Abstract
The decay of 46 day 181Hf has been investigated by absorption coincidence techniques using an integral type delayed coincidence recorder, and a special counter with which the absorption curves of low energy electrons may be obtained. The results confirm a previously published scheme for the main mode of decay, namely that a 400 kev. β-ray from 181Hf leads directly to the 20 μsec. metastable state in 181Ta. This decays by emission of a 130 kev. γ-ray, followed by a 470 kev. transition to the ground state. Instantaneous coincidences were found to involve the γ-transitions in the main branch, electrons from γ-rays of 87, 133 and 340 kev., and a β-ray of approximately 440 kev. It is suggested that about 30% of the 181Hf nuclei in the 46 day state decay by a highly forbidden γ-transition (133 kev.) with an 87 kev. γ-ray in cascade to the ground state. This decays through a 440 kev. β-transition to an excited state (340 kev.) of 181Ta. Half life and conversion coefficient values enable spins and relative parities to be assigned to each of the levels occurring in the decay scheme proposed.
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