一个低本底中子探测器的效率计算

一、引言自从M.Fleishman和S.Pons报告了他们实现冷核聚变后,引起了科学工作者的极大兴趣并掀起了热潮,我们于1989年4月也开始了这方面的研究工作。我们采用液体闪烁体耦合到光电倍增管来探测中子。ST-451液体闪烁体为φ10.5cm×5cm的圆柱体,用n-γ甄别技术排除γ射线讯号以降低本底。在设置探测阈窗从1.5～3.5 MeV中子能量时,它的平均本底计数为0.025中子/s,在中子源强度为5中子/s时,     

脉冲中子全能谱测井闪烁探测器响应特性的蒙特卡罗模拟

利用蒙特卡罗方法模拟研究NaI和BGO晶体探测器对不同γ射线的响应。模拟结果表明,BGO晶体的光电峰和第一逃逸峰对计数贡献大,而NaI晶体的逃逸峰贡献大。对于井眼和地层流体分别为油和水砂岩地层,模拟改变NaI和BGO晶体探测器的直径和长度时的非弹性散射γ射线响应能谱,采用不同能窗处理方法对地层流体的分辨能力不同,选取光电峰和第一、第二逃逸峰对应的能量窗时,BGO晶体探测器比NaI晶体探测器测量的C/O（C与O的元素含量比）差值大,但受尺寸的影响不大;采用光电峰对应的能量窗时,BGO晶体探测器测量的C/O差值比NaI的大得多,且随尺寸的增加差值增大;能量道的漂移对C/O值影响较大,而能量分辨率对差值影响相对较小。     

闪烁纤维中子探测器灵敏度研究

用蒙特卡罗方法研究了1种闪烁纤维中子探测器对不同能量中子和伽玛射线的相对灵敏度，并在实验室对几个能点的灵敏度进行了标定。实验结果表明：理论计算与实验标定的探测器能量响应曲线趋势基本一致，探测器对2．5MeV中子和1．25MeV伽玛射线的灵敏度比值为5．3。利用实验数据对计算值进行校正，可给出探测器能量响应全曲线。     

四中子-中子探测器脉冲中子测井仪

一种应用于矿场地球物理领域中的四中子一中子探测器脉冲中子测井仪，主要解决现有的中子探测器脉冲中子测井仪一次下井只能获得两组测井数据、信息量较少的不足。其特征在于：所述脉冲中子发生器为小直径井下脉冲中子发生器，所述热中子探测器单元由4个热中子探测器构成，分别为上端近源距热中子探测器、上端远源距热中子探测器、下端近源距热中子探测器、下端远源距热中子探测器。具有一次下井可获得4组地层物质测井数据、信息量大且可减少放射性统计起伏误差、增强测井曲线的可靠性、提高仪器的测量精度的特点。     

MZ—88脉冲中子测井系统软件设计

本文主要介绍了MZ-88脉冲中子测井系统软件的特点、主要功能、程序结构与框图。     

瞬发裂变中子铀矿测井中超热中子探测器的优化研究

瞬发裂变中子铀矿测井是利用脉冲中子源和超热中子探测器,记录热中子和235U发生裂变反应产生的瞬发超热中子,得到地层含铀量信息的测井方法。为提高仪器中超热中子探测器的探测效率,利用蒙特卡罗数值计算程序MCNP5对中子铀矿测井仪的探测器进行了优化计算研究,得到最优的中子慢化体和中子探测器尺寸组合,并将计算结果用于仪器的改进,取得了满意的实验结果。     

一种新型中子高效率探测器技术研究

根据现有的中子探测器多采用气体探测材料,普遍存在体积大,效率不高和响应时间长的缺点,结合中子探测的最新发展,用蒙特卡罗方法通用软件MCNP(4B版本)对中子探测材料和结构进行了研究,并在此基础上设计出了一种新型中子探测器模型,对它的探测性能进行了数值仿真。该新型中子探测器的设计不论是对民用还是对军用都将有着十分重要的意义。     

大面积中子闪烁探测器阵列技术研究

介绍了在神光Ⅲ原型上建立大面积中子闪烁探测器阵列用于诊断压缩密度的具体方法,其中包括物理实验原理、探测器工作原理、电子学系统设计和探测器系统对靶室等环境的要求。给出了各部件的具体参数,分析了影响探测系统性能的主要因素,并提出了建立大面积中子闪烁探测器阵列的实现途径。     

基于CLYC探测器的可控源中子孔隙度测井数值模拟研究

利用Cs₂LiYCl₆:Ce(CLYC)探测器替代中子孔隙度测井中的³He中子探测器,已成为石油测井仪器发展的新思路。为探究在中子孔隙度测井中使用新型探测器的可行性,通过蒙特卡罗模拟,研究了CLYC探测器在不同⁶Li纯度和探测器尺寸下的热中子计数通量,同时与不同内部气压下的³He探测器热中子计数结果进行对比;另外根据仪器使用不同探测器时获取的中子孔隙度响应,验证了CLYC探测器的可替换性。研究表明:新型CLYC探测器在⁶Li纯度高、探测器尺寸大时热中子计数效率高;相比于³He中子探测器,热中子探测效率较低的CLYC探测器经过源距组合分析优化后,得到的中子近远比响应结果与³He中子探测器近似,能够有效应用于地层孔隙度获取。     

涂硼MRPC热中子探测器用于补偿中子测井的蒙特卡罗研究

本文利用蒙特卡罗方法模拟了涂硼多气隙电阻板室(Multi-gap Resistive Plate Chamber,MRPC)热中子探测器和3He正比计数管在常规条件和欠平衡条件下的补偿中子测井中的响应。模拟结果表明,使用涂硼MRPC热中子探测器时,得到近远探测器计数随孔隙度而增加,且与使用3He正比计数管时得到的结果基本一致,说明涂硼MRPC热中子探测器可用于补偿中子测井。     

BF3中子探测器阵列探测效率的蒙特卡罗计算

在用241Am-Be中子源对BF3中子探测器阵列探测效率标定的基础上,用蒙特卡罗方法对其探测效率进行了模拟计算,获得了比较满意的结果.然后用蒙特卡罗方法对BF3中子探测器阵列的探测效率进行了研究.研究结果表明,焦面探测器具有较好的探测效率.     

应用蒙特卡罗方法确定NaI探测器的点源效率函数及其参数

为了探讨NaIγ探测器对点状γ射线源(以下简称"点源")的探测效率与点源空间位置之间的关系,采用蒙特卡罗方法通用程序模拟计算了NaIγ探测器对空间不同位置处137Cs、60Co点源的探测效率.根据模拟计算结果,通过数值拟合方法,确定了NaI探测器对点源的探测效率函数及其参数.研究表明,应用蒙特卡罗模拟方法确定NaIγ探测器对于点源的探测效率函数及其参数是一种简便、有效的方法.     

Adjoint Monte Carlo neutron transport using cross-section probability table representation

The probability table representation of cross-sections is generally used to deal with neutron interactions in the unresolved energy range. In the frame of neutron transport methods, the capability of the probability table representation of cross-sections on the whole neutron energy range has been mentioned by Cullen (1974) and it has been already demonstrated for the Monte Carlo transport calculations by Zheng et al. (1998). Such an advantage is also illustrated here with a simple neutron propagation configuration dealt with the TRIPOLI-4 Monte Carlo transport code.     

Validation of the Monte Carlo model supporting core conversion of the Portuguese Research Reactor (RPI) for neutron fluence rate determinations

The Monte Carlo code MCNP was used to calculate absolute values of thermal, epithermal and fast neutron fluence rates in the new RPI core using fresh LEU fuel. Discrepancies smaller than 20% were obtained between calculated results and activation foil measurements. A previous knowledge of general characteristics of the neutron energy spectra, provided by the MCNP reactor model itself, has been fundamental to determine the conditions yielding a proper comparison of simulated and measured results. An excellent agreement (6%) was also obtained for the relative neutron fluence rate profiles along the fuel height. The MCNP model of the reactor core was therefore validated for a tri-dimensional determination of neutron fluence rates in the fuel assemblies and neighbouring irradiation positions.     

用Monte Carlo方法模拟设计工业CT探测器

为了用Ｍｏｎｔｅ－Ｃａｒｌｏ方法设计工业ＣＴ探测器，我们开发了通用程序ＧＥＰＭＣ。该程序模拟了γ光子，次级电子和荧光光子的输运过程，主要的计算结果有ＣＴ阵列探测器的γ输出谱，积分荧光输出，探测效率和探测器之间的串扰（ｃｒｏｓｓｔａｌｋ）在实验方面，我们测量了不同尺寸单块晶体的γ能谱，其谱形与模拟计算的相符合。     

薄膜和纤维塑料闪烁体中子能响特性的Monte Carlo数值计算

根据中子与塑料闪烁体的作用机制及塑料闪烁体的荧光转换特性,研究了塑料闪烁体薄膜和塑料闪烁体纤维中子能响特性的Monte Carlo数值计算方法,给出了不同厚度的塑料闪烁体薄膜和不同直径的塑料闪烁体纤维对裂变能区中子的灵敏度计算结果,并对计算结果及其在电流型坪响应裂变中子探测器方面可能的应用进行了初步探讨。     

GPU-based Monte Carlo simulation in neutron transport and finite differences heat equation evaluation

Graphics Processing Units (GPU) are high performance co-processors originally intended to improve the use and quality of computer graphics applications. Since researchers and practitioners realized the potential of using GPU for general purpose, their application has been extended to other fields out of computer graphics scope. The main objective of this work is to evaluate the impact of using GPU in two computational expensive problems in nuclear area: a neutron transport simulation by Monte Carlo method and Poison heat equation resolution for a square thin plate. To accomplish that, GPU and CPU-based (single- and multi-core) approaches were developed. Results demonstrated that the GPU-based approach is damn faster than a parallel 8-core CPU-based approach also developed in this work.     

Monte Carlo simulation of the NaI(Tl) detector response to measure gold activated foils

This work deals with the implementation of a NaI(Tl) detector for the assessment of the specific saturation activities of pure gold foils after neutron irradiation. These gold foils can be placed in the centre of a set of polyethylene spheres with different diameters. This configuration, known as a passive Bonner sphere system, is suitable to measure neutron spectra normally extended over a wide energy range containing up to 11 decades (from thermal to a few MeV), at places where the neutron field is very intense, high frequency pulsed or where it is mixed with an important high-energy photon component. The MCNPX code was used to evaluate the NaI(Tl) responses to different incident photon energies in terms of pulse-height distributions. An experimental validation of the calculated NaI(Tl) responses, using certified standard sources at a given measurement arrangement, indicates that MCNPX is a valid tool for routine calibration and benchmarking studies of this detector. A good agreement is found between the measured pulse-height distributions of the certified standard sources and those obtained from MCNPX simulations. As a preliminary application, a bare disc Au foil was directly exposed to a Bremsstrahlung photon beam at the isocentre of an 18 MV medical LINAC, in order to test the suitability of this activation material to measure the photo-neutrons generated in such facility. Two differentiated main photo-peaks, arising from ¹⁹⁶Au and ¹⁹⁸Au predominant γ-ray emissions, were observed. The two isotopes are produced mainly by the photonuclear, ¹⁹⁷Au(γ, n)¹⁹⁶Au, and radiative capture, ¹⁹⁷Au(n, γ)¹⁹⁸Au, reactions of, respectively, high-energy photons and thermal neutrons on the gold foil. From the measured ¹⁹⁸Au saturation activity, a rough estimation of (378 ± 68) × 10⁴ cm⁻² Gy⁻¹ was derived for the thermal neutron flux within the LINAC treatment room. This value, although being very approximate, is comparable to those reported by other authors for similar LINAC facilities but with different treatment room configurations, nominal acceleration potentials and Bremsstrahlung photon irradiation areas.     

蒙特卡罗方法计算用于低能光子测量的高纯锗探测器的效率

在内照射活体测量中,为了用蒙特卡罗方法计算探测器对光子尤其是低能光子的探测效率,需要对探测器准确建模。通过使用蒙特卡罗模拟计算和实验测量相结合的方法来准确确定低能光子高纯锗探测器晶体的死层厚度、半径和长度;结果表明使用此方法确定的晶体尺寸来模拟计算探测器效率,在17．5～662keV光子能量范围内,低能光子高纯锗探测器探测效率的模拟计算结果与实验结果比较,相对偏差平均小于1．0％,最大为3．2％。     

快中子照相样品散射本底及图像特性的Monte Carlo模拟

模拟了14MeV中子在穿透样品后与闪烁体光纤的作用。对每根光纤中的能量沉积进行了计算,并转换成可见光(496nm)光子数在模拟实验中,分析了影响图像质量的因素。首先计算了散射中子本底与闪烁体和样品(聚乙烯)间距的关系。当间距为厘米量级时散射中子本底对图像的影响很小。其次,计算表明系统对样品的甄别厚度与入射中子总数N有关,在一定范围内近似与logN成线性关系。最后,通过模拟结果给出了理想平行中子束入射情况下系统的平面分辨率。