就地 HPGe γ 谱仪校准系数的蒙特卡罗计算

CALCULATION OF CALIBRATION COFFICIENTS FOR IN SITU HPGe γ SPECTROMETERS USING MONTE CARLO METHODS

本文采用蒙特卡罗（ＭＣ）方法和技术，建立了用于环境测量的就地ＨＰＧｅγ谱仪对点源的全能峰探测效率因子（Ｎ０／）和角响应校正因子（Ｎｆ／Ｎ０）的ＭＣ计算数学模式，进而利用Ｂｅｃｋ公式，给出了理论计算就地ＨＰＧｅγ谱仪测量土壤中天然和人工放射性核素的比活度校准系数（Ｎｆ／Ａ）及其地面上１ｍ高处的空气吸收剂量率校准系数（Ｎｆ／Ｄ·）的方法。本文采用自编的ＭＣ专用计算软件，计算了两台就地ＨＰＧｅγ谱仪的（Ｎ０／），（Ｎｆ／Ｎ０），（Ｎｆ／Ａ）的理论值并与它们的实验值进行了比较。在能量１２９ｋｅＶ～２．６ＭｅＶ范围内，上述两台就地ＨＰＧｅγ谱仪，（Ｎｆ／Ａ）的计算值与实验值一般在±７％的相对偏差范围内吻合，最大相对偏差小于±９％。

The method of in situ HPGe γ spectrometry for environmental measurement has widely been used in many nuclear plants,laboratories and nuclear environmental monitoring stations,because the specific activity of radionuclides on/in the soil and the dose rate in the air at l m above the ground can quickly be assayed with the method.It is important techniques to determine calibration coefficients of in situ HPGe γ spectrometers in the method.In general,there are two basic methods of determining the calibration coefficients,which are experimental calibration and theoretic calculation.In this paper,the full energy peak efficiencies( N 0/φ) and the angular correction factors (N f/ N 0) are computed using Monte Carlo for two in situ HPGe γ spectrometers;then the calibration factors,such as peak area per unit specific activity of radionuclides on/in the soil (N f/ A) and peak area per unitdose rate in the air (N f /D· ) at 1 m above the ground,are computed with Beck formula.The results are compared with experimental calibration data.They are in agreement within ±4.6% for (N 0/φ) ,within ±5.0% for (N f/ N 0) and within ±9.0% for (N f/ A ) and ( N f/ D·) from 129 keV to 2.62 MeV.A code “HPGe” has been developed for this purpose in FORTRAN language for any PC. (