Multiparticle-hole excitations in nuclei near N = Z = 20: $^{41}$K

TL;DR

This study investigates high-spin states in nuclei near N=Z=20, especially $^{41}$K, extending the level scheme and comparing experimental results with shell model calculations to understand complex nuclear excitations.

Contribution

The paper extends the high-spin level scheme of $^{41}$K and $^{41}$Ca, and compares experimental data with advanced shell model calculations to explore multi-particle excitations.

Findings

Level scheme of $^{41}$K extended to 12325 keV.

New $ extgamma$ transitions observed in $^{41}$Ca.

Shell model calculations show good agreement for simple excitations.

Abstract

This experimental study of high-spin structure near N = Z = 20 nuclei was focused on $^{41}$K, but will also mention three newly observed $\gamma$ transitions in $^{41}$Ca observed in the same reaction. High-spin states were populated using the $^{26}$Mg($^{18}$O, $p2n\gamma$)$^{41}$K and $^{26}$Mg($^{18}$O, $3n\gamma$)$^{41}$Ca reactions. The experiment was carried out at an incident beam energy of 50 MeV at the Florida State University (FSU) John D. Fox Superconducting Linear Accelerator Laboratory and used the FSU high-purity germanium detector array. The $^{41}$K level scheme was extended to 12325 keV, possibly with J$^{\pi}$ = 25/2$^-$ or 27/2$^+$, by means of 25 new transitions and that of $^{41}$Ca to 9916 keV. Linear polarization and a measure of angular distribution results are also reported and used to provide information on the spins and parities of several states in the $^{41}$K decay scheme. The results have been compared to the $spsdpf$ cross-shell FSU shell model interaction calculations. The theoretical results from configurations involving no or one additional nucleon promoted from the $sd$ to the $fp$ shell agree relatively well with the energies of known states, while those that involve multi-particle excitations paint an interesting and complex picture of interplay between single-particle excitations, collective pairing, and deformation. This presents an interesting challenge for future theory.