井型HPGe探测器探测效率的MC模拟

采用MC方法对井型HPGe探测器全能峰探测效率进行虚拟刻度。通过改变点源在井中的位置,研究了其探测效率变化规律,并进行了实验验证;同时模拟计算了探测器对0.1~1Me V能量的探测效率。模拟与实验结果表明:137Cs放射源在井中不同位置的实验测量结果与模拟值最大相对误差6.8%,最小相对误差1.5%;探测效率随放射源离井底距离增加而减小,随入射射线能量增大而减小。     

用重叠面积法计算的几何因子及其实验验证

采用源对探测器窗口的投影重叠面积法计算了特定条件下的几何因子,并对其进行了实验验证。实验验证部分是利用日本原子力研究所大洗研究所的设备,在日本STA资助的科技交流计划中完成的。探测器为半导体探测器,其面积为450mm~2。放射源为~(241)Am,~(238)U,~(233)U,~(239)Pu和~(244)Cm α标准源,此外,在真空室内的样品盘和探测器之间的距离是精确可调的。当对源和探测器之间距离的读数值重新刻度和对~(241)Am源重新校正,并对多道的ADC零点修正后,计算的几何因子与实验测得的探测效率的相对误差对薄源在6％以内。此外,为     

矿石品位仪的测量结构优化

为实现矿石品位仪的结构优化,利用蒙特卡罗（MCNP）软件,构建几何模型,模拟伽马射线在矿石品位仪系统内的输运过程。比较两种伽马放射源^60Co和^226Ra的测量效果差异,并分析了放射源与伽马探测器安装位置对测量效果的影响。结果表明,提高矿石品位仪测量效果的有效手段主要有：采用^226Ra放射源取代^60Co放射源;减小探测器与放射源距离;放射源与物料的距离调整为约30cm。     

三探头组合放射源定位探测系统模拟设计

采用MCNP法设计了一种由3个探测器组合而成的探测系统。并在3个探测器中间设计了不同形状的屏蔽层,研究不同屏蔽层形状下探测系统的探测灵敏度。理论计算和MCNP模拟结果对比表明:在相同距离下,C型探测系统的灵敏度优于A型和B型;A、B、C型三种探测系统的灵敏度都随距离的增大而降低,但C型探测系统始终优于A型和B型;针对文中建模的探测器尺寸,该结构适用于半径为5 m范围以内的放射源定位工作,通过比较模拟结果C型结构更适合作为便携式放射源准确定位仪器的探测器。     

用重叠面积法计算的几何因子及其实验验证

采用源对探测器窗口的投影重叠面积法计算了特定条件下的几何因子,并对其进行了实验验证。实验验证部分是利用日本原子力研究所大洗研究所的设备,在日本STA资助的科技交流计划中完成的。探测器为半导体探测器,其面积为450mm~2。放射源为~(241)Am,~(238)U,~(233)U,~(239)Pu和~(244)Cmα标准源,此外,在真空室内的样品盘和探测器之间的距离是精确可调的。当对源和探测器之间距离的读数值重新刻度和对~(241)Am源重新校正,并对多道的ADC零点修正后,计算的几何因子与实验测得的探测效率的相对误差对薄源在6％以内。此外,为了验证α粒子受射程限制时的几何因子,用2000mm~2的探测器,在不对样品室抽真空的条件下做了验证实验。结果表明:当作了甄别阈和窗口厚度修正以后,理论和实验值符合很好,其相关系数近似为0.9999,经X~2检验和F检验亦未见显著性差异。     

蒙特卡罗方法模拟放射源位置对井型NaI(Tl)晶体探测效率的影响

利用Geant4数值计算程序,对放射源137Cs和60Co发射的单能γ射线(0.662 MeV和1.331MeV)经过井型NaI(Tl)晶体探测器后的能谱进行了蒙特卡罗模拟,并通过改变放射源在井型NaI(Tl)晶体中的位置对探测效率的影响做了进一步的研究。计算结果表明:对比常用的圆柱形NaI(Tl)闪烁探测器,由于井型NaI(Tl)晶体对放射源所张立体角很大,所以其对γ射线的源峰探测效率更高,并随着放射源在井内高度的增加而逐渐减小;在固定了放射源在晶体井下深度的情况下,放射源位置在水平面内的变化对源峰探测效率的影响并不大。     

裂变材料中子-伽马脉冲形状甄别几何条件影响的模拟分析

快中子多重性分析技术是当前核材料衡算领域的热门研究方向。针对中子伽马脉冲形状甄别的效果在探测距离很近时明显变差的实验现象展开了研究。使用GEANT4工具箱模拟了液体闪烁体探测器测量裂变中子伽马的粒子输运过程,并基于计算机模拟数据分析了使用BC-501A液体闪烁体探测器测量裂变中子时,裂变物质与探测器的距离(几何效率)对中子-伽马甄别效果的影响。分析的结果与实验现象相符,表明在基于液体闪烁体探测器的核材料属性测量中,若单个探头的探测效率较高,裂变中子伽马脉冲叠加会严重影响甄别结果和测量计数。     

KCl校准溶液中~(40)K活度浓度的定值方法

水下就地γ谱仪的探测效率校准,要用到大体积液体~(40)K放射源。该放射源是通过在大体积水箱中配置KCl溶液制作而成。溶液活度浓度的准确定值是进行探测效率校准的基础。使用HPGe探测器进行取样能谱测量实验,并给出了KCl校准溶液活度浓度定值的质量丰度法、实验效率外推法、实验和MC模拟相结合法、半经验公式法等实用方法。     

某高校放射源库辐射场的MCNP模拟及分析

采用非现场检测方法,给出某高校放射源库的辐射场分布,并计算出该放射源库的最大存储量,提出防护优化建议。利用MCNP(Monte Carlo N particle transport code)程序模拟计算放射源库辐射场分布,并与实测值对比,验证模拟值的可靠性。结果表明,MCNP程序模拟结果与现场实测值的误差基本保持在10%,能给出较精确的辐射场分布及源库最大存储量。结果提示:利用MCNP程序模拟放射源库及其周围辐射场,能在不进入辐射场的情况下,有效获取任意点处的剂量率;该高校放射源库采取的防护措施能保证在任意关注点处剂量率均小于国家标准限值;对于~(137)Cs的最大存储能力为4.88×10~(13) Bq,对于~(60)Co的最大存储能力为9.99×10~(10) Bq。     

MURA编码板γ相机探测器模拟研究

用Geant4软件对γ相机探测器的成像原理进行模拟,γ相机探测器主要由准直器和探测单元构成,模拟得到放射源的响应矩阵,通过精细采样算法和δ解码算法进行图像重建。分别模拟了不同形态放射源在不同位置、不同距离、不同角度的成像情况,研究了编码板的偏移和尺寸变化对成像的影响。     

CBM-TOF超级模块高密度数据前端读出设计

为满足超级模块探测器质量评估的数据读出需求,设计了一种基于"三明治"结构的前端高密度数据读出方法。利用FPGA技术实现320通道时间数字化数据读出和自定义协议处理,并通过片内高速串行收发器与光纤进行长距离数据传输。在外部回环模式下的测试结果表明,6 Gb/s高速链路误码率小于10-13的置信度超过95%,接收TDC数据和自定义协议处理功能正常,系统连续稳定运行超过48 h,可满足探测器评估需求。     

四种系统矩阵建模方法的比较

构建了像素驱动、距离驱动、改进的距离驱动和射线驱动四种系统矩阵建模方法,并将其运用于ADMM算法,比较了它们的建模速度、建模精度以及收敛速度,同时比较了它们在有噪声的情况下对噪声的敏感程度。实验表明:距离驱动的建模速度最快;改进的距离驱动的建模精度最高,射线驱动在ADMM算法中的收敛速度最快。     

Application of Pattern Recognition Techniques to Location of Impact Sound Sources on Pressure Vessels

Pattern recognition techniques for loose parts location in nuclear power reactors are investigated. The location method is based on determining a reference impact position closest to the unknown impact from a library in which data for reference impacts are listed. The values of sound amplitude and arrival time as obtained from accelerometers are used for the pattern information which is inherent in impact position. The distance between unknown and reference impact positions is estimated from the similarity of each pattern. The pattern distance between two sound sources is defined as an index of the pattern similarity. Relationships between the pattern distance and the actual distance of the impacts are studied using impact data from a commercial boiling water reactor. It is found that the pattern distance and the actual distance have a very close correlation and the false probability that the zero impact distance is determined to be a distance of more than 0.6 m is 0.15. These results suggest that the pattern recognition techniques can be applied to loose parts detection and location on pressure vessels.     

X射线辐射场平方反比规律的研究

X射线辐射场强度随着距离的变化而变化,同一射线在不同距离处其强度是不同的。为了研究X射线辐射场强度和距离的平方反比规律,采用PTW-30013指形电离室进行辐射场均匀性测量,并在均匀的辐射场中用PTW-32002球形电离室进行平方反比规律的验证。结果表明:在对管电压为100kV、120kV、150kV三个防护水平辐射质在不同距离经空气衰减修正后,在一定距离内,X射线辐射场强度能够很好地满足距离的平方反比规律,其相对偏差不超过1%。由于散射光子的影响,平方反比规律误差随着距离的增大而有所增加。对于能量越高的X射线,平方反比规律更好。     

Study of Distortion of a Vacuum Arc at a Long-Gap Distance

Experimental study of the long-gap distance vacuum arc distortion for three types of axial magnetic field (AMF) contacts, by using high-speed charge coupled device (CCD), is presented. The arc current was of a half-cycle sine wave with a frequency of 50Hz, produced by an L-C discharging circuit. The time of appearance and duration of vacuum arc distortion under three conditions were studied. It was found that the gap distance, current and diameter of the electrode affected the characteristics of vacuum distortion at a long-gap distance. Some characteristics of the vacuum arc at a long-gap distance was revealed and the experience and data for further investigation were provided.     

Impact of Material Configuration Behind First Wall on Helium Formation in In-Vessel Components of Fusion Reactor

The results of neutron transport calculations of the He formation based on the JENDL gas-production cross section file are discussed for some metals and alloys, namely ²⁷A1, Ti, ⁵¹V, Cr, ⁵⁵Mn, Fe, Ni, Zr, Mo, austenitic stainless steel (Ti modified 316 SS: PCA), Ni-base alloy (Inconel 625), ferritic steel (Fe-11Cr-1Mo: HT-9), Ti-base alloy (Ti-6A1-4V) and V-base alloy (V-5Cr-5Ti). Impacts of the two shields having the steel-rich and the H₂O-rich compositions and the two blankets having the Li₂O/Be-base and the liquid Li/Be-base compositions on the He formation rate in the above-mentioned metals and alloys are discussed. The relation between the He formation rate and the fast neutron flux (14.1 MeV>E>0.1 MeV) is investigated. The decrease of He formation at any distance Δ from the first wall more than Δ_as, the distance where the shape of neutron spectrum reaches its asymptotic form, is modelled by the simple formula based on the exponential dependence, as those reported so far for the fast neutron flux and the displacement damage rate.     

Optimization of the working distance of an ion microprobe-forming system

A high-resolution ion microprobe necessitates the use of a small working distance (the distance from the final quadrupole lens of a probe-forming system to the specimen) in order to produce a large demagnification. But at the same time a small working distance is a source of a number of practical difficulties. We have presented an approach for determining a working distance that provides the best spatial resolution with the main practical limitations taken into account. We used a probe-forming system acceptance as a criterion of optimality. The calculations have revealed the existence of an optimal working distance in a set of common probe-forming systems, but it can be achieved only after changing of a design of a final quadrupole lens. We proposed a possible design of conic lens that allows solving the problem of detectors location and creating a short focus system. Three-dimensional calculations of magnetic field within this lens predicted a good quality of field structure.     

基于有限元方法计算多丝电离室的电场构型

本文采用基于有限元方法的ANSYS软件模拟计算了不同几何结构和极间偏压下多丝电离室腔室中的电场强度分布,研究了丝半径、丝间距、极间距和极间偏压变化对电离室电场的影响。结果表明,减小丝半径、丝间距、极间偏压和增大极间距可有效减小电离室中电场强度的变化幅度,从而获得稳定的电场。     

125I种子源的剂量场分布

摘要：用美国医学物理家协会工作组43号报告（AAPM TG №43）方法计算了125I种子源体内近程治疗源吸收剂量及其 剂量场分布，并用热释光剂量计（TLD）测定了125I种子源剂量场分布。理论计算和实际测量结果均表明，种子源剂量随距离呈指数衰减，而且在10 mm内衰减很快，说明种子源剂量基本集中在近距离范围内。     

Response of fully developed pipe flow to a wall-attached ring-type roughness element

The flow field downstream of a wall-attached roughness element in heated axisymmetric flow has been examined experimentally. Velocity and temperature fluctuations at selected points were examined for sensitivity to changes in position relative to the disturbance. Results indicate that the turbulent Prandtl number in the downstream flow field is in the range 0.4–1.2, that large Reynolds stresses are generated near the tip of the roughness element but diffuse towards the core with downstream distance, and that spectral peaks exist which decay rapidly with downstream distance. The restraining effect of the wall on the lateral turbulence intensity is also well illustrated. The rapidly changing features of the flow with downstream distance from the flow disturbance open up possibilities for monitoring of reactor fuel assemblies as well as in-service location of faults.