γ -ray linear polarization measurements and (g9/2) −3 neutron alignment in 91Ru

Linear polarization measurements have been performed for γ rays in 91Ru produced with the 58Ni(36Ar, 2p1nγ ) 91Ru reaction at a beam energy of 111 MeV. The EXOGAM Ge clover array has been used to measure the γ -γ coincidences, γ -ray linear polarization, and γ -ray angular distributions. The polarization sensitivity of the EXOGAM clover detectors acting as Compton polarimeters has been determined in the energy range 0.3–1.3 MeV. Several transitions have been observed for the first time. Measurements of linear polarization and angular distribution have led to the firm assignments of spin differences and parity of high-spin states in 91Ru. More specifically, calculations using a semiempirical shell model were performed to understand the structures of the first and second (21/2+) and (17/2+) levels. The results are in good agreement with the experimental data, supporting the interpretation of the nonyrast (21/2+) and (17/2+) states in terms of the Jmax and Jmax − 2
members of the seniority-three ν(g9/2) −3 multiplet.