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在Brueckner-Hartree-Fock(BHF)框架下,计算了核介质中核子-核子(N-N)散射总截面.计算中,N-N相互作用势采用Paris势的可分离表示,单粒子谱采用连续选择.计算结果表明,质子-质子散射及质子-中子散射的总截面随核密度的增加而强烈地减小,特别是对低能散射.对结果作了简单的讨论,并与已有的一些计算结果进行了比较. 相似文献
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在非相对论能量下,采用Skyrme有效相互作用,计算了在核介质中的核子-核子(N-N)碰撞截面,研究了它与能量及密度的依赖关系,以及不同Skyrme参数对所计算截面的影响.发现在低密度时,介质中的核子-核子碰撞截面大于经Pauli修正后的自由核子一核子碰撞截面.而当高密度时,总会在高于某一能量以后,介质中的N-N碰撞截面大于经Pauli修正后的自由N-N碰撞截面. 相似文献
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在最近几年我们通过使用同位旋相关的量子分子动力学模型(IQMD)系统的研究了同位旋相关的平均场和介质中核子-核子(N-N)碰撞截面对中能重离子碰撞(HIC)中碎裂和耗散的同位旋效应。我们发现原子核阻R和Qzz,中等质量碎片多重性Nimf和质子(中子)发射数Np(Nn)敏感的依赖于介质中N-N碰撞截面的同位旋效应,而弱的依赖于同位旋相关的平均场(对称势),这些物理量作为提取相对高能范围缺中子系统的同位旋相关介质中N-N碰撞截面的探针。我们也可以通过相对低能区到150MeV/u的前平衡核子发射中质比来提取关于对称势的知识和讨论它的同位旋依赖性。 相似文献
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中能强子与核的散射研究发现,400MeV以上似乎普遍存在着截面理论的现象,例如,质子-核(PA)散射、π介子-核(πA)散射、k介子-核(kA)散射的微分截面传统理论值比实验结果约代20%,引入相对论动力学可使PA散射理论结果大为改善,然而,在核子层次上的各种修正对介子-核散射的理论结果改善甚小,人们正在从更深入的非核子自由度寻找原因。 相似文献
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核子-核子碰撞截面(σNN)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(σpp)、中子-中子碰撞截面(σNN)和中子 质子碰撞截面(σnp), 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(σNN) include the proton-proton cross section, neutron-neutron cross section, and neutron-proton cross section. σNN change with the variations of the incident energies and the densities. Some parameterizations of σNNas 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 σNN parameterizations in the reaction cross sections of 12 are studied. 相似文献
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The n+d breakup cross section has been measured between 8 and 22 MeV by integrating the energy distributions of breakup protons and recoil deuterons observed in a deuterated scintillator. The results obtained deviate from the trend suggested by recent measurements of the cross section for proton-induced breakup and favour predictions based on a local N-N potential having a hard core in the singlet state. 相似文献
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M. Trefz Amand Faessler W.H. Dickhoff M. Rhoades-Brown 《Physics letters. [Part B]》1984,149(6):459-464
The contribution to the real and imaginary nucleus-nucleus (N-N) optical potential from nucleon-nucleon scattering in the medium is calculated in a local density approximation from a two Fermi sphere nuclear matter picture for the N-N collision. This reaction mechanism is shown to be dominant for 12C + 12C scattering at all considered energies (160 MeV < Elab < 2250 MeV) giving a weakly energy dependent reaction cross section of about 900 mb. Inclusion of the collective 2+, 3? excitations in a coupled channel calculations gives good agreement for both the measured elastic and inelastic 2+ cross section at Elab = 1016 MeV. This fully microscopic parameter free calculation indicates that the energy dependence of the reaction cross section for this system is mostly due to the decrease of the collective contribution with increasing energy contrary to current theoretical models. 相似文献
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《Physics letters. [Part B]》1988,215(4):602-606
Elastic scattering of protons from nuclei is studied based on the Dirac-Brueckner approach. Effective N-N interactions in the nuclear medium are obtained by solving the relativistic Brueckner-Bethe-Goldstone equation in infinite nuclear matter. Relativistic optical potentials for p-40Ca scattering at 200 MeV are calculated in the improved local density approximation. It is found that medium effects other than Pauli blocking reduce the strengths of scalar and vector potentials very much. Differential cross section and spin observables are calculated and compared with experimental data. 相似文献
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This paper presents and analyzes the results of measurements of the proton-neutron final-state interaction (FSI) at 6.4, 10.0, 15.9, 19.85 and 25.8 MeV. At each energy nine angular combinations were measured and for each experiment the cross section was measured along the whole kinematic curve. The data are compared with the predictions of S-wave rank-one and rank-two separable potential models. The potentials used in one of the models reproduce the experimental S-wave N-N phase shifts. Fairly large differences between experiment and theory are found in the FSI regions and in the other regions of the kinematic curves. These disagreements cannot be attributed to off-shell effects. The inclusion of the tensor force and the P-wave N-N interaction in the calculations reduces the disagreements considerably at the higher energies. However, systematic differences of 10% to 20% remain. 相似文献
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David Vasak Horst Stöcker Berndt Müller Walter Greiner 《Physics letters. [Part B]》1980,93(3):243-246
We investigate the dependence of pion bremsstrahlung on the deceleration of the nuclei in relativistic heavy ion collisions. The vicinity of an abnormal phase in nuclear matter can lead - owing to critical N-N scattering - to faster deceleration or decreasing transparency of the nuclei. This would result in a threshold enhancement of the pion bremsstrahlung cross section, which in turn can be used to search for abnormal nuclear states experimentally. 相似文献
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We investigate the two-body photodisintegration of 3He and its inverse, radiative p-d capture using bound-state functions corresponding to the N-N interaction being given by the Reid soft-core potential. For the two-body photodisintegration of 3He Coulomb effects and the final-state interactions between the proton and deuteron are not included. At low energy the shape of the angular distribution agrees well with experiment, but the 90° cross section exhibits an anomalous peak at 15 MeV due to electric dipole transitions connecting the deuteron and 3He D-states. The low-energy cross section is 25–40 % too small. The intermediate-energy angular distribution peaks too near the forward direction, and, contrary to experiment, has a minimum at 100°. At higher energy the 90° cross section in the center-of-momentum frame is at least an order of magnitude too small, but does display the correct energy dependence. This energy dependence is related to the properties of the bound-state wave functions and it is plausible that it will persist in an improved treatment (e.g. one which includes exchange currents) which properly accounts for the magnitude of the cross section. Contributions from the 3He S-states are negligible for photon energies between 100 and 150 MeV, but are dominant outside this energy region. 相似文献
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B.J. Wielinga J.R. Balder G.J.F. Blommestijn R. Van Dantzig W.M. Kloet J.A. Tjon I. S̆laus 《Nuclear Physics A》1976,261(1):13-34
Experimental data on the three-nucleon reaction p(d, pp)n at Ed = 26.5 MeV obtained with the multidetector system BOL, covering most of the phase space, are presented. The data are compared with Faddeev calculations using a local S-wave potential for the nucleon-nucleon interaction. The calculated cross sections, which are in general not sensitive to the precise choice of the nucleon-nucleon potential, agree well with the data over the major part of phase space. We have, though, discovered a region in phase space with a strong discrepancy. In the same region, around a neutron c.m. angle of 140°, the calculations are sensitive to the N-N potential. Theoretical and experimental angular distributions in the p-n recoil c.m. subsystem for proton- neutron energies below 0.5 MeV agree in absolute magnitude, both being isotropic. For larger relative energies, a discrepancy develops, part of which might be related to missing higher par- tial wave components in the N-N interaction, rather than to Coulomb or S-wave scattering effects. The total breakup cross section has been deduced from the data as 169 ± 36 mb. 相似文献
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利用同位旋相关的量子分子动力学,通过原子核阻止研究了中能重离子碰撞中动量相关作用对于同位旋相关的平均场(对称势)的重要性.计算结果表明动量相关作用同时加强了原子核阻止对于对称势和核子–核子碰撞截面同位旋效应的灵敏性.但相对而言核子–核子碰撞截面对于原子核阻止的作用远大于对称势对于它的作用,等价于动量相关作用提高了原子核阻止对于核子–核子碰撞截面同位旋效应的灵敏性,而减弱了原子核阻止对于对称势的灵敏性.这样就把原子核阻止作为提取同位旋相关的核子–核子碰撞截面的一个探针. 相似文献
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利用同位旋相关的量子分子动力学(IQMD)对中子晕核,8He和10He引起核反应中重要的同位旋效应和松散的中子晕结构影响的平均特征进行了研究.因为IQMD中的互作用势和介质中核子-核子碰撞截面灵敏地依赖于碰撞系统的密度分布.而扩展的中子晕密度分布包含了中子晕核的同位旋效应和松散的中子晕结构的平均特征,从而将这些信息通过动力学碰撞带入到反应机理中. 为了清楚地鉴别中子晕核带入反应机理重要的同位旋效应和松散中子晕结构的影响,通过比较中子晕核和相等质量稳定弹核在相同入射道条件下,所得物理观测量之间的差别加以确定.计算结果确实发现具有初始晕核信息的中子扩展密度分布将重要的同位旋效应和松散中子晕结构带入到各种物理观测量中.例如与相等质量稳定相比,中子晕核的晕特征引起了原子核阻止的降低;并明显地增加了核子发射中子-质子比和同位旋分馏比.
关键词:
中子晕核
原子核阻止
核子发射中子-质子比
同位旋分馏比 相似文献