(t,p) and (p,t) Reactions on Even Ce Isotopes

The ($t,p$) reaction on ${}_{}{}^{138,140}{}_{}{}^{}\mathrm{Ce}$ at 15-MeV incident energy and the ($p,t$) process on ${}_{}{}^{142}{}_{}{}^{}\mathrm{Ce}$ at 21.5 MeV have been studied. Differential cross sections were measured between 12 and 66° in 6° intervals and $L=0\mathrm{} \mathrm{and} 2$ assignments made. Less extensive data on ${}_{}{}^{136, 142}{}_{}{}^{}\mathrm{Ce}\mathrm{}(t,p)\mathrm{}$ and ${}_{}{}^{140}{}_{}{}^{}\mathrm{Ce}\mathrm{}(p,t)\mathrm{}$ were also acquired and a ${}_{}{}^{140}{}_{}{}^{}\mathrm{Ce}\mathrm{}(t,t)\mathrm{}$ angular distribution was obtained at 15 MeV. The strongest $L=0\mathrm{}$ and $L=2\mathrm{}$ transitions are discussed in relation to the pairing-vibrational model; in particular the 3226-keV state in ${}_{}{}^{140}{}_{}{}^{}\mathrm{Ce}$ was found to contain about 70% of the (1, 1) two-phonon strength and several candidates for pairing-quandrupole-vibrational states are noted. Anharmonic effects on the energies of pairing-phonon states are considered and a discussion of the observed $3^{-}$ strengths is included.