Identifying the spin-trapped character of the Si 32 isomeric state

Abstract

The properties of a nanosecond isomer in Si32, disputed in previous studies, depend on the evolution of proton and neutron shell gaps near the island of inversion. We have placed the isomer at 5505.2(2) keV with Jπ=5-, decaying primarily via an E3 transition to the 21+ state. The E3 strength of 0.0841(10) W.u. is unusually small and suggests that this isomer is dominated by the (νd3/2)-1 - (νf7/2)1 configuration, which is sensitive to the N=20 shell gap. A newly observed 41+ state is placed at 5881.4(13) keV; its energy is enhanced by the Z=14 subshell closure. This indicates that the isomer is located in a yrast trap, a feature rarely seen at low mass numbers.