用电子散射研究丰质子核的质子晕结构

理论和实验结果都表明¹⁷F的第一激发态有质子晕存在.用相对论平均场理论和Eikonal近似研究了质子晕核¹⁷F的第一激发态的电子弹性散射过程. 计算了¹⁷F的第一激发态的电荷形状因子,并与¹⁶O和¹⁹F的结果进行了对比和讨论.结果显示质子晕的存在会使中等转移动量的电荷形状因子产生明显的变化,并且使低转移动量的电荷形状因子趋于降低.这说明电子散射对质子晕的存在是非常敏感的,表明可以用电子散射对奇特核的质子晕结构进行更精细的研究.     

奇特原子核6,8He的电荷形状因子研究

应用相对论Eikonal近似计算了用不同模型给出的^6,8He的电荷半径和电荷分布的形状因子, 并将结果与⁶He和⁴He的实验结果进行了比较. 结果显示不同模型给出的电荷半径和电荷形状因子差别很大, 表明不同模型给出的晕中子与α核芯的关联有很大的差异. 计算和讨论结果为在下一代电子-原子核对撞机上可能进行的实验提供了理论参考, 同时, 也为现有讨论奇特原子核的理论模型提供了检验.     

100Sn核墓态性质的微观研究

用相对论平均场理论和非相对论平均场理论计算了双幻核¹⁰⁰Sn的结合能,核物质分布半径,中子分布半径和质子分布半径等,并对这两种理论计算结果进行了比较和讨论.这是对¹⁰⁰Sn核的第一个微观计算.     

推广的Glauber理论及其在晕核散射中的应用

介绍了推广到晕核散射的Glauber理论,并用其研究晕核¹⁴Be的散射问题.弹核的密度分布分别采用谐振子密度分布和相对论平均场理论计算得到具有两个晕中子结构的密度分布,对晕核模型的多重积分采用蒙特卡洛数值积分方法.计算了不同能量下¹⁴Be,¹²Be与靶核¹²C散射的反应截面,并与实验结果进行比较,¹⁴Be的两个中子采用具有晕中子密度分布的理论计算与实验符合较好,而采用不具有晕中子密度分布的结果与实验值相差较大.     

相对论平均场框架下偶-偶核奇-偶核计算误差的系统研究

在相对论平均场理论框架下, 用NL-3和NL-Z两组相互作用参数研究了4个同位素链²⁸Ni,⁵⁴Xe,⁷⁸Pt,⁹⁴Pu的基态性质. 发现,在Hatree近似下奇A核结合能理论计算值与实验值的相对误差反而普遍比偶偶核小. 这说明用相对论平均场理论,即使不考虑矢量介子的空间分量,仍可以比较可靠地计算奇A核结合能.     

变形核的电荷密度分布

本文应用原子核的宏观模型提出了一种比较简单的计算变形核电荷密度的方法.具体计算了¹⁹²Os、¹⁵⁴Gd、¹⁵²Sm、¹⁷⁴Yb、及^{144,148,150,152}Sm等原子核的电荷密度分布.结果表明,宏观模型计算的结果能较好地与实验测量结果相符合.因此,只要根据变形核基态到各转动态跃迁几率或电多极矩的实验值,则可按本文方法,从理论上预言变形核的电荷密度分布.     

电子准弹性散射宇称不守恒中的奇异夸克效应

采用相对论平均场模型,计算了¹²C和⁴⁰Ca的准弹性电子散射的字称不守恒不对称性A.研究了核内奇异夸克成份对A的影响.     

电子和原子核散射研究原子核结构

本文综述了近年来我们组利用电子散射结合相对论平均场模型对奇特核结构的研究.我们发展了相对论平均场框架下的磁电子散射方法,并用其研究一些中子晕及质子晕核的基态组态,例如,23O,17,29C和23Al.研究发现,原子核不同组态的弹性磁形状因子彼此差别很大.其次,我们发展了相对论平均场框架下的弹性库伦电子散射方法,并用该方法研究了奇特核的电荷分布.研究发现,丰质子核中扩展的电荷密度分布可以通过库伦电子散射来测量.这种方法还被进一步推广用于计算弹性宇称不守恒电子散射,研究了一些典型原子核的中子密度分布,例如,Ca同位素链,N=50同中子素链以及N=Z的双幻核.结果表明,宇称不守恒非对称度的振幅主要由质子和中子形状因子极小值之间的距离决定.这些结果为下一代电子-核对撞机上的电子散射实验提供了有用的参考.     

超重核294118及其α衰变链的基态性质

用形变约束的相对论平均场理论系统研究了超重核²⁹⁴118及其α衰变链的基态性质, 给出了这些原子核的每核子结合能和α衰变能以及基态形变, 并与实验结果进行了比较, 发现理论计算和实验结果符合得很好, 表明相对论平均场理论对超重核基态性质的描述是合理有效的.     

相对论Thomas-Fermi近似下的核半径公式

使用QHD-I的相对论核场论模型,在Thomas-Fermi近似下讨论核力作用半径公式 R=R₀A^1/3,发现理论计算R₀的结果与高能α粒子与原子核散射的实验结果很好地符合.     

Probing proton halo of the exotic nucleus ~(28)S by elastic electron scattering

~~Probing proton halo of the exotic nucleus ~(28)S by elastic electron scattering~~     

Probing proton halo of the exotic nucleus28S by elastic electron scattering

Elastic electron scattering on the exotic light nucleus²⁸S is investigated in the plane wave Born approximation. The variation of the squared form factors of²⁸S with momentum transfer is compared with that of³²S. It is found that the behavior of the form factors near the second minimum (with a moderate momentum transfer) is sensitive to the alteration of the charge density distribution of halo protons in²⁸S. This indicates that elastic electron scattering can be a good probe of the structure of proton-halo nuclei.     

Nuclear isospin mixing and elastic parity-violating electron scattering

The influence of nuclear isospin mixing on parity-violating elastic electron scattering is studied for the even–even, N=Z nuclei ¹²C, ²⁴Mg, ²⁸Si, and ³²S. Their ground-state wave functions have been obtained using a self-consistent axially-symmetric mean-field approximation with density-dependent effective two-body Skyrme interactions. Some differences from previous shell-model calculations appear for the isovector Coulomb form factors which play a role in determining the parity-violating asymmetry. To gain an understanding of how these differences arise, the results have been expanded in a spherical harmonic oscillator basis. Results are obtained not only within the plane-wave Born approximation, but also using the distorted-wave Born approximation for comparison with potential future experimental studies of parity-violating electron scattering. To this end, for each nucleus the focus is placed on kinematic ranges where the signal (isospin-mixing effects on the parity-violating asymmetry) and the experimental figure-of-merit are maximized. Strangeness contributions to the asymmetry are also briefly discussed, since they and the isospin mixing contributions may play comparable roles for the nuclei being studied at the low momentum transfers of interest in the present work.     

Energy dependence of optical-model parameters for the interaction of 6Li and 7Li Ions with 28Si nuclei at low energies

The results of a joint analysis of experimental data (angular distributions for scattering and total reaction cross sections) are presented for the case of the interaction of ^6,7Li ions with ²⁸Si nuclei at energies between 7.5 and 32 MeV. The respective calculations were performed on the basis of a deformed potential of the optical model by using the SPI-GENOA code. The energy dependences of the parameters of the macroscopic optical model and the total cross section for the (^6,7Li+²⁸Si) reactions were obtained over the energy interval from 7.5 to 32 MeV. The calculated angular distributions and total reaction cross sections are in good agreement with experimental data.     

Study of 16O, 20Ne, 22Ne, 28Si and 32S by inelastic scattering of polarized protons

Analyzing powers and cross sections have been measured for elastic and inelastic scattering of 24.5 MeV protons from ²⁰Ne and ²²Ne, and for ¹⁶O, ²⁸Si and ³²S at 30.3 MeV. The experimental results were analyzed in terms of the coupled-channels formalism using the rotational model and (for ³²S and ¹⁶O) the vibrational model. The results for ²⁰Ne, ²²Ne and ²⁸Si show a systematic trend of the hexadecapole deformation. Prolate shapes for ²⁰Ne and ²²Ne and an oblate shape for ²⁸Si are confirmed. The results for ³²S are almost equally well-reproduced by the vibrational or rotational model, and there is a slight preference for the prolate shape for this nucleus. The best fits for the analyzing power for all the nuclei were obtained by using the full Thomas form for the spin-orbit potential     

Parity Violating Electron Scattering in the Relativistic Eikonal Approximation

The parity violating electron scattering is investigated in the relativistic Eikonal approximation. The parity violating asymmetry parameters for many isotopes are calculated. In calculations the proton and neutron densities are obtained from the relativistic mean-field theory. We take Ni isotopes as examples to analyse the behaviour of the parity violating asymmetry parameters. The results show that the parity violating asymmetry parameter is sensitive to the difference between the proton and neutron densities. The amplitude of the parity violating asymmetry parameter increases with the distance between the minima of proton and neutron form factors. Our results are useful for future parity violating electron scattering experiments. By comparing our results with experimental data one can test the validity of the relativistic mean-field theory in calculating the neutron densities of nuclei.     

Silicon fragmentation under the effect of high-energy cosmic-ray protons

The results obtained by calculating the cross sections for the elastic and inelastic scattering of 50- to 1000-MeV protons interacting with ²⁸Si, which is the main integrated-circuit element of onboard spacecraft electronics, are presented along with the calculated mass, charge, and energy distributions of heavy products of respective nuclear reactions. To compare the results of the calculations with experimental data, similar calculations were performed for the p + ²⁷Al reaction. This comparison shows that the elasticand inelastic-scattering cross sections calculated by using the EMPIRE-II-19 code are in satisfactory agreement with available experimental data. Considerably wider scatter of available data is observed in the isotope and isobar yields. A high sensitivity of the kinetic spectrum of the final nuclei to the incident-proton energy is demonstrated.     

Electronic charge density in simple metals

The valence electron density is calculated for aluminum, magnesium, and sodium using an OPW-based pseudopotential method. The Fourier transform of the charge density is used to calculate atomic form factors which compare very well with experimental X-ray scattering form factors. The non-local and energy-dependent nature of the pseudopotential and corrections from the orthogonalization hole are shown to be important.     

Phenomenology of the deuteron electromagnetic form factors

A rigorous extraction of the deuteron charge form factors from tensor polarization data in elastic electron-deuteron scattering, at given values of the 4-momentum transfer, is presented. Then the world data for elastic electron-deuteron scattering is used to parameterize, in three different ways, the three electromagnetic form factors of the deuteron in the 4-momentum transfer range 0-7 fm⁻¹. This procedure is made possible with the advent of recent polarization measurements. The parameterizations allow a phenomenological characterization of the deuteron electromagnetic structure. They can be used to remove ambiguities in the form factors extraction from future polarization data. Received: 28 January 2000 / Revised version: 25 February 2000