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

在逆运动学中，利用(p，2p)质子与RI束和质子靶的敲除反应，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。实验上，将入射能量约为100A MeV的不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NaI(Tl)探测器被用作质子探测器，以前的实验中分离能量分辨率约为1.5 MeV(Rms)，由于这样的分辨率不能分离各种终态，我们进行了各种研究和开发，以提高分离能量分辨率。其中最重要的部分是作为质子探测器的高纯Ge探测器的研制。虽然小的Ge晶体已被用于各种核实验，但我们开发的探测器包含直径70 mm、厚度30 mm的平面HP Ge晶体。为了方便起见，晶体被装在低温恒温器中，并用薄薄的Be箔作为入射窗口。该探测器可以测量到105 MeV的质子能量。对于实际测量，还开发了其他几种探测器：用于高精度测量次级束能量的低压MWPC，用于测量质子动量矢量的高位置分辨率的位置敏感气体探测器，用于粒子识别的硅条探测器。在完成所有这些探测器元件后，在加速器装置上使用质子和12C束流对整个探测器系统进行了测试。虽然数据分析仍在进行中，但分离能量分辨率已达到0.5 MeV(RMS)。由于这个值比预期差了大约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.