Nuclear longitudinal form factors for axially deformed charge distributions expanded by nonorthogonal basis functions

In this paper,the nuclear longitudinal form factors are systematically studied from the intrinsic charge multipoles.For axially deformed nuclei,two different types of density profiles are used to describe their charge distributions.For the same charge distributions expanded with different basis functions,the corresponding longitudinal form factors are derived and compared with each other.Results show the multipoles C_λ of longitudinal form factors are independent of the basis functions of charge distributions.Further numerical calculations of longitudinal form factors of~(12)C indicates that the C_0 multipole reflects the contributions of spherical components of all nonorthogonal basis functions.For deformed nuclei,their charge RMS radii can also be determined accurately by the C_0 measurement.The studies in this paper examine the model-independent properties of electron scattering,which are useful for interpreting electron scattering experiments on exotic deformed nuclei.     

电子和原子核散射研究原子核结构(英文)

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,17,19C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。     

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.     

Empirical transverse charge densities in the nucleon and the nucleon-to-delta transition

Using only the current empirical information on the nucleon electromagnetic form factors we map out the transverse charge density in proton and neutron as viewed from a light front moving towards a transversely polarized nucleon. These charge densities are characterized by a dipole pattern, in addition to the monopole field corresponding with the unpolarized density. Furthermore, we use the latest empirical information on the N-->Delta transition form factors to map out the transition charge density which induces the N-->Delta excitation. This transition charge density in a transversely polarized N and Delta contains both monopole, dipole and quadrupole patterns, the latter corresponding with a deformation of the N and Delta charge distribution.     

Pole and quark-counting model for form factors of light nuclei

The dispersion relation approach is applied to form factors of light nuclei. The form factor is approximated by a sum of poles. The asymptotic behaviour of form factor is assumed to be determined by quark-counting rule. Examples of³He,⁴He and⁶Li are considered. Data on form factors of these nuclei have been fitted with smaller number of parameters than usual, and corresponding charge distributions have been found which differ from conventional ones in central regions of nuclei.     

The determination of the nuclear ground state and transition charge density from measured electron scattering data

The evaluation of elastic and inelastic electron scattering cross sections is discussed in terms of the Fourier-Bessel expansion of the nuclear ground state and transition charge density, respectively. The method allows one to deduce the charge distributions and the moments as well as the corresponding errors, which originate on the one hand from the uncertainties in the measured data and on the other hand from the lack of knowledge about the large-q behaviour of the form factors; these two contributions are determined separately. The method is described and proved with an evaluation of pseudodata and then applied to ²⁰⁸Pb cross sections. For this nucleus, detailed results concerning the possible structure of the charge density are presented.     

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.     

Analytic Parametrizations for Nuclear Form Factors

Two types of analytic parameterizations for nuclear form factors proposed earlier are applied to the nuclei¹²C and¹⁶O. The form factors of these nuclei are reproduced with fewer parameters than usual. The corresponding charge distributions are compared with distributions obtained by traditional methods.     

Study on Charge Form Factors of the Exotic Nuclei 6,8He

Charge radius and charge form factors of different charge density distributions for ^6,8He are calculated with the relativistic Eikonal approximation. Detailed comparisons and discussions are presented. It is found that the charge form factors curves of ^6,8He are much lower than the experimental ones of ⁴He. This is, in principle, consistent with the experimental fact. Whereas detailed comparison among the charge form factors which correspond to different charge distributions show significant deviations. This indicates that the effects of the correlations between the halo neutrons and the α-core in ^6,8He with different charge density distributions are quite different. This result would provide a useful reference for the possible experiments on the next-generation electron-nucleus collider and for the tests of different theoretical models for the exotic nuclei ^6,8He.     

用电子散射对S核和Si核同位素的进一步研究

用相对论平均场计算了^26,28,30,32S和^22,24,26,28Si的结合能, 均方根半径, 质子皮厚度, 单粒子能级等. 两套参数TM2和NL-SH的计算结果与实验值比较符合. 用平均场与相对论Eikonal近似结合计算出³²S和²⁸Si的形状因子和微分截面的结果, 与实验值也符合得较好. 进一步研究了S和Si的同位素链的基本性质和电子散射, 讨论了电子散射的电荷形状因子对电荷密度变化的敏感性. 电荷形状因子在下一代电子--不稳定原子核对撞机上可以测量, 这将能精确测量不稳定核的电荷半径和电荷密度分布, 本文计算的结果可供未来实验参考.     

Isotopic invariance of fission fragment charge distributions for actinide nuclei at excitation energies above 10 MeV

The fragment mass and energy distributions from the proton-induced fission of compound nuclei ²³³Pa, ^{234,236,237,239}Np, ^{239,240,241,243}Am, and ²⁴⁵Bk at proton energy E _p =10.3 and 22.0 MeV have been experimentally studied. It was revealed that the shapes of the asymmetric fission mass distributions are mainly defined by the proton numbers of compound nuclei and demonstrate only a weak dependence on the neutron ones. The detailed study of the fission fragment mass yields for compound nuclei Np and Am isotopic chains has shown that the asymmetric fission fragment charge distributions calculated within the unchanged charge density hypothesis for nuclei with equal Z _C practically coincide.     

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.     

Form factors in the projected linear chiral sigma model

Several nucleon form factors are computed within the framework of the linear chiral soliton model. To this end variational means and projection techniques applied to generalized hedgehog quark-boson Fock states are used. In this procedure the Goldberger-Treiman relation and a virial theorem for the pion-nucleon form factor are well fulfilled demonstrating the consistency of the treatment. Both proton and neutron charge form factors are correctly reproduced, as well as the proton magnetic one. The shapes of the neutron magnetic and of the axial form factors are good but their absolute values at the origin are too large. The slopes of all the form factors at zero momentum transfer are in good agreement with the experimental data. The pion-nucleon form factor exhibits to great extent a monopole shape with a cut-off mass ofΛ=690 MeV. Electromagnetic form factors for the vertexγNΔ and the nucleon spin distribution are also evaluated and discussed.     

Coulomb potentials between spherical heavy ions

The Coulomb interaction between spherical nuclei having arbitrary radial nuclear charge distributions is calculated. All these realistic Coulomb potentials are given in terms of analytical expressions and are available for immediate application. So in no case a numerical computation of the Coulomb integral is required. The parameters of the charge distributions are taken from electron scattering analysis. The Coulomb self-energies of the charge distributions used are also calculated analytically in a closed form. For a number of nucleus-nucleus pairs, the Coulomb potentials derived from realistic charge distributions are compared with those normally used in various nucleus-nucleus optical model calculations. In this connection a detailed discussion of the problem how to choose consistently Coulomb parameters for different approximations is given.     

Structure of unstable nuclei near proton drip line

Gamov-Teller (GT) states in nuclei near the proton drip line are studied by using a microscopic Hartree-Fock (H-F) + Tamm-Dancoff approximation (TDA) (or random phase approximation (RPA)). The calculations predict that giant Gamow-Teller (GT) β-decays are possible for N=Z nuclei heavier than ₂₈⁵⁶Ni₂₈, carrying most of the sum rule strength. The amplitude of isospin T=1 admixed to the T=0 ground state in N=Z nuclei is also discussed in relation with Fermi β-decay sum rule. Finally, the shapes of unstable nuclei near the proton drip line are studied by using the finite-range droplet model (FRDM).     

Isovector coupling channel and central properties of the charge density distribution in heavy spherical nuclei

The influence of the isovector coupling channel on the central depression parameter and the central value of the charge density distribution in heavy spherical nuclei was studied. The isovector coupling channel leads to about 50% increase of the central depression parameter, and weakens the dependency of both central depression parameter and central density on the asymmetry, impressively contributing to the semibubble form of the charge density distribution in heavy nuclei, and increasing the probability of larger nuclei with higher proton numbers and higher neutron-to-proton ratios stable.     

Quantitative analysis of proton imaging measurements of laser-induced plasmas

A method for obtaining quantitative information about electric field and charge distributions from proton imaging measurements of laser-induced plasmas is presented. A parameterised charge distribution is used as target plasma. The deflection of a proton beam by the electric field of such a plasma is simulated numerically as well as the resulting proton density, which will be obtained on a screen behind the plasma according to the proton imaging technique. The parameters of the specific charge distributions are delivered by a combination of linear regression and nonlinear fitting of the calculated proton density distribution to the measured optical density of a radiochromic film screen changed by proton exposure. It is shown that superpositions of spherical Gaussian charge distributions as target plasma are sufficient to simulate various structures in proton imaging measurements, which makes this method very flexible.     

Neutron density distributions deduced from antiprotonic atoms

The differences between neutron and proton density distributions at large nuclear radii in stable nuclei were determined. Two experimental methods were applied: nuclear spectroscopy analysis of the antiproton annihilation residues one mass unit lighter than the target mass and the measurements of strong-interaction effects on antiprotonic x rays. Assuming the validity of two-parameter Fermi neutron and proton distributions at these large radii, the conclusions are that the two experiments are consistent with each other and that for neutron rich nuclei it is mostly the neutron diffuseness which increases and not the half-density radius. The obtained neutron and proton rms radii differences are in agreement with previous results.     

应用原子核的宏观－微观模型研究远离稳定线核的性质

应用原子核的宏观－微观模型研究远离稳定线核的性质，得到了一些结果，例如质子和中子滴线，质子和中子密度分布及其均方根半径和中子皮厚度随同位素位移的变化．对一些奇异核性质的计算结果同相对论平均场方法计算的结果作了比较，对质子滴线附近核的质子放射性也作了简要讨论．     

The Brueckner-Hartree-Fock Equation of State for Nuclear Matter and Neutron Skin

The equation of state for nuclear matter is presented within the Brueckner-Hartree-Fock(BHF) scheme,by using the realistic Argonne V18 or Bonn B two-nucleon potentials plus their corresponding microscopic three-nucleon forces.It is then applied to calculate the properties of finite nuclei within a simple liquid-drop model,and we compare the calculated volume,surface,and Coulomb parameters with the empirical ones from the liquid drop model.Nuclear density distributions and charge radii in good agreement with the experimental data are obtained,and we predict the neutron skin thickness of various nuclei.