R＆D for high-resolution (p, 2p) proton knockout reactions using unstable nuclear beams

利用逆运动学中的RI束和质子靶的（p，2p）质子敲除反应，可以推导出有关单粒子轨道的信息，如轨道角动量和核子分离能。在实验上，将入射能量约为100 A MeV的非稳定核束引导到质子靶上，测量了两个质子的能量和动量。由于采用NaI（T1）探测器作为质子探测器，在以往的实验中，分离能量分辨率约为1.5MeV（rms），在这样的分辨率下，各种末态不能分离，因此我们进行了各种提高分离能量分辨率的研究与开发。最重要的部分是作为质子探测器的高纯锗探测器的开发。虽然小的Ge晶体已经被用于各种核实验中，但是我们所开发的探测器包含直径为70 mm、厚度为30 mm的平面HP Ge晶体。为了方便起见，晶体被包含在低温恒温器中，薄Be箔作为入口窗口。该探测器可以测量质子能量到105 MeV。为了进行真实的测量，还开发了其他几种探测器：用于高精度测量次级束流能量的低气压多壁光子晶体、用于测量质子动量矢量的高位置分辨率位置敏感气体探测器、用于测量粒子识别能量损失的硅条探测器，在完成所有这些探测器元件后，整个探测器系统在加速器设施中使用质子和12C束进行了测试。尽管数据分析正在进行中，但已获得0.5 MeV（rms）的分离能量分辨率。由于这个值比预期的差3倍，我们计划在修改部分探测器元件后，使用来自加速器的粒子束再次测试探测器系统。

Utilizing (p, 2p) proton-knockout reactions with RI beams and proton target in the inverse kinematics, information concerning the single-particle orbits such as the orbital angular momentum and the nucleon-separation energy can be deduced. Experimentally, unstable nuclear beams With about 100 A MeV incident energy are guided to the proton target, and the energy and the momenta of two protons are measured. Since NaI(T1) detectors were used as proton detectors, the separation-energy resolution was about 1.5 MeV (rms) in previous experiments.Since various final states can not be separated with such a resolution, we have performed various R＆D for imporoving the separation-energy resolution. The most important part was the development of the High-Purity Ge detectors as the proton detector. Although small Ge crystals have been used in various nuclear experiments, the detector we have developed contains planar HP Ge crystals with 70 mm in diameter and 30 mm in thickness. For the sake of convenience, the crystal was contained in the cryostats with a thin Be foil as the entrance window. This detector can measure proton energies unto 105 MeV.For real measurements, several other detectors were developed : Low-pressure MWPC for high-precision measurement of secondary-beam energy, position-sensitive gas detectors with high position resolution for measuring the momentum vector of protons, Si-strip detectors for measuring the energy loss for particle identification.After finishing all these detector elements, the whole detector systems were tested using proton and 12C beams in the accelerator facility. Although the data analysis are in progress, separation energy resolution of 0.5 MeV (rms) has been obtained. Since this value is about a factor of 3 worse than expected, we are planning to test the detector system again using the particle beams from the accelerator, after modifying part of the detector elements.