Theoretical calculations and evaluations of n+23Na reaction

The data for neutron-induced reactions are indispensable in a lot of applications of nuclear science and technologies. All reaction cross sections, angular distributions, energy spectra, and double-differential cross sections of neutron, proton, deuteron, triton, and alpha-particle emissions are consistently calculated and analyzed for n+~(23)Na reactions at incident neutron energies below200 Me V, based on nuclear theoretical models. The calculated results are compared with the experimental data and the evaluated data in the ENDF/B-VII, JENDL-4.0,and JEFF-3.2 libraries. In most cases, the calculated results describe the corresponding experimental data well. At the resonance energy region, evaluated experimental data are adopted to fit to the resonance structures.     

Investigation of the statistical distribution of spontaneous U238 fission acts according to the energies of the two fragments

Using an apparatus consisting of a double pulse ionization chamber, two amplifying channels, a coincidence circuit and a two-beam pulsed oscillograph, we measured the kinetic energy of each of the two fragments formed during nuclear fission. 780 cases of spontaneous U²³⁸ fission and about 4500 cases of U²³⁵ fission by slow neutrons were recorded. Using these data we plotted the statistical distributions of acts of spontaneous fission and fission with slow neutrons according to the energies of the two fragments. These distributions gave the following curves for the two fission methods: a) the energy spectrum of all fragments and that of light and heavy fragments separately; b) the distribution of acts according to the total kinetic energy of the two nuclear fragments; c) the distribution of fission fragments according to mass; d) the relation of the average total kinetic energy of the two fragments to the ratio of their masses; and e) the relation of the average kinetic energy of light and heavy fragments to their total kinetic energy. The results of the two methods of fission are quite similar. It was found that the total kinetic energy of the two fragments in spontaneous U²³⁸ fission was, on the average, 4 Mev less than the energy in U²³⁵ fission by slow neutrons.     

Energy and angular distribution of recoil proton of fast neutron in scintillation fiber： a simulation study

Due to their low cost,big reaction cross-section with neutrons,flexibility,and convenience for long distance data transfer,plastic scintillation fibers (PSF) have been increasingly used as detectors or sensors for high-energy neutron radiography.In this paper,Geant4 Monte Carlo simulation tool was used to obtain some chalacteristics of energy and angular distributions of recoil protons in plastic scintillation fibers irradiated by fast neutrons.The plastic fiber with BCF-20 as the core and an acrylic outer cladding was used in the simulation.The results show that there is a big range of energy and angular distribution of recoil protons in energies varying inversely with the recoil angle.     

用转移反应研究6He奇特核体系的光学势

由于受到放射性束强度弱、品质差的限制,奇特核体系的光学势性质一直是亟待解决的国际难题。本工作利用稳定束的转移反应作为探针,深入研究了反应出射道奇特核体系的光学势性质。利用中国原子能科学研究院的HI-13串列加速器在近库仑位垒能区高精度测量了⁷Li+⁶³Cu、²⁰⁸Pb的弹性散射以及单质子转移反应角分布,并利用扭曲波玻恩近似（DWBA）和耦合反应道（CRC）方法对实验数据进行了拟合,抽取了出射道⁶He+⁶⁴Zn、²⁰⁹Bi晕核体系的光学势参数。所得参数可重现文献中已有的6He体系的弹性散射角分布,验证了这种方法的可靠性。对所得势参数的能量相依性的分析表明,在重体系⁶He+²⁰⁹Bi中,基于因果律的色散关系并不适用,其潜在的物理原因还需进一步深入研究。     

Fragmentation of 200 and 244 MeV/u carbon beams in thick tissue-like absorbers.

Stacks consisting of thin CR-39 sheets sandwiched between thick lucite and water absorbers were perpendicularly bombarded by 12C ions at 200 and 244 MeV/u. Track radius distributions representing the charge composition of the fragmented beams were automatically measured by a particle track analysis system. After analysis of the nuclear charge distributions, the total charge removal cross-sections and elemental production cross-sections of fragments with atomic numbers from 5 to 3, were obtained down to the lower energies (approximately 50 and 100 MeV/u, respectively). It has been found that the measured total charge removal cross-section agrees with theoretical predictions within approximately 10% and very well with previous experiments in corresponding energy regions. Two model calculations for production of B fragment are in good agreement with our measured data while a third model overestimates it by approximately 12%. Theoretical cross-sections for Be and Li fragments differ strongly among the different models and from measured values.     

Calculated depth-dose distributions for H and He beams in liquid water

We have calculated the dose distribution delivered by proton and helium beams in liquid water as a function of the target-depth, for incident energies in the range 0.5-10 MeV/u. The motion of the projectiles through the stopping medium is simulated by a code that combines Monte Carlo and a finite differences algorithm to consider the electronic stopping power, evaluated in the dielectric framework, and the multiple nuclear scattering with the target nuclei. Changes in projectile charge-state are taken into account dynamically as it moves through the target. We use the MELF-GOS model to describe the energy loss function of liquid water, obtaining a value of 79.4 eV for its mean excitation energy. Our calculated stopping powers and depth-dose distributions are compared with those obtained using other methods to describe the energy loss function of liquid water, such as the extended Drude and the Penn models, as well as with the prediction of the SRIM code and the tables of ICRU.     

Calculation and analysis of p + Ca reaction cross sections at incident energies from threshold to 250 MeV

All cross sections, angular distributions and energy spectra of neutron, proton, deuteron, triton, helium, alpha particle emission for p + ^{40,42,43,44,46,48,nat}Ca reactions have been calculated and analyzed at incident proton energies from threshold to 250 MeV by nuclear theoretical models. The theoretical calculated results are in good agreement with existing experimental data.     

Measurement and analysis of species distribution in laser-induced ablation plasma of an aluminum–magnesium alloy

We proposed a theoretical spatio-temporal imaging method, which was based on the thermal model of laser ablation and the two-dimensional axisymmetric multi-species hydrodynamics model. By using the intensity formula, the integral intensity of spectral lines could be calculated and the corresponding images of intensity distribution could be drawn. Through further image processing such as normalization, determination of minimum intensity, combination and color filtering, a relatively clear species distribution image in the plasma could be obtained. Using the above method, we simulated the plasma ablated from Al–Mg alloy by different laser energies under 1 atm argon, and obtained the theoretical spatio-temporal distributions of Mg I, Mg II, Al I, Al II and Ar I species, which are almost consistent with the experimental results by differential imaging. Compared with the experimental decay time constants, the consistency is higher at low laser energy, indicating that our theoretical model is more suitable for the plasma dominated by laser-supported combustion wave.     

Calculation and evaluations for n+Cu reactions

All cross sections of neutron induced reactions, angular distributions, energy spectra and double differential cross sections are consistently calculated and analyzed for n+^63,65,nat.Cu reactions at incident neutron energies below 200 MeV based on the nuclear theoretical models. The optical model, preequilibrium and equilibrium reaction theories, the distorted wave Born approximation theory are used. Theoretical calculated results are compared with existing experimental data and the evaluated results in ENDF/B-VII and JENDL-3 libraries. The optical model potential parameters are obtained according to the experimental data of total, nonelastic scattering cross sections and elastic scattering angular distributions.     

Distribution Equilibrium of Tritium between Adsorbed Water on Molecular Sieve 5A and Environmental Water

In order to calculate airflow around a nuclear site, a new weighted interpolation method for sparse wind data at various terrain heights is developed. This method employs weighting functions for vertical distance and the topographic barrier between the station and a grid point, in addition to a weighting function for horizontal distance which is employed in usual methods. The new weighting functions are developed from the analysis of field measurements taken in complex terrain. This method can represent the wind-fields from the bottom to the upper boundary better than usual methods which use only the horizontal weighting factor, even when the upper wind data are not available.     

基于福岛核事故监测数据的辐射剂量场重构方法研究

辐射剂量场的重构是核事故后开展应急工作的一种重要手段。为了比较不同插值方法用于辐射剂量场重构的优劣,基于日本福岛第一核电站事故后发布的监测数据,分别利用反距离权重插值法、克里金插值法、线性三角网插值法和径向基函数插值法4种方法进行辐射剂量场重构。通过划分不同数量的测试集,以均方根误差、平均绝对误差以及标准偏差为判别依据...     

呈任意能量分布的核信号模拟

针对核信号在脉冲幅度和相邻脉冲产生的时间间隔上存在的随机性,探讨了核信号统计特性的模拟方法.在进行核信号的能量随机性模拟中,可将核信号的统计特性分解为均匀分布、高斯分布、指数分布、多项式分布和泊松分布等基本分布,并用本文所述方法来实现;对于不便于分解、呈任意能量分布的核信号也可用此法实现,模拟效果较好.     

Measurement of Charged-Particle Emission Double-Differential Cross Section of Fluorine for 14.2MeV Neutrons

We carried out detailed measurement of the double-differential cross sections of fluorine for the emissions of protons, deuterons, tritons, and α-particles with 14.2MeV incident neutrons. An improved charged-particle spectrometer with a pencil DT-neutron beam furnished at the FNS facility of the Japan Atomic Energy Agency enabled us to obtain precise data with a fine energy resolution over a wide energy range and an angular range from 15 to 150°. The present experiment is the first simultaneous measurement of the four different kinds of charged particles and provides useful data to establish a nuclear reaction model of fluorine as well as to confirm previous experimental data. Angular-differential cross sections for several discrete peaks corresponding to excited states of residual nuclei were extracted to discuss the reaction mechanism of charged-particle emission. The obtained data suggest that the charged-particle emission reaction of fluorine has a complicated mechanism in which there are contributions from the direct reaction, pre-equilibrium, and equilibrium processes. The obtained data were compared with the nuclear data evaluated in JENDL-3.3 and ENDF/B-VII.0. The results show large differences in the energy and angular distributions of emitted particles and the charged-particle production cross sections between the measured and evaluated data.     

Light charged particle emission for p+Fe reactions

The energy spectra and double differential cross sections of nucleon and the light composite particle (d, t, ³He and α) emissions are studied based on the exciton model included the improved Iwamoto-Harada model. All cross sections of proton induced reactions, angular distributions and energy spectra are consistent calculated and analyzed for ^{54,56,57,58,nat}Fe at incident proton energies below 250 MeV by using nuclear theoretical models which integrate the optical model, the intra-nuclear cascade model, direct, pre-equilibrium and equilibrium reaction theories. Theoretical calculated results are compared with existing experimental data.     

Neutrons and nuclear structure

Synopsis In the past few years slow neutron spectrometers of greatly improved resolving power have been developed at many laboratories throughout the world. During the same period advances in techniques of data analysis have aided in producing the information now available on hundreds of neutron resonances. The manner in which the parameters of these resonances give valuable information on nuclear structure will be described. The experimental findings will be reviewed and particular emphasis paid to their bearing on current theoretical nuclear models. The following aspects will be emphasized. 1) The radiation widths of nuclear energy levels and their relationship to theoretical transition probabilities. 2) The size distributions of neutron widths of levels and recent theoretical treatments of these distributions. 3) The average spacings of levels for different nuclei as well as the apparent non-random distribution of spacings for individual nuclei. 4) The probability of compound nucleus formation, or strength function, compared to recent calculations based on the cloudy crystal nuclear model. 5) Recent determinations of the nuclear radius at high and low neutron energies.Paper read on July 3, 1956 to the Amsterdam Nuclear Reactions Conference.     

Nuclear data uncertainty propagation: Perturbation vs. Monte Carlo

Two methods of nuclear data uncertainty propagation are compared, using the same nuclear data uncertainties and criticality-safety benchmarks. The first method, based on perturbation theory uses covariance files, covariance processing and the perturbation card of MCNP. The second method makes use of a large number of MCNP calculations, all alike, but using different random nuclear data libraries, consistent with the covariance files of the first method. The consistency of the nuclear data used by both methods is checked and results for 33 criticality-safety benchmarks are presented. Relatively good agreements are found, but depending on the benchmark cases, differences due to the elastic cross-section, ν-bar, angular and energy distributions are observed.     

Ep≤200 MeV能区p+58Ni反应的计算与分析

以现有质子诱发⁵⁸Ni的各种核反应截面、能谱、双微分截面、弹性散射角分布等实验数据为基础，利用自行研制的大型核模型计算程序MEND计算质子能量在200MeV能区内⁵⁸Ni(p,x)反应的截面、能谱、角分布和n、p、α、d、t、³He6种出射轻粒子的双微分截面。MEND程序的理论框架基于球形光学模型、核子的核内级联发射模型、以激子模型为基础的预平衡发射理论、蒸发模型和带宽度涨落修正的Hauser Feshbach统计理论。光学模型中的势参数由APMN程序通过符合p+⁵⁸Ni反应的去弹截面和弹性散射角分布获得。出射粒子的双微分截面则利用MEND程序输出的能谱再通过Kalbach系统学公式计算。将计算结果与实验数据及ENDF/B6评价库进行了比较，计算结果与实验数据基本一致，与ENDF/B6相比，增加了³He的计算，且将能区上推至200MeV。      

电子束在硅中的能量损耗

利用矩法对能量从0.5～8 MeV的电子束在硅中的能量损耗分布作了理论计算。并对相应的轫致辐射能损分布作了近似计算。得到了硅中吸收剂量对深度的分布。     

Carlo DTS: A Monte Carlo code for the dual thin scintillator neutron detector

A Monte Carlo code called CARLO DTS, developed for the efficiency and proton recoil spectra calculation of the Dual Thin Scintillator (DTS) neutron detector is described. The code CARLO DTS covers the neutron energy range between 1 and 20 MeV. The cross sections and angular distributions were taken from the ENDF/B-V data file for the nuclear reactions involved: H(n.n)H, C(n,n)C and inelastic scattering, (n,), (n,n′)3 reactions on carbon-12. The theoretical calculations are compared to experimental results at two neutron energies, namely:2.446 and 14.04 MeV, obtained by means of the Time Correlated Associated Particle Technique.     

Fission time for the U + α reaction measured by the crystal blocking technique

The crystal blocking technique has been used to measure the total time of the induced fission process for the ²³⁵U + α reaction in the energy range of bombarding α-particles from 25.9 to 31.2 MeV. Experimental fission times observed in this reaction vary from 10⁻¹⁷ to 10⁻¹⁶ s, depending on the projectile energy. Together with the corresponding experimental data on angular anisotropy in the same reaction they were analyzed within the dynamic-statistical approach with allowance for the nuclear dissipation phenomenon and the double-humped fission barrier model. It was demonstrated that the time of induced fission at low excitation energies is sensitive to the nuclear dissipation magnitude.