Gd146andSm144excited by the (p,t) reaction on radioactive targets

The (p,t) reaction has been used to study the closed-shell nuclei ${}_{}{}^{146}{}_{}{}^{}\mathrm{Gd}$ and ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$, the former exhibiting some characteristics of a doubly closed shell. Exotic radioactive targets of ${}_{}{}^{148}{}_{}{}^{}\mathrm{Gd}$ ($t_{\frac{1}{2}}=75\mathrm{}$ yr) and ${}_{}{}^{146}{}_{}{}^{}\mathrm{Sm}$ ($t_{\frac{1}{2}}=7\mathrm{}\times {10}^7$ yr) obtained from chemical and isotope separation of irradiated beam-stop material were employed. The ground-state mass excess of ${}_{}{}^{146}{}_{}{}^{}\mathrm{Gd}$ was measured as being $\Delta u=-76.083\mathrm{}\left(15\right)\mathrm{}$ MeV and the first excited state is confirmed as being a $3^{-}$ state at 1.580-MeV excitation energy. Thirteen states were observed in ${}_{}{}^{146}{}_{}{}^{}\mathrm{Gd}$ and 23 in ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$. The pairing-monopole and pairing-quadrupole states in both nuclei are observed for the first time. These levels are higher than systematics would predict, confirming a proton-subshell closure in ${}_{}{}^{146}{}_{}{}^{}\mathrm{Gd}$, and are split in ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$, indicating a strong interaction between nuclear modes.