Multiparticle-hole excitations in nuclei near N = Z = 20: ⁴¹ K

This experimental study of high-spin structure near N= Z= 20 nuclei was focused on ⁴¹K, but will also mention three newly observed γ transitions in ⁴¹Ca observed in the same reaction. High-spin states were populated using the ²⁶Mg(¹⁸O, p2 nγ)⁴¹K and ²⁶Mg(¹⁸O, 3 nγ)⁴¹Ca 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 ⁴¹K level scheme was extended to 12325 keV, possibly with J^π = 25/2^- or 27/2⁺, by means of 25 new transitions and that of ⁴¹Ca 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 ⁴¹K level 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.