Calculation of nuclide activity conversion factor for <italic style="font-style: italic">in</italic>-<italic style="font-style: italic">situ</italic> γ measurement

ZHANG Peng; ZENG Zhi; DAI Wenhan; ZHANG Qiuli; JING Mingkun; MA Hao; CHENG Jianping

doi:10.3724/j.0253-3219.2025.hjs.48.250012

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Calculation of nuclide activity conversion factor for in-situ γ measurement

NUCLEAR PHYSICS, INTERDISCIPLINARY RESEARCH | 更新时间：2025-10-31

- Calculation of nuclide activity conversion factor for in-situ γ measurement
- NUCLEAR TECHNIQUES Vol. 48, Issue 10, Article number: 100501(2025)
- 作者机构：
  
  1.清华大学工程物理系北京 100084
  2.北京师范大学物理与天文学院北京 100875
- 作者简介：
  
  ZHANG Peng, male, born in 1999, graduated from Tsinghua University in 2021, doctoral student, focusing on rare-event physics experiments and related low background technologies
  MA Hao, E-mail: mahao@tsinghua.edu.cn
  CHENG Jianping, E-mail: chengjp@tsinghua.edu.cn
- 基金信息：
  
  the National Key Research and Development Program of China(2023YFA1607101;2022YFA1604701);National Natural Science Foundation of China(12425507;12175112)
- DOI：10.3724/j.0253-3219.2025.hjs.48.250012
  CLC： TL99
- Received：03 January 2025，
  
  Revised：2025-06-20，
  
  Published：15 October 2025
- 稿件说明：
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张鹏,曾志,代文翰等.就地γ能谱测量中核素活度转化系数计算方法研究[J].核技术,2025,48(10):100501-100501.

ZHANG Peng,ZENG Zhi,DAI Wenhan,et al.Calculation of nuclide activity conversion factor for in-situ γ measurement[J].NUCLEAR TECHNIQUES,2025,48(10):100501-100501.
张鹏,曾志,代文翰等.就地γ能谱测量中核素活度转化系数计算方法研究[J].核技术,2025,48(10):100501-100501. DOI： 10.3724/j.0253-3219.2025.hjs.48.250012. CSTR： 32193.14.hjs.CN31-1342/TL.2025.48.250012.

ZHANG Peng,ZENG Zhi,DAI Wenhan,et al.Calculation of nuclide activity conversion factor for in-situ γ measurement[J].NUCLEAR TECHNIQUES,2025,48(10):100501-100501. DOI： 10.3724/j.0253-3219.2025.hjs.48.250012. CSTR： 32193.14.hjs.CN31-1342/TL.2025.48.250012.

摘要

利用就地γ能谱测量结果评估环境放射性核素水平时，需要计算放射性核素比活度与γ能谱特征峰计数率之间的转化系数。转化系数计算本质上是对周围材料中不同空间位置放出γ射线的探测效率进行积分，但在复杂几何下积分式难以进行数值求解，限制了方法的使用范围。本文提出了一种蒙特卡罗模拟与数值积分结合的转化系数计算方法：通过蒙特卡罗随机抽样解决复杂几何积分问题，并通过输运虚拟粒子提升蒙特卡罗模拟效率。将方法应用于中国锦屏地下实验室（China Jinping Underground Laboratory，CJPL）二期大型聚乙烯屏蔽仓就地γ能谱测量中的转化系数计算，给出了1 m厚聚乙烯墙体以及外部20 cm厚混凝土支护面中天然放射性核素的活度转化系数，并由此评估了聚乙烯屏蔽仓对外部混凝土中天然放射性核素本底的屏蔽能力。该方法解决了就地γ测量中传统数值积分方法在复杂几何情形转化系数难以求解的问题，并且计算效率提高了5倍以上，为实验室环境γ本底就地测量提供了关键参数。

Abstract

Background

situ

γ measurements employ radiation detectors to quantify the environmental γ spectrum

and it is necessary to calculate the conversion factor that translates the characteristic peak count rate of the measured spectrum into the specific activity of radionuclides in surrounding materials. The calculation of the conversion factor essentially involves integrating the det

ection efficiency of gamma rays emitted from different spatial positions within the surrounding materials. However

numerical solutions for the integral are challenging in complex geometries

limiting the method's application.

Purpose

This study aims to overcome the limitation of the integral method

simplify the calculation and broaden the scope of applications.

Methods

The Monte Carlo simulation technique was applied to calculating the integral of

in-situ

γ measurement. Firstly

the geometry of the surrounding materials was built in Geant4

and the emitted Geantinos facing the detector from the surroundings were sampled. Then

the positions whilst the Geantinos passed through the boundaries were logged. Subsequently

the parameters for the integral

such as the track lengths

were calculated and the conversion factor was obtained by calculating the average of the integral items of all particles. Finally

this method was applied to the conversion factor calculation for the building materials of the large polyethylene shielding chamber in the second phase of the China Jinping Underground Laboratory (CJPL).

Results

The conversion factors for the 1 m thick polyethylene walls and an external 20 cm thick concrete support in CJPL are determined by abovementioned method and the computing efficiency is increased by more than 5 times

which allow us to assess the shielding capability of the polyethylene chamber against various nuclide backgrounds in the external concrete

providing support and reference for

in-situ

measurements in the second phase of CJPL.

Conclusions

A novel method in this study to calculate the conversion factor for

in-situ

γ measurement overcomes the challenges of complex geometric integrations through random sampling and improves Monte Carlo simulation efficiency by transporting virtual particles

offering versatility in geometr

y and computational efficiency.

关键词

Keywords

references

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Calculation of nuclide activity conversion factor for in-situ γ measurement

DOI：10.3724/j.0253-3219.2025.hjs.48.250012

摘要

Abstract

关键词

Keywords

references