Radioactive isotopes abundance

Thus, the ratios of lead isotopes 204,206,207 and 208 can vary markedly depending on the source of the lead. One use of these ratios lies in determination of the ages of rocks from the abundances of the various isotopes and the half-lives of their precursor radioactive isotopes. 

It is not necessary that there be two isotopes in both the sample and the spike. One isotope in the sample needs to be measured, but the spike can have one isotope of the same element that has been produced artificially. The latter is often a long-lived radioisotope. For example, and are radioactive and all occur naturally. The radioactive isotope does not occur naturally but is made artificially by irradiation of Th with neutrons. Since it is commercially available, this last isotope is often used as a spike for isotope-dilution analysis of natural uranium materials by comparison with the most abundant isotope ( U). 

Many artificial (likely radioactive) isotopes can be created through nuclear reactions. Radioactive isotopes of iodine are used in medicine, while isotopes of plutonium are used in making atomic bombs. In many analytical applications, the ratio of occurrence of the isotopes is important. For example, it may be important to know the exact ratio of the abundances (relative amounts) of the isotopes 1, 2, and 3 in hydrogen. Such knowledge can be obtained through a mass spectrometric measurement of the isotope abundance ratio. 

Properties. Strontium is a hard white metal having physical properties shown in Table 1. It has four stable isotopes, atomic weights 84, 86, 87, and 88 and one radioactive isotope, strontium-90 [10098-97-2] which is a product of nuclear fission. The most abundant isotope is strontium-88. 

When specifically labelled compounds are required, direct chemical synthesis may be necessary. The standard techniques of preparative chemistry are used, suitably modified for small-scale work with radioactive materials. The starting material is tritium gas which can be obtained at greater than 98% isotopic abundance. Tritiated water can be made either by catalytic oxidation over palladium or by reduction of a metal oxide ... 

More precise estimates come from accurate measurements of isotope ratios. Three pairs of radioactive isotopes and their products are abundant enough for such ratios to be measured ... 

Two of these isotopes, carbon-12, the most abundant, and carbon-13 are stable. Carbon-14, on the other hand, is an unstable radioactive isotope, also known as radiocarbon, which decays by the beta decay process a beta particle is emitted from the decaying atomic nucleus and the carbon-14 atom is transformed into an isotope of another element, nitrogen-14, N-14 for short (chemical symbol 14N), the most common isotope of nitrogen ... 

Cerium, an element in the lanthanide series, has a number of radioactive isotopes. Several of these are produced in abundance in nuclear fission reactions associated with nuclear industry operations or detonation of nuclear devices. This report summarizes our present knowledge of the relevant physical, chemical, and biological properties of radiocerium as a basis for establishing radiation protection guidelines. 

The most abundant isotope of carbon has a mass of 12 atomic mass units, 12C. A less abundant stable isotope is 13C. And much less abundant is the radioactive isotope t4C, also called radiocarbon. It is convenient to express the abundances of these rare isotopes in terms of ratios of the number of atoms of the rare isotope in a sample to the number of atoms of the abundant isotope. We call this ratio r, generally a very small number. To arrive at numbers of convenient magnitude, it is conventional to express the ratio in terms of the departure of r from the ratio in a standard, which I call. v, and to express this departure in parts per thousand of s. Thus the standard delta notation is... 

As a result of slow (thermal) neutron irradiation, a sample composed of stable atoms of a variety of elements will produce several radioactive isotopes of these activated elements. For a nuclear reaction to be useful analytically in the delayed NAA mode the element of interest must be capable of undergoing a nuclear reaction of some sort, the product of which must be radioactively unstable. The daughter nucleus must have a half-life of the order of days or months (so that it can be conveniently measured), and it should emit a particle which has a characteristic energy and is free from interference from other particles which may be produced by other elements within the sample. The induced radioactivity is complex as it comprises a summation of all the active species present. Individual species are identified by computer-aided de-convolution of the data. Parry (1991 42-9) and Glascock (1998) summarize the relevant decay schemes, and Alfassi (1990 3) and Glascock (1991 Table 3) list y ray energy spectra and percentage abundances for a number of isotopes useful in NAA. 

The comprehensive dedicated research ultimately made it possible to decode the patterns of labelling in almost any type of tritium labelled compound at low isotopic abundance (e.g., 3 x 10 4 to 3 x 10 2 per cent. 3H per site) with the aid of 3H-NMR directly, rapidly, reliably and non-destructive analytical means. Since, 1971, the 3H-NMR spectroscopy, utilizing only millicurie (mCi) quantities of radioactivity, emerged as a most useful analytical tool for the study of tritium labelled compounds. 

A number of now extinct radioactive isotopes have existed in the early solar system. This is shown by the variations that they induce in the abundances in their daughter nuclides. Their main use is in establishing a chronology between their parental presolar stellar sources, and the formation of the solar system and the planets. An active debate is presently going on whether some of these short-lived nuclides could have been made within the early solar system by an intense flux of energetic protons from the young sun. 

The masses of isotopes can be measured with accuracies better than parts per billion (ppb), e.g., m40Ar = 39.9623831235 0.000000005 u. Unfortunately, determinations of abundance ratios are less accurate, causing errors of several parts per million (ppm) in relative atomic mass. The real limiting factor, however, comes from the variation of isotopic abundances from natural samples, e.g., in case of lead which is the final product of radioactive decay of uranium, the atomic weight varies by 500 ppm depending on the Pb/U ratios in the lead ore. [8]... 

Examples of isotopes are abundant. The major form of hydrogen is represented as H (or H-1), with one proton H, known as the isotope deuterium or heavy hydrogen, consists of one proton and one neutron (thus an amu of 2) and is the isotope of hydrogen called tritium with an amu of 3. Carbon-12 ( C or C-12) is the most abundant form of carbon, though carbon has several isotopes. One is the C isotope, a radioactive isotope of carbon that is used as a tracer and to determine dates of organic artifacts. Uranium-238 is the radioactive isotope (Note The atomic number is placed as a subscript prefix to the element s symbol—for example, —and the atomic mass number can be written either as a dash and number fol-... 

ISOTOPES There are a total of 59 radioactive isotopes for bismuth, ranging in half-lives from a few milliseconds to thousands of years. At one time it was thought that there was just one stable isotope (Bi-209), but it was later found that Bi-209 is radioactive with a half-life of 19,000,000,000,000,000,000 years. Such a long half-life means that BI-209 has not completely disintegrated and Is still found In nature, and Is thus considered stable. In this case, BI-209 makes up 100% of Bismuth s natural abundance. 

Table 11.2 Naturally occurring radioactive substances, a = years, d = days. Radionuclide Decay Process Half-Life Isotopic Abundance (%) Stable End-Product...

Radioactive decay is one process that produces variations in isotope abundance. The second cause for differences in isotope abundance is isotope fractionation, caused by small chemical and physical differences between the isotopes of an element. It is exclusively this important process that will be discussed in the following chapters. 

Until 1931 it was assumed that hydrogen consisted of only one isotope. Urey et al. (1932) detected the presence of a second stable isotope, which was called deuterium. (In addition to these two stable isotopes there is a third naturally oc-curing but radioactive isotope, H, tritium, with a half-life of approximately 12.5 years). Rosman and Taylor (1998) gave the following average abundances of the stable hydrogen isotopes ... 

The best illustration of radioactive astronomy is titanium-44. We shall take it as the archetype of a good radioactive isotope. It is relatively abundant and has a reasonable lifetime of around 100 years, neither too long, nor too short. Only aluminium-26 can rival it in this respect and nuclear gamma astronomy has already reaped some of the rewards (see Fig. 4.4). 

The dominant nuclear species resulting from processes at temperatures between 4 and 6 billion k include titanium-44, chromium-48, rron-52 and 53, nickel-56 and 57 and zinc-58, 60, 61 and 62. Isotopic abundances resulting from radioactive decay of these nuclei are compatible with terrestrial and meteoritic measurements relating to calcium-44, titanium-48, chromium-52 and 53, iron-56 and 57, and nickel-58, 60, 61 and 62. 

Symbol Ce atomic number 58 atomic weight 140.115 a rare-earth metal a lanthanide series inner-transition /-block element metaUic radius (alpha form) 1.8247A(CN=12) atomic volume 20.696 cm /mol electronic configuration [Xe]4fi5di6s2 common valence states -i-3 and +4 four stable isotopes Ce-140 and Ce-142 are the two major ones, their percent abundances 88.48% and 11.07%, respectively. Ce—138 (0.25%) and Ce—136(0.193%) are minor isotopes several artificial radioactive isotopes including Ce-144, a major fission product (ti 284.5 days), are known. 

Carbon dating A process that uses the relative abundance of the radioactive isotope carbon-14 to determine the age of the remains or products of living things can be used for materials up to about 60,000 years old. 

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