与核能有关的中子数据和核反应研究

介绍开展了中子核反应研究和数据测量的重要性，并扼要介绍了在北京大学重离子物理研究所４．５ＭＶ静电加速器单色中子源开展的中子实验工作。     

入射能量为5．1MeV中子~（58）Ni（n，α）~（55）Fe反应截面和出射

用屏栅电离室测量了入射中子能量为５．１ＭｅＶ的５８Ｎｉ（ｎ，α）５５Ｆｅ核反应的α粒子角分布，２３８Ｕ裂变电离室作中子注量率的测量，测得该能点５８Ｎｉ（ｎ，α）５５Ｆｅ的总截面为（４７．４±５．０）ｍｂ．用中国核数据中心推荐的理论计算程序ＵＮＦ计算了在１—８ＭｅＶ能区５８Ｎｉ（ｎ，ｐ）５８Ｃｏ，５８Ｎｉ（ｎ，α）５５Ｆｅ的反应截面和入射中子能量为５．１ＭｅＶ的５８Ｎｉ（ｎ，α）反应角分布．理论和测量数据的比较说明，用复合核模型来描写该能点的角分布是可行的．     

Multi-modal analysis for low energy neutron-induced fission of ~(235)U

Low energy neutron induced fission of 235U is studied in the framework of the multi-modal fission model. The fission fragment properties, such as the yields, the average total kinetic energy distribution and the average neutron separation energy, are investigated for incident neutron energies from thermal to 6.0 MeV. The multi-modal fission approach is also used to evaluate the prompt fission neutron multiplicity and spectra for the neutron-induced fission of 235U with an improved version of the Los Alamos ...     

Analysis of prompt fission neutron spectrum and multiplicity for 237Np（n,f） in the frame of multi-modal Los Alamos model

The improved version of Los Alamos model with the multi-modal fission approach is used to analyse the prompt fission neutron spectrum and multiplicity for the neutron-induced fission of 237Np. The spectra of neutrons emitted from fragments for the three most dominant fission modes (standard Ⅰ, standard Ⅱ and superlong) are calculated separately and the total spectrum is synthesized. The multi-modal parameters contained in the spectrum model are determined on the basis of experimental data of fission fragment mass distributions. The calculated total prompt fission neutron spectrum and multiplicity are better agreement with the experimental data than those obtained from the conventional treatment of the Los Alamos model.     

First neutron spectrometry measurement at the HL-2A Tokamak

A compact neutron spectrometer based on the liquid scintillator is presented for neutron energy spectrum measurements at the HL-2A Tokamak. The spectrometer was well characterized and a fast digital pulse shape discrimination software was developed using the charge comparison method. A digitizer data acquisition system with a maximum frequency of 1 MHz can work under an environment with a high count rate at HL-2A Tokamak. Specific radiation and magnetic shielding for the spectrometer were designed for the neutron spectrum measurement at the HL-2A Tokamak. For pulse height spectrum analysis, dedicated numerical simulation utilizing NUBEAM combined with GENESIS was performed to obtain the neutron energy spectrum. Subsequently, the transportation process from the plasma to the detector was evaluated with Monte Carlo calculations. The distorted neutron energy spectrum was folded with the response matrix of the liquid scintillation spectrometer, and good consistency was found between the simulated and measured pulse height spectra. This neutron spectrometer based on a digital acquisition system could be well adopted for the investigation of the auxiliary heating behavior and the fast-ion related phenomenon on different tokamak devices.     

Measurement of Electron-Drift Velocity in Ar＋CH4 Mixtures Using Double-Grid Method

Based on analyzing the induced signals from the double-grids of an ionization chamber, the electron-drift time between the two grids is determined and the electron-drift velocity is derived. A waveform digitizer is employed to record pulses from the two grids of the ionization chamber. The electron-drift velocity is measured as a function of the reduced electric field E/p for eight different ratios of Ar＋CH4 mixtures. By analyzing the experimental data of this study, self-consistency of experimental data is achieved, and formulae for calculating electron-drift velocity in any ratio of Ar＋CH4 mixtures are obtained.     

轻核(n,x)反应微分截面的实验测量

对本课题组十几年来的(n,x)反应实验研究工作进行了评述.介绍了屏栅电离室的特点、构造与工作原理.用屏栅电离室在北京大学4.5MV静电加速器上测量了1—7MeV中子6Li(n,t)4He和10B(n,α)7Li反应的微分截面与截面,对实验结果进行了讨论. Our research work on (n, x) reaction for more than one decade is reviewed. The characteristics, structure, and working principle of the gridded ionization chamber are discussed. Differential cross sections and cross sections of the~(6)Li(n, t)~(4)He and~(10)B(n, α)~(7)Li reactions were measured in the neutron energy range of 1—7 MeV by using the GIC method. Experiments were carried out at the 4.5 MV Van de Graaff accelerator of Peking University. Results of the measurement are discussed.     

入射能量为5.1MeV中子58Ni(n,α)55Fe反应截面和出射粒子角分布测量

用屏栅电离室测量了入射中子能量为5.1MeV的⁵⁸Ni(n,α)⁵⁵Fe核反应的α粒子角分布,²³⁸U裂变电离室作中子注量率的测量,测得该能点⁵⁸Ni(n,α)⁵⁵Fe的总截面为(47.4±5.0)mb.用中国核数据中心推荐的理论计算程序UNF计算了在1—8MeV能区⁵⁸Ni(n,p)⁵⁸Co,⁵⁸Ni(n,α)⁵⁵Fe的反应截面和入射中子能量为5.1MeV的⁵⁸Ni(n,α)反应角分布.理论和测量数据的比较说明,用复合核模型来描写该能点的角分布是可行的.     

单能中子源中低能成份对活化截面测量的影响

对用单能中子源作活化截面测量时低能中子干扰的影响作了分析研究,并从测量的两种常用中子源T(d,n)⁴He和D(d,n)³He的中子源能谱中验证了这种定性分析.最后给出了两个比较典型的反应⁵⁸Ni(n,P)⁵⁸Co和⁶⁴Zn(,P)⁶⁴Cu反应的截面测量结果.     

Multi-modal analysis for low energy neutron-induced fission of 235U

Low energy neutron induced fission of 235U is studied in the framework of the multi-modal fission model. The fission fragment properties, such as the yields, the average total kinetic energy distribution and the average neutron separation energy, are investigated for incident neutron energies from thermal to 6.0 MeV. The multi-modal fission approach is also used to evaluate the prompt fission neutron multiplicity and spectra for the neutron-induced fission of 235U with an improved version of the Los Alamos model for incident neutrons below the （n, nf） threshold. The three most dominant fission modes are taken into account. The model parameters are determined on the basis of experimental data. The calculated results are in good agreement with the experimental data.