Analogous intruder behavior near Ni, Sn, and Pb isotopes

Abstract

Near shell closures, the presence of unexpected states at lowenergies provides a critical test of our understanding of the atomic nucleus. New measurements for the N = 42 isotones Co-69(27) and Cu-71(29), along with recent data and calculations in the Ni isotopes, establish a full set of complementary, deformed, intruder states astride the closed-shell Ni-28 isotopes. Nuclei with a one-proton hole or one-proton particle adjacent to Z = 28 were populated in beta-decay experiments and in multinucleon transfer reactions. A beta-decaying isomer, with a 750(250)-ms half-life, has been identified in Co-69(27)42. It likely has low spin and accompanies the previously established 7/2(-) state. Complementary data for the levels of isotonic Cu-71(29)42 support the presence of a deformed, Delta J = 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 Ni-68, support the view that intruder states based on particle-hole excitations accompany all closed proton shells with Z >= 28.