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

Nb83 has been studied in order to locate the upper extent of large deformation in the N∼Z∼40 region and ascertain its sign and magnitude. The decay scheme has been considerably extended by studying gamma decay following the Ni58(Si28, p2n)Nb83 reaction at 204 and 215 MeV and using Gammasphere. Both signature partners of two rotational bands have been observed. The band properties support a Iπ=52+ 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 Y81. 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. Nb82,83 may be the heaviest nuclei in the A∼80 region with large deformation. The deformation is predicted to fall in heavier systems approaching Sn100. The conditions appear to be right for the occurrence of K isomers. © 2007 The American Physical Society.