不同射线能量及线衰减系数条件下体源探测效率的函数模型

基于放射性废物桶内所含介质材料和放射性核素分段均匀分布的假设, 采用蒙特卡罗程序模拟计算多种射线能量、多种样品密度条件下的线衰减系数和体源探测效率, 通过多元非线性拟合得到以线衰减系数和能量为自变量的体源探测效率函数。基于壳源法, 通过多个点源组合测试近似替代均匀体源的实验测量, 对3种能量射线和3种密度的样品进行验证实验, 利用蒙卡模拟与数值拟合结合方法和实验测量两种方式获得各自的体源探测效率, 完成活度估算。两种方式活度估算结果相对误差均小于23%。通过蒙卡模拟与数值拟合结合方法所得结果与实验结果基本吻合, 证明了该方法的有效性。     

基于虚拟刻度原理对放射性体源效率刻度方法的发展

采用蒙特卡罗模拟计算的方法,标定能够适用于不同HPGe探测器上的体源虚拟点源位置,需要对点源、体源的探测效率进行模拟计算。通过 241Am、137Cs、60Co点源和体源研究了HPGe晶体尺寸、类型对它们的虚拟点源位置的影响,模拟结果表明241Am虚拟点源位置随着探测器尺寸、类型的不同呈现明显的差异性,说明虚拟刻度原理对于探测器表面的小体积样品测量在低能区间是不可取的,最后采用 137Cs、60Co源得出体源高度与虚拟点源位置的半经验公式。通过实验室两台HPGe探测系统对尺寸Φ70 mm×65 mm标准土壤体源的探测效率进行计算,与模拟探测效率值、虚拟点源效率表征结果对比分析,验证了拟合一组表征虚拟点源位置的半经验公式是可行的。实验结果表明,对$\gamma $能量区间在300~2 000 keV进行体源的虚拟刻度时,选择可靠的定标源即可建立体源和虚拟点源位置的关系。这为解决监测工作中样品与探测器之间重复进行探测效率校准的问题提供了新的途径。     

基于蒙特卡罗的HPGe伽马谱仪无源效率刻度方法

采用MCNP5模拟与数学计算相结合,并利用探测器晶体几何的轴对称性,建立一种HPGe探测器的无源效率刻度方法。基于此方法的计算程序在使用过程中完全脱离MCNP5,运算时间为1~60 s,可实现点源和同轴圆柱体源的效率刻度,能量范围为50 keV~3 MeV。程序计算结果与实验数据以及MCNP5直接模拟结果比较,误差分别不超过12%和7%,证明方法可行。     

高纯锗探测器探测效率修正法的研究

探测效率是高纯锗探测器的一个重要指标，实际工作中面对的测试对象经常是一些不规则的辐射体，使得用标准源刻度探测效率难以实现，为此通过理论方法研究刻度体源探测效率有着重要意义。但是理论模拟面对着模型刻画准确性的问题，为此，该项研究针对实验室的两台便携式高纯锗γ谱仪开展了理论计算的验证工作，通过两种方法作为验证基准，即：实验和基准程序计算。针对计算产生的偏差，探索了影响效率差异的各种因素，推导了修正公式，并对修正公式的有效性和适应性进行验证。修正后的理论结果与基准的比较见图1和图2。     

基于蒙卡模拟的分段γ扫描无源效率刻度方法

针对200 L核废物桶分段γ扫描(SGS)过程中的效率刻度问题,提出了一种效率刻度函数模型,采用MCNP程序计算不同基质密度和γ射线能量条件下的离散断层效率,经过多元非线性回归获取函数参数,从而建立效率刻度函数,实现核废物桶SGS断层效率刻度。对核废物桶样品进行实验分析,结果表明:对于桶内基质分别为密度0.310 g·cm^-3的硅酸铝、密度0.595 g·cm^-3的木质纤维,桶内核素分别为活度3.110×10^5 Bq的点源137Cs、活度1.371×10^5 Bq的点源60Co,在桶内仅有单个点源存在的核素分布极端不均匀情况下,桶内核素活度重建误差在-37.68%~31.52%范围内。本文的方法能够准确有效实现核废物桶SGS断层效率矩阵计算,并确定核废物桶内放射性核素活度,满足实际检测要求。     

HPGe 探测器晶体尺寸及效率的研究

采用蒙特卡罗方法模拟计算光子的探测效率需对高纯锗( HPGe ) 探测器进行准确的建模。模拟计算研究了HPGe 晶体长度对探测效率的影响,并在空间不同的测量位置对放射源进行测量,将模拟计算与实验测量相结合,对探测器晶体的尺寸进行调整,获得了HPGe 探测器晶体的模拟计算的准确尺寸,并在122s1 332 keV 能量范围内对模拟结果进行了验证。结果表明,在此能量范围内HPGe 探测器的探测效率的模拟计算值与实验测量值的相对偏差大多数在5% 内,并建立点源探测效率与探测器轴向距离的关系。The accurate shape of HPGe detector is needed in order to calculate its detection efficiency with Monte Carlo methods. In our calculation, the influence of the HPGe crystal size on efficiency has been investigated; the final crystal sizes were determined by comparison with experiments and were validated by the experimental efficiency obtained at several source-to-detector positions. The results show that when the crystal dimensions determined are used to calculate the detection efficiency in the energy range 122s1 332 keV, the relative deviations between simulated and most experimental results were within 5%. In addition, the relationship between detection efficiency and axial distance to detector was established.     

NaI探测器对23.8 MeVγ射线的效率刻度方法

低能D(d,γ)4He辐射俘获反应截面的研究在聚变领域和天体物理等领域中起到非常重要的作用。由于受到标准γ源能量的制约,在研究D(d,γ)4He反应高能γ射线产额实验过程中不能用标准源进行效率刻度。采用实验测量与计算相结合的方法实现NaI探测器对23.8 MeV γ射线的效率刻度,先对6.13MeVγ射线效率进行实验刻度,然后用蒙卡程序MCNP－4C模拟计算出NaI探测器的效率曲线,再用实验数据与模拟结果进行对比校正,计算出NaI探测器在23.8MeV能量点对γ射线的探测效率。该方法对高能γ射线效率刻度给出了一种参考依据。In the study of D(d,γ)4He radiative capture reactions research, which is very important for fusion and astrophysics, the efficiency calibration of the detector is necessary. Due to the restriction on energy of the standard gamma source, the efficiency calibration of high-energy gamma-rays can not be calibrated by a standard source. In this paper, the method combining the experimental measurements and calculations for the efficiency calibrations of high energy gamma rays is given in the experiment of 6.13MeV gamma rays efficiency calibration using NaI detector, the efficiency curve of which is calculated by MCNP-4C and corrected experimentally. In this case, the detection efficiency of 23.8MeV gamma ray is known. The method provides a reference to high energy gamma ray efficiency calibration.     

NaI(Tl)探测器对23.8MeV γ射线的效率刻度方法

低能D(d,γ)~4He辐射俘获反应截面的研究在聚变领域和天体物理等领域中起到非常重要的作用。由于受到标准γ源能量的制约,在研究D(d,γ)~4He反应产生的23.8 MeV高能γ射线产额实验过程中不能用标准源进行效率刻度。采用实验测量与计算相结合的方法实现NaI(Tl)探测器对23.8 MeVγ射线的效率刻度是比较成熟可靠的。针对高能γ射线的产额低、本底大的情况,实验采用一个大型NaI(Tl)反康谱仪进行测量,以提高探测效率。NaI(Tl)探测器的效率,独特地采用了包括全能峰、单逃逸峰和双逃逸峰在内的效率来计算,经MCNP-4C程序模拟计算,结合实验测量的19F(p,αγ)~(16)O反应产生的6.13 MeVγ射线探测效率推算出该NaI(Tl)探测器在23.8 MeV的效率为(2.23±0.34)‰。该方法对研究高能γ射线效率刻度具有重要的参考价值。     

血液中Na活化放射性测量的蒙特卡罗模拟

针对超临界事故中人体受到中子辐照后感生的24Na活度测量,采用MCNP软件建立蒙特卡罗模拟模型,分别模拟不同类型NaI探测器对24Na衰变的两条射线全能峰的探测效率和塑料闪烁体探测器对24Na衰变的射线总计数的探测器效率。模拟结果表明:井型NaI探测器与圆柱型相比,24Na衰变的1.38 MeV和2.76 MeV 射线全能峰探测效率分别提高了4.30倍和4.11倍;塑料闪烁体探测器对24Na衰变的射线的探测效率是NaI探测器对24Na 射线的探测效率的1.72倍;同时粗略计算了探测器计数与人体所受中子辐照剂量之间的关系。     

~(133)Ba面源效率转移法刻度~(133)Xe气体源HPGe探测效率

提出使用面源进行效率转移法刻度133 Xe气体体源的探测效率。使用133 Ba面源模拟刻度放射性133 Xe气体体源的探测效率,在刻度的过程中利用137 Cs与133Ba的峰效率比值及133 Ba面源远端无符合相加效应,137 Cs能峰远近都无符合相加效应等,结合软件模拟建立远近距离峰效率比值的关系,来解决133 Ba的符合相加效应。最后,使用面源效率转移法进行气体体源效率刻度,转移法刻度结果和面源模拟法刻度计算值的偏差在±1%以内。     

Absolute efficiency calibration of high-purity germanium detector in the range 120–8500 keV

This article reports the efficiency response curve of the high-purity germanium detector over the wide energy range, covering from 120 to 8500 keV. The efficiencies were measured for different counting geometries by using point radionuclide standards (mono-energetic as well as multi-gamma emitters) supplied by IAEA and the capture gamma-ray facility installed at PINSTECH nuclear reactor PARR-1. The measured efficiencies were required to fit with a suitable fitting function for interpolation within the energy range of interest. Several fitting functions were proposed in the literature covering different energy ranges. The functions giving the best fit to experimental data are presented. The work has successfully extended the response curve beyond 1500–8500 keV, which is the region where the standard calibration radionuclides are not available. The thermal neutron capture gamma-ray facility provided the collimated neutron beam, extracted from the core of the reactor and made to react with ammonium chloride target to produce the capture gamma rays for determining the efficiencies in the extended region. It was found that the capture gamma-ray provides a satisfactory solution to extend the absolute efficiency calibration in the MeV range. It was also found that the fitting function that is linear in its parameter was highly satisfactory up to 1500 keV but proved insufficient upto 8500 keV. The exponential function giving the good fit over the range has been presented. Good agreement has been found between the experimentally measured absolute efficiencies and the predicted result.     

MIRD体模肺部γ内污染探测效率分布的蒙特卡罗模拟

运用MCNP5程序,建立了基于MIRD数字体模的肺部γ内污染模型以及NaI(Tl)探测器模型,模拟计算了NaI(Tl)探测器对基于MIRD数字体模的肺部γ内污染的探测效率,获得了在多种空间位置上对沉积在肺部的9 种能量 射线的探测效率。模拟结果表明,在不同位置的探测效率并不完全符合人体肺部的解剖学结构,在右下肺位置可获得最高的探测效率,左下肺次之,左上肺最低。在探测器位置固定的情况下,探测效率随能量的增加,有先增高后降低的现象。In order to obtain detection efficiencies of nine kinds of gamma rays emitted by isotopes deposited in lungs at various measurement geometry, Monte Carlo N-Particle Transport Code 5 (MCNP5) has been employed to for calculation. The results show that the detection efficiency in different locations of lung is not completely accord with human body’s anatomy structure. The efficiency decreases gradually from lower-right lung, to lowerleft lung, and then to upper-left lung. When the location of detector is fixed, with the increase of energy, thedetection efficiency rises up firstly and then falls down.     

Design and gamma sensitivity measurement of a novel dual-emitter vacuum Compton detector

A novel dual-emitter vacuum Compton detector (D-VCD) with higher gamma ray detecting efficiency is proposed. The emitters are made of Ta--Al clad metal. The gamma ray sensitivity is studied by Monte Carlo simulation using the MCNP code. A comparison between calculations and results measured by using the 1.25~MeV gamma ray of Co-60 is also performed. Experimental sensitivities for two sample D-VCDs with the same materials and structures are 1.92×10^ - 20 and 2.02×10^ - 20~C.cm²/MeV separately, which are consistent with the simulation result of 1.98×10^ - 20~C.cm²/MeV and are 4 times higher than that of VCD with a single Fe emitter. According to the simulation results, in a gamma energy range from 0.5 to 3~MeV, the maximum sensitivity variance for the D-VCD is less than 15%, and less than 5% in a range from 1 to 2~MeV in particular. The novel D-VCD is applicable to the detection of intense pulse gamma rays.     

XH-3130A在线液体γ监测仪探测效率MC模拟

为了研究改造后的XH-3130A在线液体伽马监测仪对核电站某管道一次水放射性核素的探测效率及探测限的影响因素,利用MCNP5程序计算了改造前后XH-3130A伽马监测仪对管道放射性源项伽马能量在0.08~1.5 MeV范围全谱区及特征峰区活度浓度探测效率。针对放射性管道中单一核素Cs-137,计算结果与液体放射性源标定计数刻度实验数据符合较好。并分析了不同源项伽马能量及探头布置等因素对活度浓度探测效率大小影响差异。模拟结果表明,改造后的XH-3130A在线液体伽马监测仪不再影响原有测量管道整体性且最低探测限为1.35103 Bq/m3,可以满足工程技术要求。     

双层并联碲锌镉探测器制备及性能测试

实验采用并联方法制备了叠层(双层)碲锌镉探测器,并利用241Am@59.54 keV和57Co@122 keV γ射线源测试了其γ能谱特性。相比单层探测器,对于较高能量的57Co@122 keV γ射线,叠层碲锌镉探测器表现出较高的探测效率和光峰值效率,较好地改善了康普顿连续统一体。叠层CZT探测器较之单层探测器,能谱分辨率发生轻微恶化。实验初步表明,通过并联叠加方法制备叠层碲锌镉探测器是可行的,并可推断制备更大厚度的叠层探测器将有利于中高能γ射线能谱测量。     

叠层碲锌镉探测器制备及γ能谱特性测试

实验制备了单层和叠层(双层)碲锌镉探测器,并利用241Am@59.54 keV和57Co@122 keV γ射线源测试了其γ能谱特性。相比单层探测器,对于较高能量的57Co@122 keV γ射线,叠层碲锌镉探测器表现出较高的探测效率和光峰值效率,较好地改善了康普顿连续统一体,表现出与整块等厚度碲锌镉探测器类似的性能;但光生载流子收集效率变差,能谱峰位向低道区偏移;能量分辨率未得到改善。实验初步表明,通过叠加方法制备叠层碲锌镉探测器是可行的,并可推断制备更大厚度的叠层探测器将有利于中高能γ射线能谱测量。