Calculation of prompt fission neutron spectrum for 233U（n,f） reaction by the semi-empirical method

The prompt fission neutron spectra for the neutron-induced fission of 233U for low energy neutrons （below 6 MeV） are calculated using nuclear evaporation theory with a semi-empirical method, in which the partition of the total excitation energy between the fission fragments for the nth＋233U fission reactions is determined by the available experimental and evaluation data. The calculated prompt fission neutron spectra agree well with the experimental data. The proportions of high-energy neutrons of prompt fission neutron spectrum versus incident neutron energies are investigated with the theoretical spectra, and the results are consistent with the systematics. The semi-empirical method could be a useful tool for the prompt evaluation of fission neutron spectra.     

裂变产物产额数据的评价

以中子诱发235U裂变产生的135Xe 的累积产额数据为例, 利用了所有可利用的实验数据, 介绍了裂变产物产额数据的评价方法, 包括数据的收集、 修正、 评价、 误差调整和数据处理, 特别是协方差数据的评价、 半经验模型理论计算数据的应用和相关数据的处理, 给出了135Xe热能点产额的推荐值以及0～20 MeV产额-能量关系曲线。 Takeing 135Xe produced by neutron induced fission of 235U as an example, the evaluation method for fission yield was introduced using the all experimental data available. The evaluation procedure includes the experimental data collection, correction, evaluation, error assessment and data analysis. The study of the uncertainty covariance, application of semi empirical theoretical calculation and the yield energy dependence of 135Xe in the incident energy range 0~20 MeV were emphasized in this work.     

n+233U裂变碎片质量分布的唯象模型研究

本模型基于裂变多通道无规颈断裂模型,考虑宏观液滴能、壳效应能以及壳效应与温度的关系,得到参数化的势能表示形式。通过拟合不同测量方法得到的实验数据(经过评价) 获得3 组模型参数。3 组参数计算的碎片质量分布均很好地再现了不同能点的实验数据,除了基于动能法实验数据得到的参数外,其14 MeV的计算结果与实验数据符合较差。研究发现,不同入射中子能量的裂变碎片质量分布有4 个主要交叉点,在叉点之上的产额随入射中子能量增加减少,之下的产额则随入射中子能量上升;内侧(或外侧) 的两个交叉点质量数之和近似等于裂变复合核的质量数;不同裂变系统的重峰左侧的交叉点都保持在132 附近。Present model was based upon Brosa model, where macro energy,shell effect energy and its decreasing with system temperature were considered and parameterized. 3 sets of model parameters were obtained by fitting to 3 groups of evaluated experimental data, respectively, where the groups were classified by measured method: radiochemistry (RA) method, double kinetic energy (KE) method, and both (ALL). All the 3 sets of parameters could well reproduce themeasured mass distributions on different energies, except the KE set on 14 MeV. The result shows the mass distributions mainly had 4 trend turning points, above which the yield decreasing and below which the yield increasing with energy.The sum of the 1st and 4th (or 2nd and 3rd) point positions was equal to the compound nuclei mass approximately. And the 3rd point was kept at ~132 constantly for different fission systems n+233 U, n+235U, n+233Pu.     

天体物理中爆发性核合成

简要地评述天体核过程,着重讨论爆发性氢燃烧过程,并利用最新的反应率实验数据对氢燃烧过程进行了计算.指出从热pp链通过¹¹C的质子辐射俘获反应进入CNO循环的反应流量可以超过3α过程的流量.用¹⁸F(p,γ)和(p,α)反应的新反应率计算的¹⁸F生成丰度比旧反应率给出的丰度要大1.8倍.对在X射线爆的典型天体物理条件下的快质子(rp)过程的计算表明,“等待核”⁸⁹Ru和⁹³Pd的β衰变寿命的新实验数据给出的该2核的生成丰度,比旧实验数据给出的值要大4倍.     

ISOL靶－源中铀靶的放射性活度研究

用3种方法计算在线同位素分离器(ISOL)靶－源中铀靶在100MeV, 200μA强流质子束照射下产生的放射性核素活度及γ射线强度随时间的变化, 为铀靶的设计、更换及后期处理提供一定的设计依据.     

232Th 中子诱发裂变产额数据比对评价

232Th 中子诱发裂变产额在Th/U 燃料循环的核能开发中具有重要的意义,在现有国际评价产额数据库基础上,结合最新的实验数据,对产物核的质量分布和反应堆计算所需的重点产物核进行了比对。这些产物核包括95Mo,99Tc,101Ru,103Rh,109Ag,133Cs,147Sm,149Sm,150Sm,151Sm,152Sm,143Nd,145Nd 和153Eu 等,对有分歧的133Cs,152Sm 和153Eu 累积产额数据进行了评价调整。最后推荐给出了n+232Th 裂变的产额数据库,作为CENDL 库的组成部分。The yields of n+232Th fission are important in study of the Th/U fuel cycle. Based upon the evaluated nuclear data libraries and recent experimental data,comparison and evaluation for yield mass distribution and cumulativeyield were performed for those products are needed and important in reactor calculations,including 95Mo,99Tc,101Ru,103Rh,109Ag,133Cs,147Sm,149Sm,150Sm,151Sm,152Sm,143Nd,145Nd adn 153Eu etc. Adjustments were made for 133Cs, 152Sm and 153En which have discrepancies among the libraries. Database for n+233Th fission yield is recommended as a part of CENDL update.     

The Main Path to C, N, O Elements in Big Bang Nucleosynthesis

The production of C, N, O elements in a standard big bang nucleosynthesis scenario is investigated. Using the up-to-date data of nuclear reactions in BBN, in particular the ^8Li （n,γ） ^9Li which has been measured in China Institute of Atomic Energy, a full nucleosynthesis network calculation of BBN is carried out. Our calculation results show that the abundance of 12 C is increased for an order of magnitude after addition of the reaction chain ^8Li（n,γ） ^9Li（α,n） ^12B（β） ^12C, which was neglected in previous studies. We find that this sequence provides the main channel to convert the light elements into C, N, O in standard BBN.     

质子滴线附近的β缓发质子衰变

简要回顾了实验小组在过去8年中获得的实验结果, 即采用氦喷嘴快速带传输系统 +“p-γ”符合方法, 在稀土区质子滴线附近首次观测了9种新核素的β缓发质子衰变, 在A=90核区的N=Z线附近获得了5种核素的β缓发质子衰变的新数据. 并把这14种核素的半衰期, 自旋宇称, 形变以及生成反应截面的实验值与流行的核模型理论预言进行了系统地对比讨论. 从中看出:(1)⁸⁵Mo, ⁹²Rh以及“等待点”核⁸⁹Ru和⁹³Pd半衰期的实验值比近期Moller等人的宏观-微观理论预言值[At. Data Nucl Data Tables, 66, 131(1997)]长5—10倍, 因而明显地影响天体rp过程生成的核素丰度;(2)实验指认的质子滴线核¹⁴²Ho和¹²⁸Pm的自旋宇称与流行理论预言不符, 但用Woods-Saxon-Strutinsky方法可以计算得到相符的位能面;(3)实验估计的9种稀土核的生成截面比通用的Alice和HIVAP程序的计算值要小1—2个数量级.     

New Astrophysical Reaction Rates for ^18F（P,α）^15O and ^18F（P,γ）^19Ne

The rates of the thermonuclear ^18F(P,α)^15O and ^18F(P,γ)^19Ne reactions in hot astrophysical environments are needed to understand gamma-ray emission from nova explosions. The rates for these reactions have been uncertain due to discrepancies in recent measurements, as well as to a lack of a comprehensive examination of the available structure information in the compound nucleus ^19Ne. We have examined the latest experimental measurements with radioactive and stable beams, and made estimates of the unmeasured ^19Ne nuclear level parameters, to generate new rates with uncertainties for these reactions. The rates are expressed as numerical values over the temperature range relevant for stellar explosions, as well as analytical expressions as functions of temperature in a format suitable for use in astrophysical simulations. Comparisons with the previous rate calculations are carried out, and the astrophysical implications are briefly discussed.     

Calculation of prompt fission neutron spectra for 235U(n,f)

The prompt fission neutron spectra for the neutron-induced fission of ²³⁵U at E_n < 5 MeV are calculated using nuclear evaporation theory with a semi-empirical model, in which the nonconstant and constant temperatures related to the Fermi gas model are taken into account. The calculated prompt fission neutron spectra reproduce the experimental data well. For the n(thermal)+²³⁵U reaction, the average nuclear temperature of the fission fragment, and the probability distribution of the nuclear temperature, are discussed and compared with the Los Alamos model. The energy carried away by γ rays emitted from each fragment is also obtained and the results are in good agreement with the existing experimental data.