The reaction ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}(t, p){}_{}{}^{91}{}_{}{}^{}\mathrm{Y}$ has been measured at an incident energy of 20 MeV. Differential cross sections were measured at 13 angles and an excitation range of 5 MeV was observed with 18 keV resolution. The data are compared to distorted wave calculations both for $L$ assignments and magnitude relations. Sixteen new levels are reported in ${}_{}{}^{91}{}_{}{}^{}\mathrm{Y}$ as well as many new limits on spin assignments. An interpretation of the results as a proton hole coupled to ${}_{}{}^{92}{}_{}{}^{}\mathrm{Zr}$ pairing-multipole states is presented. Such an analysis provides a qualitative description of the observed strength, but a more complex analysis is required for quantitative results.

NUCLEAR REACTIONS ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}(t, p){}_{}{}^{91}{}_{}{}^{}\mathrm{Y}$, $E_t=20\mathrm{}$ MeV; measured $\sigma (E_p, \theta )$; ${}_{}{}^{91}{}_{}{}^{}\mathrm{Y}$ deduced levels, $L$, $\pi$; DWBA analysis.

• Received 20 June 1974

DOI:https://doi.org/10.1103/PhysRevC.11.1691