First g-factor measurements on semi-magic 36S and their implications for the rigidity of the N=20 shell closure

The g-factor of the very short-lived (tau = 0.12(1) ps) 2(1)(+) state at 3.290 MeV in S-36, g(2(1)(+)) = +1.3(5), has been determined for the first time by utilizing the Coulomb excitation of S-36 beams in inverse kinematics combined with the transient field technique. In addition, for the 3(1)(-) state (with tau = 0.9(1) ps) at 4.192 MeV, a value of g(3(1)(-)) = +0.8(5) was obtained. In the same experiment, the g-factor of the 2(1)(+) state in Ar-40 has been remeasured using the alpha-transfer reaction on the same carbon target. Lifetimes of several excited states in both S-36 and Ar-40 were also redetermined using the Doppler-shift-attenuation method. The new experimental g-factors and deduced B(E2) values were compared with results of shell-model calculations with the WBT effective interaction and the sdfp shell model space. Comparisons with previous results for S-32,S-34,S-38,S-40 and Ar-36,Ar-31,Ar-40 shed light on how the properties of the Ar and S isotopes change as the N = 20 shell closure is approached, crossed, and left behind. (c) 2007 Elsevier B.V. All rights reserved.