Relative proton and γ widths of astrophysically important states in 30S studied in the β-delayed decay of 31Ar

Abstract

Resonances just above the proton threshold in 30S affect the 29P(p, γ ) 30S reaction under astrophysical conditions. The (p,γ )-reaction rate is currently determined indirectly and depends on the properties of the relevant resonances. We present here a method for finding the ratio between the proton and γ partial widths of resonances in 30S. The widths are determined from the β2p- and βpγ -decay of 31Ar, which is produced at the ISOLDE radioactive ion beam facility at the European research organization CERN. Experimental limits on the ratio between the proton and γ partial widths for astrophysical relevant levels in 30S have been found for the first time. A level at 4689.2(24) keV is identified in the γ spectrum, and an upper limit on the p/ γ ratio of 0.26 (95% C.L.) is found. In the two-proton spectrum two levels at 5227(3) keV and 5847(4) keV are identified. These levels were previously seen to γ decay and upper limits on the γ / p ratio of 0.5 and 9, respectively, (95% C.L.) are found, where the latter differs from previous calculations.