Analogous intruder behavior near Ni, Sn, and Pb isotopes

Near shell closures, the presence of unexpected states at low energies provides a critical test of our understanding of the atomic nucleus. New measurements for the N=42 isotones Co2769 and Cu2971, along with recent data and calculations in the Ni isotopes, establish a full set of complementary, deformed, intruder states astride the closed-shell Ni28 isotopes. Nuclei with a one-proton hole or one-proton particle adjacent to Z=28 were populated in β-decay experiments and in multinucleon transfer reactions. A β-decaying isomer, with a 750(250)-ms half-life, has been identified in Co422769. It likely has low spin and accompanies the previously established 7/2- state. Complementary data for the levels of isotonic Cu422971 support the presence of a deformed, ΔJ=1 band built on the proton intruder 7/2- level at 981 keV. These data, together with recent studies of lower-mass Co and Cu isotopes and extensive work near Ni68, support the view that intruder states based on particle-hole excitations accompany all closed proton shells with Z≥28

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

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 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