35 nuclides with very long half-lives (over 100 million years) and 251 that are formally considered as "stable nuclides", because they have not been observed to decay. In most cases, for obvious reasons, if an element has stable isotopes, those isotopes predominate in the elemental abundance found on Earth and in the Solar System. However, in the cases of three elements (tellurium, indium, and rhenium) the most abundant isotope found in nature is actually one (or two) extremely long-lived radioisotope(s) of the element, despite these elements having one or more stable isotopes.
Theory predicts that many apparently "stable" nuclides are radioactive, with extremely long half-lives (discounting the possibility of proton decay, which would make all nuclides ultimately unstable). Some stable nuclides are in theory energetically susceptible to other known forms of decay, such as alpha decay or double beta decay, but no decay products have yet been observed, and so these isotopes are said to be "observationally stable". The predicted half-lives for these nuclides often greatly exceed the estimated age of the universe, and in fact, there are also 31 known radionuclides (see primordial nuclide) with half-lives longer than the age of the universe.
Adding in the radioactive nuclides that have been created artificially, there are 3,339 currently known nuclides. These include 905 nuclides that are either stable or have half-lives longer than 60 minutes. See list of nuclides for details. | 0 | Isotopes |
The addition of lime to soils which are poor in calcium can reduce the uptake of strontium by plants. Likewise in areas where the soil is low in potassium, the addition of a potassium fertilizer can discourage the uptake of cesium into plants. However such treatments with either lime or potash should not be undertaken lightly as they can alter the soil chemistry greatly, so resulting in a change in the plant ecology of the land. | 1 | Fission Products + Nuclear Fission |
On 3 and 4 March 2016, unusually high levels of caesium-137 were detected in the air in Helsinki, Finland. According to STUK, the country's nuclear regulator, measurements showed 4,000 μBq/m – about 1,000 times the usual level. An investigation by the agency traced the source to a building from which STUK and a radioactive waste treatment company operate. | 1 | Fission Products + Nuclear Fission |
Xe is the heaviest noble gas in the Earth's atmosphere. It has seven stable isotopes (Xe,Xe,Xe,Xe,Xe, Xe, Xe) and two isotopes (Xe, Xe) with long-lived half-lives. Xe has four synthetic radioisotopes with very short half-lives, usually less than one month.
Xenon-129 can be used to examine the early history of the Earth. Xe was derived from the extinct nuclide of iodine, iodine-129 or I (with a half-life of 15.7 Million years, or Myr), which can be used in iodine-xenon (I-Xe) dating. The production of Xe stopped within about 100 Myr after the start of the Solar System because I became extinct. In the modern atmosphere, about 6.8% of atmospheric Xe originated from the decay I in the first ~100 Myr of the Solar Systems history, i.e., during and immediately following Earths accretion.
Fissiogenic Xe isotopes were generated mainly from the extinct nuclide, plutonium-244 or Pu (half-life of 80 Myr), and also the extant nuclide, uranium-238 or U (half-life of 4468 Myr). Spontaneous fission of U has generated ~5% as much fissiogenic Xe as Pu. Pu and U fission produce the four fissiogenic isotopes, Xe, Xe, Xe, and Xe in distinct proportions. A reservoir that remains an entirely closed system over Earth's history has a ratio of Pu- to U-derived fissiogenic Xe reaching to ~27. Accordingly, the isotopic composition of the fissiogenic Xe for a closed-system reservoir would largely resemble that produced from pure Pu fission. Loss of Xe from a reservoir after Pu becomes extinct (500 Myr) would lead to a greater contribution of U fission to the fissiogenic Xe. | 0 | Isotopes |
In the Goiânia accident of 1987, an improperly disposed of radiation therapy system from an abandoned clinic in Goiânia, Brazil, was removed, then cracked to be sold in junkyards. The glowing caesium salt was then to be sold to curious, unadvised buyers. This led to four confirmed deaths and several serious injuries from radiation contamination. | 1 | Fission Products + Nuclear Fission |
NAIL-MS can be used to produce stable isotope labeled internal standards (ISTD). Therefore, cells are grown in medium which results in complete labeling of all nucleosides. The purified mix of nucleosides can then be used as ISTD which is needed for accurate absolute quantification of nucleosides by mass spectrometry. This mixture of labeled nucleosides is also referred to as SILIS (stable isotope labeled internal standard). The advantage of this approach is, that all modifications present in an organism can thereby be biosynthesized as labeled compounds. The production of SILIS was already done before the term NAIL-MS emerged. | 0 | Isotopes |
According to the IsoRes hypothesis, there are certain resonance isotopic compositions at which terrestrial organisms thrive best. Curiously, average terrestrial isotopic compositions are very close to a resonance affecting a large class of amino acids and polypeptides, the molecules of outmost importance for life. Thus, the IsoRes hypothesis suggests that early life on Earth was aided, perhaps critically, by the proximity to an IsoRes. In contrast, there is no strong resonance for then atmosphere of Mars, which led to a prediction that life could not have originated on Mars and that the planet is probably sterile. | 0 | Isotopes |
The radioactive decay of strontium-90 generates a significant amount of heat, 0.95 W/g in the form of pure strontium metal or approximately 0.460 W/g as strontium titanatePu. It is used as a heat source in many Russian/Soviet radioisotope thermoelectric generators, usually in the form of strontium titanate. It was also used in the US "Sentinel" series of RTGs. Startup company Zeno Power is developing RTGs that use strontium-90 from the DOD, and is aiming to ship product by 2026. | 1 | Fission Products + Nuclear Fission |
Primitive meteorites have been studied using measurements of Δ47. These analyses also assume that the primary isotopic signature of the sample has been lost. In this case, measurements of Δ47 instead provide information on the high-temperature event that isotopically reset the sample. Existing Δ47 analyses on primitive meteorites have been used to infer the duration and temperature of aqueous alteration events, as well as to estimate the isotopic composition of the alteration fluid. | 0 | Isotopes |
Sr is a product of nuclear fission. It is present in significant amount in spent nuclear fuel, in radioactive waste from nuclear reactors and in nuclear fallout from nuclear tests.
For thermal neutron fission as in today's nuclear power plants, the fission product yield from uranium-235 is 5.7%, from uranium-233 6.6%, but from plutonium-239 only 2.0%. | 1 | Fission Products + Nuclear Fission |
Phosphoenolpyruvate carboxylase (PEPC) is an enzyme that combines bicarbonate and phosphoenolpyruvate (PEP) to form the four-carbon acid, oxaloacetate. It is an important enzyme in C4 photosynthesis and anaplerotic pathways. It is also responsible for the position-specific enrichment of oxaloacetate, due to the equilibrium isotope effect of converting the linear molecule CO into the trigonal planar molecule HCO-, which partitions C into bicarbonate. Inside the PEPC enzyme, HCO- reacts 1.0022 times faster than HCO- so that PEPC has a 0.22% kinetic isotope effect. This is not enough to compensate for the 13C enrichment in bicarbonate. Thus, oxaloacetate is left with a C-enriched carbon at the C4 position. However, the C1 site experiences a small inverse secondary isotope effect due to its bonding environment in the transition state, leaving the C1 site of oxaloacetate enriched in C. In this way, PEPC simultaneously partitions C into the C4 site and C into the C1 site of oxaloacetate, an example of multiple position-specific isotope effects. | 0 | Isotopes |
Compared with solar xenon, Earths atmospheric Xe is enriched in heavy isotopes by 3 to 4% per atomic mass unit (amu). However, the total abundance of xenon gas is depleted by one order of magnitude relative to other noble gases. The elemental depletion while relative enrichment in heavy isotopes is called the "Xenon paradox'". A possible explanation is that some processes can specifically diminish xenon rather than other light noble gases (e.g. Krypton) and preferentially remove lighter Xe isotopes.
In the last 2 decades, two categories of models have been proposed to solve the xenon paradox. The first assumes that the Earth accreted from porous planetesimals, and isotope fractionation happened due to gravitational separation. However, this model cannot reproduce the abundance and isotopic composition of light noble gases in the atmosphere. The second category supposes a massive impact resulted in an aerodynamic drag on heavier gases. Both the aerodynamic drag and the downward gravitational effect lead to a mass-dependent loss of Xe gases. But following research suggested that Xe isotope mass fractionation shouldn't be a rapid, single event.
Research published since 2018 on noble gases preserved in Archean (3.5–3.0 Ga old) samples may provide a solution to the Xe paradox. Isotopically mass fractionated Xe is found in tiny inclusions of ancient seawater in Archean barite and hydrothermal quartz. The distribution of Xe isotopes lies between the primordial solar and the modern atmospheric Xe isotope patterns. The isotopic fractionation gradually increases relative to the solar distribution as Earth evolves over its first 2 billion years. This two billion-year history of evolving Xe fractionation coincides with early solar system conditions including high solar extreme ultraviolet (EUV) radiation and large impacts that could energize large rates of hydrogen escape to space that are big enough to drag out xenon. However, models of neutral xenon atoms escaping cannot resolve the problem that other lighter noble gas elements don't show the signal of depletion or mass-dependent fractionation. For example, because Kr is lighter than Xe, Kr should also have escaped in a neutral wind. Yet the isotopic distribution of atmospheric Kr on Earth is significantly less fractionated than atmospheric Xe.
A current explanation is that hydrodynamic escape can preferentially remove lighter atmospheric species and lighter isotopes of Xe in the form of charged ions instead of neutral atoms. Hydrogen is liberated from hydrogen-bearing gases (H or CH) by photolysis in the early Earth atmosphere. Hydrogen is light and can be abundant at the top of the atmosphere and escape. In the polar regions where there are open magnetic field lines, hydrogen ions can drag ionized Xe out from the atmosphere to space even though neutral Xe cannot escape.
The mechanism is summarized as below.
Xe can be directly photo-ionized by UV radiation in range of
Or Xe can be ionized by change exchange with H and CO through
where H and CO can come from EUV dissociation. Xe is chemically inert in H, H, or CO atmospheres. As a result, Xe tends to persist. These ions interact strongly with each other through the Coulomb force and are finally dragged away by strong ancient polar wind. Isotope mass fractionation accumulates as lighter isotopes of Xe preferentially escape from the Earth. A preliminary model suggests that Xe can escape in the Archean if the atmosphere contains >1% H or >0.5% methane.
When O levels increased in the atmosphere, Xe could exchange positive charge with O though
From this reaction, Xe escape stopped when the atmosphere became enriched in O. As a result, Xe isotope fractionation may provide insights into the long history of hydrogen escape that ended with the Great Oxidation Event (GOE). Understanding Xe isotopes is promising to reconstruct hydrogen or methane escape history that irreversibly oxidized the Earth and drove biological evolution toward aerobic ecological systems. Other factors, such as the hydrogen (or methane) concentration becoming too low or EUV radiation from the aging Sun becoming too weak, can also cease the hydrodynamic escape of Xe, but are not mutually exclusive.
Organic hazes on Archean Earth could also scavenge isotopically heavy Xe. Ionized Xe can be chemically incorporated into organic materials, going through the terrestrial weathering cycle on the surface. The trapped Xe is mass fractionated by about 1% per amu in heavier isotopes but they may be released again and recover the original unfractionated composition, making them not sufficient to totally resolve Xe paradox. | 0 | Isotopes |
Stable isotopic analysis has also been used for tracing the geographical origin of food, timber, and in tracing the sources and fates of nitrates in the environment. | 0 | Isotopes |
A half life is the time it takes half of the radiation of a specific substance to decay. A large amount of short-lived isotopes such as Zr are present in bomb fallout. This isotope and other short-lived isotopes are constantly generated in a power reactor, but because the criticality occurs over a long length of time, the majority of these short lived isotopes decay before they can be released. | 1 | Fission Products + Nuclear Fission |
Se-79, half-life of 327k years, is one of the long-lived fission products. Given the stability of its next lighter and heavier isotopes and the high cross section those isotopes exhibit for various neutron reactions, it is likely that the relatively low yield is due to Se-79 being destroyed in the reactor to an appreciable extent. | 1 | Fission Products + Nuclear Fission |
As of 2009 the total amount in the atmosphere is estimated at 5500 PBq due to anthropogenic sources. At the end of the year 2000, it was estimated to be 4800 PBq, and in 1973, an estimated 1961 PBq (53 megacuries). The most important of these human sources is nuclear fuel reprocessing, as krypton-85 is one of the seven common medium-lived fission products. Nuclear fission produces about three atoms of krypton-85 for every 1000 fissions (i.e., it has a fission yield of 0.3%). Most or all of this krypton-85 is retained in the spent nuclear fuel rods; spent fuel on discharge from a reactor contains between 0.13–1.8 PBq/Mg of krypton-85. Some of this spent fuel is reprocessed. Current nuclear reprocessing releases the gaseous Kr into the atmosphere when the spent fuel is dissolved. It would be possible in principle to capture and store this krypton gas as nuclear waste or for use. The cumulative global amount of krypton-85 released from reprocessing activity has been estimated as 10,600 PBq as of 2000. The global inventory noted above is smaller than this amount due to radioactive decay; a smaller fraction is dissolved into the deep oceans.
Other man-made sources are small contributors to the total. Atmospheric nuclear weapons tests released an estimated 111–185 PBq. The 1979 accident at the Three Mile Island nuclear power plant released about . The Chernobyl accident released about 35 PBq, and the Fukushima Daiichi accident released an estimated 44–84 PBq.
The average atmospheric concentration of krypton-85 was approximately 0.6 Bq/m in 1976, and has increased to approximately 1.3 Bq/m as of 2005. These are approximate global average values; concentrations are higher locally around nuclear reprocessing facilities, and are generally higher in the northern hemisphere than in the southern hemisphere.
For wide-area atmospheric monitoring, krypton-85 is the best indicator for clandestine plutonium separations.
Krypton-85 releases increase the electrical conductivity of atmospheric air. Meteorological effects are expected to be stronger closer to the source of the emissions. | 1 | Fission Products + Nuclear Fission |
A Xe atom that does not capture a neutron undergoes beta decay to Cs, one of the 7 long-lived fission products, while a Xe that does capture a neutron becomes almost-stable Xe.
The probability of capturing a neutron before decay varies with the neutron flux, which itself depends on the kind of reactor, fuel enrichment and power level; and the Cs / Xe ratio switches its predominant branch very near usual reactor conditions.
Estimates of the proportion of Xe during steady-state reactor operation that captures a neutron include 90%, 39%–91% and "essentially all".
For instance, in a (somewhat high) neutron flux of 10 n·cm·s, the xenon cross section of σ = cm ( barn) would lead to a capture probability of s, which corresponds to a half-life of about one hour. Compared to the 9.17 hour half-life of Xe, this nearly ten-to-one ratio means that under such conditions, essentially all Xe would capture a neutron before decay. But if the neutron flux is lowered to one-tenth of this value, like in CANDU reactors, the ratio would be 50-50, and half the Xe would decay to Cs before neutron capture.
Xe from neutron capture ends up as part of the eventual stable fission xenon which also includes Xe, Xe, and Xe produced by fission and beta decay rather than neutron capture.
Nuclei of Xe, Xe, and Xe that have not captured a neutron all beta decay to isotopes of caesium. Fission produces Xe, Xe, and Xe in roughly equal amounts but, after neutron capture, fission caesium contains more stable Cs (which however can become Cs on further neutron activation) and highly radioactive Cs than Cs. | 1 | Fission Products + Nuclear Fission |
Algae has shown selectivity for strontium in studies, where most plants used in bioremediation have not shown selectivity between calcium and strontium, often becoming saturated with calcium, which is greater in quantity and also present in nuclear waste.
Researchers have looked at the bioaccumulation of strontium by Scenedesmus spinosus (algae) in simulated wastewater. The study claims a highly selective biosorption capacity for strontium of S. spinosus, suggesting that it may be appropriate for use of nuclear wastewater.
A study of the pond alga Closterium moniliferum using stable strontium found that varying the ratio of barium to strontium in water improved strontium selectivity. | 1 | Fission Products + Nuclear Fission |
Nuclear magnetic resonance observes small differences in molecular reactions to oscillating magnetic fields. It is able to characterize atoms with active nuclides that have a non-zero nuclear spin (e.g., C, H, O Cl, N, Cl), which makes it particularly useful for identifying certain isotopes. In typical proton or 13C NMR, the chemical shifts of protiums (1H) and carbon-13 atoms within a molecule are measured, respectively, as they are excited by a magnetic field and then relax with a diagnostic resonance frequency. With site specific natural isotope fractionation (SNIF) NMR, the relaxation resonances of the deuterium and 13C atoms. NMR does not have the sensitivity to detect isotopologues with multiple rare isotopes. The only peaks that appear in a SNIF-NMR spectra are those of the isotopologues with a single rare isotope. Since the instrument is only measuring the resonances of the rare isotopes, each isotopologue will have one peak. For example, a molecule with six chemically unique carbon atoms will have six peaks in a 13C SNIF NMR spectrum. The site of 13C substitution can be determined by the chemical shift of each of the peaks. As a result, NMR is able to identify site specific isotope enrichments within molecules. | 0 | Isotopes |
Calibration materials are compounds whose isotopic composition is known extremely well relative to the primary reference materials or which define the isotopic composition of the primary reference materials but are not the isotopic ratios to which data are reported in the scientific literature. For example, the calibration material IAEA-S-1 defines the isotopic scale for sulfur but measurements are reported relative to VCDT, not relative to IAEA-S-1. The calibration material serves the function of the primary reference material when the primary reference is exhausted, unavailable, or never existed in physical form. | 0 | Isotopes |
Fast fission is fission that occurs when a heavy atom absorbs a high-energy neutron, called a fast neutron, and splits. Most fissionable materials need thermal neutrons, which move more slowly. | 1 | Fission Products + Nuclear Fission |
Isotopes are different forms of elements; they have a different number of neutrons in the nucleus, meaning they have very similar chemical properties, but different mass. The weight difference means that some isotopes are discriminated against in chemical processes – for example, plants find it easier to incorporate the lighter C than heavy C. Other isotopes are only produced as a result of the radioactive decay of other elements, such as Sr, the daughter isotope of Rb. Rb, and therefore Sr, is common in the crust, so abundance of Sr in a sample of sediment (relative to Sr) is related to the amount of sediment which originated in the crust, as opposed to from the oceans.
The ratios of three major isotopes, Sr / Sr, S / S and C / C, undergo dramatic fluctuations around the beginning of the Cambrian. | 0 | Isotopes |
Because of the carcinogenicity of its beta radiation in the thyroid in small doses, I-131 is rarely used primarily or solely for diagnosis (although in the past this was more common due to this isotope's relative ease of production and low expense). Instead the more purely gamma-emitting radioiodine iodine-123 is used in diagnostic testing (nuclear medicine scan of the thyroid). The longer half-lived iodine-125 is also occasionally used when a longer half-life radioiodine is needed for diagnosis, and in brachytherapy treatment (isotope confined in small seed-like metal capsules), where the low-energy gamma radiation without a beta component makes iodine-125 useful. The other radioisotopes of iodine are never used in brachytherapy.
The use of I as a medical isotope has been blamed for a routine shipment of biosolids being rejected from crossing the Canada—U.S. border. Such material can enter the sewers directly from the medical facilities, or by being excreted by patients after a treatment | 1 | Fission Products + Nuclear Fission |
The fission process can be understood when a nucleus with some equilibrium deformation absorbs energy (through neutron capture, for example), becomes excited and deforms to a configuration known as the "transition state" or "saddle point" configuration. As the nucleus deforms, the nuclear Coulomb energy decreases while the nuclear surface energy increases. At the saddle point, the rate of change of the Coulomb energy is equal to the rate of change of the nuclear surface energy. The formation and eventual decay of this transition state nucleus is the rate-determining step in the fission process and corresponds to the passage over an activation energy barrier to the fission reaction. When this occurs, the neck between the nascent fragments disappears and the nucleus divides into two fragments. The point at which this occurs is called the "scission point". | 1 | Fission Products + Nuclear Fission |
Chromatography facilitates separation of distinct molecules within a mixture based on their respective chemical properties, and how those properties interact with the substrate coating the chromatographic column. This separation can happen “on-line,” during the measurement itself, or prior to measurements to isolate a pure compound. Gas and liquid chromatography have distinct advantages, based on the molecules of interest. For example, aqueously soluble molecules are more easily separated with liquid chromatography, while volatile, nonpolar molecules like propane or ethane are separated with gas chromatography. | 0 | Isotopes |
A recent international project has developed and determined the hydrogen, carbon, and nitrogen isotopic composition of 19 organic isotopic reference materials, now available from USGS, IAEA, and Indiana University. These reference materials span a large range of δH (-210.8‰ to +397.0‰), δC (-40.81‰ to +0.49‰), and δN (-5.21‰ to +61.53‰), and are amenable to a wide range of analytical techniques. The organic reference materials include caffeine, glycine, n-hexadecane, icosanoic acid methyl ester (C FAME), L-valine, methylheptadecanoate, polyethylene foil, polyethylene power, vacuum oil, and NBS-22.
The information in Table 7 comes directly from Table 2 of Schimmelmann et al. (2016). | 0 | Isotopes |
I is one of the seven long-lived fission products that are produced in significant amounts. Its yield is 0.706% per fission of U. Larger proportions of other iodine isotopes such as I are produced, but because these all have short half-lives, iodine in cooled spent nuclear fuel consists of about 5/6 I and 1/6 the only stable iodine isotope, I.
Because I is long-lived and relatively mobile in the environment, it is of particular importance in long-term management of spent nuclear fuel. In a deep geological repository for unreprocessed used fuel, I is likely to be the radionuclide of most potential impact at long times.
Since I has a modest neutron absorption cross-section of 30 barns, and is relatively undiluted by other isotopes of the same element, it is being studied for disposal by nuclear transmutation by re-irradiation with neutrons or by high-powered lasers. | 1 | Fission Products + Nuclear Fission |
Several lanthanides produced at CERN-MEDICIS, samarium and terbium, are of interest for targeted therapy alike lutetium already used in the clinics. Lutetium emits low energy β particles with a short range, used for irradiation of smaller volume tumor targets. Terbium-149 emits short-range alpha particles, gamma-rays and positrons, in its decay scheme, which makes it suitable for targeted alpha therapy. The particular study of Tb produced by ISOLDE has been in folate receptor therapy, prominent in ovarian and lung cancer.
Sm, produced in the BR2 reactor at SCK CEN, followed by the subsequent mass separation by MEDICIS to increase its molar activity, was found to be suitable for targeted radionuclide therapy (TRNT) in a proof-of-concept research project. It emits low energy β particles and gamma peaks, and presents acceptable half-life for logistics and ambulatory care, making it a candidate of choice for theranostics approaches. | 0 | Isotopes |
Most I production is from neutron irradiation of a natural tellurium target in a nuclear reactor. Irradiation of natural tellurium produces almost entirely I as the only radionuclide with a half-life longer than hours, since most lighter isotopes of tellurium become heavier stable isotopes, or else stable iodine or xenon. However, the heaviest naturally occurring tellurium nuclide, Te (34% of natural tellurium) absorbs a neutron to become tellurium-131, which beta decays with a half-life of 25 minutes to I.
A tellurium compound can be irradiated while bound as an oxide to an ion exchange column, with evolved I then eluted into an alkaline solution. More commonly, powdered elemental tellurium is irradiated and then I separated from it by dry distillation of the iodine, which has a far higher vapor pressure. The element is then dissolved in a mildly alkaline solution in the standard manner, to produce I as iodide and hypoiodate (which is soon reduced to iodide).
I is a fission product with a yield of 2.878% from uranium-235, and can be released in nuclear weapons tests and nuclear accidents. However, the short half-life means it is not present in significant quantities in cooled spent nuclear fuel, unlike iodine-129 whose half-life is nearly a billion times that of I.
It is discharged to the atmosphere in small quantities by some nuclear power plants. | 1 | Fission Products + Nuclear Fission |
There are some disputes about using I-Xe dating to estimate the Xe closure time. First, in the early solar system, planetesimals collided and grew into larger bodies that accreted to form the Earth. But there could be a 10 to 10 years time gap in Xe closure time between the Earths inner and outer regions. Some research support 4.45 Ga probably represents the time when the last giant impactor (Martian-size) hit Earth, but some regard it as the time of core-mantle differentiation. The second problem is that the total inventory of Xe on Earth may be larger than that of the atmosphere since the lower mantle hadnt been entirely mixed, which may underestimate Xe in the calculation. Last but not least, if Xe gas not been lost from the atmosphere during a long interval of early Earth's history, the chronology based on I-Xe would need revising since Xe and Xe could be greatly altered. | 0 | Isotopes |
The fissile isotope uranium-235 in its natural concentration is unfit for the vast majority of nuclear reactors. In order to be prepared for use as fuel in energy production, it must be enriched. The enrichment process does not apply to plutonium. Reactor-grade plutonium is created as a byproduct of neutron interaction between two different isotopes of uranium. The first step to enriching uranium begins by converting uranium oxide (created through the uranium milling process) into a gaseous form. This gas is known as uranium hexafluoride, which is created by combining hydrogen fluoride, fluorine gas, and uranium oxide. Uranium dioxide is also present in this process and it is sent off to be used in reactors not requiring enriched fuel. The remaining uranium hexafluoride compound is drained into strong metal cylinders where it solidifies. The next step is separating the uranium hexafluoride from the depleted U-235 left over. This is typically done with centrifuges that spin fast enough to allow for the 1% mass difference in uranium isotopes to separate themselves. A laser is then used to enrich the hexafluoride compound. The final step involves reconverting the now enriched compound back into uranium oxide, leaving the final product: enriched uranium oxide. This form of UO can now be used in fission reactors inside power plants to produce energy. | 1 | Fission Products + Nuclear Fission |
The mean generation time, Λ, is the average time from a neutron emission to a capture that results in fission. The mean generation time is different from the prompt neutron lifetime because the mean generation time only includes neutron absorptions that lead to fission reactions (not other absorption reactions). The two times are related by the following formula:
In this formula, k is the effective neutron multiplication factor, described below. | 1 | Fission Products + Nuclear Fission |
In some cases, additional functional groups will need to be added to molecules to facilitate the other separation and analysis methods. Derivatization can change the properties of an analyte; for instance, it would make a polar and non-volatile compound non-polar and more volatile, which would be necessary for analysis in certain types of chromatography. It is important to note, however, that derivatization is not ideal for site-specific analyses as it adds additional elements that must be accounted for in analyses. | 0 | Isotopes |
While there is no enrichment of S between trophic levels, the stable isotope can be useful in distinguishing benthic vs. pelagic producers and marsh vs. phytoplankton producers. Similar to C, it can also help distinguish between different phytoplankton as the key primary producers in food webs. The differences between seawater sulfates and sulfides (c. 21‰ vs -10‰) aid scientists in the discriminations. Sulfur tends to be more plentiful in less aerobic areas, such as benthic systems and marsh plants, than the pelagic and more aerobic systems. Thus, in the benthic systems, there are smaller δS values. | 0 | Isotopes |
Multiple substituted isotopologues may be used for nuclear magnetic resonance or mass spectrometry experiments, where isotopologues are used to elucidate metabolic pathways in a qualitative (detect new pathways) or quantitative (detect quantitative share of a pathway) approach. A popular example in biochemistry is the use of uniform labelled glucose (U-C glucose), which is metabolized by the organism under investigation (e. g. bacterium, plant, or animal) and whose signatures can later be detected in newly formed amino acid or metabolically cycled products. | 0 | Isotopes |
Molecules made up of elements with multiple isotopes can vary in their isotopic composition, these different mass molecules are called isotopologues. Isotopologues such as COO, contain multiple heavy isotopes of oxygen substituting for the more common O, and are termed multiply-substituted isotopologues. The multiply-substituted isotopologue COO contains a bond between two of these heavier isotopes (C and O), which is a "clumped" isotope bond.
The abundance of masses for a given molecule (e.g. CO) can be predicted using the relative abundance of isotopes of its constituent atoms (C/C, O/O and O/O). The relative abundance of each isotopologue (e.g. mass-47 CO) is proportional to the relative abundance of each isotopic species.
This predicted abundance assumes a non-biased stochastic distribution of isotopes, natural materials tend to deviate from these stochastic values, the study of which forms the basis of clumped isotope geochemistry.
When a heavier isotope substitutes for a lighter isotope (e.g., O for O), the chemical bond's vibration will be slower, lowering its zero-point energy. In other words, thermodynamic stability is related to the isotopic composition of the molecule.
CO (≈98.2%), CO (≈1.1%), COO (≈0.6%) and COO (≈0.11%) are the most abundant isotopologues (≈99%) for the carbonate ions, controlling the bulk δC, δO and δO values in natural carbonate minerals. Each of these isopotologes has different thermodynamic stability. For a carbonate crystal at thermodynamic equilibrium, the relative abundances of the carbonate ion isotopologues is controlled by reactions such as:
The equilibrium constants for these reactions are temperature-dependent, with a tendency for heavy isotopes to "clump" with each other (increasing the proportions of multiply substituted isotopologues) as temperature decreases. Reaction 1 will be driven to the right with decreasing temperature, to the left with increasing temperature. Therefore, the equilibrium constant for this reaction can be used as an paleotemperature indicator, as long as the temperature dependence of this reaction and the relative abundances of the carbonate ion isotopologues are known. | 0 | Isotopes |
In March 2015, the Norwegian University of Tromsø lost 8 radioactive samples, including samples of caesium-137, americium-241, and strontium-90. The samples were moved out of a secure location to be used for education. When the samples were supposed to be returned, the university was unable to find them. , the samples are still missing. | 1 | Fission Products + Nuclear Fission |
Cumulative fission yields give the amounts of nuclides produced either directly in the fission or by decay of other nuclides. | 1 | Fission Products + Nuclear Fission |
A neutral atom has the same number of electrons as protons. Thus different isotopes of a given element all have the same number of electrons and share a similar electronic structure. Because the chemical behavior of an atom is largely determined by its electronic structure, different isotopes exhibit nearly identical chemical behavior.
The main exception to this is the kinetic isotope effect: due to their larger masses, heavier isotopes tend to react somewhat more slowly than lighter isotopes of the same element. This is most pronounced by far for protium (), deuterium (), and tritium (), because deuterium has twice the mass of protium and tritium has three times the mass of protium. These mass differences also affect the behavior of their respective chemical bonds, by changing the center of gravity (reduced mass) of the atomic systems. However, for heavier elements, the relative mass difference between isotopes is much less so that the mass-difference effects on chemistry are usually negligible. (Heavy elements also have relatively more neutrons than lighter elements, so the ratio of the nuclear mass to the collective electronic mass is slightly greater.) There is also an equilibrium isotope effect.
Similarly, two molecules that differ only in the isotopes of their atoms (isotopologues) have identical electronic structures, and therefore almost indistinguishable physical and chemical properties (again with deuterium and tritium being the primary exceptions). The vibrational modes of a molecule are determined by its shape and by the masses of its constituent atoms; so different isotopologues have different sets of vibrational modes. Because vibrational modes allow a molecule to absorb photons of corresponding energies, isotopologues have different optical properties in the infrared range. | 0 | Isotopes |
In 1960, physicist John H. Reynolds discovered that certain meteorites contained an isotopic anomaly in the form of an overabundance of Xe. He inferred that this must be a decay product of long-decayed radioactive I. This isotope is produced in quantity in nature only in supernova explosions. As the half-life of I is comparatively short in astronomical terms, this demonstrated that only a short time had passed between the supernova and the time the meteorites had solidified and trapped the I. These two events (supernova and solidification of gas cloud) were inferred to have happened during the early history of the Solar System, as the I isotope was likely generated before the Solar System was formed, but not long before, and seeded the solar gas cloud isotopes with isotopes from a second source. This supernova source may also have caused collapse of the solar gas cloud. | 1 | Fission Products + Nuclear Fission |
A mononuclidic element or monotopic element is one of the 21 chemical elements that is found naturally on Earth essentially as a single nuclide (which may, or may not, be a stable nuclide). This single nuclide will have a characteristic atomic mass. Thus, the element's natural isotopic abundance is dominated by one isotope that is either stable or very long-lived. There are 19 elements in the first category (which are both monoisotopic and mononuclidic), and 2 (bismuth and protactinium) in the second category (mononuclidic but not monoisotopic, since they have zero, not one, stable nuclides). A list of the 21 mononuclidic elements is given at the end of this article.
Of the 26 monoisotopic elements that, by definition, have only one stable isotope, seven are not considered mononuclidic, due to the presence of a significant fraction of a very long-lived (primordial) radioisotope. These elements are vanadium, rubidium, indium, lanthanum, europium, lutetium, and rhenium. | 0 | Isotopes |
Fast neutron reactors use fast fission to produce energy, unlike most nuclear reactors. In a conventional reactor, a moderator is needed to slow down the neutrons so that they are more likely to fission atoms. A fast neutron reactor uses fast neutrons, so it does not use a moderator. Moderators may absorb a lot of neutrons in a thermal reactor, and fast fission produces a higher average number of neutrons per fission, so fast reactors have better neutron economy making a plutonium breeder reactor possible. However, a fast neutron reactor must use relatively highly enriched uranium or plutonium at the reactor startup so that the neutrons have a better chance of fissioning atoms. | 1 | Fission Products + Nuclear Fission |
The Kramatorsk radiological accident happened in 1989 when a small capsule 8x4 mm in size of caesium-137 was found inside the concrete wall of an apartment building in Kramatorsk, Ukrainian SSR. It is believed that the capsule, originally a part of a measurement device, was lost in the late 1970s and ended up mixed with gravel used to construct the building in 1980. Over 9 years, two families had lived in the apartment. By the time the capsule was discovered, 6 residents of the building had died, 4 from leukemia and 17 more receiving varying doses of radiation. | 1 | Fission Products + Nuclear Fission |
The atomic mass (m) of an isotope (nuclide) is determined mainly by its mass number (i.e. number of nucleons in its nucleus). Small corrections are due to the binding energy of the nucleus (see mass defect), the slight difference in mass between proton and neutron, and the mass of the electrons associated with the atom, the latter because the electron:nucleon ratio differs among isotopes.
The mass number is a dimensionless quantity. The atomic mass, on the other hand, is measured using the atomic mass unit based on the mass of the carbon-12 atom. It is denoted with symbols "u" (for unified atomic mass unit) or "Da" (for dalton).
The atomic masses of naturally occurring isotopes of an element determine the standard atomic weight of the element. When the element contains N isotopes, the expression below is applied for the average atomic mass :
where m, m, ..., m are the atomic masses of each individual isotope, and x, ..., x are the relative abundances of these isotopes. | 0 | Isotopes |
The biosynthesis of fatty acids begins with acetyl-CoA precursors that are brought together to make long straight chain lipids. Acetyl-CoA is produced in aerobic organisms by pyruvate dehydrogenase, an enzyme that has been shown to express a large, 2.3% isotope effect on the C2 site of pyruvate and a small fractionation on the C3 site. These become the odd and even carbon positions of fatty acids respectively and in theory would result in a pattern of C depletions and enrichments at odd and even positions, respectively. In 1982, Monson and Hayes developed technology for measuring the position specific carbon isotope abundances of fatty acids. Their experiments on Escherichia coli revealed the predicted relative C enrichments at odd numbered carbon sites. However, this pattern was not found in Saccharomyces cerevisiae that were fed glucose. Instead, its fatty acids were C enriched at the odd positions. This has been interpreted as either a product of isotope effects during fatty acid degradation or the intramolecular isotopic heterogeneity of glucose that ultimately is reflected in the position-specific patterns of fatty acids. | 0 | Isotopes |
The gun method has also been applied for nuclear artillery shells, since the simpler design can be more easily engineered to withstand the rapid acceleration and g-forces imparted by an artillery gun, and since the smaller diameter of the gun-type design can be relatively easily fitted to projectiles that can be fired from existing artillery.
A US gun-type nuclear artillery weapon, the W9, was tested on May 25, 1953, at the Nevada Test Site. Fired as part of Operation Upshot–Knothole and codenamed Shot GRABLE, a 280 mm shell was fired 10,000 m and detonated 160 m above the ground with an estimated yield of 15 kilotons. This is approximately the same yield as Little Boy, although the W9 had less than 1/10 of Little Boy's weight (365 kg vs. 4,000 kg, or 805 lbs vs. 8,819 lbs). The shell was 1,384 mm long.
This was the only nuclear artillery shell ever actually fired (from an artillery gun) in the US test program. It was fired from a specially built artillery piece, nicknamed Atomic Annie. Eighty shells were produced from 1952 to 1953. It was retired in 1957.
The W19 was also a 280 mm gun-type nuclear shell, a longer version of the W-9. Eighty warheads were produced and the system was retired in 1963.
The W33 was a smaller, 8 inch (203 mm) gun-type nuclear artillery shell, which was produced starting in 1957 and in service until 1992. Two were test fired (detonated, not fired from an artillery gun), one hung under a balloon in the open air, and one in a tunnel.
Later versions were based on the implosion design. | 1 | Fission Products + Nuclear Fission |
All of the known 251 stable nuclides, plus another 35 nuclides that have half-lives long enough to have survived from the formation of the Earth, occur as primordial nuclides. These 35 primordial radionuclides represent isotopes of 28 separate elements.
Cadmium, tellurium, xenon, neodymium, samarium, osmium, and uranium each have two primordial radioisotopes (, ; , ; , ; , ; , ; , ; and , ).
Because the age of the Earth is (4.6 billion years), the half-life of the given nuclides must be greater than about (100 million years) for practical considerations. For example, for a nuclide with half-life (60 million years), this means 77 half-lives have elapsed, meaning that for each mole () of that nuclide being present at the formation of Earth, only 4 atoms remain today.
The seven shortest-lived primordial nuclides (i.e., the nuclides with the shortest half-lives) to have been experimentally verified are (), (), (), (), (), (), and ().
These are the seven nuclides with half-lives comparable to, or somewhat less than, the estimated age of the universe. (Rb, Re, Lu, and Th have half-lives somewhat longer than the age of the universe.) For a complete list of the 35 known primordial radionuclides, including the next 28 with half-lives much longer than the age of the universe, see the complete list below. For practical purposes, nuclides with half-lives much longer than the age of the universe may be treated as if they were stable. Rb, Re, Lu, Th, and U have half-lives long enough that their decay is limited over geological time scales; K and U have shorter half-lives and are hence severely depleted, but are still long-lived enough to persist significantly in nature.
The longest-lived isotope not proven to be primordial is , which has a half-life of , followed by () and (). Pu has been reported to exist in nature as a primordial nuclide, although a later study did not detect it. Taking into account that all these nuclides must exist for at least , Sm must survive 45 half-lives (and hence be reduced by 2 ≈ ), Pu must survive 57 (and be reduced by a factor of 2 ≈ ), and Nb must survive 130 (and be reduced by 2 ≈ ). Mathematically, considering the likely initial abundances of these nuclides, primordial Sm and Pu should persist somewhere within the Earth today, even if they are not identifiable in the relatively minor portion of the Earth's crust available to human assays, while Nb and all shorter-lived nuclides should not. Nuclides such as Nb that were present in the primordial solar nebula but have long since decayed away completely are termed extinct radionuclides if they have no other means of being regenerated.
Because primordial chemical elements often consist of more than one primordial isotope, there are only 83 distinct primordial chemical elements. Of these, 80 have at least one observationally stable isotope and three additional primordial elements have only radioactive isotopes (bismuth, thorium, and uranium). | 0 | Isotopes |
Caesium-137 has a half-life of about 30.05 years.
About 94.6% decays by beta emission to a metastable nuclear isomer of barium: barium-137m (Ba, Ba-137m). The remainder directly populates the ground state of Ba, which is stable. Barium-137m has a half-life of about 153 seconds, and is responsible for all of the gamma ray emissions in samples of Cs. Barium-137m decays to the ground state by emission of photons having energy 0.6617 MeV. A total of 85.1% of Cs decay generates gamma ray emission in this manner. One gram of Cs has an activity of 3.215 terabecquerel (TBq). | 1 | Fission Products + Nuclear Fission |
Bombs in the arctic area of Novaja Zemlja and bombs detonated in or near the stratosphere released cesium-137 that landed in upper Lapland, Finland. Measurements of cesium-137 in 1960's was reportedly 45,000 becquerels. Figures from 2011 have a mid range of about 1,100 becquerels, but strangely, cancer cases are no more common there than elsewhere. | 1 | Fission Products + Nuclear Fission |
Fallout comes in two varieties. The first is a small amount of carcinogenic material with a long half-life. The second, depending on the height of detonation, is a large quantity of radioactive dust and sand with a short half-life.
All nuclear explosions produce fission products, un-fissioned nuclear material, and weapon residues vaporized by the heat of the fireball. These materials are limited to the original mass of the device, but include radioisotopes with long lives. When the nuclear fireball does not reach the ground, this is the only fallout produced. Its amount can be estimated from the fission-fusion design and yield of the weapon. | 1 | Fission Products + Nuclear Fission |
Chemical reactions in biological processes are controlled by enzymes that catalyze the conversion of substrate to product. Since enzymes can alter the transition state structure for reactions, they also change kinetic and equilibrium isotope effects. Placed in the context of a metabolism, the expression of isotope effects on biomolecules is further controlled by branch points. Different pathways of biosynthesis will use different enzymes, yielding a range of position specific isotope enrichments. This variability allows position-specific isotope measurements to discern multiple biosynthetic pathways from the same metabolic product. Biogeochemists use position specific isotope enrichments from amino acids, lipids, and sugars in nature to interpret the relative importance of different metabolisms. | 0 | Isotopes |
Natural isotopes are either stable isotopes or radioactive isotopes that have a sufficiently long half-life to allow them to exist in substantial concentrations in the Earth (such as bismuth-209, with a half-life of 1.9 years, potassium-40 with a half-life of 1.251(3) years), daughter products of those isotopes (such as Th, with a half-life of 24 days) or cosmogenic elements. The heaviest stable isotope is lead-208, but the heaviest natural isotope is U-238.
Many elements have both natural and artificial isotopes. For example, hydrogen has three natural isotopes and another four known artificial isotopes. A further distinction among stable natural isotopes is division into primordial (existed when the Solar System formed) and cosmogenic (created by cosmic ray bombardment or other similar processes). | 0 | Isotopes |
Analyses carried out at Pierrelatte and Cadarache showed that magnesium uranates (or yellow cakes) from Gabon had a variable but constant U depletion. On July 7, 1972, researchers at Cadarache discovered an anomaly in uranium ore from Oklo in Gabon. Its U content was much lower than usual. Isotopic analyses revealed the origin of the U depletion: the depleted uranium came from Oklo ore in Gabon, mined by COMUF. A systematic analysis campaign was then carried out in the Cadarache and Pierrelatte laboratories (uranium content measurements, isotopic content measurements). On Oklo samples, Cadarache analysts noted a U depletion for magnesium uranate from the Mounana plant (U = 0.625%) and an even greater depletion for a magnesium uranate (Oklo M) (U = 0.440%): Oklo 310 and 311 ores have uranium contents of 12% and 46% respectively, and U contents of 0.592% and 0.625%.
In this context, J.F. Dozol took the initiative of analyzing magnesium uranate and ore samples from Oklo on the AEI MS 702 Spark Source Mass Spectrometer (SSMS).
The advantage of the SSMS is its ability to produce substantial quantities of ions from all the elements present in the electrodes. The electrodes, between which a spark is generated, have to be conductive (to achieve this, Oklo samples were mixed with high-purity silver). All the isotopes in the sample, from lithium to uranium, are plotted on a photo plate. On examining the plate (see below), J.F. Dozol noted in particular the very high uranium content of Oklo 311 ore:
- elements present in significant quantities around masses 85-105 and 130-150, corresponding to the two bumps of U fission yields. (The mass distribution of fission products follows a "camel's hump" curve, with two maxima),
- the last lanthanides (holmium to lutetium) are not detected (beyond mass166). In nature, all 14 lanthanides are found; in nuclear fuel, having undergone fission reactions, the isotopes of the last lanthanides are not detected.
The next step is isotopic analysis of certain elements on a thermal ionization mass spectrometer, after chemical separation of neodymium and samarium. From the first analyses of Oklo "M" uranate and "Oklo 311" ore, it is clear that neodymium and samarium have an isotopic composition much closer to that found in irradiated fuel than to that of the natural element. The detection of Nd and Sm isotopes not produced by fission indicates that these elements are also present in the natural state, from which their contribution can be subtracted.
These results were passed on to neutron scientist Jean Claude Nimal (CEA Saclay), who estimated the neutron flux received by the analyzed sample on the basis of its U deficit. This made it possible to estimate the neutron capture by the isotopes Nd and Nd, leading to the additional formation of Nd and Nd respectively. This excess must be subtracted to obtain fission yields for uranium 235. As can be seen from the table below, the fission yields (M) agree with the results corrected (C) for the presence of natural neodymium and neutron capture. | 1 | Fission Products + Nuclear Fission |
Primary reference materials define the scales on which isotopic ratios are reported. This can mean a material that historically defined an isotopic scale, such as Vienna Standard Mean Ocean Water (VSMOW) for hydrogen isotopes, even if that material is not currently in use. Alternatively, it can mean a material that only ever existed theoretically but is used to define an isotopic scale, such as VCDT for sulfur isotope ratios. | 0 | Isotopes |
The IsoRes hypothesis has been tested experimentally by means of growth of E. coli and found to be supported by extremely strong statistics (p ). Particular strong evidence of faster growth was found for the “super-resonance”.
Fig. 1. 2D plot of molecular masses of 3000 E. coli tryptic peptides. A – terrestrial isotopic compositions (red arrow shows the line representing the resonance); B – O abundance is increased by 20%, which destroyed the terrestrial resonance; C – isotopic compositions of the “super-resonance”, where all dots (molecules) are perfectly aligned. Adapted from ref. 4. | 0 | Isotopes |
Late or delayed effects of radiation occur following a wide range of doses and dose rates. Delayed effects may appear months to years after irradiation and include a wide variety of effects involving almost all tissues or organs. Some of the possible delayed consequences of radiation injury, with the rates above the background prevalence, depending on the absorbed dose, include carcinogenesis, cataract formation, chronic radiodermatitis, decreased fertility, and genetic mutations.
Presently, the only teratological effect observed in humans following nuclear attacks on highly populated areas is microcephaly which is the only proven malformation, or congenital abnormality, found in the in utero developing human fetuses present during the Hiroshima and Nagasaki bombings. Of all the pregnant women who were close enough to be exposed to the prompt burst of intense neutron and gamma doses in the two cities, the total number of children born with microcephaly was below 50. No statistically demonstrable increase of congenital malformations was found among the later conceived children born to survivors of the nuclear detonations at Hiroshima and Nagasaki. The surviving women of Hiroshima and Nagasaki who could conceive and were exposed to substantial amounts of radiation went on and had children with no higher incidence of abnormalities than the Japanese average.
The Baby Tooth Survey founded by the husband and wife team of physicians Eric Reiss and Louise Reiss, was a research effort focused on detecting the presence of strontium-90, a cancer-causing radioactive isotope created by the more than 400 atomic tests conducted above ground that is absorbed from water and dairy products into the bones and teeth given its chemical similarity to calcium. The team sent collection forms to schools in the St. Louis, Missouri area, hoping to gather 50,000 teeth each year. Ultimately, the project collected over 300,000 teeth from children of various ages before the project was ended in 1970.
Preliminary results of the Baby Tooth Survey were published in the November 24, 1961, edition of the journal Science, and showed that levels of strontium-90 had risen steadily in children born in the 1950s, with those born later showing the most pronounced increases. The results of a more comprehensive study of the elements found in the teeth collected showed that children born after 1963 had levels of strontium-90 in their baby teeth that was 50 times higher than that found in children born before large-scale atomic testing began. The findings helped convince U.S. President John F. Kennedy to sign the Partial Nuclear Test Ban Treaty with the United Kingdom and Soviet Union, which ended the above-ground nuclear weapons testing that created the greatest amounts of atmospheric nuclear fallout.
Some considered the baby tooth survey a "campaign [that] effectively employed a variety of media advocacy strategies" to alarm the public and "galvanized" support against atmospheric nuclear testing,, and putting an end to such testing was commonly viewed as a positive outcome for a myriad of reasons. The survey could not show at the time, nor in the decades that have elapsed, that the levels of global strontium-90 or fallout in general, were life-threatening, primarily because "50 times the strontium-90 from before nuclear testing" is a minuscule number, and multiplication of minuscule numbers results in only a slightly larger minuscule number. Moreover, the Radiation and Public Health Project that currently retains the teeth has had their stance and publications criticized: a 2003 article in The New York Times states that many scientists consider the groups work controversial, with little credibility with the scientific establishment, while some scientists consider it "good, careful work". In an April 2014 article in Popular Science, Sarah Fecht argues that the groups work, specifically the widely discussed case of cherry-picking data to suggest that fallout from the 2011 Fukushima accident caused infant deaths in America, is "junk science", as despite their papers being peer-reviewed, independent attempts to corroborate their results return findings that are not in agreement with what the organization suggests. The organization had earlier suggested the same thing occurred after the 1979 Three Mile Island accident, though the Atomic Energy Commission argued this was unfounded. The tooth survey, and the organization's new target of pushing for test bans with US nuclear electric power stations, is detailed and critically labelled as the "Tooth Fairy issue" by the Nuclear Regulatory Commission. | 1 | Fission Products + Nuclear Fission |
CERN-MEDical Isotopes Collected from ISOLDE (MEDICIS) is a facility located in the Isotope Separator Online DEvice (ISOLDE) facility at CERN, designed to produce high-purity isotopes for developing the practice of patient diagnosis and treatment. The facility was initiated in 2010, with its first radioisotopes (terbium-155) produced on 12 December 2017.
The target used to produce radioactive nuclei at the ISOLDE facility only absorbs 10% of the proton beam. MEDICIS positions a second target behind the first, which is irradiated by the leftover 90% of the proton beam. The target is then moved to an off-line mass separation system and isotopes are extracted from the target. These isotopes are implanted in metallic foil and can be delivered to research facilities and hospitals.
MEDICIS is a nuclear class A laboratory and takes into account various radioprotection procedures to prevent irradiation and contamination. | 0 | Isotopes |
As of today and for the next few hundred years or so, caesium-137 and strontium-90 continue to be the principal source of radiation in the zone of alienation around the Chernobyl nuclear power plant, and pose the greatest risk to health, owing to their approximately 30 year half-life and biological uptake. The mean contamination of caesium-137 in Germany following the Chernobyl disaster was 2000 to 4000 Bq/m. This corresponds to a contamination of 1 mg/km of caesium-137, totaling about 500 grams deposited over all of Germany. In Scandinavia, some reindeer and sheep exceeded the Norwegian legal limit (3000 Bq/kg) 26 years after Chernobyl. As of 2016, the Chernobyl caesium-137 has decayed by half, but could have been locally concentrated by much larger factors. | 1 | Fission Products + Nuclear Fission |
In chemistry, isotopologues are molecules that differ only in their isotopic composition. They have the same chemical formula and bonding arrangement of atoms, but at least one atom has a different number of neutrons than the parent.
An example is water, whose hydrogen-related isotopologues are: "light water" (HOH or ), "semi-heavy water" with the deuterium isotope in equal proportion to protium (HDO or ), "heavy water" with two deuterium isotopes of hydrogen per molecule ( or ), and "super-heavy water" or tritiated water ( or , as well as and , where some or all of the hydrogen atoms are replaced with the radioactive tritium isotope). Oxygen-related isotopologues of water include the commonly available form of heavy-oxygen water () and the more difficult to separate version with the isotope. Both elements may be replaced by isotopes, for example in the doubly labeled water isotopologue . All taken together, there are 9 different stable water isotopologues, and 9 radioactive isotopologues involving tritium, for a total of 18. However only certain ratios are possible in mixture, due to prevalent hydrogen swapping.
The atom(s) of the different isotope may be anywhere in a molecule, so the difference is in the net chemical formula. If a compound has several atoms of the same element, any one of them could be the altered one, and it would still be the same isotopologue. When considering the different locations of the same isotopically modified element, the term isotopomer, first proposed by Seeman and Paine in 1992, is used.
Isotopomerism is analogous to constitutional isomerism of different elements in a structure. Depending on the formula and the symmetry of the structure, there might be several isotopomers of one isotopologue. For example, ethanol has the molecular formula . Mono-deuterated ethanol, , is an isotopologue of it. The structural formulas and are two isotopomers of that isotopologue. | 0 | Isotopes |
Because of the relative rarity of the heavy isotopes of C, H, and O, isotope-ratio mass spectrometry (IRMS) of doubly substituted species requires larger volumes of sample gas and longer analysis times than traditional stable isotope measurements, thereby requiring extremely stable instrumentation. In addition, the doubly-substituted isotopologues are often subject to isobaric interferences, as in the methane system where CH and CHD ions interfere with measurement of the CHD and CHD species at mass 18. A measurement of such species requires either very high mass resolving power to separate one isobar from another, or modeling of the contributions of the interfering species to the abundance of the species of interest. These analytical challenges are significant: The first publication precisely measuring doubly substituted isotopologues did not appear until 2004, though singly substituted isotopologues had been measured for decades previously.
As an alternative to more conventional gas source IRMS instruments, tunable diode laser absorption spectroscopy has also emerged as a method to measure doubly substituted species free from isobaric interferences, and has been applied to the methane isotopologue CHD. | 0 | Isotopes |
In nuclear engineering, fissile material is material that can undergo nuclear fission when struck by a neutron of low energy. A self-sustaining thermal chain reaction can only be achieved with fissile material. The predominant neutron energy in a system may be typified by either slow neutrons (i.e., a thermal system) or fast neutrons. Fissile material can be used to fuel thermal-neutron reactors, fast-neutron reactors and nuclear explosives. | 1 | Fission Products + Nuclear Fission |
The δ values and absolute isotope ratios of common reference materials are summarized in Table 1 and described in more detail below. Alternative values for the absolute isotopic ratios of reference materials, differing only modestly from those in Table 1, are presented in Table 2.5 of Sharp (2007) (a [http://digitalrepository.unm.edu/unm_oer/1/ text freely available online]), as well as Table 1 of the 1993 IAEA report on isotopic reference materials. For an exhaustive list of reference material, refer to Appendix I of Sharp (2007), Table 40.1 of Gröning (2004), or the website of the International Atomic Energy Agency. Note that the C/C ratio of Vienna Pee Dee Belemnite (VPDB) and S/S ratio of Vienna Canyon Diablo Troilite (VCDT) are purely mathematical constructs; neither material existed as a physical sample that could be measured.
In Table 1, "Name" refers to the common name of the reference, "Material" gives its chemical formula and phase, "Type of ratio" is the isotopic ratio reported in "Isotopic ratio", "δ" is the δ value of the material with indicated reference frame, "Type" is the category of the material using the notation of Gröening (2004) (discussed below), "Citation" gives the article(s) reporting the isotopic abundances on which the isotope ratio is based, and "Notes" are notes. The reported isotopic ratios reflect the results from individual analyses of absolute mass fraction, aggregated in Meija et al. (2016) and manipulated to reach the given ratios. Error was calculated as the square root of the sum of the squares of fractional reported errors, consistent with standard error propagation, but is not propagated for ratios reached through secondary calculation. | 0 | Isotopes |
Isotope analysis has widespread applicability in the natural sciences. These include numerous applications in the biological, earth and environmental sciences. | 0 | Isotopes |
Fission products have half-lives of 90 years (samarium-151) or less, except for seven long-lived fission products that have half lives of 211,100 years (technetium-99) or more. Therefore, the total radioactivity of a mixture of pure fission products decreases rapidly for the first several hundred years (controlled by the short-lived products) before stabilizing at a low level that changes little for hundreds of thousands of years (controlled by the seven long-lived products).
This behavior of pure fission products with actinides removed, contrasts with the decay of fuel that still contains actinides. This fuel is produced in the so-called "open" (i.e., no nuclear reprocessing) nuclear fuel cycle. A number of these actinides have half lives in the missing range of about 100 to 200,000 years, causing some difficulty with storage plans in this time-range for open cycle non-reprocessed fuels.
Proponents of nuclear fuel cycles which aim to consume all their actinides by fission, such as the Integral Fast Reactor and molten salt reactor, use this fact to claim that within 200 years, their fuel wastes are no more radioactive than the original uranium ore.
Fission products emit beta radiation, while actinides primarily emit alpha radiation. Many of each also emit gamma radiation. | 1 | Fission Products + Nuclear Fission |
Commercial nuclear fission reactors are operated in the otherwise self-extinguishing prompt subcritical state. Certain fission products decay over seconds to minutes, producing additional delayed neutrons crucial to sustaining criticality. An example is bromine-87 with a half-life of about a minute. Operating in this delayed critical state, power changes slowly enough to permit human and automatic control. Analogous to fire dampers varying the movement of wood embers towards new fuel, control rods are moved as the nuclear fuel burns up over time.
In a nuclear power reactor, the main sources of radioactivity are fission products along with actinides and activation products. Fission products are most of the radioactivity for the first several hundred years, while actinides dominate roughly 10 to 10 years after fuel use.
Most fission products are retained near their points of production. They are important to reactor operation not only because some contribute delayed neutrons useful for reactor control, but some are neutron poisons that inhibit the nuclear reaction. Buildup of neutron poisons is a key to how long a given fuel element can be kept in the reactor. Fission product decay also generates heat that continues even after the reactor has been shut down and fission stopped. This decay heat requires removal after shutdown; loss of this cooling damaged the reactors at Three Mile Island and Fukushima.
If the fuel cladding around the fuel develops holes, fission products can leak into the primary coolant. Depending on the chemistry, they may settle within the reactor core or travel through the coolant system and chemistry control systems are provided to remove them. In a well-designed power reactor running under normal conditions, coolant radioactivity is very low.
The isotope responsible for most of the gamma exposure in fuel reprocessing plants (and the Chernobyl site in 2005) is caesium-137. Iodine-129 is a major radioactive isotope released from reprocessing plants. In nuclear reactors both caesium-137 and strontium-90 are found in locations away from the fuel because they're formed by the beta decay of noble gases (xenon-137, with a 3.8-minute half-life, and krypton-90, with a 32-second half-life) which enable them to be deposited away from the fuel, e.g. on control rods. | 1 | Fission Products + Nuclear Fission |
Nuclear fallout can occur due to a number of different sources. One of the most common potential sources of nuclear fallout is that of nuclear reactors. Because of this, steps must be taken to ensure the risk of nuclear fallout at nuclear reactors is controlled.
In the 1950s and 60s, the United States Atomic Energy Commission (AEC) began developing safety regulations against nuclear fallout for civilian nuclear reactors. Because the effects of nuclear fallout are more widespread and longer lasting than other forms of energy production accidents, the AEC desired a more proactive response towards potential accidents than ever before. One step to prevent nuclear reactor accidents was the Price-Anderson Act. Passed by Congress in 1957, the Price-Anderson Act ensured government assistance above the $60 million covered by private insurance companies in the case of a nuclear reactor accident. The main goal of the Price-Anderson Act was to protect the multi-billion-dollar companies overseeing the production of nuclear reactors. Without this protection, the nuclear reactor industry could potentially come to a halt, and the protective measures against nuclear fallout would be reduced. However, because of the limited experience in nuclear reactor technology, engineers had a difficult time calculating the potential risk of released radiation. Engineers were forced to imagine every unlikely accident, and the potential fallout associated with each accident. The AECs regulations against potential nuclear reactor fallout were centered on the ability of the power plant to the Maximum Credible Accident (MCA). The MCA involved a "large release of radioactive isotopes after a substantial meltdown of the reactor fuel when the reactor coolant system failed through a Loss-of-Coolant Accident". The prevention of the MCA enabled a number of new nuclear fallout preventive measures. Static safety systems, or systems without power sources or user input, were enabled to prevent potential human error. Containment buildings, for example, were reliably effective at containing a release of radiation and did not need to be powered or turned on to operate. Active protective systems, although far less dependable, can do many things that static systems cannot. For example, a system to replace the escaping steam of a cooling system with cooling water could prevent reactor fuel from melting. However, this system would need a sensor to detect the presence of releasing steam. Sensors can fail, and the results of a lack of preventive measures would result in a local nuclear fallout. The AEC had to choose, then, between active and static systems to protect the public from nuclear fallout. With a lack of set standards and probabilistic calculations, the AEC and the industry became divided on the best safety precautions to use.
This division gave rise to the Nuclear Regulatory Commission (NRC). The NRC was committed to regulations through research, which gave the regulatory committee a knowledge bank of research on which to draw their regulations. Much of the research done by the NRC sought to move safety systems from a deterministic viewpoint into a new probabilistic approach. The deterministic approach sought to foresee all problems before they arose. The probabilistic approach uses a more mathematical approach to weigh the risks of potential radiation leaks. Much of the probabilistic safety approach can be drawn from the radiative transfer theory in Physics, which describes how radiation travels in free space and through barriers. Today, the NRC is still the leading regulatory committee on nuclear reactor power plants. | 1 | Fission Products + Nuclear Fission |
I is not deliberately produced for any practical purposes. However, its long half-life and its relative mobility in the environment have made it useful for a variety of dating applications. These include identifying older groundwaters based on the amount of natural I (or its Xe decay product) present, as well as identifying younger groundwaters by the increased anthropogenic I levels since the 1960s. | 1 | Fission Products + Nuclear Fission |
Chemical chain reactions were first proposed by German chemist Max Bodenstein in 1913, and were reasonably well understood before nuclear chain reactions were proposed. It was understood that chemical chain reactions were responsible for exponentially increasing rates in reactions, such as produced in chemical explosions.
The concept of a nuclear chain reaction was reportedly first hypothesized by Hungarian scientist Leó Szilárd on September 12, 1933. Szilárd that morning had been reading in a London paper of an experiment in which protons from an accelerator had been used to split lithium-7 into alpha particles, and the fact that much greater amounts of energy were produced by the reaction than the proton supplied. Ernest Rutherford commented in the article that inefficiencies in the process precluded use of it for power generation. However, the neutron had been discovered by James Chadwick in 1932, shortly before, as the product of a nuclear reaction. Szilárd, who had been trained as an engineer and physicist, put the two nuclear experimental results together in his mind and realized that if a nuclear reaction produced neutrons, which then caused further similar nuclear reactions, the process might be a self-perpetuating nuclear chain-reaction, spontaneously producing new isotopes and power without the need for protons or an accelerator. Szilárd, however, did not propose fission as the mechanism for his chain reaction, since the fission reaction was not yet discovered, or even suspected. Instead, Szilárd proposed using mixtures of lighter known isotopes which produced neutrons in copious amounts. He filed a patent for his idea of a simple nuclear reactor the following year.
In 1936, Szilárd attempted to create a chain reaction using beryllium and indium, but was unsuccessful. Nuclear fission was discovered by Otto Hahn and Fritz Strassmann in December 1938 and explained theoretically in January 1939 by Lise Meitner and her nephew Otto Robert Frisch. In their second publication on nuclear fission in February 1939, Hahn and Strassmann used the term Uranspaltung (uranium fission) for the first time, and predicted the existence and liberation of additional neutrons during the fission process, opening up the possibility of a nuclear chain reaction.
A few months later, Frédéric Joliot-Curie, H. Von Halban and L. Kowarski in Paris searched for, and discovered, neutron multiplication in uranium, proving that a nuclear chain reaction by this mechanism was indeed possible.
On May 4, 1939, Joliot-Curie, Halban, and Kowarski filed three patents. The first two described power production from a nuclear chain reaction, the last one called Perfectionnement aux charges explosives was the first patent for the atomic bomb and is filed as patent No. 445686 by the Caisse nationale de Recherche Scientifique.
In parallel, Szilárd and Enrico Fermi in New York made the same analysis. This discovery prompted the letter from Szilárd and signed by Albert Einstein to President Franklin D. Roosevelt, warning of the possibility that Nazi Germany might be attempting to build an atomic bomb.
On December 2, 1942, a team led by Fermi (and including Szilárd) produced the first artificial self-sustaining nuclear chain reaction with the Chicago Pile-1 (CP-1) experimental reactor in a racquets court below the bleachers of Stagg Field at the University of Chicago. Fermis experiments at the University of Chicago were part of Arthur H. Comptons Metallurgical Laboratory of the Manhattan Project; the lab was later renamed Argonne National Laboratory, and tasked with conducting research in harnessing fission for nuclear energy.
In 1956, Paul Kuroda of the University of Arkansas postulated that a natural fission reactor may have once existed. Since nuclear chain reactions may only require natural materials (such as water and uranium, if the uranium has sufficient amounts of U), it was possible to have these chain reactions occur in the distant past when uranium-235 concentrations were higher than today, and where there was the right combination of materials within the Earths crust. made up a larger share of uranium on earth in the geological past due to the different half life of the isotopes and , the former decaying almost an order of magnitude faster than the latter. Kurodas prediction was verified with the discovery of evidence of natural self-sustaining nuclear chain reactions in the past at Oklo in Gabon in September 1972. To sustain a nuclear fission chain reaction at present isotope ratios in natural uranium on earth would require the presence of a neutron moderator like heavy water or high purity carbon (e.g. graphite) in the absence of neutron poisons, which is even more unlikely to arise by natural geological processes than the conditions at Oklo some two billion years ago. | 1 | Fission Products + Nuclear Fission |
The MEDICIS facility is located in the extension of building 179 at the CERN Meyrin site, next to the ISOLDE building. The facility was established by CERN in 2010, along with contributions from the CERN Knowledge Transfer Fund, as well as receiving a European Commission Marie-Skłodowska-Curie training grant under the title MEDICIS-PROMED. The construction of the facility started in September 2013 and was completed in 2017.
ISOLDE directs a 1.4 GeV proton beam from the Proton Synchrotron Booster (PSB) onto a thick target, the material dependent on the desired produced isotopes. Only 10% of the proton beam used in the ISOLDE facility is absorbed by the target, with the rest otherwise hitting the beam dump. MEDICIS uses these wasted protons to irradiate a second target, which produces specific isotopes, placed behind each of ISOLDE's target stations, the High Resolution Separator (HRS) and the General Purpose Separator (GPS). Alternatively, the facility uses pre-irradiated targets that are provided by external institutions. MEDICIS was one of the few facilities operating throughout the Long Shutdown 2, due to it being provided with 34 externally irradiated target materials.
Due to the high levels of radiation, the targets are transferred from the irradiation station to the radioisotope mass-separation beamline using an automated rail conveyer system (RCS). A KUKA robot is used to transport the target to the station, where the isotope of interest can be collected and radiochemically purified. This is done by heating the target up to very high temperatures, often more than 2000 °C, which causes the specified isotopes to diffuse. The isotopes are then ionised and accelerated by an ion source to be sent through a mass separator. The mass separator extracts the isotope of interest so that it can be implanted onto thin gold foils with a one-sided metallic or salt coating.
In 2019, the MEDICIS Laser Ion Source Setup At CERN (MELISSA) became fully operational, containing the individual lasers, auxiliary and control systems, and optical beam transport. The MELISSA laser laboratory has helped to successfully increase the separation efficiency and the yield of the isotopes. The laser excites only isotopes of the desired element, allowing an element-selective isotope separation for a given atomic mass from other isobars by the mass separator.
A shielded trolley is used to retrieve the samples after the radioisotopes have been collected, in order to avoid risk of contamination. Once the target is finished being used, it is sent to a hot cell in order to be safely dismantled and put in waste bins. Once collected, the samples can be sent to hospitals and research facilities with the purpose of developing patient imaging and treatment, and therapy protocols.
Additionally next to the MEDICIS facility, there is a nanolab laboratory designed for the development and assembly of nanomaterials. The nanomaterials are sealed in a glovebox, meaning there is no contact with the outside environment. It builds up on the development of the first nanostructured targets used for isotope production, and further exploits developments initiated in MEDICIS-Promed under the guidance of Prof. "Kostya" Novozelov. | 0 | Isotopes |
Deuterium-depleted water has a lower concentration of deuterium (H) than occurs in nature at sea level. Deuterium is a naturally-occurring, stable (non-radioactive) isotope of hydrogen with a nucleus consisting of one proton and one neutron. The nucleus of ordinary hydrogen (protium) consists of one proton only, and no neutron. Deuterium atoms have about twice the atomic mass of normal hydrogen atoms as a result. Heavy water consists of water molecules with two deuterium atoms instead of the two normal hydrogen atoms. The hydrogen in normal water consists of about 99.98% (by weight) of normal hydrogen (H).
The production of heavy water involves isolating and removing deuterium-containing isotopologues within natural water. The by-product of this process is deuterium-depleted water.
Due to the heterogeneity of hydrological conditions, the isotopic composition of natural water varies around the Earth. Distance from the ocean and the equator and the height above sea level have a positive correlation with water deuterium depletion.
In Vienna Standard Mean Ocean Water (VSMOW) that defines the isotopic composition of the ocean water, deuterium occurs at a concentration of 155.76 ppm. For the SLAP (Standard Light Antarctic Precipitation) standard that determines the isotopic composition of natural water from the Antarctic, the concentration of deuterium is 89.02 ppm.
Snow water, especially from glacial mountain meltwater, is significantly lighter than ocean water. Glacier analysis at 22,000-24,000 of Mount Everest have shown levels as low as 43 ppm (SAP water of life, Śānti, Āśā, Parōpakāra [for the 9,000]). The weight quantities of isotopologues in natural water are calculated on the basis of the data collected using molecular spectroscopy:
According to the table above, the weight concentration of heavy isotopologues in natural water can reach 2.97 g/kg, which is mostly due to HO, i.e. water with light hydrogen and heavy oxygen. Furthermore, there are about 300 milligrams of deuterium-containing isotopologues in each liter of water. This presents a significant value comparable, for example, with the content of mineral salts. | 0 | Isotopes |
Oxygen isotopic ratios are commonly compared to both the VSMOW and the VPDB references. Traditionally oxygen in water is reported relative to VSMOW while oxygen liberated from carbonate rocks or other geologic archives is reported relative to VPDB. As in the case of hydrogen, the oxygen isotopic scale is defined by two materials, VSMOW2 and SLAP2. Measurements of sample δO vs. VSMOW can be converted to the VPDB reference frame through the following equation: δO = 0.97001*δO - 29.99‰ (Brand et al., 2014). | 0 | Isotopes |
Nuclear fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and the shock wave has passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes. The amount and spread of fallout is a product of the size of the weapon and the altitude at which it is detonated. Fallout may get entrained with the products of a pyrocumulus cloud and fall as black rain (rain darkened by soot and other particulates, which fell within 30–40 minutes of the atomic bombings of Hiroshima and Nagasaki). This radioactive dust, usually consisting of fission products mixed with bystanding atoms that are neutron-activated by exposure, is a form of radioactive contamination. | 1 | Fission Products + Nuclear Fission |
Tc, half-life 211k years, is produced at a yield of about 6% per fission; see also the main fission products page. It is also produced (via the short lived nuclear isomer Technetium-99m) as a decay product of Molybdenum-99. Technetium is particularly mobile in the environment as it forms negatively charged pertechnetate-ions and it presents the biggest radiological hazard among the long lived fission products. Despite being a metal, Technetium usually doesn't form positively charged ions, but Technetium halides like Technetium hexafluoride exist. TcF is a nuisance in uranium enrichment as its boiling point () is very close to that of uranium hexafluoride (). The issue is known to enrichment facilities because spontaneous fission also yields small amounts of Technetium (which will be in secular equilibrium with its parent nuclides in natural uranium) but if fluoride volatility is employed for reprocessing, a significant share of the "uranium" fraction of fractional distillation will be contaminated with Technetium requiring a further separation step.
Technetium-99 is suitable for nuclear transmutation by slow neutrons as it has a sufficient thermal neutron cross section and as it has no known stable isotopes. Under neutron irradiation, Tc-99 forms Tc-100 which quickly decays to stable a valuable platinum group metal. | 1 | Fission Products + Nuclear Fission |
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Wikipedia Isotopes vs Nuclear Fission Products Binary Classification
This dataset is derived from the English Wikipedia articles and is designed for binary text classification tasks in the field of nuclear chemistry and physics. The dataset is divided into two classes based on the thematic content of the articles:
Isotopes: This class includes articles that focus on isotopes, which are variants of a particular chemical element that have the same number of protons but different numbers of neutrons. Topics may cover the properties, applications, and significance of various isotopes in fields such as medicine, archaeology, and nuclear energy.
Nuclear Fission Products: This class comprises articles related to:
- Fission Products: Articles that discuss the fragments left after a nucleus undergoes fission, including a variety of isotopes of different elements. These products are typically radioactive and play a significant role in nuclear reactor operation and nuclear waste management.
- Nuclear Fission: Articles that cover the process by which a heavy atomic nucleus splits into two smaller nuclei, releasing a significant amount of energy. This process is fundamental to the operation of nuclear reactors and the principles behind nuclear weapons.
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