Simulation study of neutrino nucleus crosssection measurement in a segmented detectorat a spallation neutron source

Knowledge of ν_e-Fe/Pb differential cross sections for ν_e energy below several tens of MeV scale is believed to be crucial in understanding supernova physics. In a segmented detector at a spallation neutron source, ν_e energy reconstructed from the electron range measurement is strongly affected because both multiple scattering and electromagnetic showers occur along the electron passage in target materials. In order to estimate these effects, a simulation study has been performed with a cube block model assuming perfect tracking precision. The energy spectrum distortion is observed to be proportional to the atomic number of the target material. Feasibility of unfolding the distorted ν_e energy spectrum is studied for both Fe and Pb. An evaluation of the statistical accuracy attainable is therefore provided for a segmented detector.     

太赫兹目标RCS缩比测量技术

论述了国外基于微波上倍频、激光下变频、THz时域光谱三种典型太赫兹波目标雷达散射截面(RCS)缩比测试系统的构成、技术特点和应用范围。采用固态器件、基于微波上倍频技术集成研制了宽带太赫兹低频端目标RCS测量系统,采用基于扫频的时域法RCS测量技术和小角度旋转目标雷达合成孔径（ISAR）成像方法对小目标进行了电磁散射特性测量,获取了目标RCS和二维散射成像信息。     

Differential phase contrast with a segmented detector in a scanning X‐ray microprobe

Scanning X‐ray microprobes are unique tools for the nanoscale investigation of specimens from the life, environmental, materials and other fields of sciences. Typically they utilize absorption and fluorescence as contrast mechanisms. Phase contrast is a complementary technique that can provide strong contrast with reduced radiation dose for weakly absorbing structures in the multi‐keV range. In this paper the development of a segmented charge‐integrating silicon detector which provides simultaneous absorption and differential phase contrast is reported. The detector can be used together with a fluorescence detector for the simultaneous acquisition of transmission and fluorescence data. It can be used over a wide range of photon energies, photon rates and exposure times at third‐generation synchrotron radiation sources, and is currently operating at two beamlines at the Advanced Photon Source. Images obtained at around 2 keV and 10 keV demonstrate the superiority of phase contrast over absorption for specimens composed of light elements.     

太赫兹目标RCS缩比测量技术

论述了国外基于微波上倍频、激光下变频、THz时域光谱三种典型太赫兹波目标雷达散射截面(RCS)缩比测试系统的构成、技术特点和应用范围。采用固态器件、基于微波上倍频技术集成研制了宽带太赫兹低频端目标RCS测量系统,采用基于扫频的时域法RCS测量技术和小角度旋转目标雷达合成孔径（ISAR）成像方法对小目标进行了电磁散射特性测量,获取了目标RCS和二维散射成像信息。     

截面依赖动量转移条件下屏蔽效应的理论研究

利用BBK模型及修正方案, 对电子入射电离氦原子(e,2e)反应过程中截面依赖动量转移条件下的三重微分散射截面(TDCS)进行了理论计算, 把计算结果与实验测量结果进行比较, 分析了截面结构, 并研究了末通道屏蔽效应对三重微分截面所产生的影响.     

激光辅助电子-He原子散射 --一种特殊情况下的微分截面的计算

利用二阶微扰论的方法计算了动量转移与激光场的偏振方向垂直条件下,电子－Ｈｅ原子碰撞的自由－自由跃迁的单光子和两光子交换的微分截面,结果与最近的实验结果符合得很好。     

Measurement of fast neutron induced fission cross section of thorium using Lexan plastic track detector

Fission-track registration characteristics of Lexan solid state nuclear track detectors have been used to measure the fast neutron induced fission cross section of²³²Th. The fast neutrons (?14.2MeV) were produced with the help of an AN-400 model Van-de-Graaff accelerator at Banaras Hindu University laboratory using³H(²H,n)⁴He reaction and were used to irradiate the fissile target deposited on the plastic detector. The track densityT, registered on the plastic detector is related to the fission cross sectionσ _f, through the relationT=knσ _føt wheren is the number of fissile atoms per cm² in the deposit, ø is the neutron flux,k is fission track registration efficiency andt is the time of irradiation. The fission cross sectionσ _f of²³²Th, relative to the well measured fission cross section of²³⁸U, was found to be 0.36±0.04 barn.     

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.     

1KeV电子入射单电离氦原子三重微分散射截面的理论研究

用3C模型、DS3C模型对1KeV电子入射氦原子(e,2e)反应中的三重微分散射截面进行了计算,并将理论计算结果与实验数据进行了比较,研究了各种屏蔽效应对散射平面内以及垂直平面内三重微分散射截面的影响,并对三重微分散射截面变化规律进行了探讨.结果表明:各种屏蔽效应对散射平面内三重微分散射截面的贡献可以忽略;而在垂直平面内,这些效应对三重微分散射截面结构存在较强影响;另外,末态出射电子与靶核的相互作用直接影响散射平面内和垂直平面内截面的结构及其变化规律.     

（n,2n）反应实验研究中的中子准直器设计

用3He球形4中子探测器,通过直接反应法可以对核素的（n,2n）反应截面进行测量。在此类实验中,要求对中子束进行很好的准直。好的准直器设计要求能够提高样品处的中子注量率的均匀性,同时保证中子束流边缘处的下降幅度,能够降低低能中子所占份额。本工作采用FLUKA和MCNPX对圆柱形准直器、单锥形准直器及三种不同斜率的双锥形准直器对中子注量率的均匀性和低能中子所占份额进行了对比研究,结果表明,低斜率的双锥形准直器可以满足实验对这两方面的要求。同时,在有样品和无样品两种条件下,对探测系统经由这五种不同准直器准直后的中子束流的响应做了对比,结果显示,经过低斜率的双锥形准直器准直的中子束流,探测系统在有样品时表现为较高的计数率,在无样品时表现为较低的本底。除此之外,对准直器出口处的斜率对准直效果的影响也做了比较。最终中子准直器选用为这种低斜率的双锥形准直器,材料选用为紫铜、不锈钢、聚乙烯和铅。准直孔开口处直径为2.64 cm,长度为137 cm,经准直后样品处的中子束斑直径为3.2 cm。     

Transmission measurement of photo-absorption cross section of aluminum in soft X-ray region of 50 to 250 eV

The photo-absorption cross section of aluminum was obtained from the ratio of transmission of aluminum thin-films with different area densities from 50 to 250 eV with synchrotron radiation monochromatic beam.Two samples with different area densities were used to minimize the uncertainty caused by the sample surface oxidation and systematic factors of the X-ray source,beamline,and detector.The experimental results are in good agreement with the published data and FEFF program calculations in general.     

Transmission measurement of photo-absorption cross section of aluminum in soft X-ray region of 50 to 250 eV

The photo-absorption cross section of aluminum was obtained from the ratio of transmission of aluminum thin-films with different area densities from 50 to 250eV with synchrotron radiation monochromatic beam. Two samples with different area densities were used to minimize the uncertainty caused by the sample surface oxidation and systematic factors of the X-ray source, beamline, and detector. The experimental results are in good agreement with the published data and FEFF program calculations in general.     

同位旋相关的核子碰撞截面的不同形式与核子的集体流

在详细比较同位旋相关的核子-核子碰撞截面的几种常用形式的基础上,利用IBUU模型, 分别对具有相同质量的⁶⁰Ca+⁶⁰Ca和⁶⁰Ni+⁶⁰Ni的中能重离子碰撞进行了模拟计算,定量地分析了碰撞过程中不同形式的同位旋相关的核子-核子碰撞截面对于核子的快度分布和集体流的影响.结果显示: 不同形式的核子碰撞截面,可以给出相差较大的核子的快度分布和横向流, 但在同一种截面形式下,对称势的变化对横向流的影响较小.这表明在新的动量相关的对称势下, 中能重离子碰撞中集体流对于截面的敏感性依然成立;同时表明,在相同的碰撞截面和对称势形式下, 当入射能量在平衡能附近时,入射粒子的中质比对核子在平面流的影响较大,反之,影响较小.     

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.     

Effective response and scattering cross section of spherical inclusions in a medium

The Maxwell-Garnett theory for a right-handed homogeneous system is extended in order to investigate the effective response of a medium consisting of low density distributed 3-dimensional inclusions. The polarisability factor is modified to account for inclusions with binary layered volumes and it is shown that such a configuration can yield doubly negative effective permittivity and permeability. Terms representing second-order scattering interactions between binary inclusions in the medium are derived and are used to reformulate conventional effective medium theory. In the appropriate limit, the one-body theory of Maxwell-Garnett is recovered. The scattering cross section of the spherical inclusions is determined and comparison is made to homogeneous dielectric scatterers in the Rayleigh limit. It is found that the scattering resonances can be manipulated using the inclusion parameters. Furthermore, the effect that two-interacting spherical inclusions in a medium have on the scattering cross section is investigated via higher order dipole moments while the issue of reducing the scattering cross section to zero is also examined.     

Triple differential cross section in (e, 2e) collisions for sodium in a coplanar symmetric geometry

The triple differential cross sections for (e, 2e) ionization of sodium in a coplanar symmetric geometry have been studied in distorted wave Born approximation with the modified semiclassical exchange potential. The present calculations improve the agreement between the theoretical and experimental results. The post-collision interaction and target polarization effects have also been studied. In addition, the variation trends of the shape and ratio for the forward and backward scattering peaks have been discussed. Besides, the small bump observed between these two peaks has been analyzed by the interaction between active electron and passive electrons.     

A formula used to subtract the effect of gamma-ray of the others to that of measured reaction in measurement of cross section of nuclear reaction and its application

According to the regulation of growing and decay of artificial radioactive nuclide, a formula used to subtract the effect of characteristic γ-ray of the others to that of measured reaction was deduced. And then the cross sections of ¹²⁰Te (n,2n)^119mTe reaction induced by neutrons around 14~MeV were measured by activation relative to the ⁹³Nb (n, 2n) ^92mNb. In the process of the cross sections measured to be calculated, it was subtracted that the effect of characteristic γ-ray of ¹²⁶Te (n, p) ¹²⁶Sb to that of measured ¹²⁰Te (n, 2n) ^119mTe reaction using the formula deduced. The experimental results were (689±37) and (750±41) mb at the neutron energies of (13.5±0.3) and (14.6±0.3)MeV, respectively. Measurements were carried out by γ-detection using a coaxial HPGe detector. As samples, spectroscopically pure tellurium powder has been used. The fast neutrons were produced by the T(d, n)⁴He reaction. The neutron energies in these measurements were determined by the method of cross-section ratios between ⁹⁰Zr (n, 2n) ^89m+gZr and ⁹³Nb (n, 2n) ^92mNb reactions.     

A formula used to subtract the effect of gamma-ray of the others to that of measured reaction in measurement of cross section of nuclear reaction and its application

Abstract According to the regulation of growing and decay of artificial radioactive nuclide, a formula used to subtract the effect of characteristic γ-ray of the others to that of measured reaction was deduced. And then the cross sections of 120Te (n, 2n)119mTe reaction induced by neutrons around 14 MeV were measured by activation relative to the 93Nb (n, 2n)92mNb. In the process of the cross sections measured to be calculated, it was subtracted that the effect of characteristic γ-ray of 126Te (n, p)126Sb to that of measured 120Te (n, 2n)119mTe reaction using the formula deduced. The experimental results were (689±37) and (750±41) mb at the neutron energies of (13.5±0.3) and (14.6±0.3) MeV, respectively. Measurements were carried out by γ-detection using a coaxial HPGe detector. As samples, spectroscopically pure tellurium powder has been used. The fast neutrons were produced by the T(d, n)4He reaction. The neutron energies in these measurements were determined by the method of cross-section ratios between 90Zr (n, 2n) 89m+gZr and 93Nb (n, 2n) 92mNb reactions.     

共面不对称条件下低能电子碰撞电离Ar(3p)的三重微分截面

采用修正的扭曲波玻恩近似方法, 在共面不对称几何条件下, 计算了能量为70.8 eV电子与Ar(3p)碰撞电离的(e, 2e)三重微分截面, 并与最新实验数据进行了比较. 结果表明电子交换效应和后碰撞相互作用在低能电子碰撞的(e, 2e)过程中起着重要作用. 关键词： (e,2e)三重微分截面 扭曲波玻恩近似 后碰撞相互作用 电子交换效应     

Effect of relativistic elliptical beam modulation on excitation of surface plasma waves in a magnetized dusty plasma column with elliptical cross section

Abstract

The excitation of surface plasma waves due to the interaction of an elliptical relativistic density modulated electron beam with the magnetized dusty plasma column with elliptical cross-section has been studied. The dispersion relation of surface plasma waves has been retrieved from the derived dispersion relation by considering that the beam is absent and there is no dust in the plasma elliptical cylinder. It is shown that the Cherenkov and fast cyclotron interactions appear between the beam and eigen-modes of plasma column. The growth rate of the instability increases with the beam density and modulation index as one-third power of the beam density in Cherenkov interaction and is proportional to the square root of beam density in fast cyclotron interaction. The numerical results and graphs are presented, too.