Binary-reaction spectroscopy of Mo-99,Mo-100: Intruder alignment systematics in N=57 and N=58 isotones

Abstract

The near-yrast states of Mo-99,Mo-100 have been studied following their population via a binary reaction between a Xe-136 beam and a thin, self-supporting Mo-100 target. The yrast sequence in Mo-100 has been extended to a tentative spin/parity (20(+)), while the decoupled band built on the I-pi=11(-)/2 isomeric state in Mo-99 has been extended through the first alignment up to a tentative spin/parity of (43(-)/2). The results are compared with self-consistent, cranked-mean-field calculations using a Woods-Saxon potential. The alignment systematics of the intruder h(11/2) bands in the N=57 isotones from Mo (Z=42) to Cd (Z=48) and the yrast sequences in their N=58 even-even neighbors are discussed. An overall picture emerges, where the alignment properties evolve from being due to positive-parity neutrons in the Cd-105(48) to predominantly (g(9/2))(2) proton crossings closer to the Z=40 subshell. Qualitatively, this can be explained by an increase in the quadrupole deformation and a simultaneous lowering of the proton Fermi surface in the g(9/2) shell with decreasing proton number. These data provide excellent examples of rotational-alignment phenomena in weakly deformed nuclei.

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