Isotopes decay scheme

The signamres of long-lived radioactive isotope decay schemes provide some of the most unequivocal evidence for chemical evolution of the mantle. Excellent reviews of the application... 

The influence of the decay scheme on the retention (through differences in the percent conversion of y-transitions) was demonstrated by comparison of the -decay products of Pb and Pb in Pb(CgH5)3Cl. The retention of Bi in Bi(CgH5)3Cl2 was 17—19% and of Bi about 50%. According to Nefedov, this isotope effect is directly proportional to the conversion coefficients of the two isotopes. Corresponding to the complement of the conversion coefficient, 1—a, the molecular structure should be preserved to the extent of 80% for the two isotopes. The probability of chemical reaction for change or preservation of molecular structure is the same for the two cases. 

Fig. 7.36 Nuclear decay schemes for the hafiiium isotopes ,i77,i78,i80jj (from [162])...

Fig. 7.52 Simplified nuclear decay schemes for the four osmium Mdssbauer isotopes...

There are two iridium isotopes, ir and Ir, suitable for Mossbauer spectroscopy. Each of them possesses two nuclear transitions with which nuclear resonance absorption has been observed. Figure 7.58 (from [266]) shows the (simplified) nuclear decay schemes for both iridium Mossbauer isotopes the Mossbauer transitions are marked therein with bold arrows. The relevant nuclear data known to date for the four Mossbauer transitions are collected in Table 7.1 at the end of the book. 

Figure 4. The decay schemes of 23SU and 235 U, showing the longer-lived isotopes used in radiometric dating of Pleistocene and Holocene deposits.

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. 

Nelson DR, McCulloch MT (1989) Petrogenic applications of the "K- Ca radiogenic decay scheme—a reconnaissance study. Chem Geol (Isot Geosci Sect) 79 275-293 Niederer FR, Papanastassiou DA (1984) Ca isotopes in refractory inclusions. Geochim Cosmochim Acta 48 1279-1293... 

The most familiar radioactive element is uranium, which has two naturally occurring isotopes of mass numbers 235 and 238 that decay very slowly. Review the first few steps in the decay of uranium-238, which changes to lead-206 after the emission of 8 alpha and 6 beta particles. The earliest stages of the decay scheme involve only three elements, as shown in Figure 3-2. 

The Thorium Series. This series commences with U2Th and ends with the stable isotope 3n Pb. The decay scheme is represented by ... 

Table 3-2 lists important physical properties of radium and selected radium compounds. Radioactive properties of the four naturally-occurring radium isotopes are listed in Table 3-3. In addition to the naturally occurring isotopes, there are 12 other known isotopes of radium. The principal decay schemes of the uranium and thorium decay series that produce the naturally-occurring radium isotopes are presented in Figure 3-1.

The radioactive decay schemes of radon and thoron are shown in Fig. 1.1. The old generic nomenclature (RaA, ThB etc.) is now superseded by the isotopic designation (218Po, 212Pb etc.), but where necessary for clarity the old designation will be added. 

The salt used in this experiment is potassium chloride (KC1). Potassium-40 is a naturally-occurring isotope of potassium (abundance = 0.0117%) whose half life is 1.28 x 109 years. It emits a gamma ray at 1.461 MeV with a decay fraction of 10.7%, in addition to beta particles with a decay fraction of 89.3%. The decay scheme for 40K is given in Fig. 3.1. A tared container (see Experiment 2) is filled with solid KC1, closed, weighed, and counted. 

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