Satti Khizar Hayat, Dilband Muhammad, Siddique Muhammad Tariq, Rehman Shakeel Ur, Malik Azhar Hussain, Mansoor Shahid
Department of Physics and Applied Mathematics, Pakistan Institute of Engineering and Applied Sciences, Islamabad, Pakistan; Health Physics Division, Pakistan Institute of Nuclear Science and Technology, P.O Nilore, Islamabad, Pakistan.
Health Physics Division, Pakistan Institute of Nuclear Science and Technology, P.O Nilore, Islamabad, Pakistan.
Appl Radiat Isot. 2024 Oct;212:111471. doi: 10.1016/j.apradiso.2024.111471. Epub 2024 Aug 10.
The current study proposes a procedure to estimate the activity concentration of natural radionuclides and to optimize passive shielding solutions for HPGe detectors using adjoint Monte Carlo (MC) simulation technique of Geant4 for the first time. The background spectrum is acquired for 1.56 × 10 s using an HPGe detector model (GC3020), set inside a shielding solution, during 2021-2022 to estimate the activity concentration of natural radionuclides inside the shielding. While, a background spectrum for 65,000 s is acquired with shielding removed to estimate the concentration of natural radionuclides in the building materials of the laboratory. The detector design used in the simulations is validated by comparing computed and measured Full Energy Peak Efficiency (FEPE) for point sources Am, Eu, Cs, Ba, and Co. Adjoint MC simulations are used to compute the activity concentration of natural radionuclides assuming an isotropic distribution. The activity concentration of K, Ra and Th in the building material is found to be 524 ± 140, 83 ± 20 and 65 ± 18 Bqkg, respectively. The computed values are found in good agreement with the published data. The natural radioactivity levels of K, Ra and Th measured in lead shielding are 155.7 ± 0.1 mBqkg, 24 ± 13 mBqkg and 33 ± 17 mBqkg respectively. The radiological risks arising due to natural radioactivity is assessed by calculating radium equivalent activity (Raeq), indoor radiation hazard index (Hin) and annual effective dose equivalent. All the radiological parameters are found below their permissible limits and building materials may be considered radiologically safe. The optimal lead shield thickness for the detector is determined to be 12 cm, resulting in reduction of background signal by two orders of magnitude compared to an unshielded detector. The adjoint MC simulations in Geant4 are 10-10 times more rapid as compared to normal simulations for shield optimization of HPGe detectors and therefore, are identified as viable computing solution to calculate the activity of the background radiation.
本研究首次提出了一种使用Geant4的伴随蒙特卡罗（MC）模拟技术来估计天然放射性核素活度浓度并优化HPGe探测器被动屏蔽解决方案的程序。在2021年至2022年期间，使用置于屏蔽解决方案中的HPGe探测器模型（GC3020）采集1.56×10秒的本底谱，以估计屏蔽内部天然放射性核素的活度浓度。同时，去除屏蔽后采集65000秒的本底谱，以估计实验室建筑材料中天然放射性核素的浓度。通过比较计算得到的和测量得到的点源Am、Eu、Cs、Ba和Co的全能峰效率（FEPE），对模拟中使用的探测器设计进行了验证。伴随MC模拟用于计算假设为各向同性分布的天然放射性核素的活度浓度。发现建筑材料中K、Ra和Th的活度浓度分别为524±140、83±20和65±18 Bq/kg。计算值与已发表的数据高度吻合。在铅屏蔽中测量的K、Ra和Th的天然放射性水平分别为155.7±0.1 mBq/kg、24±13 mBq/kg和33±17 mBq/kg。通过计算镭当量活度（Raeq）、室内辐射危害指数（Hin）和年有效剂量当量来评估由天然放射性引起的辐射风险。发现所有辐射参数均低于其允许限值，建筑材料可被视为辐射安全的。确定探测器的最佳铅屏蔽厚度为12厘米，与未屏蔽的探测器相比，背景信号降低了两个数量级。与用于HPGe探测器屏蔽优化的常规模拟相比，Geant4中的伴随MC模拟速度快10-10倍，因此被确定为计算背景辐射活度的可行计算解决方案。
