Development of seven-dimensional detector system for low-energy light heavy-ions and its application to research on nuclear data of astrophysical interest

研制了一种用于九州大学双列加速器实验室反冲质量分离器的新型焦平面探测系统，能够同时获取能量小于1 MeV/u的轻重离子在二维倾斜角度和焦平面上的位置、能量、质量数和原子序数的信息。该系统由一个固态探测器（SSD）和两个二维位置敏感微通道板（mcp）组成，用于检测位于固态探测器前面的薄箔的离子感应电子。开始计划采用大活动面积的固态硬盘，实现飞行时间测量的长飞通。然而，利用串列加速器的束流对大活跃区固态硬盘的性能测试表明，即使在原子序数小于10的范围内，脉冲高度赤字也与被测粒子的原子序数有显著的相关性，而在相对较小的活跃区固态硬盘中没有观察到这种相关性。这些发现要求改变检测系统的设计，将小活动面积的固态硬盘放置在焦平面上。我们采用了一种利用下游箔的电子发射产率进行粒子识别的方法。利用串联加速器的^<12>C束流测试了商用薄膜的均匀性，发现聚酯薄膜的不均匀性小于3%。利用这种箔，考虑到能量分散，估计0.2和0.5 MeV/u ^<16>O的原子序数分辨率分别为0.2和0.1。整个系统的性能测试正在进行中，利用分离器和探测器系统确定恒星能量下^4He(^<12>C,^<16>O)γ反应速率的试验即将开始。

A new focal plane detector system for a recoil mass separator at Kyushu University tandem accelerator laboratory, designed to be capable of obtaining information of light heavy-ions with energies of less than 1 MeV/u on two-dimensional inclined angles and positions on the focal plane, energy, mass number and atomic number simultaneously, has been developed. The system consists of a solid state detector (SSD) and two two-dimensional position sensitive microchannel plates (MCPs) to detect ion-induced electrons from thin foils located in front of the SSD.The SSD with large active area was in beginning planned to be adopted to realize long flight pass for the measurement of time-of-flight. However, the performance test of the SSD with large active area using beams from the tandem accelerator has revealed significant dependence of pulse height deficit on the atomic number of the measured particles even in the range of atomic numbers less than 10, which has not been observed for the SSDs with relatively small active area. These findings imposed change of the design of the detection system to place the SSD with small active area at focal plane.We adopted a particle identification method using the emission yield of electrons from the downstream foil. Homogeneity of commercial foils was tested using a ^<12>C beam from the tandem accelerator and found that the Mylar foil has inhomogeneity of less than 3%. With this foil, the atomic number resolution has been estimated for 0.2 and 0.5 MeV/u ^<16>O to be 0.2 and 0.1, respectively, taking the energy straggling into account.The performance test of the whole system is now in progress and a trial to determine the ^4He(^<12>C,^<16>O)γ reaction rate at stellar energies using the separator and the detector system is about to start.