We report on the observation of excited states in the neutron-deficient phosphorus isotopes 26,27,28 P via in-beam γ-ray spectroscopy with both high-efficiency and high-resolution detector arrays. In 26 P, a previously-unobserved level has been identified at 244(3) keV, two new measurements of the astrophysically-important 3/2 + resonance in 27 P have been performed, γ decays have been assigned to the proton-unbound levels at 2216 keV and 2483 keV in 28 P, and the γ-ray lineshape method has been used to make the first determination of the lifetimes of the two lowest-lying excited states in 28 P. The expected Thomas-Ehrman shifts were calculated and applied to levels in the mirror nuclei. The resulting level energies from this procedure were then compared with the energies of known states in 26,27,28 P.
Energy levels and branching ratios for the rp-process nucleus 25 Si were determined from the reactions 9 Be( 26 Si, 25 Si)X and 9 Be( 25 Al, 25 Si)X using in-beam γ-ray spectroscopy with both highefficiency and high-resolution detector arrays. Proton-unbound states at 3695( 14) and 3802(11) keV were identified and assigned tentative spin-parities based on comparison to theory and the mirror nucleus. The 24 Al(p,γ) 25 Si reaction rate was calculated using the experimental states and states from charge-dependent USDA and USDB shell-model calculations with downward shifts of the 1s 1/2 proton orbital to account for the observed Thomas-Ehrman shift, leading to a factor of 10-100 increase in rate for the temperature region of 0.22 GK as compared to a previous calculation. These shifts may be applicable to neighboring nuclei, impacting the proton capture rates in this region of the chart.
The γ-ray tracking array GRETINA was coupled to the S800 magnetic spectrometer for spectroscopy with fast beams of rare isotopes at the National Superconducting Cyclotron Laboratory on the campus of Michigan State University. We describe the technical details of this powerful setup and report on GRETINA's performance achieved with source and in-beam measurements. The γ-ray multiplicity encountered in experiments with fast beams is usually low, allowing for a simplified and efficient treatment of the data in the γ-ray analysis in terms of Doppler reconstruction and spectral quality. The results reported in this work were obtained from GRETINA consisting of 8 detector modules hosting four high-purity germanium crystals each. Currently, GRETINA consists of 10 detector modules.
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