The structure of25Mg

Abstract

Gamma-decay modes and spin(-parity) assignments of levels in25Mg have been systematically investigated up to 10 MeV excitation energy by particle-γ-ray angularcorrelation measurements with the24Mg(d, pγ) reaction at 6.5 MeV bombarding energy and with the22Ne(α,nγ) reaction at 11.8, 12.5, 14.4 and 15.5 MeV bombarding energy. A level scheme has been established which is comprehensive up to 8.3 MeV excitation energy forI≦9/2 and up to 10 MeV for 9/2<I≦15/2. The excitation energies and electromagnetic properties of more than 70 states for which positive parity has been established or is most probable are compared with the results of shell-model calculations which use the complete configuration space of theO d5/2 — 1s1/2-O d3/2 shell and the unifieds-d shell Hamiltonian. The agreement is good to excellent. The first intruder states are located near 6.8 MeV excitation energy. The collective properties of25Mg beyond the well established rotational bands are investigated using both the new experimental information and theB(E2)'s obtained from the shell model. The spectrum of25Mg is completely rotational for the first five to six MeV above the yrast line. Shell modelB (M 1)'s reflect the Nilsson model structure of25Mg in great detail. The prospectiveIπ=9/2−, 13/2−, and 15/2− members of the established negative-parity,K=1/2 band are found in levels atEx=7801, 9410, and 8896 keV.