九大原子核セミナー

2012年2月16日(木) 16:00

講師：笹野 匡紀 氏 (理化学研究所)
演題：
Gamow-Teller transitions from 56Ni

場所：理学部 物理第三講義室(理学部2号館2階2249室)

概要：
The Gamow-Teller (GT) transition is the simplest excitation mode of atomic nuclei reflecting the interplay between spin and isospin degrees of freedom and, therefore, the transition strength is a key quantity for understanding the nuclear structures and interactions. Furthermore, electron-capture (EC) and beta-decay, which play important roles in type-II and typeIa supernovae, occur through the GT transitions. Thus, their strengths are also extensively studied to reliably estimate the weak-interactions rates. Experimentally, a powerful probe to study GT transitions has been provided by the charge-exchange reactions at intermediate energies such as the (p,n), (3He,t) rections. They can selectively excite the GT transitions in a wide excitation energy region. Until recently, however, such studies have been restricted to stable nuclei, or to a few low-lying states in a limited number of light unstable nuclei, because of difficulties in inverse-kinematics measurements with rare isotope (RI) beams. In this talk, we present a new experimental technique to measure the (p,n) reaction on any unstable nuclei and up to any excitation energy region, and its first application to study the GT transitions from 56Ni via the (p,n) reaction at 110 MeV/u in inverse kinematics. 56Ni is produced in large abundances during the pre-explosion phase of core-collapse supernovae and considered to be as one of the most important contributors to the change in the electron-to-baryon ratio in core-collapse supernovae. In addition, to study the GT transition in 56Ni serves as a stringent test of the effects of the N=Z=28 core not being inert on GT transitions for a large number of nearby nuclei in the Fe region. In this first study, a newly developed Low-Energy Neutron Detector Array (LENDA) was used in combination with the S800 spectrometer. To employ thus developed experimental method in conjunction with a high-intensity RI beam provided by RIKEN RI beam facility will provide a unique opportunity to study exotic properties of unstable nuclei near the proton/neutron drip lines through their GT transitions.