A search for radioactivity among the naturally occurring isobaric pairs

Abstract

Abstract Low-background techniques have been used to search for radioactivity among the naturally occurring isobaric pairs Cd-113-In-113, In-115-Sn-115, Sb-123-Te-123 and Re-187-Os-187. No activity was observed from Cd-113 which is found to have a minimum half-life of 1.3 × 1015 years for emission of β-rays with energy > 1.2 kev. A new value of 480 ± 30 kev has been obtained for the beta-disintegration energy of In-115 and the half-life measured to be 5.1 ± 0.4 × 1014 years. The unstable member of the Sb-Te-123 pair is shown to be Te-123 which decays by K electron capture with a half-life of 1.24 ± 0.10 × 1013 years. The decay of Re-187 is established by observation of the beta spectrum with maximum energy 1.2 ± 0.10 kev. The half-life is estimated to be of the order of 3 × 1010 years.