医用同位素~(125)I放射性强度的测定

~(125)I是发射低能γ的同位素,衰变纲图见图1。它通过电子俘获衰变到~(125)Te的激发态(其中产生的27.5keV KX射线,分支比为68.5％),然后经γ跃迁(发射35keVγ,分支比为6.4％)或发射内转换电子(也产生 上述KX射线,分支比为66.0％)退激到基态。 测定~(125)I溶液放射性强度的较好办法是采用单晶 NaI闪烁谱仪,利用γ能谱上的符合和峰(coincident sum peak)面积来推求之,它的γ能谱见图2。在这个 衰变过程中发射的LX射线能量3.8keV,很低,谱上记     

反符合法测量152Eu放射性溶液的活度

¹⁵²Eu的衰变纲图复杂,包括72.1%的EC衰变和27.9%的β-衰变,衰变子体退激过程中又放出140多条γ射线,其中,12条能量处在122~1408keV之间,是主要γ射线。¹⁵²Eu常用于HPGeγ谱仪能量校准和效率校准等,¹⁵²Eu的放射性活度准确测量极为重要。本工作利用4πβ(PPC)-γ(HPGe)反符合测量装置对¹⁵²Eu的活度进行绝对测量,并与4πβ-4πγ符合效率外推法和HPGeγ谱仪、4πγ高气压电离室测量的结果进行了比较。这几种方法的测量结果在不确定度范围内一致。     

~(61)Cu的衰变

使用Ge(Li)和HpGe探测器、Nal-Ge(Li)γ-γ符合谱仪、半导体电子谱仪研究了~(81)Cu的衰变。测到了来自12个激发能级的35条γ射线,结果表明:“Table of Isotopes”(7th edition 1978)的~(61)Cu纲图中的545keV、1019keV γ射线及1019keV能级是不正确的。测得~(61)Cu的半衰期和67keVγ跃迁的内转换系数分别为T_(1/2)=207.7±1.6min及α=0.12±0.01,并作出衰变纲图。本文着重讨论有分歧的1014、1019、1997三个能级及一些弱γ射线的存在问题。     

~(99m)Tc的活度绝对标定

本文介绍了用4πβ-γ符合方法测定~(99m)TC绝对活度的技术及测量结果。并观测了2.12,140.5和142.6 keV跃迁的γ射线和内转换电子在4πβ计数管中的探测效率随VYNS膜厚度的变化。从而得到2.12 keV射线完全吸收后~(99m)Tc每一次衰变在4πβ计数管中的“β”计数贡献为0.1117±0.0005。     

~(101)Tc衰变的研究

采用γ -γ -t(HpGe -HpGe) 3参数快慢符合谱仪研究了10 1Tc β-10 1Ru的衰变 ,利用符合测量结果修正了10 1Tc β-10 1Ru的衰变纲图。实验首次观测到 174 .91、2 2 6.0 2、312 .4 0、4 0 8.77、4 17.91keV的γ射线 ,并确认其跃迁位置 ,同时确定了 616.3keVγ射线的跃迁位置。计算了各能级的β- 衰变强度和logft值。     

~(161)Tb低能γ射线发射几率的精确测量

利用4疴-γ符合装置和低能光子谱仪精确测量了161Tb衰变γ射线的发射几率。对于25.7 keV、48.9 keV和74.6 keV的低能γ射线,测定结果分别为0.2327 0.0053、0.1700 0.0031和0.1001 0.0019。表明本测量结果的不确定度明显减小。     

~(57)Fe共振过滤γ射线的时间相依性和穆斯堡尔谱

~(57)Fe 14.4keVγ射线的衰变几率在这个态形成后,随时间指数衰减。1960年R.E.Holland观察到当与14.4keV入射γ射线共振的~(57)Fe薄膜用作过滤片(即吸收体)时,由符合测量技术测得的γ射线数目偏离指数型。随后M.Hamermesh和S.Harris分别用经典力学和量子力学的方法推导出理论曲线,经过厚度修正,使理论和实验曲线符合较好。     

体源中60Coγ射线的符合相加修正因子测量

对于存在级联辐射的γ核素,如,其衰变产生的γ1（1173．2keV）和γ2（1332．5keV）射线会发生级联符合,造成γ1,γ2的全能峰计数比不存在级联符合时有所减少,有些核素的多个γ符合会出现部分γ全能峰计数增加,部分γ全能峰计数减少。在标准源或样品距离探头较远时,级联符合比较小。一般认为在25cm以外的距离,符合效应小到可以忽略。但在实际工作中（环境样品的γ谱分析中）,由于环境样品的放射性活度比较小,为了在一定的测量时间内尽可能地降低统计误差,样品与探头距离只有1cm左右,这种情况下,就会有明显的级联符合效应。为了尽量减小在刻度和测量过程中由级联符合带来的偏差,必须对级联符合进行修正。     

^161Tb低能γ射线发射几率的精确测量

利用4πβ-γ符合装置和低能光子谱仪精确测量了161Tb衰变γ射线的发射几率.对于25.7 keV、48.9 keV和74.6 keV的低能γ射线,测定结果分别为0.2327±0.0053、0.1700±0.0031和0.1001±0.0019.表明本测量结果的不确定度明显减小.     

~(56)Fe(n,p)~(56)Mn反应截面的测量

在E_n=12.8—18.2兆电子伏能区,用活化法测量了~(56)Fe(n,p)~(56)Mn反应截面,在E_n=14.63±0.20兆电子伏处做了绝对测量,结果为108.0±2.9毫靶。中子通量用伴随粒子法测定。对T(d,n)~4He反应的中子角分布也作了测定。~(56)Mn的放射性用φ10×7.6厘米的Nal(Tl)闪烁谱仪测量,~(56)Mn特征γ射线的探测效率用4πβ-γ符合法测定的~(56)Mn标准源刻度。本文还对用伴随粒子法测量中子通量作了较详细的叙述。测量结果同国外数据作了比较,并做了简短讨论。     

元素级联γ射线的符合测量技术

介绍了一种符合测量技术,可极大地抑制康普顿坪和逃逸峰,从而凸显全能峰,使数据分析变得更为简单。该技术利用元素释放的级联衰变γ射线,用满足峰与峰相加的幅度信号作为符合信号,将符合信号作为门输入与原输入信号再进行符合即可得到凸显元素特征的不带康普顿坪的γ能谱。通过符合窗的选取,该技术可在复杂的辐射场中对特定元素进行选择性测量。     

夹层式中子-γ射线联合探测器设计原理

针对可能存在的单次脉冲高γ射线与中子比、10ns级γ射线和10ms级聚变中子辐射场,根据射线与物质的相互作用原理,初步提出了综合利用电流和计数模式的方法对辐射场中的γ射线和聚变中子进行探测。该辐射场中的γ射线脉冲比聚变中子提前到达,从而降低了辐射探测背景,更有利于信号的提取。     

用于中子单色器镶嵌分布测量的γ衍射源设计

用γ衍射法测量中子单色器镶嵌角分布,要求γ入射束具有强度大、单能性好、发散度小等特点。为了满足上述要求,须对γ射线源(金材料)的形状和尺寸进行设计。本工作通过分析束流强度、束流发散度与束斑形状的关系,给出了金材料的矩形设计方案;通过蒙特卡罗计算,分析γ自吸收和γ康普顿散射在不同厚度下分别对束流密度和单能性的影响,给出矩形金材料在x、y、z3个方向的尺寸分别为0.6、6和10mm。用所设计的金材料制成γ源,成功实现了用γ衍射法对Ge单晶中子单色器镶嵌分布的测量。     

Measurement of keV-Neutron Capture Cross Sections and Capture Gamma-Ray Spectra of 167 Er

The neutron capture cross sections and capture γ-ray spectra of ¹⁶⁷Er were measured in the neutron energy region of 10 to 90keV and at 550 keV. Using a neutron time-of-flight method with a 1.5-ns pulsed neutron source by the ⁷Li(p, n)⁷Be reaction, the measurement was performed by detecting prompt γ rays from an enriched capture sample with a large anti-Compton Nal(Tl) spectrometer. A pulse-height weighting technique was applied to observed capture γ-ray pulse-height spectra to extract capture yields. The capture cross sections were derived with the error of about 5% by using the standard capture cross sections of ¹⁹⁷Au. The present results were compared with the evaluated values of ENDF/B-VI and the previous measurement. The present measurement at 550 keV was the first one. The capture γ-ray spectra were obtained by unfolding the observed capture γ-ray pulse-height spectra. An anomalous shoulder was clearly observed around 3 MeV in the γ-ray spectra and the energy position of the shoulder was consistent with the systematics obtained in our previous work. The multiplicities of the observed γ rays were derived from the γ-ray spectra.     

用NaI谱仪识别γ放射源

采用NaI谱仪系统,开展了放射源辐射指纹识别技术研究。利用数据库开发平台,采用谱形比较法、半衰期修正法和谱形相似度等概念,编制了放射源辐射指纹识别软件,实现了放射源在线可视化识别,并通过放射源同一性的识别实验验证了软件的有效性。研究结果表明:在总计数和峰面积识别条件下,能较快实现放射源同一性的识别。     

Geant4 simulation of 238U(n,f) reaction induced by D-T neutron source

Knowledge of actinides(n,f) fission process induced by neutron is of importance in the field of nuclear power and nuclear engineering,especially for reactor applications.In this work,fission characteristics of~(238)U(n,f) reaction induced by D-T neutron source were simulated with Geant4 code from multiple perspectives,including the fission production yields,total nubar,kinetic energy distribution,fission neutron spectrum and cumulative γ-ray spectrum of the fission products.The simulation results agree well with the experimental nuclear reaction data(EXFOR) and evaluated nuclear data(ENDF).Mainly,this work was to examine the rationality of the parametric nuclear fission model in Geant4 and to direct our future experimental measurements for the cumulative fission yields of ~(238)U(n,f) reaction.     

Emission Probabilities of Gamma Rays from the Decay of 233Pa and 238Np,and the Thermal Neutron Capture Cross Section of 237Np

In order to determine the thermal neutron capture cross section of ²³⁷Np, the relevant γ emission probabilities of the 312-keV γ-ray from the decay of ²³³Pa and the 984-keV γ-ray from the decay of ²³⁸Np are deduced from the ratio of the emission rate to the activity. The emission rate and activity are measured with a Ge detector and a Si detector, respectively. The measured emission probability for 312-keV γ-ray is 41.6±0.9% and that for 984-keV γ-ray is 25.2±0.5%. The emission probabilities are used to correct the thermal neutron capture cross section of ²³⁷Np reported previously, and gives 168±6b. The neutron capture cross section is also determined as 169±6b by α-ray spectroscopic method. The measured emission probabilities and capture cross section are compared with others from references. By averaging these values deduced by different methods, the value of 169±4b is recommended as the thermal neutron capture cross section of ²³⁷Np for 2,200 m/s neutrons.     

Benchmark Experiment on Vanadium with D-T Neutrons and Validation of Evaluated Nuclear Data Libraries by Analysis of the Experiment

A neutronics benchmark experiment on vanadium, which is a low activation fusion reactor material, was conducted by using the D-T neutron source facility of FNS/JAERI. Neutron spectra, dosimetry reaction rates, γ-ray spectra and γ-ray heating rates were measured in a vanadium experimental assembly. Benchmark tests for four evaluated nuclear data files were performed by analyzing the experiment. As a result, the following problems were pointed out in view of accuracy of fusion reactor designs. (1) JENDL-FF and JENDL-3.2: Total cross section should be reexamined especially at ～2keV. (2) ENDF/B-VI: Double differential cross sections for 14 MeV neutrons should be revised because of the isotropic angular distribution for continuum neutron emission. Gamma-ray production cross sections are too small and discrete γ-ray peaks are not represented clearly. (3) EFF-3: Gamma-ray production cross sections are too large.     

Evaluation of Neutron Capture Gamma-Ray Spectra in Hafnium and Tantalum

A method has been developed for evaluation of neutron capture γ-ray spectrum. It couples measured intensities of primary and secondary discrete—-ray with a γ-ray cascade model to calculate the unresolved part of the capture spectrum, and adds the discrete part and the unresolved part to obtain the whole spectrum. The cascade model uses the level density formula proposed by Gilbert & Cameron and the Brink & Axel form of El γ-ray profile function with a modification. This method was applied to thermal neutron capture spectra in six hafnium isotopes and ¹⁸¹Ta and was extended also to non-thermal capture spectra in ¹⁸¹Ta for 0.25 and 0.5 MeV neutrons with empirical assumptions. The calculated results were compared with experiments and agreement was good not only in terms of the gross structure, but also in terms of the fine structure which appears at high and low γ-ray energies.     

MC法模拟不同中子源激励铀材料中子和γ飞行时间谱

为探索中子源激励探测铀材料应用技术,基于Geant4平台建立了中子源激励铀材料模拟中子和γ飞行时间谱的数学模型,模拟计算了利用不同中子源激励铀材料、使用不同探测器计数的中子和γ飞行时间谱,结果与已有相应实验谱特征相符。模拟结果表明:D-D和~(252)Cf源激励得到的中子和γ飞行时间谱有明显差异;在相同激励源和测量几何条件下,使用液体闪烁体探测器和塑料闪烁体探测器记录到的中子和γ飞行时间谱基本相同。本文结果可为外中子源激励探测铀材料技术研究提供参考。