Qβ measurements of neutron-rich isotopes with a total-absorption type Ge detector using the KUR-ISOL

Abstract

To measure Qβs of neutron-rich nuclei far from the stability, the total-absorption-type Ge detector has been developed. The detector is composed of a large true-coaxial type HPGe detector and an annular BGO scintillation detector for the Compton suppression. To check the detector performance, nineteen nuclides having precisely measured Qβs are measured. The nuclei of interest were prepared by (n, γ) reactions and 235U(n,f) reactions using the Kyoto University Reactor (KUR). The response functions of γ-rays and monoenergetic electrons were calculated by means of the Monte Carlo simulation code (EGS4), and the folding method was used to deduce Qβs. The nuclei 147�149 La, 151 Ce, and 153 Pr, for which precise information of the decay schemes were not reported, were prepared by the on-line mass separator (KUR-ISOL) and were measured by the total-absorption type Ge detector. The deduced Qβs were consistent with preliminarily measured ones by a total absorption BGO detector. The evaluated values by Audi et al. were systematically smaller than the present ones.