1Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, Michigan.
Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, Michigan.
Health Phys. 2019 Oct;117(4):362-377. doi: 10.1097/HP.0000000000001051.
Experiments were performed with 30 11 cm × 42.5 cm × 5.5 cm NaI(Tl) detectors to better understand their positional response. Spectra were collected using 0.02 to 0.15 MBq point sources of Am, Cs, Co, and Ba positioned on lines parallel and perpendicular to the long axis of the crystal along both the narrow and wide detector faces as well as at different distances from them. A greater density of positions was sampled at the ends of the detector, and repeated measurements were made to examine potential gain drifts during the experiment. Spectroscopic peak counts, spectroscopic pulse heights, and net counts were analyzed. Empirical equations were fit to the aforementioned data for each specific source energy as a function of source position. In addition, a Monte Carlo radiation transport code was used to simulate the expected positionally variable response based solely upon radiation absorption. The simulated radiation transport efficiency functions were compared to the experimental data. The effects of the geometric radiation efficiency, the attenuation and scattering of emitted light within the scintillation crystal, and combined effects such as nonuniformity of the photomultiplier tube, photocathode response, and crystal irregularities were then distinguished. Functions describing each effect were derived. The results suggest potential new corrections to data obtained with large scintillation detectors as well as a novel approach to partial positional gamma-ray detection with minimal collimation, given that the energy resolution is within reason for particular photopeaks.
进行了 30 个 11cm×42.5cm×5.5cm 的碘化钠（Tl）探测器实验，以更好地了解它们的位置响应。使用 Am、Cs、Co 和 Ba 的 0.02 到 0.15MBq 点源，在平行和垂直于晶体长轴的线上，以及在晶体窄面和宽面的不同位置处，收集了光谱。在探测器的末端采集了更多位置的密度，并进行了重复测量，以检查实验过程中潜在的增益漂移。分析了光谱峰计数、光谱脉冲高度和净计数。针对每个特定的源能量，针对上述数据拟合了经验方程，作为源位置的函数。此外，使用蒙特卡罗辐射传输代码仅基于辐射吸收来模拟预期的位置可变响应。将模拟的辐射传输效率函数与实验数据进行了比较。然后区分了几何辐射效率、闪烁晶体中发射光的衰减和散射的影响，以及光电倍增管的不均匀性、光电阴极响应和晶体不规则性等综合效应。推导出了描述每个效应的函数。结果表明，对于大闪烁探测器获得的数据，可能需要进行新的修正，并且对于最小准直的部分位置伽马射线检测，也提供了一种新的方法，因为对于特定的光电峰，能量分辨率在合理范围内。
