Nuclear Spectroscopic Studies of Neutron-Deficient Isotopes in the Rare Earth Region

The conversion-electron spectra of four neutron-deficient rare earth isotopes are presented and discussed. The four isotopes are ${\mathrm{Tb}}^{153}$, ${\mathrm{Tb}}^{154}$, ${\mathrm{Dy}}^{155}$, and ${\mathrm{Ho}}^{160}$. Mihelich, Harmatz, and Handley in a recent publication have presented the conversion-electron data of a large number of rare earth isotopes, including all but one (${\mathrm{Dy}}^{155}$) of the four above-mentioned activities. The agreement between the two works is good. Some additional conversion lines, not reported by Mihelich et al., have been identified in this work as belonging to the decay of ${\mathrm{Tb}}^{153}$, ${\mathrm{Tb}}^{154}$, and ${\mathrm{Ho}}^{160}$. Decay schemes are proposed for ${\mathrm{Dy}}^{155}$ and ${\mathrm{Tb}}^{153}$. ${\mathrm{Tb}}^{154}$ and ${\mathrm{Ho}}^{160}$ decay to levels in ${\mathrm{Gd}}^{154}$ and ${\mathrm{Dy}}^{160}$, respectively. The electron-capture decay data of ${\mathrm{Tb}}^{154}$ and ${\mathrm{Ho}}^{160}$ are compared with data obtained by other workers in the negatron decay of ${\mathrm{Eu}}^{154}$ and ${\mathrm{Tb}}^{160}$ to levels in ${\mathrm{Gd}}^{154}$ and ${\mathrm{Dy}}^{160}$, respectively, and transitions common to both modes of decay are noted.