The decay schemes of the following terbium isotopes were investigated: 2.3 ± 0.2-min ${}_{}{}^{148}{}_{}{}^{}\mathrm{Tb}$, 1.9 ± 0.1-min and 1.6 ± 0.1-h ${}_{}{}^{147}{}_{}{}^{}\mathrm{Tb}$, and a previously unreported 23 ± 2-sec nuclide assigned to ${}_{}{}^{146}{}_{}{}^{}\mathrm{Tb}$. These radioactivities were produced by bombarding ${}_{}{}^{141}{}_{}{}^{}\mathrm{Pr}$ with ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ ions accelerated in the Oak Ridge isochronous cyclotron. Both singles and coincidence $\gamma$-ray spectral measurements were made. Our data for 2.3-min ${}_{}{}^{148}{}_{}{}^{}\mathrm{Tb}$ are in excellent agreement with the recently published results of Bowman, Haenni, and Sugihara. We also confirm their discovery of a new 1.9-min high-spin isomer in ${}_{}{}^{147}{}_{}{}^{}\mathrm{Tb}$ and provide additional information concerning its decay properties. Levels in ${}_{}{}^{147}{}_{}{}^{}\mathrm{Gd}$ populated by this (presumably $h_{\frac{11}{2}}$) ${}_{}{}^{147}{}_{}{}^{}\mathrm{Tb}$ state are: 997.6 keV, ${\frac{9}{2}}^{-}$; 1397.7 keV, (${\frac{9}{2}}^{-}$); (1778.9 keV); and 1797.8 keV, (${\frac{9}{2}}^{-}$). Contrastingly, the 1.6-h low-spin (probably $d_{\frac{5}{2}}$) ${}_{}{}^{147}{}_{}{}^{}\mathrm{Tb}$ isomer was found to populate the following ${}_{}{}^{147}{}_{}{}^{}\mathrm{Gd}$ levels: 0 keV, ${\frac{7}{2}}^{-}$; 1152.2 keV, ${\frac{3}{2}}^{-}$; 1292.0 keV, (${\frac{3}{2}}^{+}$); 1411.5 keV, (${\mathrm{½}}^{+}$); 1699.2 keV; 1759.1 keV; and 1846.6 keV, (${\frac{5}{2}}^{-}$). The assignment of the new 23-sec activity to ${}_{}{}^{146}{}_{}{}^{}\mathrm{Tb}$ is based primarily on the fact that five of its $\gamma$-rays have been observed by Kownacki et al. in a ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ ($\alpha ,2n\gamma$) study. Levels in ${}_{}{}^{146}{}_{}{}^{}\mathrm{Gd}$ seen in the decay of ${}_{}{}^{146}{}_{}{}^{}\mathrm{Tb}$ (probable spin of 3) are as follows: 1579.5 keV, $2^{+}$; 2658.4 keV, $4^{+}$; 2982.4 keV, $6^{+}$; 2996.9 keV; 3099.4 keV; (3139.6 keV); and 3313.4 keV. In contrast to the results of Kownacki et al. $\gamma$ rays either feeding or deexciting their tentatively proposed $3^{-}$ level at 1584.5 keV were not observed.

[RADIOACTIVITY ${}_{}{}^{146,147,148}{}_{}{}^{}\mathrm{Tb}$; measured $T_{\frac{1}{2}}$, $E_{\gamma }$, $I_{\gamma }$, $\gamma \gamma$ coin; discovered new isotope ${}_{}{}^{146}{}_{}{}^{}\mathrm{Tb}$; ${}_{}{}^{146,147,148}{}_{}{}^{}\mathrm{Gd}$ deduced levels, $J$, $\pi$. Ge (Li) detectors, 2.1 and 3.0 keV at 1.33 MeV.]

• Received 27 August 1973

DOI:https://doi.org/10.1103/PhysRevC.9.674