Medium-spin excited levels in Rb90, populated in the fission of U235 induced by neutrons, have been observed for the first time. γ radiation from fission has been measured by using the EXILL array of Ge detectors at the cold-neutron-beam facility PF1B of the Institut Laue-Langevin, Grenoble. Low-energy levels are interpreted as members of the πp3/2-1ν(d5/2)3, πf5/2-1ν(d5/2)3, and πg9/2ν(d5/2)3 multiplets with the 0- ground state due to the seniority-3 coupling in the νd5/2 shell. Analogous anomalous coupling within the πg9/2ν(d5/2)3 configuration explains the 5+, 6+, and 7+ triplet of states, observed at medium spins, similar to the triplet seen in the N=53 isotone, Br88. Shell-model calculations reproduce well the proposed structures in Rb88,90 and support the seniority-3 coupling in N=53 isotones and its absence in N=51 isotones. The structure of the odd-odd Rb88 and Rb90 nuclei provides an argument in favor of the collectivity building up at the neutron number N=53.
ASJC Scopus subject areas
- Nuclear and High Energy Physics