Decay schemes

Decay Schemes. Eor nuclear cases it is more useful to show energy levels that represent the state of the whole nucleus, rather than energy levels for individual atomic electrons (see Eig. 2). This different approach is necessary because in the atomic case the forces are known precisely, so that the computed wave functions are quite accurate for each particle. Eor the nucleus, the forces are much more complex and it is not reasonable to expect to be able to calculate the wave functions accurately for each particle. Thus, the nuclear decay schemes show the experimental levels rather than calculated ones. This is illustrated in Eigure 4, which gives the decay scheme for Co. Here the lowest level represents the ground state of the whole nucleus and each level above that represents a different excited state of the nucleus. 

Fig. 4. Decay scheme ofas an example of /5 -decay, showing the spins and parities of the levels populated in the daughter nucleus and the energies in keV of these levels, where (" ) represents the principal decay mode, (—fc.) an alternative mode, and (- - ) is a highly improbable transition.

Fig. 5. Decay scheme of showing the energies, spins, and parities of the levels populated in the daughter nucleus, Xe, and the energies in keV, emission probabihties (in %), and multipolarities of the y-ray transitions. There is a strong dependence of the y-ray lifetime on the y-character. The Ml + E2 y-ray of 177 keV has a half-hfe of 2.1 ps the half-hfe of the 164-keV M4 y-ray is 1.03 X 10 s.

Similar to beta decay is positron emission, where tlie parent emits a positively cliargcd electron. Positron emission is commonly called betapositive decay. Tliis decay scheme occurs when tlie neutron to proton ratio is too low and alpha emission is not energetically possible. Tlie positively charged electron, or positron, will travel at higli speeds until it interacts with an electron. Upon contact, each of tlie particles will disappear and two gamma rays will... 

Others which formed a coherent decay scheme down to Em ... 

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. 

The process of j3-decay in some respects offers simpler radiochemical consequences than do neutron capture and other reactions, because (a) the nuclear recoil energy is very low and (b) the decay schemes, and thus the probability of Auger cascades, are generally well known. Despite this, no clear mechanisms have been worked out. 

Fig. 3.6 (a) Decay scheme of and (b) ideal emission spectrum of Co diffused into rhodium metal. The nuclear levels in (a) are labeled with spin quantum numbers and lifetime. The dashed arrow up indicates the generation of Co by the reaction of Mn with accelerated deuterons (d in Y out). Line widths in (b) are arbitrarily set to be equal. The relative line intensities in (%) are given with respect to the 122-keV y-line. The weak line at 22 keV, marked with ( ), is an X-ray fluorescence line from rhodium and is specific for the actual source matrix... 

In the following sections, we discuss the decay schemes for all Mossbauer-active transition metal nuclides other than iron. For the sake of completeness, the decay scheme for Fe (see Fig. 7.1) is inserted here. The relevant nuclear data,... 

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. 

Fig. 7.58 Simplified decay scheme leading to the population of the four nuclear Mossbauer transitions of lr and Ir (from [266])...

There are two y-transitions in Pt amenable to the Mossbauer effect - the 130 keV transition between the 5/2 excited state and the 1/2 ground state and the 99 keV transition between the first excited 3/2 state and the ground state. Figure 7.70 shows the simplified decay scheme of Pt. The relevant nuclear data may be taken from Table 7.1 (at the end of the book). 

Fig. 7.70 Simplified decay scheme of The two Mossbauer transitions have energies of 98.86 keV and 129.74 keV (from [1])...

Criteria for successful U-Th-Pb dating are similar to those of standard U-series techniques, but in addition (1) sufficient amounts of ° Pb and ° Pb must have accumulated by radiogenic ingrowth to be distinguished from the initial Pb that is always present at the time of formation and (2) the decay scheme must be closed for all intermediate daughters from °Th and Pa to stable ° Pb and ° Pb, respectively. 

Ac is available from the decay of 229Th, which is present in old samples of 233U. The decay scheme for generating 225Ac is as follows ... 

Pb is a ft emitting radionuclide with a half-life of 10.64 h. It is the parent radionuclide of the a-emitting 212Bi. The decay scheme is shown below ... 

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