On the identification of gamma rays from the 232Th decay

Abstract A planar germanium detector was used to study the γ-rays emitted in the disintegration of 232 Th. The samples were four different thorium salts on which radiochemical purifications were carried out. Two γ-rays at 63.9 and 140.8 keV were observed in those purified salts and assigned to 232 Th. The emission probabilities are: P γ (63.9) = (0.255 ± 0.017)% and P γ (140.8) = (0.026 ± 0.003)%. This finding leads to a re-evaluation of the decay scheme of 232 Th; the energies of the first and second excited states of 228 Ra become 63.9 and 204.7 keV while the energies of the second and third alpha groups which populate these states become 3948 and 3807 keV respectively.