Excitation of 6(-) and 7(+) stretched states in the 38Ar(p,n)38K reaction at 135 MeV.

Abstract

High-spin, stretched-state excitations were studied in the $^{38}\mathrm{Ar}$(p,n${)}^{38}$K reaction at 135 MeV with the beam-swinger system at the Indiana University Cyclotron Facility. Neutron kinetic energies were measured by the time-of-flight technique with large-volume plastic-scintillator neutron detectors at flight paths ranging from 81 to 131 m. Overall time resolutions of about 825 ps provided energy resolutions from 320 to 450 keV. The target was a 4-cm-long gas cell filled to \ensuremath{\sim}3 atm absolute. Angular distributions were extracted for the low-lying excitations observed at wide angles. A known ${7}^{+}$ state at ${\mathit{E}}_{\mathit{x}}$=3.5 MeV was observed, plus two states at 5.3 and 5.9 MeV, which are tentatively identified as ${6}^{\mathrm{\ensuremath{-}}}$ excitations, based on comparisons with distorted wave Born approximation and sdpf shell-model calculations. The $^{38}\mathrm{K}$ spectrum is in reasonable agreement with the shell-model calculations. In contrast to the analysis of 80 MeV $^{40}\mathrm{Ca}$(d,\ensuremath{\alpha}${)}^{38}$Ar measurements, these results do not indicate a significant problem for the nuclear shell model near A=40.