探测系统γ能量响应标定技术

要对具有能谱分布的脉冲辐射场进行精密物理测量，就必须刻度出探测系统的γ能量响应。由于没有合适的系列单能γ辐射源，为此利用compton散射原理将强^60Co源释放出的γ射线转换为系列单能γ射线进行了探测系统γ能量响应的标定。     

光谱型椭偏仪对各向异性液晶层的测量

探讨了利用普通光谱型椭偏仪对各向异性液晶层进行综合性测量的可行性. 并利用法国Jobin Yvon公司的UVISEL SPME(Spectroscopic Phase Modulated Ellipsometer)光谱型椭偏仪测量了光学各向异性液晶层的折射率n_o和n_e及液晶层厚d，进一步利用椭偏仪在透射方式下测量了平行排列液晶层的光延迟特性Δnd，二者取得了很好的一致性，说明利用光谱型椭偏仪可以实现对光学单轴性液晶层及其他材料的测量，测厚精度为纳米量级. 关键词： 光谱型椭偏仪 各向异性 折射率 相位延迟     

液体闪烁体探测器γ射线测量研究

利用几种单能γ源对BC501A型液体闪烁体探测器进行能量刻度, 以得到探测器对电子的光输出响应函数。 介绍了用蒙特卡罗模拟法确定康普顿边缘所对应的电子能量的方法, 得到的结果与用半高点确定康普顿边缘方法所得的结果做了比较。 利用德国PTB开发的PHRESP蒙特卡罗程序计算出液体闪烁体探测器对各种单能γ射线的光响应矩阵, 阐述了利用γ射线响应函数矩阵和γ射线的反冲电子谱求解待测γ能谱的原理, 对解谱的误差来源也进行了简要的分析。 The light output of the BC501A liquid scintillation detector for γ rays was calibrated by serial monoenergetic γ ray sources. The Monte Carlo simulation method to confirm Compton edge was described briefly. The result was compared with that obtained by the semi height method. The γ ray response matrix of BC501A liquid scintillation detector was calculated by the Monte Carlo code PHRESP from PTB. The method of using response function matrix and recoil electron spectrum to unfold γ ray energy spectrum was introduced and the error of unfolding spectrum was also briefly discussed.     

用计算机模拟γ射线无损检测物理实验

本简单介绍用计算机模拟γ射线无损检测物理实验教学软件。     

上海激光电子γ源

激光具有高强度、 高极化度等优异的性能。 用激光束轰击高能电子束就可以产生高强度、 高极化度的γ射线束。 上海激光电子γ源就是上海同步辐射装置上的这样一条束线站。 预计可以获得能量范围为1—22 MeV的准单色、 高强度（109—1011 s-1）和高极化度（线极化或圆极化）的γ射线束。 介绍了这条束线站目前的进展情况。 Shanghai Laser Electron Gamma Source (SLEGS) is a high intensity,short pulse and compact γ ray source which is based on inverse Compton scattering via interaction between pulsed high power laser beams and picosecond relativistic electron bunches. One of the attractive features of the laser Compton scattering is the easy control of polarization of the produced high energy photons that duplicates polarization of the applied laser beam. The γ ray with energy up to 22 MeV and intensity of 109—1011s 1 are expected to be produced by Compton backscattering of CO2 laser photons on the 3.5 GeV electrons bunches in the Shanghai Synchrotron Radiation Facility (SSRF). In this communication, we report same simulation results and the progressing status of SLEGS.     

玻璃在线激光测厚误差的透反互补抑制

为了抑制激光在线测厚时入射角波动引起的误差,根据几何光学分析了激光透射式和反射式测厚原理,发现激光在特定入射角附近波动时,两种方式的测厚误差一正一负,具有互补性,在此基础上提出基于透射和反射同时测量的互补式测厚方法,该方法可将误差限定在透射式和反射式测量误差之间,抑制在线测厚误差.对于有机玻璃平板,理论计算表明,当激光入射角在67.013°±4°波动时,相对误差绝对值在1%以内,误差抑制率均值大于90%;当入射角为61.536°时,误差抑制率为100%.利用线结构激光器和两个线阵CCD相机搭建互补式测厚实验系统,测量了标称厚度为1~5mm的有机玻璃平板,与透射式和反射式测厚结果进行对照,除厚度为1mm的玻璃外,互补式测厚误差被限制在透射式和反射式之间,最大误差抑制率达61%.实验结果表明,该互补式方法有效抑制了误差,提高了在线厚度测量准确度,解决了在线测量不可重复性导致的无法通过均值法减小误差的问题.     

1032—A型可控中子源

本文介绍一种适用快中子与介质发生非弹散射，同时产生非弹γ射线，以及用于测量非弹γ特征能量、检测炸药和其它物质成分而研制的脉冲中子源－１０３２－Ａ型可控中子源。     

掺Er3+光纤的γ射线辐射特性

本文研究掺Er³⁺光纤的γ射线辐射特性,发现在800到1600nm之间损耗都有显著的增加,有的增加800倍之多。光纤的γ射线辐照损耗特性具有β射线辐照类似的规律性。用γ射线的康普顿效应半定量地解释了这种类似性。对γ射线辐照损耗进行紫外线UV漂白,表明比热退火有更好的效果,能使损耗恢复50%。指出选用原子序数小的元素作光纤掺杂剂会有利于光纤抗辐照性能的提高。 关键词：     

用γ射线做康普顿散射测量

用能量为661.67keV的γ射线做不同材料散射靶的康普顿散射,对是否有多个电子同时与同一γ射线散射进行了分析.测量了电子质量,分析了相干散射线宽,测量了非相干散射光子的能量,算出了非相干散射微分截面,给出了Θ~Θ dΘ内散射光子微分截面与散射角关系.     

101Mo衰变的研究

采用γ－γ－ｔ三参数快慢符合谱仪研究了＾１０１Ｍｏ→β＾－＾１０１Ｔｃ的衰变,利用符合测量结果构造了一个新的＾１０１Ｍｏ→β＾－＾１０１Ｔｃ的衰变纲图,首次确定了１０４．７０,１０５．９５,７７４．１５ｋｅＶγ射线的位置,首次观测到１５０８．０１ｋｅＶ的γ射线并确认了其跃迁位置。     

氘氘中子产额铟活化诊断方法

提出了活化法测量DD中子产额的实验方法,该方法可提高DD中子产额测量的精度。方法基于铟同位素115In与DD中子的非弹性散射反应,活化反应释放的射线被HPGe探测器记录,根据活化系统标定灵敏度推算出中子产额。分析了探测器记录的活化射线数与中子产额间的关系。介绍了一套活化测量的系统设计。通过蒙特卡罗方法模拟了活化样品出射的射线数与样品厚度的关系,模拟结果表明:样品厚度取为1 cm可兼顾活化效率和测量精度。在加速器上对铟活化样品进行了标定实验,实验结果表明:在聚变中子产额大于2109的实验中可使用铟活化诊断方法,中子产额测量的相对标准误差在10%以内。随着聚变中子产额的不断提高,铟活化测量中子产额的精度可进一步提高。     

C/O γ能谱测井新的解析理论和方法

报道了快中子非弹性散射γ能谱测井(C/O γ能谱测井)新的解析理论和方法, 也就是由C/O能谱测井仪在井眼中获取地层的快中子非弹性散射γ射线、 NaI(Tl)探测器测量得到的256道谱, 再由实测非弹谱确定地层中主要元素C, O, Si, Ca和Fe等对非弹γ谱的贡献分额, 利用同一地层F因子相同, 求出C产额与O产额比, C的百分含量与O的百分含量和原子含量比, 及Ca和Si相应比值.A new analyzing theory and method of C/O spectrometry logging is reported. Fast neutron enelastic scattering γ ray spectra(256 channels) were acquired in borehole by NaI(Tl) detector. The enelastic scattering γ ray from major elements C, O, Si, Ca, Fe, etc. have the fractions of mixed enelastic spectrum in formation respectively. Because F factor is the same for identical formation, then the ratio of yield of C to O, the ratio of weight percent of C to O, and the ratio of atoms C to O could be found, and the corresponding ratio of Ca to Si was found.     

中子检测爆炸物的原理实验研究

传统的X射线无损检测应用广泛, 但X射线对低原子序素构成为主的爆炸物不能进行有效的甄别; 中子穿透能力较强, 能和原子核相互作用产生特征γ射线, 因此中子无损检测方法能有效弥补X射线无损检测方法的不足。 介绍了几种常用的中子无损检测方法, 并采用脉冲快热中子法（为PFTNA）的方法对模拟爆炸物进行了测量。 实验结果表明, 利用密封中子发生器和采用PFTNA方法进行爆炸物检测是可行的。 Traditional X ray scatheless detecting method is used widely, but it is not useful to discriminate explosive consisting of low Z atomic elements. The penetrability of neutron is much better, and it can interact on atomic nucleus to emit characteristic γ ray. So neutron scatheless detecting methods can the used to detect the low Z atomic elements. In this paper, several neutron scatheless detecting methods are introduced briefly, and the principium experiment using Pulse Fast Thermal Neutron Analysis(PETNA) to detect a kind of explosive simulacrum is carried out. The experiment results show that PFTNA based on the sealed neutron generator is feasible to detect explosive.     

Determination of Moisture Content in Coke with <Superscript>239</Superscript>Pu–Be Neutron Source and BGO Scintillation Gamma Detector

A series of experiments has been conducted at the Frank Laboratory of Neutron Physics (FLNP) of the Joint Institute for Nuclear Research (JINR) in order to study the possibility of determining the moisture content of coke using a standard neutron source. The proposed method is based on a measurement of the spectrum of prompt γ rays emitted when samples are irradiated by fast and/or thermal neutrons. The moisture content is determined from the area of the peaks of characteristic γ rays produced in the radiative capture of thermal neutrons by the proton (E_γ = 2.223 MeV) and inelastic scattering of fast neutrons by ¹⁶O (E_γ = 6.109 MeV). The ²³⁹Pu–Be neutron source (〈E _n 〉 ~ 4.5 MeV) with an intensity of ~5 × 10⁶ n/s was used to irradiate the samples under study. A scintillation detector based on a BGO crystal was used to register the characteristic γ radiation from the inelastic fast neutron scattering and slow (thermal) neutron capture. This paper presents the results of humidity measurement in the range of 2–50% [1, 2].     

Observation of neutron truncation rod scattering

We report measurements of neutron truncation rod scattering. This surface-induced neutron scattering has been observed at the (111) surface of a perfect Si single crystal by a high-resolution three-crystal scattering experiment. We describe the details of the experiment and discuss the experimental findings within a kinematic approach. Possible applications of this new neutron scattering method lie in the field of surface magnetism and the study of surfaces of light-element systems.     

Experimental study of quasi-elastic scattering of ultracold neutrons

Ultracold neutrons (UCN) are lost from traps if they are quasi-elastically scattered from the wall with an energy gain sufficient to exceed the Fermi potential for the wall. Possible mechanisms of a quasi-elastic energy transfer are, for instance, scattering from hydrogen diffusing in an impurity surface layer or on surface waves at a liquid wall. Using two different experimental methods at the UCN source of the Institut Laue-Langevin we have investigated both the energy-gain and the energy-loss side of quasi-elastic UCN scattering on Fomblin grease coated walls. For Fomblin oil and similar new types of oil we report up-scattering data as a function of temperature and energy transfer. These low-temperature oils may be used in an improved measurement of the neutron lifetime, which requires extremely low wall reflection losses. Received 13 March 2002 Published online 31 July 2002     

Reconstruction of scattering properties of rough air-dielectric boundary

The article is devoted to elaboration of the method of reconstruction of rough surface scattering properties. The object with rough surface is made of transparent dielectric material. Typically these properties are described with bi-directional scattering distribution function (BSDF). Direct measurement of such function is either impossible or very expensive. The suggested solution provides physically reasonable method for the rough surface BSDF reconstruction. The method is based on Monte-Carlo ray tracing simulation for BSDF calculation. Optimization technique is further applied to correctly reconstruct the BSDF. The results of the BSDF reconstruction together with measurement results are presented in the article as well.     

血液中Na活化放射性测量的蒙特卡罗模拟

针对超临界事故中人体受到中子辐照后感生的24Na活度测量,采用MCNP软件建立蒙特卡罗模拟模型,分别模拟不同类型NaI探测器对24Na衰变的两条射线全能峰的探测效率和塑料闪烁体探测器对24Na衰变的射线总计数的探测器效率。模拟结果表明:井型NaI探测器与圆柱型相比,24Na衰变的1.38 MeV和2.76 MeV 射线全能峰探测效率分别提高了4.30倍和4.11倍;塑料闪烁体探测器对24Na衰变的射线的探测效率是NaI探测器对24Na 射线的探测效率的1.72倍;同时粗略计算了探测器计数与人体所受中子辐照剂量之间的关系。     

基于Geant4 的4π多单元载Gd 液闪探测系统的初步设计

采用基于蒙特卡罗方法的Geant4 软件设计了由40 个载Gd 液闪探测器组成的多单元4π 立体角探测系统。该探测系统与置于其几何中心的裂变室构成了一个研究平台,该平台主要用于可裂变核(n, 2n)反应截面的测量工作。首先对该系统的物理模型进行了初步检验,然后计算并分析了该探测系统的一些基本性能。通过计算发现,系统空腔半径的变化对中子探测效率的影响十分有限;而探测效率随探测器的厚度增加先是迅速增大,然后逐渐趋于平缓;计算还表明,Gd 同位素俘获中子后发射的级联γ 射线的能量主要沉积在局部几个相邻的探测器中。基于以上计算,初步确定了系统的厚度以及空腔半径的大小,并对下一步将要开展的工作做了初步规划。A gadolinium-loaded neutron detection system with 40 liquid scintillators is designed and simulated by using Geant4 Package based on Monte Carlo method. This system with a fission chamber placed in its center is mainly used for the cross section measurement of (n, 2n) reaction of fissile nuclides. We firstly test the physics model, and then calculate and analyze some basic performance of this system. According to the calculation, the detecting efficiency is not sensitive to the inner radius of the detecting system. The efficiency increase with the system thickness at limited thickness value . The calculated results also indicate that the energy of the γ rays emitted from Gd isotope after capturing a thermal neutron is mainly deposited in a few adjacent detectors. Based on above calculations, the thickness and inradius of this detecting system have been preliminarily determined.     

Experimental verification of the 1/v law for the absorption cross section of ultracold neutrons in natural gadolinium

The results of a new experiment on the transmission of ultracold neutrons through a natural gadolinium film are reported. The results indicate that the transmission of the sample is unchanged when the sample moves parallel to its surface. The neutron velocity in the sample coordinate system varies in a range of 6–35 m/s. It follows from the constancy of the sample transmission that the imaginary part of the scattering length is constant; i.e., the law 1/v is valid for the capture cross section of the free nucleus with an accuracy of about 0.5%.