Proton removal from ${}^{73,75}$Br to ${}^{72,74}$Se at intermediate energies

Abstract

We report new experimental data for excited states of ${}^{72,74}$Se obtained from proton removal from ${}^{73,75}$Br secondary beams on a proton target. The experiments were performed with the Ursinus-NSCL Liquid Hydrogen Target and the combined GRETINA+S800 setup at the Coupled Cyclotron Facility of the National Superconducting Cyclotron Laboratory at Michigan State University. Within uncertainties, the inclusive cross sections for proton removal from ${}^{73,75}$Br on a proton target are identical suggesting that the same single-particle orbitals contribute to the proton-removal reaction. In addition, details of the partial cross section fragmentation are discussed. The data might suggest that $l=1,2,3$, and 4 angular momentum transfers are important to understand the population of excited states of ${}^{72,74}$Se in proton removal. Available data for excited states of ${}^{74}$Ge populated through the ${}^{75}$As$(d,{}^3\mathrm{He}){}^{74}$Ge proton-removal reaction in normal kinematics suggest indeed that the $fp$ and $sd$ shell as well as the $1g_{9/2}$ orbital contribute. A comparison to data available for odd-$A$ nuclei supports that the bulk of the spectroscopic strengths could be found at lower energies in the even-even Se isotopes than in, for instance, the even-even Ge isotopes. In addition, the population of high-$J$ states seems to indicate that multi-step processes contribute to proton-removal reactions at intermediate energies in these collective nuclei.

Comments: 9 pages, 5 figures