一种宽能谱多球中子谱仪能量响应的MC模拟

利用蒙特卡罗程序FLUKA模拟计算了聚乙烯慢化球和辅助材料慢化球对低能中子到高能中子的响应函数曲线。结果表明,对纯聚乙烯球来说,随着聚乙烯层厚度的增加,响应曲线峰逐步右移,峰值在高能区有所下降,对20 Me V以上的中子,无论纯聚乙烯球的尺寸有多大,其响应均下降到很低的程度;对辅助材料慢化球来说,中子能量小于1 Me V时,辅助材料慢化球与聚乙烯慢化球的响应曲线相似,但当中子能量大于20 Me V时,中子与辅助材料层发生(n,xn)反应,慢化球的响应呈显著上升趋势。分析计算结果,最终能够确定宽能谱多球中子谱仪的尺寸组合。     

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.     

利用GEANT4和FLUKA研究质子诱发散裂反应出射中子双微分截面

在中高能质子诱发散裂反应相关核工程设计中,可靠的蒙特卡罗模拟程序结合核反应理论模型具有较好的理论指导意义。本工作中,利用GEANT4耦合INCL4和ABLA理论模型以及FLUKA耦合PEANUT模型模拟计算了几百MeV至几个GeV质子轰击Be,Al,Fe,W,U等靶后30°,60°,120°,150°出射角产生的散裂中子双微分截面,并与现有实验数据进行了比较。结果发现,FLUKA和GEANT4模拟计算较好地再现了Al,Fe,W,U等靶实验测量数据。然而,模拟结果明显低估了Be靶出射中子能量小于10 MeV能区的实验数据。For the design of nuclear engineering related with medium-high energy proton induced spallation reaction,the reliable Monte Carlo simulation codes coupled with nuclear reaction models have a good theoretical guidance.In this work,the production spallation neutron double differential cross sections at 30°,60°,120°,150°emission angle for Be,Al,Fe,W,U target materials at incident proton energies between several hundred MeV and GeV are theoretically calculated by using the GEANT4 coupled INCL4 and ABLA,and the FLUKA coupled PEANUT.The calculated results were compared with the available experimental data.It is found that the GEANT4 and FLUKA calculations well reproduced the experimental measurement of Al,Fe,W,U target materials.However,calculations obviously underestimated the emission neutrons of Be target for lower than 10 MeV energy range.     

Study on the selection of BLM detector for C-ADS Injector Ⅱ

The injector of C-ADS (Chinese Accelerator Driven Sub-critical System) project is a high current, fully super-conducting proton accelerator. Meanwhile, a BLM system is indispensable for this facility, especially in low energy segments. This paper presents some basic simulations for 10 MeV proton by Monte Carlo program FLUKA, as well as the distributions on different secondary particles in three aspects: angular, energy spectrum, and current. These results are beneficial to selecting the detector type and its location and determining its dynamic range matching different requirements for both fast and slow beam loss. Furthermore, in this paper the major impact of the background is also analyzed, such as superconducting cavity X radiation and radiation caused by material activation. This work is meaningful in BLM system research.     

A method to enhance coincidence time resolution with applications for medical imaging systems (TOF/PET)

A coincidence timing spectrometer was assembled using NaI(Tl) inorganic and BC418 type organic (plastic) scintillation detectors. The constant fraction timing method was used. Coincidence time resolution values of the detectors, which have great importance in TOF/PET measurements, were obtained separately. The resolutions were enhanced using a different method in a start-stop coincidence spectrometer: the signals from the start detectors were delayed. The results from the FLUKA Monte Carlo simulation code agreed well with the experimental results.     

Simulation of a modified neutron detector applied in CSNS

We simulate the response of a modified Anderson-Braun rem counter in the energy range from thermal energy to about 10 GeV using the FLUKA code. Also, we simulate the lethargy spectrum of CSNS outside the beam dump. Traditional BF3 tube is replaced by the 3He tube, a layer of 0.6 cm lead is added outside the boron doped plastic attenuator and a sphere configuration is adopted. The simulation result shows that its response is exactly fit to H＊（10） in the neutron energies between 10 keV and approximately 1 GeV, although the monitor slightly underestimates H＊（10） in the energy range from thermal energy to about 10 keV. According to the characteristics of the CSNS, this modified counter increases the neutron energy response by 30% compared with the traditional monitors, and it can be applied in other kinds of stray field rich of high eeergy neutrons.     

400~1500 MeV质子轰击铅靶和钨靶的出射中子能谱的FLUKA和Geant4模拟研究

在ADS散裂靶系统的优化设计中,蒙特卡罗方法结合可靠的散裂反应理论模型进行中子学计算具有重要的作用。本工作利用Geant4程序中的INCLXX模型、BIC模型以及BERT模型和FLUKA程序分别模拟了597 MeV和1 500 MeV质子轰击薄铅靶不同出射角度的中子双微分截面,500,1 500 MeV质子轰击厚铅靶不同出射角度的中子双微分产额,以及400,600,800,1 000和1 200 MeV质子轰击厚钨靶在反角方向（175 °）的中子双微分产额,并与实验数据进行比较。研究表明,对于薄铅靶,Geant4程序的INCLXX模型和FLUKA程序模拟结果与实验符合得更好。能量在10～40 MeV范围内,BIC模型模拟结果明显高于实验数据,而BERT模型模拟结果略微低于实验数据。对于厚铅靶,在40 MeV左右所有的模拟结果都低于实验数据。对于厚钨靶,Geant4程序的BIC模型和FLUKA程序与实验数据符合得较好,INCLXX模型在能量高于60 MeV时模拟结果低于实验数据,BERT模型与实验数据差异较大。总体来看,Geant4程序的INCLXX模型和FLUKA程序进行ADS散裂靶相关的中子学的计算是合理和可靠的。The reliable Monte Carlo simulation codes coupled with nuclear reaction models play an important role in the neutronic calculation for the design and optimization of the ADS spallation target. In this work, the double differential cross sections at different angles produced from a thin lead target bombarded with 597 and 1 500 MeV protons, the neutron energy spectra at different angles produced from a thick lead target bombarded with 500 and 1 500 MeV protons, and the neutron energy spectra in the backward direction(175°) produced from a thick tungsten target bombarded with 400, 600, 800, 1 000 and 1 200 MeV protons are calculated with the Geant4 code coupled INCLXX, BIC and BERT models and the FLUKA code. The calculations are compared with the available experimental data. The results show that, for the thin lead target, the calculations with the Geant4 coupled INCLXX model and FLUKA code well reproduce the experimental results. In a energy range from 10 to 40 MeV, BIC model obviously overestimates the experimental results, and BERT model slightly underestimates the experimental results. For the thick lead target, all of the calculations underestimate the experimental results around 40MeV. For the thick tungsten target, the Geant4 coupled BIC model and FLUKA code well reproduce the experimental results. INCLXX model underestimates the experimental results above 60 MeV. BERT model bad reproduces the experimental results. Overall, the neutronic calculations with the Geant4 code coupled INCLXX model and FLUKA code for the ADS spallation target is reasonable and reliable.     

基于FLUKA计算压力容器快中子注量的可行性研究

基于知识产权的考虑,通过与蒙特卡罗程序MCNP计算结果比对,研究使用FLUKA程序替代MCNP程序进行反应堆压力容器快中子注量计算的可行性。通过修改和调用子程序对次级粒子堆栈进行操作,解决了关闭裂变中子这一关键问题,FLUKA程序的计算结果与MCNP程序的计算结果相对偏差在5%以内,符合得较好,证明使用FLUKA程序替代MCNP程序用于计算反应堆压力容器快中子注量在技术上是可行的。     

X-Ray,Gamma, and Neutron Radiation Tests on Epoxy-Ferrochromium Slag Composites by Experiments and Monte Carlo Simulations

Radiation shielding effects of ferrochromium slag loading hardened epoxy resin samples were investigated. Five different samples including different percentages of epoxy resin and ferrochromium slag were produced. X-ray, gamma ray, and neutron particle transmission experiments were performed for epoxy-ferrochromium slag composites. Also, FLUKA Monte Carlo simulations were made to obtain absorbed doses. As a result, radiation shielding performance increases with increasing ferrochromium slag additive in epoxy.     

Monte Carlo simulations of bremsstrahlung photon yields from thin targets with electron beams between 10 and 40 MeV

A linear accelerated electron beam is a powerful source of highly energetic photons that can be used for various nuclear applications. In this work, the bremsstrahlung photon yields from thin targets such as Ta, Nb, Cu and Al have been calculated using the FLUKA simulation code. The simulation calculations were performed for incident electrons with energies in the range of 10–40 MeV and targets with thicknesses between 4×10^?4 and 10^?3 radiation lengths.