High-spin states in26Mg

Abstract

Theγ-decays of levels in26Mg have been investigated up to 12.5 MeV excitation energy by proton-γ-ray coincidence measurements in the23Na(α, pγ) reaction at 14.2 and 16 MeV bombarding energy. Lifetime-measurements, made with the Doppler-shift attenuation method, and proton-γ-ray angular-correlation measurements were performed at Eα=14.2 MeV. Many high-spin states were observed, among them levels at 6,978 (5+), 7,283(4−), 7,395(5+), 7,953(5−), 8,202(6+), 8,472(6+), 9,065(5), 9,112(6+), 9,169(6−), 9,383 (6+), 9,542(5), 9,829(7+), 9,989(6+) and 12,479(8+, 7−) keV excitation energy. The spectrum of positive-parity states and their electromagnetic properties are reproduced with good accuracy by shell-model calculations which employ a unifieds-d shell Hamiltonian and the unrestricted configuration space of the 0d5/2 1s1/2 0d3/2 shell. Members of five inferred rotational bands, withKπ=0+, 2+, 3+, 0+ and 3− have been observed up to at leastI=6. TheKπ=2+ band shows strong anomalies of excitation energies andE2 transition rates near theI=6 state. The static intrinsic quadrupole moments calculated from the shell model wave functions indicate transitions from prolate to oblate deformation within theKπ=2+ band and also the ground state band. The lowest lyingIπ=4+ state appears to be “spherical” and cannot be associated with a rotational band.