The Decay Scheme ofHf181

The radiations of ${\mathrm{Hf}}^{181}$ have been studied with delayed coincidence and absorption techniques. No $\gamma$-rays are found to precede the formation of the 20-microsecond metastable state in ${\mathrm{Ta}}^{181}$, thus confirming the decay scheme of Chu and Wiedenbeck. From the values of the internal conversion coefficients together with delayed coincidence absorption measurements it is concluded that the previously reported 0.134-Mev $\gamma$-ray is most probably emitted from another metastable state of about one-second duration in ${\mathrm{Ta}}^{181}$. A theoretical discussion of the multipole order of the different radiations lead to assignments of probable spin and relative parity values to the excited states of ${\mathrm{Ta}}^{181}$. Beginning with the ground state, the deduced spin and parity values are: 7/2(±), 1/2(±), 5/2(±), and 1/2(∓).