Relative proton andγwidths of astrophysically important states in30S studied in theβ-delayed decay of

G. T. Koldste

¹

,

Β. Blank

²

,

María José García Borge

³

et al.

Abstract

Resonances just above the proton threshold in 30 S affect the 29 P(p, γ ) 30 S 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 30 S. The widths are determined from the β2p-and βpγ -decay of 31 Ar, 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 30 S 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.

Multiparticle emission in the decay ofAr31

“…Experimental limits on the ratio between the proton and γ partial widths have been found for low-lying levels in 30 S using the β2p decay of 31 Ar from the same experiment discussed below [11]. As demonstrated here, the 2p decay mode can also be used to determine level spins by analyzing proton-proton angular correlations.…”

“…This and the discussion in Ref. [11] indicates that there might be other contributions to the peak. From the 59(15) events in the 1p-gated spectrum one would expect 13(3) events in the 2p-gated spectrum.…”

“…Ref. [11] and in the results presented above for the IAS, there are additional contributions. In addition to the 3p channel, all the levels up to the vicinity of the proton thresholds should, in principle, be included for both the 1p and the 2p channels.…”

“…In this spectrum clear peaks are identified from the lowest states of both 30 S and 29 P (see Ref. [11]), but owing to background in the spectrum there are no clear signatures of levels above the second excited state in 29 P. In Fig. 7 the two-proton-gated γ spectrum is shown.…”

“…A comprehensive description of the setup can be found in Ref. [11]. The pad detectors behind the DSSSDs were energy calibrated by using a standard α calibration source (containing 148 Gd, 241 Am, 239 Pu, and 244 Cm).…”