Decay modes listed

Table 20-1 lists some of the more useful radioisotopes, along with their half-lives and decay modes (we discuss these modes earlier in this chapter). 

The various decay modes are listed in Table 5.1. Unstable, radioactive nuclei may be transformed by emission of nucleons (a decay and, very rarely, emission of protons or neutrons) or by emission of electrons or positrons and decay, respectively). Alternatively to the emission of a positron, the unstable nucleus may capture an electron of the electron shell of the atom (symbol e). 

A number of uncommon decay modes exist which are of little direct relevance to gamma spectrometrists and I will content myself with just listing them delayed neutron emission, delayed proton emission, double beta decay (the simultaneous emission of two 3 particles), two proton decay and the emission of heavy ions or clusters , such as and Ne. Some detail can be found in the more recent general texts in the Further Reading section, such as the one by Ehmann and Vance (1991). 

Radionuclides are, by definition, unstable and decay by one, or more, of the decay modes alpha, beta-minus, beta-plus, electron capture or spontaneous fission. Although strictly speaking a de-excitation rather than a nuclear decay process, we can include isomeric transition in that list from the mathematical point of view. The amount of a radionuclide in a sample is expressed in Becquerels -numerically equal to the rate of disintegration - the number of disintegrations per second. We refer to this amount as the activity of the sample. Because this amount will change with time we must always specify at what time the activity was measured. 

Any single radionuclide not listed above with decay mode other than alpha emission or spontaneous fission and with radioactive half-life less than 2 hours Submersion[1].. 

Table 1 Production of superheavy element isotopes for chemistry experiments. Known nuclides with half-lives longer than 0.7 s are listed along with their decay modes, representative reactions of synthesis and production cross sections. If the element does not have a long-lived isotope, the longest-lived isotope is given...

C22-0048. Preidct the most likely mode or modes of decay for each of the isotopes of Mn listed in Problem... 

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. 

EC, and IT refer to p-decay, positron decay, electron capture, and isomeric transition, respectively. Where a nudide is known to have more than one mode of decay, they are listed in the order of their prevalence. 

Finally, results on second rank correlation functions for a second rank potential are collected in Table V. The situation is now very similar to the corresponding set of data for a first rank potential (Table III), since even rank correlation functions are not sensitive, for symmetry reasons, to jump motions. The slow mode is then again mostly due to the FRD of the larger solvent body while the fast modes are mainly dominated by motions of the first body (cf. the entries for D2 = 0.01, Uj = 2 and 4 in Table V). Note that other faster eigenvalues are present, with smaller weights, whose nature is mostly mixed, but are not listed in the table. Their individual contribution to the overall decay of the correlation function is small, but their cumulative weights may be around 0.1-0.3 or even more. 

Several radionuclides, radioactive isotopes that decay to noble gases, are listed in Table 1. In a radioactive decay, the radioactive isotope is referred to as the parenf isotope, while the decay product, the noble gas isotope, is referred to as the daughter isotope. In some cases listed, there is more than one mode of decay possible. In other cases, a single decay starts a chain that will ultimately produce several noble gas atoms. To take both into account, the yield (the number of noble gas atoms produced for each parent atom) is also given. Finally, radionuclides that fission may produce any of the several different isotopes of Xe in a characteristic spectrum (Table 2). All of the systems listed, with the exception of the decay of U and Th to Xe, have been exploited in extraterrestrial samples at one time or another. 

B modes are charge conjugates of the modes below. Reactions indicate the weak decay vertex and do not include mixing. Modes which do not identify the charge state of the B are listed in the B" "/B ADMIXTURE section. 

Mode-specific unimolecular decomposition has been observed in much of the theoretical work listed in table 8.1. In some cases more than one zero-order Hamiltonian is necessary to assign resonance states for an excited molecule. For the Henon-Heiles Hamiltonian two zero-order Hamiltonians are used to identify assignable resonances as either restricted processors (Q ) or quasiperiodic liberators (Q ) (Bai et al., 1983 Hose and Taylor, 1982). Similarly, Manz and co-workers (Bisseling et al., 1987 Joseph et al., 1988) assigned many stretching resonances of ABA molecules as either hyperspherical mode or local mode states. At the same energy, the 2" states for the Henon-Heiles Hamiltonian decay about an order of magnitude faster than the g states. 

Figure 10.15 The RRK, RRKM, and RRK with ZPE decay rates for the dissociation of (HjOj,. The calculations used the van der Waals modes vibrational frequencies listed in Table 10.4.

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