Coexisting intruder bands inSe83and evidence for the role of proton subshell closure in inhibiting formation of odd-neutron intruder bands

Abstract

Low-lying one-particle, two-hole (1p-2h) intruder bands which coexist with hole states are established in $^{83}\mathrm{Se}$ ($N=49$) and are shown to exhibit properties similar to those of known intruder bands in odd-proton In ($Z=49$) nuclei. Systematics of ($N=49$) nuclei show that $^{83}\mathrm{Se}$ ($Z=34$) has the lowest-lying 1p-2h intruder state rather than midshell $^{89}\mathrm{Zr}$ ($Z=40$) as would be expected by comparing with the In isotopes. We discuss the well established occurrence of intruder bands in odd-proton nuclei in contrast to the paucity of such bands in odd-neutron nuclei, and suggest that the $Z=40$ and 64 subshell closures inhibit the core collectivity necessary for the lowering of particle states and formation of intruder bands in odd-neutron nuclei.