贫铀球壳中D-T中子诱发的铀反应率的测量与分析

为校验次临界能源堆的概念设计,在R19.4/30.0 cm的贫铀球壳装置上采用活化法开展14 MeV中子学积分实验.布放6片贫铀活化片于球壳中与入射D离子束90°方向上的不同位置处活化,用HPGe探测器测量238U(n,γ)反应、238U(n,f)及235U(n,f)反应和238U(n,2n)各反应产物发射的特征γ射线,得到了相应的反应率.238U(n,γ)反应率的不确定度为3.6％-3.7％,238U(n,D和235U(n,f)反应率的不确定度为5.1％-5.9％,238U(n,2n)反应率的不确定为4.3％-4.7％.用MCNP5程序在ENDF66c数据库下进行模拟计算,238U(n,γ)反应率的计算值/实验值(C/E)为0.972-1.034,238U(n,f)和235U(n,f)反应率的C/E为0.983-1.058,238U(n,2n)反应率的C/E为0.979-1.019.     

Sorption kinetics of uranium-238 and neptunium-237 on a glacial sediment

Studies of uptake of radionuclides by natural materials have shown that sorption may occur via fast equilibrium exchange and/or slow kinetic processes, which can be described using a series of box models. This paper describes the use of such models to evaluate the solid-solution partitioning of ²³⁸U and ²³⁷Np on a clay rich sediment. Experimental data are obtained using the batch sorption technique, which are then analysed using 1, 2, and 3 box kinetic models. Uptake of ²³⁸U is initially rapid, with approximately 90% sorbed within the first 30 minutes. Sorption continues, but at a slower rate. Uptake of ²³⁷Np is initially slower than U, with approximately 30% sorbed within the first 30 minutes. Sorption again continues, at a slower rate. Analysis of the experimental data indicates that sorption can be described using 2 and 3 box kinetic models. The results demonstrate that sorption of uranium and neptunium on clay rich sediments occurs via equilibrium and kinetically controlled pathways, with neptunium being controlled by kinetics to a greater extent than uranium. The 2 or 3 box model can describe sorption of neptunium, uranium requires the 3 box model.     

Observation of thermoluminescence induced by fission fragments

Abstract

Thermoluminescence induced in CaF₂ powder by fission fragments emanating from a uranium foil bombarded by fast neutrons has been measured as a function of neutron fluence. A linear relationship between the glow produced and the fast neutron fluence between 5 × 10¹⁰ and 6.5 × 10¹¹ n/cm² has been obtained, thus establishing the feasibility of the use of this method for fast-neutron dosimetry. A limitation of the method is that, if the fissile foil is not separated from the phosphor after irradiation, the TL produced by the α-disintegration of ²³⁸U may eventually mask the fission-induced TL.     

Effets produits par l'irradiation avec des neutrons et avec des rayons gammas sur la série jaune et la série verte du spectre d'absorption excitonique de la cuprite

The effects of irradiations in a reactor and in a Cobalt 60 source on the green and yellow series of the excitonic absorption spectrum of cuprous oxide are studied. In the reactor irradiation experiments, the effects of fast neutrons are separately studied from those of thermal neutrons and of gamma rays. It is shown that the perturbations of the absorption spectra of Cu₂O by fast neutrons are very similar to those produced by an external electric field. They are also similar to those produced by quenching which creates probably internal strains. Charged defects occur probably in the crystal during bombardment and these charged defects produce an internal electric field and strains. It is not possible to study separately the effects of the electric field and the effects of strains. The electric field can be evaluated by comparison of its effects on the excitonic spectrum with those of an external field. An evaluation of the rate of creation of defects by fast neutrons in the crystal is deduced. It is also shown that the effects of gamma-rays are very different from those of fast neutrons. It is possible with gamma-ray irradiations to decrease residual internal fields which may exist in a crystal.     

Production of neutron-rich nuclei in fission induced by neutrons generated by the p + <Superscript>13</Superscript>C reaction at 55 MeV

Cross-sections for the production of neutron-rich nuclei obtained by neutron-induced fission of natural uranium have been measured. The neutrons were generated by bombarding a ¹³C target with 55 MeV protons. The results, position of the maximum in the (Z, A)-plane, width and magnitude, are very comparable with those where the neutrons are generated by bombardment of natural ¹²C graphite with 50 MeV deuterons. Depending on the geometry of the converter/target assembly the isotope yields, however, are a factor of 2-3 lower due to less efficient production of neutrons per primary projectile, especially at small forward angles. Received: 8 November 2002 / Accepted: 20 December 2002 / Published online: 15 April 2003     

铀矿坑水样中铀电沉积层的表征

描述了硫酸铵溶液中铀矿坑水样品中铀的电沉积层特性。 电沉积液为10 ml 0.8 M的硫酸铵溶液, 电流密度0.6 A/cm2, pH值为2.5, 电镀1 h。 电沉积经化学分离后的水样品和电沉积的纯硝酸铀酰样品进行了比较, 并对二者分别做了红外(IR)光谱、 扫描电镜(SEM)、 元素分析以及α能谱测量。 IR谱上铀酰离子的反对称伸缩振动峰在887 cm-1附近, 使电沉积在不锈钢片上的铀主要以铀酰离子水合物的形式存在, 有一部分NH+4以NH3的形式替代水合物中的水, 使电沉积层中铀的化合物形式为UO2(OH)2·xNH3·yH2O或者UO2(OH)2-x·(ONH4)x·yH2O, 铀酰离子通过链的形式形成聚合结构。 SEM照片显示电沉积层均匀, 没堆积成团现象出现。 α谱表明电沉积层中铀的同位素主要是238U和234U, 相应的α能量峰4198和4773 keV很显著, 没其它峰的干扰。 Characteristics of electrodeposited uranium films of uranium ore water sample in ammonium sulphate was investigated in this work. The optimized electrodeposited conditions were as follows: electrolyte was ammonium sulphate of 0.8 M, and current density at the cathode was 0.6 A/cm2, electrolyte pH value was 2.5, the time of plating on the electrodeposition was 1 h. In this situation, the uniform, thin and adheresive films were produced by electrodeposition method. Two samples were made, one electrodeposition of pure uranyl nitrate, and another electrodeposition of uranium ore water sample after chemical separation. Characteristics of electrodeposited uranium films of uranium ore water sample after chemical separation was studied, making comparisons with electrodeposited films of uranyl nitrate. The analysis of film characteristics was done through infrared (IR) spectrum, scanning electron microscopy(SEM), element analysis and α spectrum measurment. According to Fourier transform infrared spectra, the asymmetric stretching vibration band of uranyl group is around 887 cm-1. In addition, according to IR spectrum, we know that uranium exists mainly as the form of hydrated polymeric compound in the film. Electrodeposited uranium films also included many NH+4. Polymeric structures of variable composition were present in the electrodeposited samples, with the unit monomeric formula UO2(OH)2·xNH3·yH2O or UO2(OH)2-x·(ONH4)x·yH2O. Scanning electron microscopy shows that the two samples have similar surface characteristics and no cluster is observed. The samples were also measured by spectrometer equipped with Passivated Implanted Planar Silicon(PIPS) detector. From the α spectrum, we know that isotopes of uranium in the film are 238U and 234U. 235U is not found in the α spectrum. It also shows that the chemical separation process can isolate uranium from other interfering elements effectively, the result of chemical separation is very satisfactory and electrodeposited process is rather efficient. Source electrodeposited in ammonium sulphate through optimized conditions satisfies the need of high resolution α spectrum.     

An EDXRF method for determination of uranium and thorium in AHWR fuel after dissolution

A fast energy dispersive x‐ray fluorescence (EDXRF) method requiring only microgram amounts of analytes, i.e. uranium (U) and thorium (Th), in their mixtures in solution form is described. Calibration solutions and samples covering the fuel composition range (0–5% of U in U + Th) of advanced heavy water reactor (AHWR) were prepared by mixing uranium and thorium solutions. A known fixed amount of internal standard yttrium (Y) was added to these solutions. EDXRF spectra of calibration solutions and samples were measured by taking 20 µl aliquots on 30 mm diameter filter papers, after drying, using a Rh target tube operated at 40 kV and 500 µA. Calibration plots were made by plotting U/Y, U/Th and Th/Y amount ratios against the respective intensity ratios of Th Lα, U Lα and Y Kα. In the first set, U was determined using Y as an internal standard, and for Th determination, U, thus determined, was used as an internal standard since the amounts of Th and Y were kept constant in the calibration solutions and samples. In the second set, both U and Th were varied and determined using Y as internal standard. The results of U and Th determinations showed a precision of about 3% (1s) and the results deviated from the expected values by <3% in most of the cases. This approach has an advantage that it requires only microgram amounts of sample, thus mitigating radiation hazards associated with radioactive samples as well as the amount of radioactive analytical waste generated is quite less. Copyright © 2009 John Wiley & Sons, Ltd.     

U：CaF2晶体的分凝特性与光谱性质

应用TGT法生长了直径为75mm的U：CaF2晶体，宏观上透明完整.应用公式K0=Cs/Cl计算了U在CaF2晶体中的分凝系数等于0.53.应用溶质分布一般公式Cs=K0C0(1-g)K0-1，计算U的浓度分布与测量值，数值符合说明晶体生长过程接近平衡状态.分析不同条件下生长的U: CaF2晶体的晶胞参数和吸收光谱，结果表明生长气氛决定U的价态及电荷补偿机理：无PbF2存在的条件下，U为+4价，晶体呈绿色；PbF2的加入起到氟化去氧作用，U倾向于以离子半径最接近于Ca2+的U3+存在，晶体呈红色.从晶体生长开始到结束的部位，U3+:CaF2晶体吸收光谱的峰位不变，峰强呈现与U浓度相同的增加趋势.U3+:CaF2晶体外层厚约5mm处呈黄色，含有U3+和U2+的混合价态离子，其原理是石墨坩埚的还原作用通过单质铅，使部分的U3+进一步还原成了U2+. 关键词： 铀 氟化钙晶体 分凝系数 晶胞参数     

U:CaF_2晶体的分凝特性与光谱性质

应用TGT法生长了直径为 75mm的U :CaF2 晶体 ,宏观上透明完整 .应用公式K0 =Cs Cl 计算了U在CaF2 晶体中的分凝系数等于 0 5 3.应用溶质分布一般公式Cs=K0 C0 (1-g) K0 - 1 ,计算U的浓度分布与测量值 ,数值符合说明晶体生长过程接近平衡状态 .分析不同条件下生长的U :CaF2 晶体的晶胞参数和吸收光谱 ,结果表明生长气氛决定U的价态及电荷补偿机理 :无PbF2 存在的条件下 ,U为 4价 ,晶体呈绿色 ;PbF2 的加入起到氟化去氧作用 ,U倾向于以离子半径最接近于Ca2 的U3 存在 ,晶体呈红色 .从晶体生长开始到结束的部位 ,U3 :CaF2 晶体吸收光谱的峰位不变 ,峰强呈现与U浓度相同的增加趋势 .U3 :CaF2 晶体外层厚约 5mm处呈黄色 ,含有U3 和U2 的混合价态离子 ,其原理是石墨坩埚的还原作用通过单质铅 ,使部分的U3 进一步还原成了U2 .     

Conceptual Design of a Hybrid Fusion–Fission Power Reactor with a Tokamak and a Depleted Uranium Blanket

Physics of Atomic Nuclei - We assess the viability of energy generation with depleted uranium irradiated with fast neutrons from the reaction of DT fusion driven by a tokamak reactor. Since...     

Die Anwendung der Methode der zeitlich korrelierten assoziierten Teilchen (MEZKAT)

The TCAPM was developed to absolute and precise fission cross section measurement for neutron energies from 2 MeV up to 19 MeV. Experimental results of absolute fission cross section measurements on ²³³U, ²³⁵U, ²³⁸U, -²³⁷Np, ²³⁹Pu and ²¹²Pu are given. Furthermore the TCAPM is suitable for the application of inelastic scattering of neutrons by the analysis of element contents.     

Fission decay properties of ultra neutron-rich uranium isotopes

The fission decay of highly neutron-rich uranium isotopes is investigated which shows interesting new features in the barrier properties and neutron emission characteristics in the fission process. ²³³U and ²³⁵U are the nuclei in the actinide region in the beta stability valley which are thermally fissile and have been mainly used in reactors for power generation. The possibility of occurrence of thermally fissile members in the chain of neutron-rich uranium isotopes is examined here. The neutron number N = 162 or 164 has been predicted to be magic in numerous theoretical studies carried out over the years. The series of uranium isotopes around it with N = 154–172 are identified to be thermally fissile on the basis of the fission barrier and neutron separation energy systematics; a manifestation of the close shell nature of N = 162 (or 164). We consider here the thermal neutron fission of a typical representative ²⁴⁹U nucleus in the highly neutron-rich region. Semiempirical study of fission barrier height and width shows that ²⁵⁰U nucleus is stable against spontaneous fission due to increase in barrier width arising out of excess neutrons. On the basis of the calculation of the probability of fragment mass yields and the microscopic study in relativistic mean field theory, this nucleus is shown to undergo exotic decay mode of thermal neutron fission (multi-fragmentation fission) whereby a number of prompt scission neutrons are expected to be simultaneously released along with the two heavy fission fragments. Such properties will have important implications in stellar evolution involving r-process nucleosynthesis.      

DerK-Konversionskoeffizient für den Zerfall des Os191m

Os^191m was produced by bombarding natural osmium with fast neutrons. The gamma-rays were studied with Ge(Li)-detectors. TheK-conversion coefficient was determined by comparing the gamma-spectrum of Os^191m with the spectrum emitted by the osmium anode of a X-ray tube. The result is α _K =38.4 _?4.6 ^+7.7 . This result is compared with theory.     

Measurement and analysis of the 238U(n, 2n) reactionrate in depleted uranium/polyethylene shells

In order to check the conceptual design of the subcritical blanket in a fusion-fission hybrid reactor, a depleted uranium/polyethylene simulation device with alternate shells has been established. The measurement of the ²³⁸U(n, 2n) reaction rate was carried out using an activation technique, by measuring the 208 keVγ rays emitted from ²³⁷U. The self-absorption of depleted uranium foils with different thicknesses was experimentally corrected. The distribution of the ²³⁸U(n, 2n) reaction rate at 90° to the incident D⁺ beam was obtained, with uncertainty between 5.3% and 6.0%. The experiment was analyzed using MCNP5 code with the ENDF/BVI library, and the calculated results are all about 5% higher than the measured results.     

Evolution of isotopic composition of reprocessed uranium during the multiple recycling in light water reactors with natural uranium feed

A complex approach based on the consistent modeling of neutron-physics processes and processes of cascade separation of isotopes is applied for analyzing physical problems of the multiple usage of reprocessed uranium in the fuel cycle of light water reactors. A number of scenarios of multiple recycling of reprocessed uranium in light water reactors are considered. In the process, an excess absorption of neutrons by the ²³⁶U isotope is compensated by re-enrichment in the ²³⁵U isotope. Specific consumptions of natural uranium for re-enrichment of the reprocessed uranium depending on the content of the ²³²U isotope are obtained.     

变形核强阻尼碰撞中巨复合体系的形成和衰变

利用改进的量子分子动力学（ImQMD）模型研究了质心系入射能量为980 MeV时变形核238U+238U体系的3种不同碰撞模式（腹对腹、 尖对腹和尖对尖）下强阻尼反应过程中初级超重碎块的产生几率和复合体系的寿命、 形状和拉长取向等性质, 发现尖对腹碰撞模式有利于初级超重碎块的产生, 还发现这种碰撞模式产生的复合体系有最长的寿命。Three different collision modes ( Belly belly, Belly tip and Tip tip) of the deformed uranium nucleus 238U bombarding the deformed 238U in strongly damped reaction at the incident energy 980 MeV has been investigated based on the improved quantum molecular dynamics (ImQMD) model. The formation and properties of the formed composite system during the reaction process were carefully studied including the lifetime, the shape configuration and the angular distribution of primary fragment. It was found that the Belly tip mode is suitable for producing the super heavy fragments, and the composite system has the longest lifetime in this mode.     

The problem of obtaining U237

Two methods of obtaining U²³⁷ are considered: irradiation of U²³⁵ and U²³⁶ in different neutron beams from a nuclear reactor (10¹³-10¹⁶ neutrons/cm²·sec), and the accumulation of U²³⁷ in plutonium enriched with the isotope Pu²⁴¹. Optimal methods of irradiating uranium and plutonium in order to obtain maximum accumulation of U²³⁷ and Pu²⁴¹ respectively are suggested. In the calculations data is used on the cross sections for thermal neutrons taken from the literature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, Vol. 12, No. 1, pp. 28–31, January, 1969.     

On Dating of Old Groundwater

Groundwater dating is known to be determination of the residence time of groundwater. This residence time is commonly defined as the length of time the water has been isolated from the atmosphere. The paper reviews isotope methods available for dating of old groundwater. Their residence time is supposed to be far outside the range of C-14 dating which is about 50000 years. These dating methods are based on the radioactive decay of long-lived radionuclides produced by interaction of cosmic radiation with gases in the atmosphere (Kr-81, Cl-36, I-129), on the accumulation of noble gases suo-surface produced by nuclear reactions including radioactive decay of U/Th series radionuclides (He-4, He-3), and on the disequilibrium between uranium isotopes due to water-rock interaction and radioactive decay (U-234, U-238). The paper presents the principles of these dating methods, refers to recent case studies and summarizes problem areas for further development and application of these methods.     

Band Displacement Process with Redox Reactions for Uranium Isotope Separation by Chemical Exchange between U(IV)-Resin and U(VI)-Solution

The extreme limits for ²³⁵U/²³⁸U % at ambiant temperature were determined experimentally with a long time band displacement process (almost 1 year) using the isotope exchange reaction between U(IV)_resin and U(VI)_solution. These limits are 0.738 and 0.712, considering ²³⁵U/²³⁸ = 0.725% for natural uranium. The redox reactions, allowing the band displacement were: 1) in front of the band is the reduction of U(VI) in solution by a cathionic resin in Ti(III)-form; 2) in the tail of the band is the oxydation of U(IV) in resin by a solution containing Fe(III) ions.