Development of New type PET using liquid Xe scintillation light

液态Xe是透明液体，原子序数为54，密度约为3.0 g/cm^3。对于伽马射线，其闪烁效率几乎与NaI（T1）相同，闪烁衰减时间常数2nsec和22nsec比NaI（T1）快得多。据估计，在不使用反射光的情况下，用多个pmt检测直射光将获得高能量分辨率。也可以通过比较多个pmt的输出来估计伽马射线的反应位置。通过对0.5 MeV伽马射线的模拟，在良好的条件下获得了数mm的位置分辨率。因此，我们考虑了以液态Xe作为探测介质的新型PET的可能性，并制作了液态Xe探测器，获得了开发PET所需的实验数据。该腔室为两层圆柱形式，外层真空抽真空隔热，内层包括pmt的检测器部分。内层填充液态氙，其中设置有44个pmt的探测器部分。窗户为内厚500 μm的不锈钢蜂蜜凸轮窗，外厚100 μm的密耳窗。有效体积为12x12x12cm ^3，周围有44个1英寸和2英寸的pmt。我们此次开发的pmt是滨松光电公司生产的2英寸圆柱型（R6041-06MOD）和1英寸矩形型（R5900-06MOD），它们具有石英窗对真空紫外光的高透射效率，即使在低温（-110℃）和高压（3atm）下也不会出现任何问题。同时，它还可以减少导致闪烁光减少的气体或杂质。位置分辨率为7.8 mm，时间分辨率为0.69nsec。在有效体积的中心部分，511kev伽马射线的能量分辨率为45%。

Liquid Xe is transparent liquid with atomic number 54 and density about 3.0 g/cm^3. For gamma rays its scintillation efficiency is almost same as NaI(T1) and the decay time constants of scintillation, 2nsec and 22nsec, are much faster than that of NaI(T1). It is estimated that the high energy resolution will be obtained, by detecting direct light with a plural PMTs, without using the reflected light. Also it is possible to estimate the reaction position of the gamma ray by comparing the output from plural PMTs. By the simulation for the 0.5 MeV gamma ray, the position resolution of several mm was obtained with the good condition. Thereupon, we think the possibility of new-type PET using liquid Xe as detector medium and produced the liquid Xe detector and made to obtain the experimental data needed for PET development. The chamber is the cylinder forms of 2 layers and the outside layer is evacuated vacuously for heat insulation and detector part of PMTs is included in the inside layer. The inside layer is filled with liquid xenon and the detector part of 44 PMTs is set in it. The windows are the honey cam window made of the stainless steel of 500 μm thick at inside and the miler window of 100 μm thick at outside. The effective volume is 12X12X12 cm^3 that is surrounded with 44 PMTs of 1 inch and 2 inch. PMTs that we developed this time are 2 inch cylinder type(R6041-06MOD) and 1 inch rectangular type (R5900-06MOD) made by Hamamatsu Photonics company, and these hold the quartz window to have high transmission efficiency for vacuum ultraviolet light and is designed to act without any problem even with the low temperature (-110 ℃) and the high pressure (3atm). Also, it is made to decrease the outgas or the impurities that becomes the cause of the decrease of scintillation light. The position resolution is 7.8 mm and the time resolution is 0.69nsec. In the central part of effective volume, the energy resolution is 45 % for 511 keV gamma ray.