基于中国散裂中子源反角白光中子束线的天然锂中子全截面测量

锂是熔盐堆燃料载体盐的主要材料之一,其中子核反应截面数据是熔盐堆芯中子物理设计及堆芯长期安全运行中的重要基础数据.本工作基于中国散裂中子源反角白光中子束线(CSNS Back-n)飞行时间谱仪,利用中子全截面测量谱仪(NTOX),采用透射法测量了天然锂中子全截面.实验中,中子飞行距离约为76.0 m,采用15.0 mm和8.00 mm两种厚度的天然锂金属样品,在0.4 e V—20 Me V中子能量范围内测得了统计计数较好的中子全截面.特别是在ke V及以下能区增补了实验数据,为锂的核数据评价工作提供了更加丰富和可靠的实验数据.在此基础上,采用1/v律和R矩阵理论对Me V以下能区的新测量数据进行了理论分析,获得了7Li和6Li在260 ke V能量附近的中子共振参数.     

旋转靶强流中子源及其应用

 一、旋转靶强流中子源的现状一般讲,强流中子源是指中子注量在4π空间中一秒钟内具有近于或等于或大于1×10¹²个中子的辐射场。它可以利用反应堆得到平均能量为1MeV的中子;利用高能电子或质子加速器可得能量为数MeV的中子。国内外最近一、二十年来,在强流中子源方面做了大量的研究实验工作,除了利用加速器的（d-Be）,（p-Be）和（d-D）反应产生中子外,大量的工作集中在用（d-T）反应并使用高速旋转的氚靶以产生强流中子场。     

InP中子位移损伤效应的Geant4模拟

磷化铟(In P)作为第二代化合物半导体材料,抗辐照能力强,光电转换效率高,在光子领域和射频领域具有优势.大气空间中, In P半导体器件受大气中子辐照影响,器件性能发生退化.本文采用蒙特卡罗模拟软件Geant4对In P中子辐照效应进行模拟,得到In P中不同能量中子产生的位移损伤初态分布.结果表明:在微米量级内,非电离能量损失(NIEL)随深度均匀分布,在厘米及更高量级上, NIEL随着入射深度的增大而降低,当靶材料足够厚时可以降低至零;分析1—20 Me V中子入射3μm In P产生的NIEL及其随深度分布,发现NIEL随入射中子能量的增加呈现出先升后降的趋势,该趋势主要由非弹性散射反应产生的初级反冲原子(PKA)造成;分析1—20 Me V中子入射3μm In P产生的PKA种类、能量,发现In/P的PKA占比较大,是产生位移损伤的主要因素,中子能量越高, PKA的种类越丰富, PKA最大动能越大,但PKA主要分布在低能部分.研究结果对In P基5G器件在大气中子辐射环境中的长期应用具有理论和指导价值.     

基区表面势对栅控横向PNP晶体管中子位移损伤的影响

通过在常规横向PNP晶体管基区表面氧化层上淀积栅电极,制作了可以利用栅极偏置调制基区表面势的栅控横向PNP晶体管。对无栅极偏置电压和偏置电压分别为-10V和10V的栅控横向PNP晶体管,在西安脉冲反应堆上开展注量为2×1012,4×1012,6×1012,8×1012,1×1013 cm-2的中子辐照实验,研究基区表面势的增加和降低对栅控横向PNP晶体管中子位移损伤退化特性的影响。研究结果表明,基区表面势的增加引起栅控横向PNP晶体管共射极电流增益倒数的变化量随辐照中子注量的退化速率增加,基区表面势的降低对位移损伤退化速率无明显影响。     

电子束在VO_2薄膜中引起的价态、相结构和光学性能的改变

利用能量为 1 .7Me V,注量分别为 1 .2 5× 1 0 13 /cm2 ,1 .2 5× 1 0 14 /cm2 ,1 .2 5× 1 0 15/cm2 的电子束辐照 VO2 薄膜 ,采用 XPS,XRD等测试手段对电子辐照前后的样品进行分析 ,并研究了电子辐照对样品相变过程中光透射特性的影响。结果表明电子辐照引起 VO2 薄膜中 V离子出现价态变化现象 ,并使薄膜的 X射线衍射峰发生变化。电子辐照在样品中产生的这些变化显著改变了 VO2 薄膜的热致相变光学特性     

300#研究堆寿期内上联箱铝材中子注量分析

材料在辐照过程中所受的中子注量是辐照性能研究中的一个重要参数。上联箱铝材作为300#研究堆关键结构材料,经历了从反应堆首次临界到退役的全过程,极具材料辐照效应研究价值。为获取整个反应堆运行寿期内的上联箱中子注量水平,须克服堆芯装载变化频繁与堆芯不断扩大装载两大关键难点,故提出了堆芯归并等效计算方法。通过该方法的成功应用,得到了300#研究堆寿期内上联箱铝材的中子注量,并进行了误差分析。     

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。     

快中子束应用研究现状

在中子物理中,一般将能量大于1MeV的中子称为快中子。它可以从裂变堆、同位素中子源获得,也可以由各种加速器获得。考虑到便于应用、降低费用等因素,目前多由小型加速器产生快中子,其中14MeV 中子源居多数。     

基于4MV静电加速器的高温辐照装置研制及离子辐照初步实验北大核心CSCD

为了模拟钍基熔盐堆(TMSR)材料的中子辐照损伤,基于中国科学院上海应用物理研究所(SINAP)的4 MV静电加速器,研制了一台专用的离子束辐照装置。装置主要由束流传输线和高温、高真空靶室组成。束流传输线装有用于束流磁场扫描和束流监测的设备。装置可提供H^+,He^+,Ar^+等束流用于离子束辐照,束流最高能量4 Me V,最大流强2μA。辐照温度范围为液氮温度至950℃。辐照面积最大为30 mm×30mm。装在靶室的由旋转铝片构成的变能器对束流能量进行调制,可以在样品中得到均匀的辐照损伤。初步的实验结果表明,装置适用于高温合金及其他熔盐堆材料的辐照损伤研究。     

基于紧凑型D-D中子发生器的热中子照相慢化准直器设计

热中子照相是一种重要的无损检测技术,是X射线照相技术的重要补充,小型化热中子照相系统有重要研究应用前景。基于紧凑型D-D中子发生器,采用蒙特卡罗程序MCNP-4C,通过中子和γ射线的输运模拟,完成了热中子照相慢化准直器的模拟研究与设计。慢化准直器准直比约为3.58,模拟研究结果显示,在D-D中子发生器中子产额大于5×10⁸ n/s条件下,样品平面内热中子注量率可大于10³ n/(cm²·s),准直中子束中热中子占比可大于74%,在Φ70 mm的照射视野范围内,热中子注量的不均匀度约为7.3%,基本满足热中子照相的成像要求。     

CFETR磁体系统的中子学计算及活化分析

用蒙特卡洛中子输运程序(MCNPX)对中国聚变工程实验CFETR超导磁体进行中子学输运计算,利用欧洲活化计算程序FISPACT对其进行活化计算分析,针对计算结果重点分析了磁体系统的中子学剂量分布以及活化情况。计算结果表明,中子能量通量最大处出现在聚变堆内侧线圈处,为3.97×10¹⁴ MeV•m^–2,在该条件下超导线圈可以满足设计要求。停机后磁体组件的活度为3.33×10¹⁰Bq•kg^–1,停机10年后下降2个数量级达到6.14×10⁸Bq•kg^–1。研究结果验证了所使用的CFETR 3维模型满足初步设计条件。     

快重离子辐照对非晶态SiO2薄膜光致发光谱的影响

用湿氧化法在单晶硅表面生长了非晶态SiO2薄膜,再用高能Pb和Xe离子对薄膜进行辐照,最后用荧光光谱分析了辐照参数(剂量、电子能损值)与发光特性改变的相关性.研究发现,快重离子辐照能显著影响薄膜的发光特性,进一步分析显示,辐照导致了SiO2薄膜内O-Si-O缺陷、缺氧缺陷和非桥式氧空位缺陷的产生,且缺氧缺陷和非桥式氧空...     

THE EXCITATION OF 9.5 MeV LEVEL OF 13C IN QUASI-Δ33 DOORWAY STATE MODEL

We have studied the excitation mechanism of 9.5 MeV Level of ¹³C in ¹³C(π^±,π^1±)¹³C (9.5 MeV) inelastic scattering in the framework of Quasi-X33 Doorway State. Model .Assuming. the transition to 9.5 MeV state is of a pure neutron has received satisfactory agreement with experiment. The results strongly suggest that the spin and parity assignment of state,9.5 MeV of ¹³C should be Jπ=9/2⁺.     

Proton radiation effect on GaAs/AlGaAs core–shell ensemble nanowires photo-detector

We demonstrate that the GaAs/AlGaAs nanowires(NWs) ensemble is fabricated into photo-detectors. Current–voltage(I–V) characteristics are measured on Ga As/Al Ga As core–shell ensemble NW photo-detectors at room-temperature before and after 1-MeV proton irradiation with fluences from 1.0 × 10~(13) cm~(-2) to 5.0 × 10~(14) cm~(-2). The degradation of photocurrent suggests that the point defects induced by proton radiation could cause both carrier lifetime and carrier mobility to decrease synchronously. Comparing with a GaAs quantum well, the degradations of light and dark current for the irradiated NWs photo-detector indicate that NWs material is a preferable potential candidate for space applications.     

基于D-T紧凑型中子源的快中子照相准直屏蔽体设计及中子束特性模拟研究

中子照相是一种重要的无损检测技术,它能用于火工产品、毒品和核燃料元件等的检测。基于紧凑型D-T中子发生器,完成了一个用于快中子照相的准直屏蔽体系统（BSA）的物理设计。根据D-T中子源的能谱和角分布建立了中子源模型,采用MCNP4C蒙特卡罗程序,模拟了准直屏蔽体系统中中子和γ射线的输运,准直中子束相对于单位源中子的中子注量可以达到9.30×10-6 cm-2,准直中子束中主要是能量大于10 MeV的快中子;在设置的样品平面直径14 cm的照射视野范围,准直束中子注量的不均匀度为4.30%,准直束中中子注量与γ注量的比值为17.20,中子通量和中子注量比值J/Φ为0.992,说明准直中子束有好的平行性;准直屏蔽体外的泄露中子注量率与准直束中子注量率相比降低了2个量级。所设计的准直屏蔽体能满足快中子照相的要求。Neutron radiography is an important nondestructive testing technique. It can be used to detect the explosive devices, drug and the nuclear fuel element, etc. A beam-shaping-assembly (BSA) based on a compact D-T neutron generator is designed for fast neutron radiography in this paper. D-T neutron source model is constructed based on the neutron energy spectrum and angular distribution data. The transportation of neutron and γ-ray in the BSA is simulated using MCNP4C code. The neutron fluence of the collimated neutron beam with respect to the neutron source of the unit source is 9.30×10-6 cm-2. The collimated neutron beams is mainly fast neutrons with energies greater than 10 MeV. In the irradiation field range with a diameter of 14 cm, the neutron fluence uniformity of the collimated beam is 4.3%, the ratio of the neutron fluence to the gamma fluence in the collimated beam is 17.20, and the neutron flux and the neutron fluence ratio (J/Φ) is 0.992 which indicates that the collimated neutron beam has good parallelism. The leakage neutron fluence in outside of BSA is two orders of magnitude lower than that of the collimated neutron beam. The designed BSA can meet the need of fast neutron radiography.     

Radiation effects of electrons and protons on the ceramic oxide superconductor YBaCuO

The irradiation of the high T_c superconducting material YBaCuO has been carried out by using 200 keV proton, and 400 keV and 8 MeV electron beams. The temperature of zero resistance increases from 86.7 to 89.8 K with proton implantation while 8 MeV electron irradiation reduces the zero resistance temperature by 3 K with an irradiation dose of 2.25×10¹⁴e^-/cm². However, wich an irradiation dose of 1.35×10¹⁵e^-/cm² the 8 MeV electron beam can make the superconductor become insulating. The in situ examination of a high resolution transmission electron microscope has proved that the amorphous region in the system has ordered arrangement whereas the crystalline region turns disordered under 400 keV electron irradiation with very high doses up to 10²⁶ e^-/cm². The experiments demostrate that proton and electron irradiations exhibit quite different effects both in its structure and property.     

In0.53Ga0.47As/InP量子阱与体材料的1 MeV电子束辐照光致发光谱研究

为获得对In_0.53Ga_0.47As/InP材料在电子束辐照下的光致发光谱变化规律, 开展了1 MeV电子束辐照试验, 注量为 5×10¹²-9×10¹⁴ cm^-2. 样品选取量子阱材料和体材料, 在辐照前后, 进行了光致发光谱测试, 得到了不同结构In_0.53Ga_0.47As/InP材料在1 MeV电子束辐照下的不同变化规律; 对比分析了参数退化的物理机理. 结果显示: 试验样品的光致发光峰强度随着辐照剂量增大而显著退化. 体材料最先出现快速退化, 而五层量子阱在注量达到6×10¹⁴ cm^-2时, 就已经退化至辐照前的9%. 经分析认为原因有: 1)电子束进入样品后, 与材料晶格发生能量传递, 破坏晶格完整性, 致使产生的激子数量减少, 光致发光强度降低; 电子束辐照在材料中引入缺陷, 增加了非辐射复合中心密度, 导致载流子迁移率降低. 2)量子阱的二维限制作用使载流子运动受限, 从而能够降低载流子与非辐射复合中心的复合概率; 敏感区域截面积相同条件下, 体材料比量子阱材料辐射损伤更为严重. 3)量子阱的层数越多, 则异质结界面数越多, 相应的产生的界面缺陷数量也随之增多, 辐射损伤越严重.     

Study on irradiation-induced defects in GaAs/AlGaAs core–shell nanowires via photoluminescence technique

To gain a physical insight into the radiation effect on nanowires(NWs), the time resolved photoluminescence(TRPL)technique is used to investigate the carrier dynamic behaviors in GaAs/AlGaAs core–shell NWs before and after 1-MeV proton irradiation with fluences ranging from 1.0 × 10~(12) cm~(-2) to 3.0 × 10~(13) cm~(-2). It is found that the degradations of spectral peak intensity and minority carrier lifetime show similar trends against irradiation fluence, which is closely related to the displacement defects induced by irradiation. We also find that the proton irradiation-induced defects behave as Shockley–Read–Hall(SRH) recombination center trapping free carriers. Finally, the defect concentration could be estimated through measuring the minority carrier lifetime.     

Search for a light neutral particle in the decay of the 3.68 MeV state in C

A search is made for a short lived neutral particle, ø, in the decay of the 3.68 MeV (3/2^-) state in ¹³C. No evidence for such a particle with a rest mass in the region of 1.7–2.0 MeV/c² is found with a limit on the branching ratio Γ _ø/Γ_γ7×10 ⁻⁵. An upper limit of 10⁻⁶ is placed for the coupling of such a particle to proton/neutron.     

Effects of 230 MeV Au irradiation on Bi2Sr2CaCu2Ox

Bi₂Sr₂CaCu₂O_x tapes were irradiated using 230 MeV Au¹⁴⁺ ions. Columnar defects were presumably produced due to irradiation. Zero-field-cooling (ZFC) magnetization increased up to a fluence of 1.6 × 10¹¹ Au⁺/cm², but field-cooling (FC) magnetization decreased, indicating the strong pinning effects resulting from the columnar defects. The critical current density as well as the irreversibility field, obtained from the hysteresis loops, were enhanced. Irreversibility fields are fitted by H_irr = A exp(−T/T_A). An effective activation energy for flux motion was obtained from the measurements of magnetization relaxation. The features of flux pinning as a result of the columnar defects were compared with those of point defects brought about by 120 MeV O⁷⁺ irradiation.