Nuclear Spectroscopy ofTa181

The nuclear levels of ${\mathrm{Ta}}^{181}$ were investigated by a study of the $\beta$ decay of ${\mathrm{Hf}}^{181}$ and the electron capture decay of ${\mathrm{W}}^{181}$. Evidence for weak $M$-shell conversion lines of an ∼6-kev transition in the ${\mathrm{Hf}}^{181}$ was found with a $\beta$ spectrometer. An investigation of the ${\mathrm{W}}^{181}$ 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 ${\mathrm{Hf}}^{181}$ decay occurs between the 482-kev level and a new level at 6 kev. On using an argon proportional counter, a 6-kev $\gamma$ ray was also found in the ${\mathrm{W}}^{181}$ decay. The conversion coefficient of this transition was determined to be ${\alpha }_T=44\mathrm{}\pm 7$. This conversion coefficient and the $M$-subshell conversion ratios indicate that the 6-kev transition is of $E1\mathrm{}$ multipolarity. The 6-kev level is assigned as the $\frac{9}{2}-$ [514] Nilsson intrinsic state. It is also concluded that the previously reported 152-kev transition in the ${\mathrm{W}}^{181}$ decay occurs between a new $\frac{11}{2}-$ ($K=\frac{9}{2}-$) rotational level at 158 kev and the 6-kev level. From a measurement of the tantalum $\frac{L}{K}$ x-ray intensity ratio, the ${\mathrm{W}}^{181}$ decay energy is found to be ${176}_{-22\mathrm{}}^{+44\mathrm{}}$ kev. The branchings of this decay to the various ${\mathrm{Ta}}^{181}$ 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.