核查中的中子探测技术研究

介绍了通过探测中子辐射,用被动方法研究了包括模拟核弹头装置在内的各钚组合系统的可探测性和中子能谱等内容．用主动方法研究了核材料铀的裂变缓发中子测量技术和区分核与非核材料的方法．讨论了进一步开展的核查技术实验.In this paper,by neutron radiation detection with the passive method, the study on detectability, neutron spectra, etc. for the plutonium combined systems including the stimulated nuclear warhead assembly are introduced. The sutdy on technique of measuring fission delayed neutrons from uranium materials and the method of distinguished nuclear from non nuclear materials with the active method are described. Further experiments on verifying technique are also discussed.     

利用MCNPX模拟研究不同中子源对有源符合中子法的影响

利用MCNPX软件建立了有源井型符合计数器(简称AWCC)测量模型,模拟了诱发中子源分别为Am-Li源和Am-Be源时AWCC测量贫化铀的中子符合计数率,研究了两种诱发中子源下AWCC测量贫化铀质量的精度.研究表明,Am-Be源引起的诱发中子符合计数率低于Am-Li源引起的诱发中子符合计数率,Am-Be源下的质量刻度曲...     

裂变瞬发中子多重性研究

本文介绍了裂变瞬发中子多重性这一研究领域的概况，着重介绍获第二届吴有训物理奖的“自发裂变和中子诱发裂变的瞬发中子多重性的研究”成果的主要内容和意义．     

氘-氚中子源辐照旋转靶剂量演化模拟计算

首次将蒙特卡罗自动建模系统(MCAM)、蒙特卡罗粒子输运程序(MCNP)及自主研发的活化程序BURNDOT相结合,实现了中子输运、材料活化、光子输运模拟计算的耦合。对14MeV氘-氚(D-T)中子源旋转靶室剂量演化分析,计算了氘-氚中子源辐照旋转靶室的瞬发中子、γ三维辐射剂量场分布及连续辐照8小时后缓发γ剂量变化情况,并考察了材质、栅元、主要核素对缓发γ剂量贡献的影响,得到了旋转靶的剂量时空演化规律,把计算结果与欧洲活化程序FISPACT-2007进行了对比。     

瞬发中子衰减常数的脉冲中子源法测量系统建立

在向没有任何缓发中子先驱核存在的次临界系统中注入一束脉冲中子后，系统中的瞬发中子强度随空间和能量分布的形状在经过很短一段时间的调整后，将A=Aoexp(λ，t）衰减，A为瞬发中子强度，s^-1；A0为初始瞬发中子强度，s^-1；t为瞬发中子衰减时间，s；λ为瞬发中子衰减常数，s^-1。     

基于裂变γ标识技术的瞬发裂变中子谱测量新方法

瞬发裂变中子谱（prompt fission neutron spectrum,PFNS）是用于核实验诊断过程中十分重要的参数数据,传统的测量主锕系核素（U,Pu）PFNS的技术手段是采用裂变室,利用裂变碎片标识裂变中子,通过中子飞行时间技术获得裂变中子谱.目前出现了一种新的用于PFNS测量的技术,其原理是基于如下的物理事实：在一次裂变过程中,释放中子的同时伴随着释放7–8个γ射线光子,而非弹性散射效应产生的γ射线光子只有1–2个.据此,可以通过裂变γ射线的多重性将裂变中子和其他杂散中子甄选出来,达到测量PFNS的目的.本文建立了基于裂变γ标识技术的PFNS测量实验系统.利用该系统对²⁵²Cf中子源的PFNS进行了实验测量,测量结果与传统的裂变碎片标识法及ENDF/B-VⅡ数据库的标准谱进行了比较,对新方法的裂变标识率以及实验不确定度也一并进行了分析.     

以中子作外源的假想核弹头主动探测

通过对不同入射能量的中子在假想的核弹头中的输运计算,分析了弹头中的裂变材料芯部的核裂变、各层对中子的吸收和(n,xn)反应以及出壳中子随角度的变化,论证了以外中子源(不随时间变化的外源)对弹头作主动探测的可行性.通过对14 1MeV脉冲中子源和产生的缓发中子在模型中的输运计算,分析了用脉冲外中子源产生的缓发中子探测核弹头的可行性.     

D-D中子源中子反射实验

根据检验计算方法和参数的需要，开展D-D中子源水泥材料反射中子实验研究。实验中，通过对直穿透射中予以及水泥反射体反射中子引发^235U（包镉）和^238U裂变率的测量，得到在不同测量点上反射体对中子的反射系数。由于反射中子注量率通常较弱，因此采用固体核径迹法进行裂变率测量。     

基于蒙特卡罗方法的中子屏蔽材料设计

基于蒙特卡罗粒子输运程序MCNP,设计了一种强度高、密度低、具有优异中子屏蔽性能的新型玻璃纤维/B4C/环氧树脂复合材料,模拟计算了镅-铍（Am-Be）中子源产生中子对该材料的透射率;研究了该材料的中子屏蔽性能与传统屏蔽材料的差异以及不同B4C质量分数对该材料的屏蔽性能影响;根据模拟结果分析了该材料对不同能区中子（慢中子、中能中子、快中子）具有的不同屏蔽性能。研究发现：B4C质量分数为10%的该种新型玻璃纤维/B4C/环氧树脂复合材料的中子屏蔽性能,尤其是慢中子屏蔽性能较传统的含硼聚乙烯和Al-B4C合金材料更为优异;但随着B4C质量分数的增大,屏蔽性能提升不明显。结果验证了蒙特卡罗方法用于中子屏蔽材料优化设计的可行性。     

ADS中子源散裂靶物理研究

运用蒙卡程序DCM CEM对ADS标准散裂中子靶进行了计算研究.计算了在0.1~1.6GeV的质子轰击下,标准Pb靶发生散裂反应产生的泄漏中子产额及分布、中子能谱以及靶内能量沉积分布.计算结果与文献理论数据、实验数据进行了比较.     

Measuring Neutron Lifetime on an IBR-2 Pulsed Neutron Source

A new method of measuring neutron lifetimes on pulsed neutron sources based on changes in the neutron spectrum during the time of the neutron transit along a rather large path length due to their decay is proposed. The main advantage of this method is the use of relative measurements. Simulating the experiment made it possible to explore the influence of background and neutron losses caused by both the interaction with residual gas and the different level of detector efficiency on the systematic errors. All parameters can be measured experimentally.     

Study on induced radioactivity of China Spallation Neutron Source

China Spallation Neutron Source (CSNS) is the first High Energy Intense Proton Accelerator planned to be constructed in China during the State Eleventh Five-Year Plan period, whose induced radioac- tivity is very important for occupational disease hazard assessment and environmental impact assessment. Adopting the FLUKA code, the authors have constructed a cylinder-tunnel geometric model and a line-source sampling physical model, deduced proper formulas to calculate air activation, and analyzed various issues with regard to the activation of different tunnel parts. The results show that the environmental impact resulting from induced activation is negligible, whereas the residual radiation in the tunnels has a great influence on maintenance personnel, so strict measures should be adopted.     

Study on induced radioactivity of China Spallation Neutron Source

China Spallation Neutron Source (CSNS) is the first High Energy Intense Proton Accelerator planned to be constructed in China during the State Eleventh Five-Year Plan period, whose induced radioactivity is very important for occupational disease hazard assessment and environmental impact assessment. Adopting the FLUKA code, the authors have constructed a cylinder-tunnel geometric model and a line-source sampling physical model, deduced proper formulas to calculate air activation, and analyzed various issues with regard to the activation of different tunnel parts. The results show that the environmental impact resulting from induced activation is negligible, whereas the residual radiation in the tunnels has a great influence on maintenance personnel, so strict measures should be adopted.     

快中子物理和实验技术研究

综述近年来在北师大低能所的国内第一台脉冲化高压倍加器上开展的快中子物理，及有关的实验和数据处理技术研究. The study on fast neutron physics and relative technique of experiment and data analysis made at a pulsed neutron generator in Beijing Normal University during recent yeras is introduced.     

Neutron Photoproduction Measurements Using the TOF Method

As the neutron is uncharged, kinetic energy of the knocked-out neutron after the (,n) reaction is usually determined by measuring its flight time, the so-called time-of-flight (TOF). Here the TOF method is detailed and a number of photoneutron measurements which have different physical motivations, performed at Maxlab using this method, is presented.     

China Spallation Neutron Source - an overview of application prospects

The China Spallation Neutron Source (CSNS) is an accelerator-based multidisciplinary user facility to be constructed in Dongguan, Guangdong, China. The CSNS complex consists of an H^－ linear accelerator, a rapid cycling synchrotron accelerating the beam to 1.6 GeV, a solid-tungsten target station, and instruments for spallation neutron applications. The facility operates at 25 Hz repetition rate with an initial design beam power of 120 kW and is     

基于脉冲中子源法的CiADS反应性测量蒙卡模拟分析

脉冲中子源法(PNS)是加速器驱动次临界系统反应性测量的一种重要技术.利用蒙卡软件建立CiADS次临界反应堆模型,模拟注入脉冲质子束的过程,获得的中子通量的时间演化谱.采用Python语言编程实现脉冲叠加过程,给出稳定缓发中子本底,实现脉冲中子源法的次临界反应堆的反应性测量模拟,给出脉冲周期注入下堆芯不同位置处的中子变...     

主动中子多重性法估算铀材料质量的不确定性（英文）

近年来,国际社会对核材料保护、控制和衡算日益加强。对不明材料损失量(MUF)的关注逐渐提升。铀材料质量不确定性测量在估算铀材料生产量中扮演重要角色。由于铀材料自发裂变相对较弱,主动中子多重性法被应用于估算铀材料质量。通过拟合对不同系列铀金属壳的数值模拟结果,获得了描述铀材料质量与主动中子多重性特征之间的算法和参数。得到的关系表明,可以通过分析不同重数中子多重性探测结果获得铀部件的质量。对不同探测条件下的模拟结果的定量分析,确定了探测系统设置对铀质量估算的影响,以及认知不确定性和随机不确定在估算过程中传播对质量估算的影响。对不确定度的分析获得了本文模拟采用的探测系统的最佳源强和探测时间窗设置,在此设置下,质量估算的不确定性最小。     

A Study of the Spatial Charge Effect on 2-MeV Proton Beam Transport in an Accelerator-Based Epithermal Neutron Source

Technical Physics - A neutron source composed of a tandem accelerator with vacuum insulation and a lithium target is used to develop the boron neutron capture therapy and other applications. The...