Application of the alpha transfer reactions at incident energies below the Coulomb barrier to determination of the astrophysical reaction rate

本研究旨在发展一种新的实验方法，利用九州大学串列加速器实验室最近研制的反冲质量分离器，通过测量库仑势垒以下入射能量下的重离子引起的转移反应来确定天体物理核反应率。该分离器的设计目的是在逆运动学条件下获得尽可能高的背景抑制能力。将所提出的方法应用于推导α粒子引起的辐射俘获反应的速率，这些辐射俘获反应的截面太小，无法在加速器设备上直接测量，有望提供关于大质量恒星演化的丰富和新的信息。加速器和测量设备都进行了仪器开发，以便于在逆运动学条件下观察从传递反应发出的0和180度质心角的反应产物，而主束粒子和与主束相关的背景粒子的污染可以忽略不计。在加速器上，已经开发了束流脉冲系统和无窗气体剥离器，以产生发射度良好的脉冲束流，这对于消除背景是必不可少的。对质量分离器的性能和硅半导体探测器对低能轻重粒子的响应进行了详细的研究，确保了测量系统的背景抑制能力，足以实现无歧义的测量。有了这些发展和研究，我们即将开始实验，以检验在低入射能量下的转移反应数据对提取天体物理核反应速率的适用性。

The present study aims to develop a new experimental method of determining the astrophysical nuclear reaction rate by the measurement of the heavy-ion induced transfer reactions at incident energies below the Coulomb barrier with the recoil mass separator which has recently been developed at Kyushu University tandem accelerator laboratory. This separator is designed to achieve highest possible capability of the background rejection in the condition of inverse kinematics. Application of the proposed method to the deduction of the rate of the α-particle induced radiative capture reactions which cross sections are too small to measure directly at the accelerator facilities is expected to provide rich and new information on the evolution of the massive stars.Instrumental developments have been carried out at both the accelerator and the measuring devices for facilitating the observation of the reaction products emitted at center-of-mass angles of 0 and 180 degrees from the transfer reactions in the condition of the inverse kinematics with negligible contamination of the primary beam particles and the background particles associated with a primary beam. At the accelerator, the beam pulsing system and the windowless gas stripper have been developed to derive a pulsed beam of good emittance, essential to the elimination of the background. The detailed investigations on the performance of the mass separator and the response of a silicon semiconductor detector for low energy light-heavy particles have assured the background rejection capability of the measuring system enough to realize the unambiguous measurement. With these developments and investigations, we are about to start the experiments to examine the applicability of the transfer reaction data at low incident energies to the extraction of the astrophysical nuclear reaction rate.