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

Abstract

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.

Two-neutron knockout as a probe of the composition of states in Mg22,Al23 , and Si<

“…In the present work, this configuration sensitivity of the two-neutron knockout-residue p distributions is explored with three sd-shell cases where the incoming projectiles each have 12 neutrons: 9 Be( 24 Mg, 22 Mg+γ)X, 9 Be( 25 Al, 23 Al+γ)X, and 9 Be( 26 Si, 24 Si+γ)X. From analysis of the exclusive p distributions in two-neutron knockout, J π values are assigned and the dependence of the width on the L composition of the shell-model TNAs is explored, demonstrating the significant utility of this reaction as a spectroscopic tool.…”

“…Excitation energies and J π values in 24 Si are critical for the 23 Al(p,γ) rate, which has significant impact on energy generation in Type-I X-ray bursts [13,14]. Energy values differing by several 10 keV were reported originally [5,15] and only recently, a d( 23 Al, 24 Si+γ)n measurement resolved the discrepancy and, in addition to states at 1874(3) and 3449(5) keV, suggested a new level at 3471(6) keV to be either the 0 + 2 state with an extremely large Thomas-Ehrman shift [16,17] or the 4 + 1 state [18]. To date, all J π assignments are reported as tentative.…”

“…Two-neutron knockout reactions were induced on a 287(3) mg/cm 2 9 Be target in front of the S800 spectrograph [21]. The mid-target energies for 24 Mg, 25 Al, and 26 Si were 95 MeV/u, 102 MeV/u, and 109 MeV/u, respectively. Event-by-event identification of the incoming projectiles and outgoing reaction products was performed using plastic timing scintillators and the S800 focal-plane detectors [22].…”

“…1 of Refs. [23,24]. For each event, the p of the reaction residue at the target was determined using the magnetic rigidity of the S800 spectrograph and the particle trajectory reconstructed from the position and angle measured in the S800 focal plane.…”

“…[12]. 1569 71622 61870 61622 ( Doppler-corrected γ-ray spectra for the reactions 9 Be( 24 Mg, 22 Mg+γ)X (a), 9 Be( 25 Al, 23 Al+γ)X (b), and 9 Be( 26 Si, 24 Si+γ)X (c). The solid red curves are GEANT4 simulations of the observed transitions.…”