Development of a Low Energy Proton Detector Using a Ruby Scintillator

N. Inoue， H. Nihei和N. Akiyama提出了一种基于永久磁铁的多尖配置的超冷中子（UCN）磁瓶。UCN的约束可以通过检测瓶子中UCN衰变产生的质子来证实。质子探测器安装在瓶顶，偏置电压约为-50 ~ -100kV，可有效地收集和检测质子。研制对中子和γ射线不敏感的低能质子探测器系统是必要的，因为这种探测器是在原子反应堆附近使用的。探测器使用的是含有铬（Al_2O_3(Cr_2O_3)）的红宝石闪烁体。在该闪烁体中，（n, p）反应速率非常小，而且由于该闪烁体可以层合，γ射线的影响也可以很小。闪烁体的厚度为0.02 mm。介绍了本研究的结果。(1)将^<241>Am源发射的α粒子（5.5 MeV）和Van-deGraph加速器加速的质子（0.2 ~ 1.0 MeV）照射到安装在低噪声型光电倍增管表面的闪烁体上。当单个带电粒子被照射时，光电倍增管的输出信号由许多孤立的信号组成。信号的总衰减时间约为2.5 ms。(2)用光谱仪观察到不同波长的发光光谱。这一结果与其他地方报道的数据一致。(3)在日本京都大学反应堆（KUR）的反应堆室内测试了探测器系统对中子和γ射线的灵敏度。实验证明，该探测器系统对中子和γ射线几乎不敏感。(4)结合上述实验结果得到的特性，可以研制出高信噪比的低能质子探测器。

A magnetic bottle of ultracold neutrons (UCN) based on a multiple cusp configuration using permanent magnets has been proposed by N. Inoue, H. Nihei and N. Akiyama. Confinement of UCN can be confirmed by detecting protons produced by the decay of UCN in the bottle. The protons are collected efficiently and detected by a proton detector which is installed on the ceiling of the bottle and biased at about -50 〜 -100kV. It is necessary to develop a low-energy proton detector system insensitive to neutron and γ-ray, since the detector is used near an atomic reactor.The detector used is a ruby scintillator containing chromium (Al_2O_3(Cr_2O_3)). In this scintillator the (n, p) reaction rate is very small, and the effect of γ-ray also can be made very small since the scintillator can be laminated. The thickness of the scintillator is 0.02 mm. The results obtained in this research are described. (1) Alpha-particles (5.5 MeV) emitted from ^<241>Am source and protons (0.2 〜 1.0 Mev) accelerated by a Van-deGraph accelerator were irradiated to the scintillator installed on the surface of a low noise type photomultiplier. When a single charged prticle has been irradiated, the output signal from the photomultiplier consists of many isolated signals. The gross decay time of the signal has been about 2.5 ms. (2) The luminescence spectrum having some different wavelengths was observed by a spectrometer. This result is consistent with the data reported elsewhere. (3) The sensitivity of the detector system to neutron and γ-ray was tested in the reactor room of KUR (Kyoto Univ. Reactor). It has been confirmed that the detector system is almost insensitive to neutron and γ-ray. (4) It is given as a conclusion that by combining the characteristics obtained by the above mentioned experimental results, it is possible to make a low-energy proton detector with high S/N ratios.