单能中子诱发~(235)U和~(238)U裂变的产物产额

本文利用碎片质量分布5-Gauss半经验公式,计算了单能中子诱发~(235)U和~(238)U裂变放中子前碎片产额,并采用七点拟合公式和线性内插方法求得碎片发射的中子产额。然后按照Terrell给出的转换方法,把放中子前碎片的产额换算为放中子后产物的产额。具体计算了_(40)~(95)Zr、_(58)~(144)Ce、_(60)~(147)Nb三种产物产额随入射中子能量的变化关系,并与实验观测结果作了比较。     

热中子诱发239Pu裂变初级裂变产物质量分布测量

原子核裂变是最复杂的物理过程之一,至今仍缺乏可以统一描述裂变前和裂变后过程的理论。中子诱发239Pu裂变产额数据是重要的核数据,完整的初级裂变产物质量分布数据有助于完善裂变理论模型并提高产额评价数据的质量。本文研制了初级裂变产物鉴别谱仪（FFIS）,通过屏栅电离室和微通道板时间探测器分别测量裂变碎片的动能和飞行时间,基于动能 速度关联的方法直接获得碎片放中子后的质量分布,在BNCT医院中子照射器（IHNI 1）上开展了热中子诱发239Pu裂变初级裂变产物的质量分布测量。测量结果表明,对轻峰碎片质量分辨约为1 amu,对重峰碎片质量分辨约为15 amu。239Pu(nth,f)初级裂变产物质量分布的精确测量可为裂变产额理论计算和评价提供重要的实验数据。     

放中子前后裂变碎片质量分布的换算

给出了一个裂变中子产额分布的七点计算公式。经与从Ac到Cf范围内的裂变核素、其激发能由自发裂变高到45MeVα粒子诱发裂变的实验比较,该公式能较好地反映中子分布的主要特征。由于中子分布在产额的换算中只是起次要的作用,因此可以用来换算放中子前后质量分布。利用该公式进行换算后的质量分布能很好地再现实验分布的平均趋势。如果将该公式与放中子前裂变碎片质量分布半经验公式联合使用,将可直接计算放中子后的质量产额,而不需要利用任何实验数据,给出的绝对产额预测精度约为±0.5%。     

~(99)Mo的裂变产额及产额分布的结构现象

我们多次测定了裂变谱中子引起~(235)U裂变中~(99)Mo的产额值Y_(fo)分别用放化法及Ge(Li)直接γ能谱法测定了绝对产额及与热中子裂变产额Y_(th)的相对比值R=Y_f/Y_(tho) 。其中,对~(99)Mo都得到R>1的结果,即裂变谱中子引起~(235)U中裂变时的~(99)Mo产额比热中子裂变的产额值高。这种在产额质量分布峰上的产额与入射中子能量有明显依赖、而且随能量而增高的现象是与以前实验及编评数据以及峰上产额值不随能     

基于Potential-driving模型的中子诱发~(239)Pu裂变产物计算与模拟研究

当前新型核能利用系统及核数据评价的发展对快中子诱发~(239)Pu裂变核数据提出了更高的精度需求。本工作基于已提出并构建的Potential-driving模型,通过中子诱发~(239)Pu(n,f)裂变驱动势研究,计算了几个典型能量中子诱发~(239)Pu(n,f)反应发射中子前裂变碎片质量分布,并与实验数据进行了对比。结果显示:Potential-driving模型计算数据能够很好地与实验数据符合。将Potential-driving模型植入GEANT4程序,开展了快中子诱发~(239)Pu(n,f)反应相关的模拟研究,给出了14 Me V中子诱发~(239)Pu(n,f)反应的裂变碎片独立产额质量分布和电荷分布、累积产额质量分布和电荷分布、动能分布、裂变中子能谱以及~(239)Pu(n,f)反应裂变碎片平均总动能随入射中子能量的变化等数据,并与GEANT4程序原有的参数化裂变模型(G4Para Fission Model)模拟结果、ENDF/B-VII.1库评价数据以及实验数据进行了比较。结果显示:所发展的Potential-driving模型能很好地预测快中子诱发~(239)Pu(n,f)反应裂变产物数据,为快中子诱发~(239)Pu(n,f)反应裂变产物核数据的研究提供了一种更可靠的计算方法。     

裂变碎片瞬发中子数随质量分布的研究

基于TALYS程序计算结果，我们研发了利用放中子前后裂变碎片的质量分布计算裂变碎片瞬发中子数随碎片质量分布的方法。裂变碎片瞬发中子数随裂变碎片质量分布的形状依赖于裂变产生的激发能如何在两个碎片中分配。这个问题一直以来没有得到很好的解决。     

锕系核裂变数据关键科学问题研究

<正>本项目2019年进一步完善了C_6D_6探测系统,开展了多个中子俘获截面测量实验,并完成了全吸收型氟化钡探测装置(GTAF)的升级改造。完成了低气压裂变电离室性能测试~(252)Cf自发裂变碎片质量分布试测量,并开展初级裂变产物电荷鉴别实验。初步掌握了裂变产额唯象模型计算方法,建立了唯象模型计算程序,并通过了验证,计算的中子诱发~(235)U裂变碎片质量分布的结果与JEFF-3.1评     

24.4KeV中子诱发^235U裂变的产额测量

一、前言 对~(235)U热中子裂变已经作了充分的研究,裂变产物的产额作了广泛的测量,并对实验数据进行了多次编评。但是对于其它单能中子诱发~(235)U裂变研究还远远不够,尤其是keV能区的中子更是如此。J.G.Cuninghame等测量了130-1700keV中子诱发~(235)U裂变中一些核素的产额。但是低于130keV中子诱发的裂变研究,文献中未见过报道。为了研究产额随中子能     

240Pu自发裂变气体产物产额的唯像模型研究

基于裂变多模式无规颈断裂物理思想,建立了中子诱发²³⁹Pu裂变、²⁴⁰Pu自发裂变系统裂变产额计算的唯像模型。以实验数据为基础,利用最小二乘法确定了唯像模型参数。基于唯像模型计算的产额,结合实验数据系统规律进行分析和再评价,给出²⁴⁰Pu自发裂变气体产物^87,88Kr和^133,135Xe的累积产额推荐值。     

~(235)U裂变碎片在PIN探测器中沉积能量的实验研究

利用中子与235U发生裂变反应的截面在裂变中子能区基本不变这一特点,可设计研制裂变靶室探测系统,该系统中子能量响应较平坦,在脉冲中子总数测量中有广阔的应用前景。利用K-400加速器稳态DT中子源,实验标定了235U裂变碎片在PIN探测器中的平均沉积能量,并与理论计算结果进行了比较。裂变靶室系统探测效率可通过数值计算准确给出,与平均沉积能量实验测量值相结合,可得到准确的中子灵敏度数据,进而获得裂变靶室探测系统中子能量响应曲线。     

239Pu(nth,f)短寿命裂变产物产额测量

采用γ能谱相对测量方法,以97Zr为内标参考核素,完成了239Pu(nth,f)短寿命裂变产物88 Rb、95 Y、101 Mo、101 Tc、138 Csg、142 La等核素的累积产额测量。实验测得88 Rb、95 Y、101 Mo、101 Tc、138 Csg、142 La的累积产额数据分别为(1.32±0.05)%、(4.69±0.22)%、(6.13±0.32)%、(6.10±0.22)%、(6.24±0.24)%、(4.74±0.17)%。对高纯锗探测器中高能端效率刻度、样品封装与辐照、γ谱测量几何条件设计、γ谱测量与数据分析进行了研究。实验测量裂变产物核素分别位于非对称裂变质量分布双驼峰曲线轻峰的左侧、中部和右侧,重峰的中部与右侧。     

Neutron energy dependence of delayed neutron yields and its assessments

Incident neutron energy dependence of delayed neutron yields of uranium and plutonium isotopes is investigated. A summation calculation of decay and fission yield data is employed, and the energy dependence of the latter part is considered in a phenomenological way. Our calculation systematically reproduces the energy dependence of delayed neutron yields by introducing an energy dependence of the most probable charge and the odd–even e?ect. The calculated fission yields are assessed by comparison with JENDL/FPY-2011, delayed neutron activities, and decay heats. Although the fission yields in this work are optimized to delayed neutron yields, the calculated decay heats are in good agreement with the experimental data. Comparison of the fission yields calculated in this work and JENDL/FPY-2011 gave an important insight for the evaluation of the next Japanese evaluated nuclear data library (JENDL) .     

最优化方法应用于裂变核反应理论计算的研究

中子诱发裂变核反应的反应机制十分复杂,需由光学模型、复合核模型等共同描述,因此需同时对大量参数进行调节才能正确描述裂变核反应数据。本文在FUNF裂变核反应模型基础上,利用先进的最优化方法MINUIT,结合MPI的并行计算方法,研究了MINUIT对裂变核反应调参的工作原理,并以中子诱发238U的裂变核反应为例,验证了裂变核反应数据优化方法的可靠性。     

Impact of Incident Energy Dependence of Prompt Fission Neutron Spectra on Uncertainty Analyses

This paper investigates the impact of the incident energy dependence of prompt fission neutron spectra (PFNS) on uncertainty propagation calculations. Uncertainty propagation from incident energy-dependent PFNS to criticality is formulated and its impact is evaluated numerically. It is found that the conventional procedure, in which representative PFNS covariance data for a specific incident energy are used, results in a larger PFNS-induced uncertainty than the straightforward procedure, in which different PFNS covariance data are used for each incident energy range given in the nuclear data libraries. The present study suggests that the correlation between different incident energies of PFNS has a large impact on uncertainty propagation calculation results for nuclear characteristics.     

热能点裂变截面系统规律

为建立缺乏实验测量数据的热能点裂变截面的评价方法和手段,本文从裂变理论基本公式出发,提出了其系统学公式的基本形式。在推荐热能点裂变截面以及单峰裂变位垒高度的基础上,研究了热能点裂变截面与鞍点态激发能之间的关系,发现了核素的热能点裂变截面与激发能之间的对数关系,通过拟合得到了质子数Z对应的系统学参数。进一步研究这些参数随Z的变化规律,发现了参数与Z的奇偶的关系,并通过拟合建立了全局的系统学公式。研究结果表明,热能点裂变截面与Z相关。     

Measurement of 232Th(n,f) and 232Th(n,γ) reaction rates in thorium powder cylinder bombarded with D-T neutrons†

In order to provide reference for the evaluation of thorium parameters for the conceptual design of fusion–fission hybrid energy reactor, a dedicated integral experiment was carried out in a thorium powder cylinder bombarded with D-T neutrons. Thorium capture and fission rates in the 0° direction to the incident D⁺ beam were obtained using the activation method followed by the off-line gamma-ray technique, experimental uncertainties were ～3.1% for thorium capture rate, and were 5.5%, 8.1%, and 6.3% for thorium fission rates based on fission products ^85mKr, ¹⁴³Ce, and ⁸⁷Kr, respectively. The thorium fission rate based on ^85mKr agreed well with the simulation employing ENDF/B-VII.0 library data. The influence of the oxygen contained in the thorium oxide powder and the scattering neutrons from the experimental hall was also evaluated. MCNP simulations employing ENDF/B-Ⅶ.0, JENDL-4.0 library data agreed with experiment within uncertainties except that employing ENDF/B-Ⅶ.1 (6.0%) and CENDL-3.1 (7.9%) for thorium fission rate, while for thorium capture rate, simulation employing JENDL-4.0 agreed with experiment best. The influence of reaction channels of thorium transport medium employing different library data on the thorium reaction rates could be neglected according to the simulation. The thorium capture to fission ratio demonstrated that the fuel breeding efficiency is quite low and energy production plays a leading role under the neutron spectra in this experiment.     

Sensitivity and uncertainty analysis for reactor stable period induced by positive reactivity using one-point adjoint kinetics equation

In order to better predict the kinetic behavior of a nuclear fission reactor, improvement of delayed neutron parameters is essential. Since it is required to establish a path from the microscopic nuclear data to the macroscopic delayed neutron parameters for the improvement, the present paper identifies important nuclear data for reactor kinetics. Sensitivities of the reactor stable period, which describes reactor kinetic behavior, to microscopic nuclear data such as independent fission yields, decay constants and decay branching ratios are calculated efficiently by using the adjoint kinetics equation. Furthermore, nuclide-wise and nuclear data-wise uncertainties of the reactor stable period are quantified using the variance data given in the nuclear data file, and the nuclear data that require further improvement are identified.

The results obtained through the present study are quite helpful, and can be a driving force for further nuclear physics studies.     

十年来核裂变电荷分布研究的新进展

近十年来电荷分布研究取得了显著进展。独立产额测量技术的进步加快了实验数据积累,得到了较为丰富的信息。在分析总结现有效据基础上提出并建立了某些新的电荷分布经验模型。新模型为低能核裂变电荷分布系统学研究、独立产额实验数据评价和预报提供了一个更为有效的方法。     

Neutron Excess Generation by Fusion Neutron Source for Self-Consistency of Nuclear Energy System

The present day fission energy technology faces with the problem of transmutation of dangerous radionuclides that requires neutron excess generation. Nuclear energy system based on fission reactors needs fuel breeding and, therefore, suffers from lack of neutron excess to apply large-scale transmutation option including elimination of fission products. Fusion neutron source (FNS) was proposed to improve neutron balance in the nuclear energy system. Energy associated with the performance of FNS should be small enough to keep the position of neutron excess generator, thus, leaving the role of dominant energy producers to fission reactors. The present paper deals with development of general methodology to estimate the effect of neutron excess generation by FNS on the performance of nuclear energy system as a whole. Multiplication of fusion neutrons in both non-fissionable and fissionable multipliers was considered. Based on the present methodology it was concluded that neutron self-consistency with respect to fuel breeding and transmutation of fission products can be attained with small fraction of energy associated with innovated fusion facilities.     

Estimation of 239Pu independent and cumulative fission product yields from the chain yield data using a Bayesian technique

The independent and cumulative fission product yields (FPYs) are obtained by using the Bayesian technique based on the evaluated mass chain yield, where required constraints such as the normalization can be straightforwardly included. We apply this technique to the ²³⁹Pu FPY data at neutron incident energies of 0.5, 2.0, and 14 MeV, where the most updated mass chain yield ENDF/B-VII.1 data are available. The obtained yield data are compared with the evaluated values by England and Rider in ENDF/B-VI, and differences from their values are investigated. We show that the modern decay data used, such as branching ratios to ground and metastable states, cause differences in the evaluated individual and cumulative fission yields.