Atomic mass determination through beta-decay energy measurements for nuclei far off the stability line by using total absorption detector.

用一个大体积HPGe探测器和一个环形BGO闪烁探测器组成的全吸收型探测器测量β衰变能量（Q_β），HPGe探测器有一个中心孔，孔中引入放射源，可以测量大立体角，BGO闪烁探测器可以测量HPGe探测器的散射和/或透射光子。最后，将该探测器安装在京都大学反应堆（KUR-ISOL）的在线质量分离器上，测试了它作为Q_β探测器的性能。测量了Q_β值较好的富中子Rb和Cs同位素核（3 ~ 1.8MeV）。利用EGS 4蒙特卡罗程序模拟的单能电子和光子的响应函数，确定了总吸收谱的终点。与评价值的终点相比，检测器的系统不确定度被评价为20 keV。在上述分析的基础上，对^ Pr的核<153>进行了测量。用另一种由两个大体积BGO闪烁器组成的全吸收探测器测量了该核的Q_β。我们计划用KUR-ISOL对A=150附近的核进行测量，并将测量结果与系统学或理论预测值进行比较。

Beta-decay energy(Q_β) has been measured with a total absorption type detector which consists of a large volume HPGe detector and an annular BGO scintillation detector for the anti-coincidence detector.The HPGe detector, which has a center hole in which are introduced the radioactive sources, can be measured with large solid angle, and the BGO scintillation detector can measure the scattering and/or transmitting photons from the HPGe detector. Finally, the highest energy point of the measured spectra, namely end-point, corresponds to the Q_β.This detector was set at the on-line mass separator installed at the Kyoto University Reactor (KUR-ISOL) and tested its performance as a Q_β detector. The nuclei of neutron-rich Rb and Cs isotopes that have well-determined Q_β values (3〜8 MeV) were measured. By using the response functions for mono-energetic electrons and photons simulated by the Monte Carlo Code of EGS4, the end-point of the obtained total absorption spectra were determined. Compared with the end-points to the evaluated values, the systematic uncertainty for the detector was evaluated to be 20 keV. On the basis of the above analysis, the nucleus of ^<153>Pr was measured. The Q_β of this nucleus had been measured with another type total absorption detector which consists in two large-volume BGO scintillators. The present value is in agreement with the previous value with in the uncertainty.We are scheduled to measure the nuclei around A=150 with KUR-ISOL and to compare the results with systematics or theoretically predicted values.