Abstract:
New high spin states in Mg25 (up to 13.3 MeV in excitation) have been located using the N12,p)25Mg reaction at a laboratory beam energy of 23.5 MeV. Gamma decay from 28 neutron unbound levels has been observed (24 of which are reported here for the first time) up to 7 MeV above the neutron drip line. Tentative identification of the yrast line up to (17/2+ has been made, along with an extension of the ground-state rotational band up to (15/2+ and the location of several other states with J=(11/2+ and (15/2+. Extensive comparison with the s-d shell model and the cranked Nilsson-Strutinsky model has been made for the states in Mg25. Very good agreement is observed between the shell model and experimental level energies and -decay branches. Potential energy surfaces for J=(11/2+, (13/2+, and (17/2+ in the cranked Nilsson-Strutinsky model show a noncollective oblate local minimum at (μ2,)=(0.34,60°) for (11/2+ and prolate configurations at (0.2,-120°) for (13/2+ and (17/2+. These states compete with the collective ground-state band members at 0 and become yrast for (17/2+. The stabilization of these prolate aligned states relative to more deformed, collective states of the same spin results from shell effects at high spin in the cranking model, and provides a description of the configuration in the yrast 8+; (11/2+, (13/2+, and (17/2+; and 4+ states in Mg24, Mg25, and Mg26, respectively. © 1988 The American Physical Society.
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