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 (τ=0.12(1)ps) 21+ state at 3.290 MeV in 36S, g(21+)=+1.3(5), has been determined for the first time by utilizing the Coulomb excitation of 36S beams in inverse kinematics combined with the transient field technique. In addition, for the 31− state (with τ=0.9(1)ps) at 4.192 MeV, a value of g(31−)=+0.8(5) was obtained. In the same experiment, the g-factor of the 21+ state in 40Ar has been remeasured using the α-transfer reaction on the same carbon target. Lifetimes of several excited states in both 36S and 40Ar 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 32,34,38,40S and 36,38,40Ar 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.