圆柱体源与点源的照射量累积因子对比

依据《辐射防护手册》中圆柱体源的公式做剂量率相关计算时会用到累积因子,但手册中对放射源发出的光子在圆柱体内部散射效应造成的累积因子并未做过多描述。本文应用程序模拟计算出这个因子,并与点源时用等效于圆柱体半径厚度的板状几何屏蔽体的照射量累积因子做比较,给出两者之间的近似数学关系。     

GD-300系列辐射光致发光玻璃剂量计的辐射剂量学特性

为掌握新引进的辐射光致发光玻璃剂量计的辐射剂量学特性,通过用次级标准剂量学实验室的X射线照射装置、⁶⁰Coγ放射源（1250keV）及经检定的¹³⁷Csγ放射源（662keV）照射,考察了GD-300系列辐射光致发光玻璃剂量计的剂量线性、均匀性、重复性、衰退特性和能量响应等剂量学性能。实验研究结果表明,GD-300系列辐射光致发光玻璃剂量计的辐射剂量学性能良好,适合作为放射工作人员外照射剂量、放射诊疗受检者与患者剂量的测量,也适用于环境辐射的长期累积测量。     

钴-60操作热室窥视窗设计及性能分析

为避免放射性物质操作人员受到电离辐射的外照射,需要在放射性物质与操作人员之间设置带有窥视窗的屏蔽,而搭建窥视窗常用的材料为耐辐射玻璃和防辐射玻璃。为满足~(60)Co密封放射源产品的操作要求,本文设计一套由国产耐辐射和防辐射玻璃构成的~(60)Co操作热室窥视窗,并采用等比级数(G-P)逼近法和ANSI/ANS-6.4.3中的数据计算其照射量积累因子,根据此计算结果、玻璃的技术性能和基本物理公式分别分析该窥视窗的屏蔽性能和透光性。结果表明:该窥视窗的屏蔽性能达到了设计要求,可满足~(60)Co密封放射源产品的操作要求。入射角的大小对窥视窗透射率的影响很大,当入射角超过60°后透光率迅速下降。     

基于MC方法的高放废液玻璃固化厂屏蔽窗辐射屏蔽性能设计研究

屏蔽窗是高放废液玻璃固化厂重要的观察设备,安装在热室与操作廊之间的混凝土墙体内,起辐射防护和气密通风隔离作用.为确保厂房运行人员所受的照射剂量控制在电离辐射防护标准的限值内,需要对屏蔽窗的辐射屏蔽性能进行优化设计.本文使用MCNP蒙卡模拟程序,对硼玻璃和铅玻璃两种屏蔽窗进行辐射屏蔽性能的蒙卡模拟研究,计算出能保障运行操...     

宁德核电站γ射线探伤管理

γ射线探伤所用放射源活度较高,在管控不当的情况下会给人员带来辐射伤害,甚至造成社会恐慌。本文分析了γ射线探伤工作存在的安全风险,从辐射防护与安全监督角度对宁德核电站γ射线探伤的安全管理进行了总结。     

钴-60放射源热室建设（303热室改扩建工程）项目进展

1项目概述 中国同位素有限公司与中国原子能科学研究院经过友好协商于2005年3月签订了“合建钴-60放射源热室协议”，双方决定共同出资建设用于秦山三期CANDU堆钴源生产的分装热室。钴．60放射源热室建设（303热室改扩建工程）是在303工号原有设施的基础上进行改扩建，故称作303热室改扩建工程。     

γ放射性门式检测系统的蒙特卡罗模拟及设计

针对γ放射源非法携带转移的危害性,设计了一种适用于放射性敏感区域的γ放射性门式检测系统。该系统首先采用塑料闪烁体探测器对放射性物质发出的γ射线进行甄别,然后采用Na I(Tl)探测器阵列进行核素识别和初步定位经137Cs和60Co两个常用γ放射源蒙特卡罗模拟验证,理论上其放射性检测下限可达370 Bq,并能有效地对放射性核素进行识别和初步模块化定位,对防止γ放射源的非法转移具有很好的技术途径。     

高纯锗探头γ能谱测量中的加合效应修正研究

在γ能谱绝对测量中,除对放射源和探头之间的效率几何因子进行研究和计算外,由于大量γ辐射具有级联性质,又由于受放射源活度和被测物体放射性半衰期的限制,使得待测源与探测器之间的距离不能过远。在这种情况下,测量结果的γ的加合效应修正就显得很重要了。     

高活度废放射源整备装置热室照明设计

良好的照明是保证在热室中顺利完成废放射源整备的关键因素之一。本文根据国际照明委员会照明标准和热室照明的特殊要求,分析了高活度废放射源整备装置内部照明的设计、灯具布置及其他问题,确定采用了泛光照明方式,并对照度分布进行了验证。     

废放射源长期贮存现状

简单介绍了国际上对对废放射源的长期贮存方法一直接贮存、加外包装贮存和整备后贮存,分别介绍了英国、奥地利、白俄罗斯、捷克、比利时等国废放射源的贮存现状;介绍了我国对废放射源的贮存方法及北京城市放射性废物库、中国辐射防护研究院废放射源贮存库、核工业废放射源集中贮存库、国家废放射源集中贮存库对废放射源的贮存情况,以期对我国废放射源的长期贮存研究有所帮助。     

Gamma-Ray Shielding Effectiveness of Some Alloys for Fusion Reactor Design

The gamma-ray shielding effectiveness of some oxide dispersion-strengthen (ODS) alloys by means of mass attenuation coefficients, mean free path, exposure buildup factors and energy absorption buildup factors have been investigated in the present study. The buildup factors were calculated using geometrical progression method for photon energy 0.015–15 MeV up to 40 mfp penetration depth. The mass attenuation coefficients were calculated by using XCOM program and Geant4 simulation methods and found a very good agreement. Our investigation signifies that the low iron content ODS alloys are superior shielding materials with the lower buildup factors. This study should be useful for selection of shielding materials for their applications in fusion reactors design and future nuclear reactor technologies.     

Photon energy absorption and exposure buildup factors for deep penetration in human tissues

Using photons in therapeutic and diagnostic medicine requires accurate computation of their attenuation coefficients in human tissues.The buildup factor,a multiplicative coefficient quantifying the ratio of scattered to primary photons,measures the degree of violation of the Beer-Lambert law.In this study,the gamma-ray isotropic point source buildup factors,specifically,the energy absorption buildup factor (EABF) and exposure buildup factor,are estimated.The computational methods used include the geometric progression fitting method and simulation using the Geant4 (version 10.4) Monte Carlo simulation toolkit.The buildup factors of 30 human tissues were evaluated in an energy range of 0.015-15 MeV for penetration depths up to 100 mean free paths (mfp).At all penetration depths,it was observed that the EABF seems to be independent of the mfp at a photon energy of 1.5 MeV and also independent of the equivalent atomic number (Zeq)in the photon energy range of 1.5-15 MeV.However,thebuildup factors were inversely proportional to Zeq for energies below 1.5 MeV.Moreover,the Geant4 simulations of the EABF of water were in agreement with the available standard data.(The deviations were less than5%.) The buildup factors evaluated in the present study could be useful for controlling human exposure to radiation.     

Gamma-ray and neutron shielding efficiency of Pb-free gadolinium-based glasses

The radiation shielding efficiency of material depends upon photon attenuation, exposure buildup factors and neutron removal capacity. A newly developed Pb-free gadolinium-based glasses in compositions(80-x) B_2O_3-10 Si O_2-10 Ca O-x Gd_2O_3(where x = 15, 20, 25, 30 and35 mol%) had completely been investigated for their shielding efficiency with Geant4 simulation for mass attenuation coefficients and neutron total macroscopic cross section and by calculating exposure buildup factors.The exposure buildup factors for photon energy from 0.015 to 15 Me V had been calculated up to 40 mean free paths using five factors geometric progression method. The mass attenuation coefficients of the Pb-free glasses were simulated for energies from 223 to 2614 ke V and compared with the possible available experimental results. The neutron shielding efficiency of these glasses was discussed by calculating neutron total macroscopic cross section for energies from 1 e V to 14.1 Me V. Present investigations are found to be very useful for applications in nuclear engineering.     

基于等比级数公式的积累因子拟合

从积累因子随穿透深度增加而增大的物理原理入手,简要说明积累因子等比级数拟合公式的推导思路,并给出各参数的物理意义。采用该公式对积累因子进行拟合时,程序编写困难。通过对各参数进行分析,给出一套程序编写方案。采用几种现行的积累因子拟合方案对几种典型的积累因子数据进行拟合,证明等比级数拟合公式最优。对几种常用屏蔽材料在不同入射γ射线能量下的照射量积累因子进行拟合,并给出等比级数拟合公式系数,拟合结果的最大相对偏差均在±5%以内。     

Comparison of Gamma-Ray Point Isotropic Buildup Factors Including Fluorescence and Bremsstrahlung in Lead Using Discrete Ordinates and Point Monte Carlo Methods

Exposure buildup factors and energy spectra of γ-rays, including fluorescence or bremsstrahlung radiations, in Pb for a point isotropic source have been calculated in the vicinity of the K edge and at 10 MeV using a discrete ordinate code, PALLAS. Comparisons of PALLAS results with those by the point Monte Carlo code, EGS4 showed good agreement for exposure buildup factors and energy spectra in two energy regions. Exposure buildup factors calculated with another discrete ordinate code, ASFIT, are also compared with those calculated by the PALLAS and EGS4 codes. The values obtained by all three codes showed good agreement. The effects of the cross section data on the buildup factors were investigated by using the PALLAS code.     

Chemical composition dependence of exposure buildup factors for some polymers

Exposure buildup factors for some polymers such as poly-acrylo-nitrile (PAN), poly-methyl-acrylate (PMA), poly-vinyl-chloride (PVC), synthetic rubber (SR), tetra-fluro-ethylene (Teflon) have been computed using the G.P. fitting method in the energy range of 0.015–15.0 MeV, up to the penetration of 40 mean free paths (mfp). The variation of exposure buildup factors for all the selected polymers with incident photon energy at the fixed penetration depths has been studied, mainly emphasizing on chemical composition (equivalent atomic number) of the selected polymers. It has been observed that for the lower penetration depths (below 10 mfp), the exposure buildup factor decreases with the increase in equivalent atomic number of the selected polymers at all the incident photon energies. However, at the penetration depth of 10 mfp and incident photon energy above 3 MeV, the exposure buildup factor becomes almost independent of the equivalent atomic number of the selected polymers. Further, above the fixed penetration depth of 15 mfp of the selected polymers and above the incident photon energy of 3 MeV, reversal in the trend has been observed, i.e., the exposure buildup factor increases with the increase in equivalent atomic number.     

某轻混凝土γ屏蔽积累因子的计算

使用蒙特卡罗程序EGS4计算了光子能量范围0.015~15MeV、屏蔽厚度达40个平均自由程的某核电厂中使用的轻混凝土的γ照射量积累因子,程序计算中考虑了轫致辐射、荧光效应和相干（瑞利）散射对积累因子的影响。使用G-P近似拟合公式对γ屏蔽积累因子计算结果进行拟合计算,给出了相应的积累因子G-P拟合公式的拟合参数。利用此方法可得到此种轻混凝土的任意光子能量和屏蔽厚度的γ屏蔽积累因子。     

241Am-Be中子源紧凑型屏蔽装置及辐照器设计

²⁴¹Am-Be中子源被广泛用于实验研究,为保护实验人员免受中子及γ射线照射,需要设计适当的屏蔽。利用蒙特卡罗方法计算中子透射不同材料后的能谱分布与剂量,优选各层屏蔽材料种类与厚度,设计一套²⁴¹Am-Be中子源紧凑型屏蔽装置。装置由内而外采用钨+聚乙烯+含硼聚乙烯+不锈钢进行防护,外表面周围剂量当量率H^*(10)低于10μSv/h,满足辐射防护要求。同时对装置内部热中子、超热中子和快中子注量分布进行研究,确定装置快中子和热中子输出通道最佳位置。在辐照装置同时开放快中子和热中子通道进行实验测试时,需要设置距离大于130 cm的控制区,以保障操作人员安全。     

铅眼镜对介入手术中职业人员防护效果的研究现状

眼晶体剂量限值的降低,引起了人们对眼晶体剂量监测、评价和防护的关注。通过近期国内外的研究工作,本文从蒙卡计算、基于人体模型或临床实践的实验测量深入调查了铅眼镜的防护效果,强调了铅眼镜对介入手术中职业人员眼晶体防护的重要性。基于铅眼镜防护效果的研究现状,分析了防护效果的影响因素:通过铅眼镜和眼睛间隙的射线,是眼晶体剂量的主要来源;决定铅眼镜防护效果的并不是射线能量、铅当量厚度、镜片面积等因素,而是眼镜结构、佩戴间隙、投照角度、位置布局、人员姿态等几何条件。调研分析铅眼镜防护效果旨在为眼晶体防护研究和临床实践提供参考。     

Fuel Pin and Subassembly Heterogeneity Effect on Neutronics Properties of Fast Power Reactor

The PALLAS (discrete ordinates-integral transport) code was improved to include secondary sources, such as bremsstrahlung and fluorescence, to assure accurate and reliable results. The point buildup factors for high-Z materials were calculated with this code in the energy range of 0.015~15 MeV up to 40 mean free paths. The buildup factors for low-Z materials in the low energy range, which are most difficult to calculate, were calculated with PALLAS and were validated by comparison with the results of the EGS4 (point Monte Carlo), and ANISN codes.

A function to calculate coherent scattering was added to the EGS4 code. It was suggested that neglecting coherent scattering and assuming free-electron Compton scattering can result in an error in the buildup factor.

A fitting formula, the geometric progression (G-P) form, was developed to reproduce the data in codes used for shielding design. This formula can reproduce the data over the full range of distance, energy and atomic number within a few percent.

The above cited buildup factor data and the G-P formula have been adopted for proposed standard ANS-6.4.3 “Gamma Ray Attenuation Coefficient and Buildup Factors for Engineering Materials”. The G-P fitting function has been implemented in the CCC-493/QAD-CGGP and CCC-494/G33-GP codes available from the Radiation Shielding Information Center (RSIC) at Oak Ridge National Laboratory. These are used for γ-ray shielding calculations throughout the world.

Also, the data and the method of evaluation for 1 cm dose equivalent, introduced into the Japanese law according to ICRP recommendations, have been offered by this team.