Calculation of Total Cross Sections for Positron-Mg Collision

Total cross sections in positron-Mg collision are calculated in the range 2.0-60.0 eV using the momentum space coupled channels optical potential approach. The target ionization continuum and the positronium formation are included in the optical potential. The present total cross sections are compared with the experiment data and the other theoretical results.     

Positronium Formation in e^＋-K Collision at Low Energies

Positronium (Ps) formation cross section for positron scattering on potassium is calculated at low impact energies (0.2-15.0eV). The present calculation uses an optical-model method with an equivalent local polarization potential. The results for the Ps (n = 1) and Ps (n = 2) formation cross sections are calculated and compared with the experimental measurements and other theoretical results.     

Calculation of Absolute Outer-Shell Electron Impact Ionization Cross Sections

The recently developed semiempirical DM-approach for the calculation of electron impact single ionization cross sections is applied here to the ionization of the rare gases (Ne, Ar, Kr and Xe) via ejection of an outer s-shell electron. The results obtained are compared with previous experimental and theoretical s-shell ionization cross section functions.     

温度相关核截面数据库在MCNP计算中的必要性研究

MCNP程序由于其几何模拟和核数据上的优越性,现在在反应堆的研究分析中已经得到较多应用。通过基准题的计算,定量地说明MCNP通过其自带的常温（294K）下的核素截面数据库不能够对反应堆进行非常准确的计算（由于反应堆内各种材料／位置的温度不同）,而且,它也不能够计算反应堆中与温度相关的量,如反应性温度系数。选用了一个带有不同温度下核素截面数据的MCNP输入格式的数据库,使用MCNP-4C对基准题进行了计算,发现计算结果与基准值符合得非常好。这说明通过使用不同温度下的核素截面数据库,MCNP可以准确计算温度系数和增殖系数等,从而说明在反应堆设计计算中制作不同温度下的核素截面库的必要性。Due to the advantage of geometry simulation and nuclear data, the code MCNP is now widely used in the reactor analysis. Based on our calculation of the fuel temperature reactivity coefficient benchmark, it is quantificationally proved that MCNP with its own cross section library can＇ t be used to simulate the reactor accurately and to calculate the temperature reactivity coefficient. Furthermore, we use MCNP- 4C with a database that contains temperature dependent nuclear cross sections to calculate the benchmark. The results are well agreement with benchmark results. This means that, with the temperature dependent nuclear cross sections library, MCNP can calculate the temperature reactivity coefficient and reactor multiplication factor accurately. So the temperature dependent nuclear cross section library should be processed to meet the requirement of reactor calculation.     

Experimental Study of Single and Double Electron Detachment Cross Sections for Cl^- in Collision with He

Single-electron detachment （SED） and double-electron detachment （DED） for chlorine negative ions in collision with helium are investigated in the energy region of 5-30 keV （SED） and 5-19 ke V （DED） by growth rate method, respectively. Experimental data from this work are compared with the previous reported data, and a general discussion is given.     

Calculation of the Cross Sections for Neutron Scattering at Spin Waves in Helimagnets

An analytical dependence of the cross section for the small-angle scattering of polarized neutrons at spin waves in helimagnets formed because of Dzyaloshinskii—Moriya interaction in cubic crystals without an inversion center (the space group is P2₁3) is obtained. It is assumed that the dispersion of spin waves in helimagnets with the wave vector k _s polarized by a magnetic field is larger than the critical field H_C2 of the transition to the ferromagnetic phase and has the form E _q = A(q ? k _s ) + gμ_B(H ? H_С2). It is shown that the cross section for neutron scattering at the two-dimensional map of angles (θ _x , θ _y ) is two circles of the radii θ_C with the centers ±θ _S , corresponding to the Bragg angle of diffraction by a helix oriented along the applied magnetic field H. The radii of these two circles θ_C are directly related to the stiffness of spin waves A of the magnetic system and depends on the applied magnetic field: \(\theta _C^2 = \theta _0^2 - \frac{{g{\mu _B}H}}{{{E_n}}}{\theta _0}\), where \({\theta _0} = \frac{{{h^2}}}{{2A{m_n}}}\) and E _n and m _n are the neutron energy and mass. It is shown that the scattering cross section depends on the neutron polarization, which is evidence of the chiral character of spin waves in the Dzyaloshinskii—Moriya helimagnets even in the completely polarized phase. The cases of neutron scattering at magnons where θ₀ ≤ θ _S and θ _S ≥ θ₀ are considered. The case of neutron scattering at spin waves in helimagnets is compared with analogous scattering at ferromagnets where θ _S → 0.     

Cross Sections of Electron Detachment for Si^- and Ge^- in Collision with Ar

Single electron detachment cross section for 10-40keV Si^- and Ge^- in collisions with Ar are measured and compared with other available experimental results. In our experimental energy region, the trend of cross sections is almost constant. The cross sections of Ge larger than Si can be understood by including electron affinity and size of negative ions.     

重离子熔合反应形成超重核的截面研究

在双核系统框架下,通过数值法解主方程计算了双核间的核子跃迁全熔合几率.两碰撞核内部激发能由相对运动能损提供,因此能够将核子转移过程与相对运动耦合起来.对一些以Pb为靶的形成超重核的冷熔合反应,计算了最佳激发能、形成双核系统的俘获截面、复合核形成几率及存活几率等,所得到的形成超重核蒸发剩余截面与已知实验值符合较好. In the concept of Dinuclear system (DNS) the complete fusion probability of two touch nuclei via nucleon transfer is described by numerically solving the Master equation. The excitation energy of two colliding nuclei is supplied by the energy dissipation of their relative motion, thus the nucleon transfer process and the relative motion are coupled. For Pb based cold fusion reactions to form super heavy nuclei, the optimal excitation energy, the capture cross section to form a DNS ...     

精确计算SM中混合链图传播下e■→f■反应截面

采用电弱统一标准模型（SM）,分析了由参与电弱相互作用的各种混合圈构成的光子γ,中间玻色子Zo重整化链图传播子的构架方式,并完成了相关解析计算,进而获得了γ,Z₀重整化混合圈链图传播子的解析计算结果.作者又将γ,Z₀混合圈链图传播子D_γ^{（m-chain）}（s）,D_Z^{（m-chain）}（s）和D_γZ^{（m-chain）}（s）应用到粒子反应e■→f■中,精确计算了e■→f■反应总截面σ_SM^（chain）.通过与LEP实验组的实验观测值的比较,发现本文理论计算结果比最低（树图）阶的结果与实验吻合更好.     

Total Hadronic Cross Sections

<正>(Updated September 2013,COMPAS group,fflEP,Protvino)This updated version of the total hadronic cross sections review is based on the first half of 2013 update of the database for total cross section and the ratio of the real-to-imaginary parts of the forward elastic scattering hadronic amplitudes.New data on total pp coUisions cross sections from CERN-LHC-TOTEM[1]and new data from cosmic rays experiment PAO[2]were added.We use a procedure for ranking models as described in[3]to identify the safest parameterizations for extrapolations.Incidentally,the models giving the best fit of accelerator data also reproduce the experimental cosmic ray nucleon-nucleon data extracted from nucleon-air data with no     

Two-Photon Detachment Cross Section of the Positronium Negative Ion

The two-photon detachment cross section of positronium negative ion is calculated within the lowest-order perturbation theory for the final-state energies below the Ps(n = 2) threshold. A coupled-channel method with positronium orbital expansion is used to prepare the wavefunctions. The resonance structure below the threshold is clearly seen.     

核子-核子碰撞截面的参数化公式

核子-核子碰撞截面(σ_NN)是描述原子核反应模型中的重要物理量。 核子-核子碰撞截面包括质子-质子碰撞截面（σ_pp）、中子-中子碰撞截面（σ_NN）和中子 质子碰撞截面（σ_np）, 它们随着核子能量与核物质密度的改变而变化。人们在目前研究中提出了多种核子-核子碰撞截面关于能量和核物质密度的参数化公式,通过计算12C+12C的完全反应截面,比较了不同入射能量下使用各种核子-核子碰撞截面参数化公式对12C完全反应截面的影响。 The nucleus-nucleus cross sections(σ_NN) include the proton-proton cross section, neutron-neutron cross section, and neutron-proton cross section. σ_NN change with the variations of the incident energies and the densities. Some parameterizations of σ_NNas a function of incident energy and density have been proposed in the theoretical and experimental study of nuclear reactions. Through the calculation of reaction cross sections of 12C+12C at different energies, the effect of different σ_NN parameterizations in the reaction cross sections of 12 are studied.      

双光子过程中的跃迁截面

重新检验了双光子过程中跃迁截面的概念：当密度矩阵中对角元随时间的变化缓慢时，速率方程和相关的跃迁截面是很好的近似。导出速率系数的表达式：在强光场中描述单光子过程中的系数要作很大的修改，而描述双光子过程的系数可从单光子过程的系数导出。激光场的功率分配的最佳化随总功率的强度而激烈变化。当有多个能级或多个激光模式的干涉效应时，利用跃迁截面的计算比直接利用布洛赫方程的计算还要复杂。     

Calculation of Double—Differential Cross Sections of n＋^7Li Reactions Below 20 MeV

A new reaction model for light nuclei is proposed to analyze the measured data,especially for analysis of the double-differential cross sections of the outgoing particles.Many channels arc opened in the n + 7Li reaction below En＜ 20 MeV.The reaction mechanism is very complex,beside the sequential emissions there are also three-body breakup processes.Because of a strong recoil effect of light nucleus reactions,the energy balance is strictly taken into account.The comparisons of the calculated results with the double-differential measurements indicate that the model calculations are successful for the total outgoing neutrons.     

17C反应截面和去中子截面

利用日本理化学研究所的放射性束流线RIPS, 测量了能量为79A MeV的¹⁷C在¹²C反应靶上的反应截面, 并同时得到了¹⁷C的移去1个、2个及3个中子的截面; 分别利用有限力程Glauber模型和少体Glauber模型结合壳模型的谱因子分析了反应截面和移去1个中子截面, 研究了¹⁷C的密度分布、结构和价中子布居. 反应截面和中子移去截面是两个相互独立的量, 通过对两者的分析, 都可以得出¹⁷C由芯核¹⁶C和价中子组成, 并且价中子主要处于d_5/2轨道的结论. 总结了现有的碳同位素的反应截面和相互作用截面的工作.     

Resonances and Fluctuations in Nuclear Reaction Cross Sections

On the basis of the continuum shell model, an expression for the S-matrix is derived. The external mixing between shape resonances and resonance states of complicated nuclear structure is investigated. It is shown that the doorway properties of the shape resonances may lead to an l-dependent transparency of the optical potential and, consequently, to an energy dependence of large back angle scattering if the unitarity of the S-matrix is taken into account.     

对称核物质中核子-核子散射截面的研究

在扩展的Brueckner-Hartree-Fock (BHF)理论框架下, 采用Argonne V₁₄ 两体相互作用势研究了对称核物质中核子-核子散射的总截面和微分截面, 分别讨论了三体核力(TBF)重排效应和基态关联效应对全同和非全同核子散射截面的影响。 计算表明: 低动量区域的基态关联效应会导致介质中核子-核子散射截面的增大; 而随着密度的增加,TBF重排效应的逐渐加强会减小介质中的核子-核子散射截面。 The nucleon nucleon cross sections in symmetric nuclear matter were investigated in the framework of the extended Brueckner-Hartree-Fock(BHF) approach with Argonne V₁₄ two body interaction. The influences of the ground state correlation and the rearrangement contribution of the three body force (TBF) on the cross section have been obtained and discussed separately for identical and non identical nucleon collisions. It is shown that the magnitudes of the cross section are increased by the effects of the ground state correlation in low momentum transfers,and are suppressed in medium with increasing density when the rearrangement contribution of the TBF force is considered.     

激光辅助的电子偶素对反质子的反氢生成反应

在一级玻恩近似下, 研究了在激光辅助的电子偶素-反质子碰撞中的反氢合成. 发现在小角范围内, 平行于电子偶素入射方向极化的激光使反氢生成截面变小. 在中等角度范围, 截面有一定的增加, 特别当偏振方向垂直于入射方向时, 截面增加比较明显.