New transitions and levels for ${}^{163}\mathrm{Tb}$ obtained from $\beta$-decay studies

Transitions in ${}^{163}\mathrm{Tb}$ following $\beta$ decay of ${}^{163}\mathrm{Gd}$ were obtained as part of investigations of $\gamma$ rays emitted following ${}^{163}\mathrm{Eu}\beta$ decay to ${}^{163}\mathrm{Gd}$. Detailed analysis of the low-energy structure of ${}^{163}\mathrm{Tb}$ has been carried out with these data to expand previous $\beta$-decay studies and reactions studies of levels in ${}^{163}\mathrm{Tb}$. Data were collected at the LeRIBSS station of the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory with an array of four Clover HPGe detectors for $\gamma$ rays and two plastic scintillators for $\beta$ detection. The $\gamma$ rays were identified as belonging to ${}^{163}\mathrm{Gd}$ and ${}^{163}\mathrm{Tb}$ via mass selection and $\gamma -\gamma -\beta , \gamma -\gamma$, or $\gamma$-x-ray coincidence. In total, 38 new $\gamma$-ray transitions were observed in ${}^{163}\mathrm{Tb}$ from 15 newly identified levels and 12 previously identified levels. Potential energy surface calculations were performed which support a rigid prolate deformation. Previously identified unplaced transitions in ${}^{163}\mathrm{Tb}$ have been placed within the level scheme of ${}^{163}\mathrm{Tb}$ and additional states and transitions have been identified.

Figure 1

Level scheme of ${}^{163}\mathrm{Tb}$. New transitions and levels are shown in black, while previously observed transitions and levels seen in reaction studies are in blue. Of the previously observed transitions, only the 213.8-, 288.1-, and 373.5-keV transitions were placed in the level scheme. Tentative transitions are dashed and tentative levels have labels in parentheses. Relative intensities corrected for internal conversion are detailed in Table 1.

Figure 2

Coincidence spectra for gates on ${}^{163}\mathrm{Tb}$ transitions (a) 1200.0, (b) 885.0, (c) 574.9, (d) 373.5, (e) 396.8, and (f) 288.1 keV.

Figure 3

PES calculation for $\pi {3/2}^{+}$ [411]. ${\beta }_2=0.286, \gamma =0$, and ${\beta }_4=0.028.$