Lifetime Measurements and Triple Coexisting Band Structure in S43

Abstract

Lifetime measurements of excited states in the neutron-rich nucleus ^{43}S were performed by applying the recoil-distance method on fast rare-isotope beams in conjunction with the Gamma-Ray Energy Tracking In-beam Nuclear Array. The new data based on γγ coincidences and lifetime measurements resolve a doublet of (3/2^{-}) and (5/2^{-}) states at low excitation energies. Results were compared to the π(sd)-ν(pf) shell model and antisymmetrized molecular dynamics calculations. The consistency with the theoretical calculations identifies a possible appearance of three coexisting bands near the ground state of ^{43}S: the K^{π}=1/2^{-} band built on a prolate-deformed ground state, a band built on an isomer with a 1f_{7/2}^{-1} character, and a suggested excited band built on a newly discovered doublet state. The latter further confirms the collapse of the N=28 shell closure in the neutron-rich region.

Shell structure of S43 and collapse of the N=28 shell closure

“…The latter is opposite to the suggestion of Ref. [33] and thus challenges the result of the very similar lifetimes of the states at 185 and 1162 keV proposed in that work. The present ordering of the cascade is also consistent with earlier measurements of Coulomb excitation [27] assuming that the transition observed around 940 keV corresponds to the 977 peak observed in the present work.…”

“…This is in agreement with the level scheme proposed in Ref. [33] with a doublet of states at 1155 and 1162 keV. The high statistics obtained in the present work makes it possible to determine the order of the γ -ray transitions in the cascades by the comparison of the measured γ -ray intensities in Table I.…”

“…It should be noted that the level scheme and the interpretation of Ref. [33] are at variance with the results presented here. In the present work, the neutron knockout reaction is measured with the additional capability to distinguish between decays to the isomer and to the ground state.…”

“…Figure 2 shows the prompt, Doppler-corrected γ -ray energy spectrum measured with GRETINA gated on the one-neutron knockout reaction from 44 S to 43 S. Most of the previously observed γ rays [32,33] were confirmed and their energies are shown in Fig. 2 together with their uncertainty.…”

“…Most recently, excited state lifetimes in 43 S were measured. Using the proton knockout reaction from 44 Cl several states were populated [33]. The level ordering was reversed compared to the earlier study [32].…”