Abstract

Detecting the activity of ²¹⁰Pb in the human skull by counting its 46.5-keV gamma rays in vivo is a promising method to reconstruct one’s cumulative radon intake, based on which associated lung cancer risk can be evaluated. However, this technique is strongly challenged by the background radiation level, which can be largely categorized as room background and subject background. In this work, we quantitatively assess the performance of the phoswich detector in suppressing background radiation resulting from ⁴⁰K ubiquitously present in human subjects under in vivo measurements using Monte Carlo simulations. We first determined the region of interest for ²¹⁰Pb gamma-ray detection to be 31 to 61 keV and focused on the background level inside this region caused by two ⁴⁰K decay processes. It is found that the 1.46-MeV gamma-ray–led background can be reduced by 40% by the phoswich detector operating in anticoincidence mode whereas the 1.31-MeV beta-particle–led background is almost unaffected. This observation is understood through the dependence of the anticoincidence efficiency on the incident gamma-ray energies. Our results suggest that the 1.31-MeV beta-particle–led background is much larger and harder to suppress than the 1.46-MeV gamma-ray–led background, and they call for more investigations in the background reduction techniques for ²¹⁰Pb in vivo measurement.

摘要

通过在体内计数其 46.5-keV 伽马射线来检测人头骨中²¹⁰ Pb的活动是重建一个人累积氡摄入量的有前途的方法，基于此可以评估相关的肺癌风险。然而，这种技术受到背景辐射水平的强烈挑战，背景辐射水平主要可分为房间背景和主体背景。在这项工作中，我们使用蒙特卡罗模拟在体内测量中定量评估了 phoswich 检测器在抑制由普遍存在于人类受试者中的^{40 K 产生的背景辐射方面的性能。}我们首先确定了^{210的感兴趣区域}Pb 伽马射线探测为 31 至 61 keV，并集中在该区域内由两个⁴⁰ K 衰变过程引起的背景水平。发现 1.46-MeV 伽马射线主导的背景可以通过以反重合模式运行的 phoswich 探测器减少 40%，而 1.31-MeV β-粒子主导的背景几乎不受影响。通过反重合效率对入射伽马射线能量的依赖性来理解这一观察结果。我们的研究结果表明，1.31-MeV β 粒子主导的背景比 1.46-MeV 伽马射线主导的背景更大且更难抑制，他们需要对²¹⁰ Pb 体内测量的背景减少技术进行更多研究.