Dependence of Half-lives on Chemical Bonding

As already mentioned, changes of transmutation properties are observed if electrons of the electron shell are involved in the transmutations, as in the case of electron capture (e) or of emission of conversion electrons (e ). The rate of both processes depends on the electron density at the nucleus. Consequently, the half-life of electron capture and the probability of emission of conversion electrons vary to a small degree with the number and the distribution of the electrons, in particular K electrons, in the electron shell. 

An influence of chemical bonding on the half-life of electron capture has been measured for light nuclides such as Be. In metallic Be the density of the 1 s electrons at the nucleus is somewhat higher than in Be + ions. The relative changes of the decay constants of Be in various compounds compared with that in metallic Be are listed in Table 10.1. 

Application of external pressure also leads to an increase of the decay constant of Be AX/1 2.2 10 per kilobar for BeO. 

8% directly from the metastable state at 142.66 keV into the ground state (h/2 = 2.13-10 y) and in 99.2% via an excited state at 140.49 keV. The 2.17 keV transition is practically fully converted by emission of electrons from the M and N shells which are involved in chemical bonding. Correspondingly, changes A2/i of about 10 have been observed for Tc metal, TC2S7 and KTCO4. 

Relatively great effects have been found for 235m j 25 1 min). The energy of 

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