Beta-decay spectroscopy of $^{27}$S

Abstract

Background Beta-decay spectroscopy provides valuable nuclear physics input for thermonuclear reaction rates of astrophysical interest and stringent test for shell-model theories far from the stability line.Purpose The available decay properties of proton drip-line nucleus 27 S are insufficient to constrain the properties of the key resonance in 26 Si(p, γ) 27 P reaction rate and probe the possible mirror asymmetry. The decay scheme of 27 S is complicated and far from being understood, which has motivated but also presented substantial challenges for our experiment.Method The 27 S ions were implanted into a double-sided silicon strip detector array surrounded by the high-purity germanium detectors, where the β-delayed protons and γ rays were measured simultaneously. ResultsThe precise half-life of 27 S, the excitation energies, β-feeding intensities, log f t values, and B(GT) values for the states of 27 P populated in the β decay of 27 S are determined. The improved spectroscopic properties including are compared to the mirror β decay of 27 Na and to the shell-model calculations using the recently-developed USD * interaction. The present work has expanded greatly on the previously established decay scheme of 27 S. ConclusionsThe precise mass excess of 27 P, the energy and the ratio between γ and proton partial widths of the 3/2 + resonance were obtained, thereby determining the 26 Si(p, γ) 27 P reaction rate based mainly on experimental constraints. The first experimental evidence for the observation of mirror asymmetries for the transitions in the decays of 27 S and 27 Na is also provided. The shell-model calculations with the Hamiltonians including the modifications on single-particle energies and two-body matrix elements related to the proton 1s 1/2 orbit give a better description of the spectroscopic properties.

Spectroscopy and lifetime measurements near the proton drip line: P26,27,28

“…Although CAESAR has modest resolution conpared to SeGA, the uncertainties for the reported energies are similar due to the statsitics advantage of the highefficiency array. Both values agree well with the highestprecision measurements available for the energy of the astrophysically-important 3/2 + resonance, 1120 (8) keV from in-beam γ-ray spectroscopy [22] and 1125(2) keV from the detection of β-delayed γ rays following the decay of 27 S [23,24]. The proton separation energy for 27 P deduced in Refs.…”

“…The SeGA spectrum includes data from 9 Be( 30 S, 27 P+γ)X taken under two S800 magnetic field settings and 9 Be( 34 Ar, 27 P+γ)X. The transition observed with both arrays is consistent with the γ decay of the 3/2 + state reported at 1120 (8) keV from the previous in-beam γ-ray spectroscopy experiment [22] and at 1125(2) keV in a recent 27 S β-decay measurement [23,24].…”

“…The proton separation energy for 27 P deduced in Refs. [23,24] from the measured γ and proton decays of the 3/2 + resonance is 807 (9) keV and no γ decay branch from the 5/2 + second excited state at 1569 (12) keV was observed. In this work, there are also no clear γ-ray transitions corresponding to the decay of the 5/2 + or higher-lying resonances.…”

“…1. For this measurement, the magnetic rigidity of the S800 spectrograph was set to center the 24 Si products from two-neutron knockout in the focal plane but the large acceptance of the S800 also allowed detection of 26,27 P residues.…”

“…Subsequent Coulomb dissociation experiments at incident energies of 54.2 and 500 MeV/u, respectively, yielded energies of 1176 (32) keV [20] and 1137 (33) keV [21] for the 3/2 + resonance. The highest-precision measurements of the energy of the 3/2 + resonance are 1120 (8) keV from in-beam γ-ray spectroscopy of 27 P produced from one-proton knockout [22] and 1125 (2) keV from β-delayed γ rays observed in the recent β-decay spectroscopy of 27 S [23,24].…”