Nuclear spectroscopy of Ta181

Abstract

The nuclear levels of Ta181 were investigated by a study of the β decay of Hf181 and the electron capture decay of W181. Evidence for weak M-shell conversion lines of an ∼6-kev transition in the Hf181 was found with a β spectrometer. An investigation of the W181 decay with this instrument revealed strong M-shell conversion lines corresponding to a 6.25±0.3-kev transition. With the aid of additional evidence, the conclusion is made that the 476-kev transition in the Hf181 decay occurs between the 482-kev level and a new level at 6 kev. On using an argon proportional counter, a 6-kev γ ray was also found in the W181 decay. The conversion coefficient of this transition was determined to be αT=44±7. This conversion coefficient and the M-subshell conversion ratios indicate that the 6-kev transition is of E1 multipolarity. The 6-kev level is assigned as the 9/2- [514] Nilsson intrinsic state. It is also concluded that the previously reported 152-kev transition in the W181 decay occurs between a new 11/2- (K=9/2-) rotational level at 158 kev and the 6-kev level. From a measurement of the tantalum L/K x-ray intensity ratio, the W181 decay energy is found to be 176-22+44 kev. The branchings of this decay to the various Ta181 levels are as follows: 158 kev (0.11%), 136 kev (0.067%), 6.25 kev (∼35%), and ground state (∼65%). All findings and proposals are consistent with predictions of the unified model of the nucleus.

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