Lifetime measurements in sd shell nuclei (VII). Mean lives of 27Si and 27Al levels

Abstract

Abstract The mean lives and excitation energies of the lowest six levels of 27Si were measured by means of the 28Si(, αγ)27Si reaction. Coincidence Doppler-shift attenuation measurements lead to mean lives of τm = 2200±400, 56±12, 16±8, < 10 and 79±11 fs for the 27Si levels at E× = 0.96, 2.17, 2.65, 2.87 and 2.91 MeV, respectively. With the recoil-distance method applied to the 24Mg(α, n)27Si and 24Mg(α, p)27Al reactions, the mean lives of the 0.78 MeV level in 27Si and the 0.84 MeV level in 27A1 were measured to be m = 50±6 ps and 48±3 ps, respectively. Branchings were measured for the states at E× = 2.17, 2.65, 2.87 and 2.91 MeV in 27Si. From the presently known information it is possible to assign positive parity to the level at 2.17 MeV. The spectroscopic data on the A = 27 mirror nuclei are compared with the results of many-particle shell-model calculations