Mapping the periphery of deformation in the A∼80 region: A study of Nb83

Nb-83 has been studied in order to locate the upper extent of large deformation in the N similar to Z similar to 40 region and ascertain its sign and magnitude. The decay scheme has been considerably extended by studying gamma decay following the Ni-58(Si-28, p2n)Nb-83 reaction at 204 and 215 MeV and using Gammasphere. Both signature partners of two rotational bands have been observed. The band properties support a I-pi=5/2(+) ground state spin assignment. The in-band branching ratios and multipole mixing ratios were found to be consistent with significant prolate deformation, as found in other N=42 isotones. The bands are particularly similar to the isotone Y-81. A projected shell model analysis has been performed which provides good reproduction of the features of both bands. The calculations indicate the nucleus to be nearly axially symmetric. Nb-82,Nb-83 may be the heaviest nuclei in the A similar to 80 region with large deformation. The deformation is predicted to fall in heavier systems approaching Sn-100. The conditions appear to be right for the occurrence of K isomers.