基于150 MeV电子束的光中子特性模拟分析

高能中子源是研究高能太空宇宙射线中子对人体和电子仪器辐射损伤的必备装置,基于高能电子加速器的光中子源是目前能够提供较高能量白光中子的方式之一。本工作以清华大学先进加速器实验室的激光电子加速器束流参数为基础,借助Geant4对产生的光中子的能量特性、产额特性、角分布特性、时间特性进行了分析。模拟结果表明,Φ2 cm×2 cm的圆柱体Ta靶时,150 MeV电子束流可产生最高能量约为110 MeV、中子产额约为1.2×10~5n/10~7e-、出射时间在0~100 ns之间呈负指数分布的几乎各向同性的光中子。根据拟合的中子能量-出射时间离散指数函数,估算得到对产生的1~100MeV中子,在飞行距离为5m时中子飞行时间的时间分辨率好于2.23%。本工作为该加速器的光中子产生和实验测量工作提供了参考依据。     

12MeV无损检测用电子直线加速器靶的验证计算

本文研究12MeV无损检测用电子直线加速器靶的验证计算。首先通过具体分析无损检测用电子直线加速器中电子与靶相互作用的物理机理,由经验公式计算推得最佳靶厚及对应的靶产额、剂量率分布、X光子的转换效率;其次运用MCNP对常用靶材W、Au、Ta产生的X光子剂量率分布和转换效率进行对比计算,确定最佳靶材及靶厚;最后与实验结果对比,验证了靶计算过程的正确性。     

13 100MeV回旋加速器剥离引出系统研制

100MeV回旋加速器加速H^-离子，要求引出束流能量为75～100MeV、束流强度为200μA的质子束流，因此决定采用剥离引出。本工作依据100MeV主磁场数据和平衡轨道数据，通过理论研究，计算100MeV回旋加速器不同能量束流引出剥离点的位置；着重计算分析70～100MeV能量的束流剥离引出的光学特性；通过理论计算确定剥离膜各项参数；完成剥离靶及其伺服驱动装置的设计；对真空系统、控制系统等相关专业提出明确的工艺流程和技术要求。最终确定100MeV强流质子回旋加速器双向引出系统初步设计。     

10MeV高能大功率电子辐照加速器研制

辐照杀菌是基于电离辐射在物质内经过直接和间接作用引起生物体内DNA失活的一种生物效应。辐照灭菌使用的射线可以是放射性同位素源产生的γ射线、加速器产生的高能电子束或电子束打靶而产生的X射线。目前，以电子加速器产生的高能电子束灭菌方法正在成为发展趋势。因此，核技术所电子直线加速器研究室和原子高科股份有限公司开展了10MeV、15kW电子辐照加速器装置的研制工作。     

~7Be和~7Li注入玉米种子的示踪研究

进行了用HI-13串列加速器产生的33MeV和14MeV~7Be放射性离子束照射玉米种子的研究,~7Be在种皮的沉积份额分别为58％和94.5％,在胚体中的沉积份额分别为42％和5.5％。按运动离子射程公式计算,14MeV的~7Be离子束在种子中的射程只有30μm左右,不能直接穿过75～135μm厚的种皮。事实说明离子注入种子有更复杂的机制。试验还用36MeV剂量为1.6×10~(15)离子/cm~2的~7Li离子束照射玉米种子,剥皮前后也都探测到了~7Be离子的存在,~7Be在胚体中沉积份额达12％,用放射性自显影方法也证实了~7Be在种子内的存在。~7Be属于内靶核反应~1H(~7Li,~7Be]n的产物。~7Li束流是进行生物诱变研究的理想束流,它通量高,诱变机制不仅有能量、质量和电荷的作用,还有内靶核反应效应,预期有较高的诱变频率,有希望诱变出自然库中尚没有的突变体。     

CIAE Application of Patent in 2004

高气压组织等效电离室内中子（尤其是高能中子）的输运过程是中子、光子、质子以及电子等粒子的复杂的偶合输运过程，使用Geant4程序模拟该输运过程，并在Linux6．2操作系统下利用Geant4软件计算了有铝层和无铝层，次外层材料为A—150组织等效材料，厚度分别为2、5、10、20mm，平行入射的单能中子的能量分别为1、100、500keV和2、10、14、20、30、50、80、100MeV时，以及有铝层、次外层材料为聚乙烯，厚度为5mm，平行入射的单能中子的能量分别为0．0253eV、100eV、lkeV、100keV、500keV、2MeV、10MeV、14MeV、20MeV、30MeV、100MeV时的中子沉积能量。在中高能入射中子能量条件下，计算结果与实验数据基本符合。     

辐射消毒用电子束剂量场的研究

通过模拟跟踪2、3MeV电子在1cm纸层中的相互作用过程，记录统计电子及其辐射次级粒子在纸层及其周围环境的能量沉积。在假定病毒的致死当量剂量为200Sv的情况下，计算离柬靶不同距离的水介质（水模）的当量剂量。还给出了采用电子柬扫描传输带上的信件的方式，不同处理信件速率对加速器电子柬平均流强的要求。例如，要处理1t／h信件，要求2、3MeV电子柬流强为29、22μA。     

利用EGS4程序对复合靶的初步研究

为了使Ｘ射线能谱硬化以利于放射治疗国外中,高能医用加速器较多采用复合靶技术。本工作利用ＥＧＳ４程序对复合靶进行了初步感觉敢不同能量电子入射到复合靶所产生光子和电子的剂量分布。计算表明：采用结构为２ｍｍ厚钨靶片,再加上３ｍｍ厚的铜或１０ｍｍ厚的石墨作过滤片的复合靶后,电子剂量降为仅用钨靶剂量的１０％,光子剂量仍保持最佳值,且光子的平均能量得到提高。     

~7Be和~7Li注入玉米种子的示踪研究

进行了用HI-13串列加速器产生的33MeV和14MeV~7Be放射性离子束照射玉米种子的研究,~7Be在种皮的沉积份额分别为58％和94.5％,在胚体中的沉积份额分别为42％和5.5％。按运动离子射程公式计算,14MeV的~7Be离子束在种子中的射程只有30μm左右,不能直接穿过75～135μm厚的种皮。事实说明离子注入种子有更复杂的机制。试验还用36MeV剂量为1.6×10~(15)离子/cm~2的~7Li离子束照射玉米种子,剥皮前后也都探测到了     

150 MeV加速器驱动的反应堆系统固态金属靶优化研究

对150MeV加速器驱动的反应堆系统的固态靶进行了优化，就靶的几何设计、靶中泄漏中子产额、泄漏中子能谱及靶中能量沉积问题进行了研究。提出了钨饼与水组成的组合靶的概念，在中子产额影响较小的情况下，较好地解决了固态靶散热问题。     

Measurements of induced activity in concrete by secondary particles at forward direction produced by intermediate energy heavy ions on an Fe target

Spallation and neutron capture reaction rate distributions were measured using activation detectors inside a 90-cm thick ordinary concrete pile exposed to a field of secondary particles escaping a thick (stopping length) iron target bombarded with various intermediate energy ions, 230 MeV/u He, 400 MeV/u C, and 800 MeV/u Si. Activation detectors of aluminum, bismuth, gold, and gold covered with cadmium were inserted at various depths in the concrete pile. In addition, the distributions of activation reaction rate were simulated by FLUKA and PHITS Monte-Carlo codes. Generally, comparison of measured and calculated reaction rates show agreement within a factor of two. The experimental data will be useful for benchmarking Monte-Carlo radiation transport simulation code capabilities in estimating radioactivity induced in accelerator radiation shielding.     

Target optimization for a 10-MeV E-beam neutron converter

Accelerator-based target design and optimization is an approach for neutron generation. The target plays an important role for a neutron source on an electron accelerator. For optimizing a neutron source using 10 MeV electron beams of Rhodotron-TT200, Pb, Ta, or W alloys with Be were calculated as photo-neutron converter. The neutron yield, flux and energy were simulated using the MCNPX code. The results indicate that a 10 MeV electron beam is capable of producing high-intensity neutron flux of 1013n·cm–2·s–1 with average energy of 0.8 MeV.     

高能电子单粒子效应模拟实验研究

本文基于2 MeV自屏蔽电子加速器和10 MeV电子直线加速器,开展了电子单粒子效应实验研究,并分析了其机理。在保持入射电子能量不变的情况下,在±20%范围内改变器件的工作电压进行了单粒子翻转实验。实验结果表明：45 nm SRAM（额定工作电压1.5 V）芯片在电子直线加速器产生的高能电子照射下能产生明显的单粒子翻转,单粒子翻转截面随入射电子能量的变化趋势与文献数据相符合;电子引起的单粒子翻转截面随器件工作电压的变化趋势与理论预期一致,即工作电压越小,单粒子翻转临界电荷越小,翻转截面也越高。     

Basic information on new regulatory criteria requiring on-site emergency preparedness for accelerator facilities in Japan

For basic information on new regulatory criteria, the dose rate around a thick target bombarded by proton, electron, or carbon beam having incident energy of 10 MeV–50 GeV (per nucleon in case of carbon) was simulated using the PHITS Monte Carlo code. Based on this simulation, the benchmark which is ‘1 Sv/h at 1 m away from the beam line’ assuming 1% beam loss was evaluated, and compared with the criteria in France and Canada. Based on this evaluation, a new regulatory criteria has been established for requiring on-site emergency preparedness for accelerator facilities in Japan, which is required for the ion accelerator beyond the ion beam of 100 MeV/nucleon and 0.5 kW beam power, and the electron accelerator beyond the electron beam of 50 MeV energy and 1 kW beam power.     

基于多层吸收法的6 MeV电子能谱重建的研究

电子能谱的测量是电子加速器性能检测的重要环节。本文设计了一种新的测量方法--多层吸收法来对电子能谱进行测量,它是基于在辐照电子加速器上应用最多的射程法,加入Monte-Carlo模拟和迭代算法而重建出入射电子能谱的一种方法。该方法具有操作简便、测量准确、无需复杂设备等优点。本文用该方法对6 MeV加速器的电子能谱进行了测量,得到了较好的结果,且与磁谱仪的测量结果在误差范围内符合得很好,验证了其可行性。     

Measurement and Analysis of Neutron Spectra in Lithium Fluoride and Polytetrafluoroethylene Piles

For the assessment of neutron cross section data for fluorine, angular neutron spectra in the lithium fluoride (LiF) and polytetrafluoroethylene ((CF₂)n) piles were measured in the energy range from a few keV to a few MeV by the time-of-flight method with an electron linac, and the results were compared with those calculated by using nuclear data from JENDL-2 and ENDF/B-IV. Spatial distributions of neutron and X-ray fluxes were also measured in the test piles by the activation method, and the influence of photoneutrons generated in the sample material on the neutron spectrum in each pile was estimated. As a result, it was found that their influence on the neutron spectrum shape below 1 MeV was not so large as was necessary to be taken into account for the present assessment.

The calculated spectra using the JENDL-2 data and the ENDF/B-IV data show generally good agreement with those measured in both piles. However, both calculations underestimate the neutron fluxes around several 100 keV, and overestimate those below 100 keV, when they are normalized in the energy range of 10 keV～1 MeV. Large discrepancies are found between the shapes of the measured and calculated spectra around the resonances of fluorine cross section below 100 keV. The present measurements and analyses suggest that the reevaluations of the inelastic and elastic scattering cross sections below 1MeV and the resonance cross sections below 100 keV are necessary to reduce the observed discrepancies.     

光子注量到空气比释动能转换系数的Monte-Carlo模拟

本文采用蒙特卡罗程序EGS5模拟计算单位注量的10keV～10MeV的光子在空气中所产生的空气比释动能,并将计算结果拟合成公式。模拟计算结果与ICRP74号报告中建议值的相对偏差在±2.0%以内,与ICRU47号报告中建议值的相对偏差在±3.5%以内;拟合值与前者的相对偏差在±4.0%以内,与后者的相对偏差在±7.0%范围内。     

Calculation of photon shielding properties for some neutron shielding materials

The objective of the present study is to calculate photon shielding parameters for seven polyethylene-based neutron shielding materials. The parameters include the effective atomic number(Z_(eff)), the effective electron density(N_(eff)) for photon interaction and photon energy absorption,and gamma-ray kerma coefficient(kc). The calculations of Z_(eff)are presented as a single-valued and are energy dependent. While Z_(eff)values were calculated via simplistic powerlaw method, the energy-dependent Z_(eff)for photon interaction(Z_(PI-eff)) and photon energy absorption(Z_(PEA-eff)) are obtained via the direct method for energy ranges of 1 keV–100 GeV and 1 keV–20 Me V, respectively. The kccoefficients are calculated by summing the contributions of the major partial photon interactions for energy range of 1 keV–100 MeV. In most cases, data are presented relative to pure polyethylene to allow direct comparison over a range of energy. The results show that combination of polyethylene with other elements such as lithium and aluminum leads to neutron shielding material with more ability to absorb neutron and crays. Also, the kerma coefficient first increases with Z of the additive element at low photon energies and then converges with pure polyethylene at energies greater than 100 keV.     

厚铍靶9Be(d,n)反应中子产额测量

能量在3MeV以下厚靶D-Be反应的中子产额实验数据至关重要,但较为缺乏。本工作在北京大学4.5MV静电加速器上对氘束轰击厚铍靶的中子产额进行测量。对入射氘核能量在0.35~2MeV之间的若干能量点用长中子计数管进行了0°方向中子产额、中子角分布及中子总产额的测量。与已有的测量结果和经验公式进行了比较,并拟合出氘束轰击厚铍靶中子总产额的经验公式。     

SND-S1型液体闪烁体光输出的能量响应

采用不同能量的γ射线标准源及D-D、D-T核反应的单能中子源分别测定了新型液体闪烁体SND-S1的光输出随粒子能量的变化,采用Monte-Carlo程序Penelope模拟计算了¹³⁷Csγ射线的能量分布谱,最大康普顿电子能量的计算值和实验值相差2.7%。将实验结果与文献值作了比较,能量低于3MeV时,符合较好;能量高于6MeV时,略有差别。结果表明,液体闪烁体的光输出与电子能量呈线性正比关系,而与中子能量呈非线性关系。