Isotope Dependence of Widths of Hole Analog States

Abstract

Recent experiments of the neutron pick up reaction with high energy resolution make it possible to extract the values of narrow widths of isobaric analog states in medium and heavy nuclei.!) Taketani et a1. 2 ) ob· served a systematic increase of the widths (20 keY ~40 keY) of the hole analog states (HAS) in the tin isotopes (A=lll~123). They estimated the spreading width due to the coupling of the analog state to the iso­ vector monopole state to be from 18 ke V to 16.5 keY and almost independent of the mass number A. They suggested therefore that the spreading width is dominant for the light isotopes and that the escape width causes the additional broadening for the heavy iso­ topes. In this short note, we examine their conjecture and elucidate the mechanism of these strong isotope dependence of the escape width. All the HAS's in the tin isotopes are un­ stable for proton, neutron and a-particle de­ cays. However, the a-decay width may be negligible as discussed in Ref. 2). We inves­ tigate the proton decay width in detail and consider the neutron decay width briefly. At first we make a rough estimate of the proton decay width, using the single particle escape width,3)