利用QMD分析中高能质子入射208Pb的(p,xn)反应双微分截面

中高能质子入射重金属靶产生散裂中子是加速器驱动洁净核能系统的一个关键部分.利用量子分子动力学(QMD)模型研究入射质子能量在300MeV—1.5GeV,散裂靶为²⁰⁸Pb的(p,xn)核反应的双微分截面,QMD计算结果很好再现了实验数据,且QMD的计算结果明显优于HETC和LAHET.QMD在较宽的能区和核区满足加速器驱动洁净核能系统散裂靶物理计算的要求.     

Theoretical Calculations and Analysis of n+208Pb Reaction for Intermediate Energy Neutron

Based on experimental data of total, nonelastic, elastic cross section and elastic scattering angular distributions for n+Pb reactions, a set of neutron optical model potential parameters is obtained in the region of incident neutron energy from 1—300 MeV. The cross sections, angular distributions and energy spectra are calculated and analyzed by optical model, distorted wave Born approximation theory, Hauser-Feshbach theory, exciton model and cascade mechanism inside nuclear. The results indicate that the cross sections can be given for n+ ²⁰⁸Pb reactions which are all in good agreement with experimental data.     

208Pb平均振幅或形变参数系统研究及中子直接非弹性散射截面计算

对２０８Ｐｂ的低激发态分立能级属性和相关平均振幅或形变参数进行了系统研究,利用扭曲波波恩近似方法系统计算了１２个分立能级的中子直接非弹性散射截面． The amplitudes or form factors of the low discrete levels of 208 Pb are investigated systematically, the neutron direct inelastic scattering cross sections from 12 levels on 208 Pb are calculated.     

Stuty on the Process of the Fast Neutron Radiative Capture for 40Ca and 208Pb

The pre-equilibrium correction for the nuclear reactions induced by fast neutron is considered as follows: the nuclear reaction processes with the exciton number equal to or larger than five can still be described by the statistical theory of the nuclear reaction. The particle emission processes, in which less than five excitons are involved, are calculated by means of the exciton model and the γ emission of one exciton state is calculated by the direct capture mechanism. For the three-exciton state, only the semidirect capture mechanism, which plays the main role in the researched energy region, is taken into account. The interference effect between the direct and semidirect capture is also considered. The radiative capture cross sections for ⁴⁰Ca and ²⁰⁸Pb in the neutron incident energy region from 3 MeV to 20 MeV are calculated and a better coincidence with the experimental values is obtained. At the same time, the contribution to the (n, γ) reaction cross sections of the γ emissions before and after statistical equilibriums as well as the characteristics of the direct capture, semidirect capture and their interferece terms are discussed.     

Theoretical Calculations of Microscopic Nuclear Reaction Data for p+209Bi in Energy Region up to 300MeV

Based on nuclear reaction models, i.e., the optical model, evaporation model, exciton model and the direct reaction theory, cross sections of (p,xn) reactions and residual nuclei productions for p+²⁰⁹Bi reaction were calculated in energy region from threshold up to 300MeV and a set of proton optical potential parameters for ²⁰⁹Bi up to 500MeV were obtained. The direct inelastic cross sections were calculated with the distorted wave Born approximation theory. Theoretical results show that the direct inelastic cross sections of about 550mb are reasonable.     

中能中子与208Pb反应的理论计算和分析

在中子与原子核Pb及其同位素反应的总截面,去弹性散射截面,弹性散射截面和弹性散射角分布的实验数据基础上,获得了入射中子能量从1—300MeV的一组普适中子与Pb及其同位素反应的光学模型势参数.应用光学模型,扭曲波玻恩近似理论,宽度涨落修正的Hauser-Feshbach理论,预平衡反应的激子模型和核内级联模型,计算和分析了中子与²⁴⁸Pb反应的所有截面、角分布和能谱.理论计算与实验数据进行了分析比较     

Probability Distribution and Entropy of Nonequilibrium State for 208Pb Nuclei Under Different Excited Energies

The probability distribution and the entropy of ²⁰⁸Pb nuclei under different excited energies are calculated.Comparison is made between the probability distributions and the entropies with time for different excited energies.The result shows that our previous calculation is reasonable.     

Study on Deformation and Shape Coexistence for 188Pb

The deformation and shape coexistence in ¹⁸⁸Pb have been investigated in terms of the Projected Shell Model. Comparing the experimental data with the calculated results, it is shown that three shape configurations of sphere (Z=82 shell closure), oblate (two particle-two hole in proton h_9/2 orbital) and prolate (multi-particle-hole)coexist each other in the low-lying excited states and the prolate band exhibits a mixture between two kinds of multi-particle-hole configurations, which means that the neutron i_13/2 alignment happens gradually in this case. The mixing is discussed and the mixing coefficients are given. The oblate band structure is predicted and the 2⁺ prolate state is estimated to be in the energy range of 804—80keV.     

Measurement of Reaction Cross Section for 17C and Finite-Range Glauber Model Analysis

We have measured the reaction cross section σ_R of ¹⁷C on the carbon target at the intermediate energy of 97A MeV by using transmission method.finite-range Glauber model has been employed to investigate the density distribution of ¹⁷C by fitting the present result and the previous result of interaction cross section σ_I.By contrast with the result from the analysis of σ_I,a tail in the neutron density distribution of ¹⁷C is found necessary to interpret the present result.Considering the configuration of the valence neutron,a dominant 1d_5/2(77±21%)occupancy is found,which is in agreement with results of momentum distribution measurements.     

Measurements of Reaction Cross Section for F Isotopes and Possible Proton Skin Structure for 17F

The reaction cross sections σ R of F isotopes on carbon target were measured at intermediate energies via the transmission method. It was found that the reaction cross section of ¹⁷F has a little enhancement compared with that of its neighbor isotopes. The difference factor d has been deduced from the measured σ R by using the BUU model and Glauber model. It is enhanced also for ¹⁷F compared with its neighbor isotopes. From the above analysis, a possible proton skin structure is suggested for ¹⁷F.     

Study of 2n-Removal and Total Reaction Cross Section Induced by 11Li in BUU Framework

The σ_R and σ_－2n have been calculated via the BUU model by using soft EOS and 0.8σ_Cug. The density distribution which come from RMF model has been introduced to replace the normal used square-type distributions in BUU calculation. The calculated results can reproduce the experimental data well for various reaction systems. Here σ_－2n is calculated as the difference between σ_R of halo nucleus and core nucleus, by assuming σ_corr=0. It indicates that this assumption works very well in the BUU calculation.     

On the Gross Structure of Fusion Cross Section for 16O+12C System

The gross structure appeared in the total fusion cross section for ¹⁶O+¹²C system is studied by using the LCNO theory and the folding model of the paritydependent potential.The experimental data of the fusion cross section,elastic scattering excitation functions and angular distributions for this system are well explained.     

Measurement of Neutron-Removal Cross Section of Neutron-Rich Nucleus 8He by Using the Transmission Method

The neutron-rich nucleus ⁸He is selected by RIBLL from the breakup of 50MeV/u ¹³C on be target at HIRFL. The 2n-removal and 4n-removal cross section of ⁸He was measured by using the transmission method. The point that ⁴He is ⁸He core can be reduced from the experiment data via the Ogawa's theory.     

The Cross Section Fluctuation of the Isotope Projectile-Like Fragments in the Dissipative Process of Reaction 19F+51V

By using a detection system combining Time-of-Flight(TOF)method with(△E-E)technique,the excitation functions,the dependence of energy coherence widthΓon product mass A and the dependence of Γon the degree of freedom of neutron excess N/Z for some elements and their isotope products in the dissipative process of reaction ¹⁹F+⁵¹V at energies from 102.25MeV to 109.50 MeV(in 250 keV steps)were presented and discussed for the first time.     

中能轻奇异核反应总截面的激发函数测量

通过对中能区和相对论能区反应总截面的比较, 可对了解核中核子密度分布的尾巴分量提供重要的信息, Ｇｌａｕｂｅｒ 模型的计算总是低估中能区的反应总截面, 对中子晕核和中子皮核, 这种低估更为严重． 因此, 基于 Ｇｌａｕｂｅｒ 模型从反应总截面提取核的大小存在着一些问题． 对一些轻的奇异核进行中能区核反应总截面的激发函数测量可能会有助于上述问题的解决.A comparison of interaction cross section at relativistic and intermediate energy provides important information about the existence of tail component in the density distribution. The Glauber model calculation always underestimates the total reaction cross section at intermediate energy. The differences are enhanced for halo and skin nuclei. The method to extract the size of nuclei via Glauber model seems to have some ambiguity. The excitation function of total reaction...     

Ab Initio Calculations of Differential Cross Sections for Single Charge Transfer in ^3He^2＋ ＋ ^4He Collisions

The single charge transfer process in ^3He^2＋ ＋ ^4He collisions is investigated using the quantum-mechanical molecular- orbital close-coupling method, in which the adiabatic potentials and radial couplings are calculated by using the ab initio multireference single- and double-excitation configuration interaction methods. The differential cross sections for the single charge transfer are presented at the laboratorial energies E = 6 keV and lOkeV for the projectile ^3He^2＋. Comparison with the existing data shows that the present results are better in agreement with the experimental measurements than other calculations in the dominant small angle scattering, which is attributed to the accurate calculations of the adiabatic potentials and the radial couplings.     

Dispersion Optical Model Analysis of the Neutron Cross Section Anomalv for 16O

The optical model of ¹⁶O is studied based on the dispetsion relation theory at neutron energy up to 20MeV.The total cross section anomaly is removed essendally at low energies for ¹⁶O.     

用反应48Ca+254Es合成119号元素的可能性研究

利用最近发展起来的两步模型分析重离子核反应48Ca+254Es 的熔合过程。在这个模型中,熔合过程被分为前后独立的两个过程,即粘连过程和形成过程。本研究组计算了对应的粘连概率和形成概率,并结合适用于蒸发过程的统计蒸发模型,计算了该反应合成119 号超重元素的剩余截面,即当Elab = 250:2 MeV时,得到最大剩余截面为0.7 pb。Two-step model is adopted to analyze the fusion process of heavy-ion reaction 48Ca+254 Es. Based on this model, the fusion process is divided into two consecutive steps, i.e., the sticking step and the formation step, and corresponding sticking probability and formation probability are calculated. Combining the statistical evaporation model for the evaporation stage, the maximum evaporation residue cross section for reaction 48Ca+254 Es is 0.7 pb at 4n, Elab =250.2 MeV.     

Cross Section Measurements of Neutron-Rich Hg Isotopes in Reaction of 28MeV/u 18O with Thick Natural Lead Target

By using 28MeV/u ¹⁸O beam,an on-line melting lead target equipment and 4π-ΔEβ-γcoincident technique,the relative cross section ratios and absolute cross sections of neutron-rich nuclides ^205—208Hg have been measured. The production cross section of ²⁰⁹Hg is extrapolated.The cross section of ²⁰⁷Hg produced by-2p +1n from target decreases suddenly,which may be explained by change of reaction Q value.     

Theoretical Analysis of Double Differential Cross Sections for n+ 238U Reaction

Based on the new measurements of total, nonelastic, elastic cross section and elastic scattering angular distributions for n+U reactions, a set of neutron optical model potential parameters is obtained in the region of incident neutron energy from 0.1 to 20 MeV. The cross sections, angular distributions, energy spectra and double differential cross sections are calculated and analyzed by optical model, nuclear fission theory, distorted wave Born approximation theory, coupled channel theory, the unified Hauser-Feshbach theory, as well as exciton model. The results indicate that our theoretical model can reasonably analysis n+ ²³⁸U reaction data with neutron energy lower than 20 MeV.