Momentum distributions of nucleons in nuclei

We present a microscopic evaluation of nuclear momentum distributions for the ground states of ⁴He and ¹⁶O. The momentum distribution is the sum of a single particle part and a correlation part. Beyond a momentum of 2 fm^?1 the correlation part becomes dominating and exceeds the single particle part by arbitrary orders of magnitude for sufficiently high momenta. Even a quite crude experimental determination of momentum distributions would yield extremely useful information on nuclear correlations.     

Skyrme-QRPA calculations for low-lying excitation modes in deformed neutron-rich nuclei

Low-frequency modes of excitation in deformed neutron-rich nuclei are studied by means of the quasiparticle random-phase approximation on the Skyrme-Hartree-Fock-Bogoliubov mean field. We investigate the microscopic structure of the soft $\ensuremath K^{\pi} = 0^{+}$ modes systematically in neutron-rich magnesium isotopes with N = 22, 24, 26 and 28 close to the drip line, and it is found that the strong collectivity in ³⁴Mg and ⁴⁰Mg is acquired due to the coherent coupling between the $ \beta$ vibration and the pairing vibration of neutrons. Microscopic structure of the $\ensuremath K^{\pi} = 2^{+}$ modes changes gradually associated with the location of the Fermi level of neutrons, and it is found that the proton particle-hole excitation generating the $ \gamma$ -vibrational mode in ²⁴Mg continues to play a key role in the near-drip-line nucleus ⁴⁰Mg . The low-frequency octupole excitations are also investigated and the microscopic mechanism for the enhancement of transition strengths is discussed.     

Nonadiabatic excitation of nucleons in a fissile system

The probabilities for nonadiabatic transitions of nucleons in a fissile system are analyzed. Nearly all the excitation energy is expended in exciting single-particle degrees of freedom. The occupation numbers of the nucleon states and the potential energies of the collective motion are calculated for U²³⁸ for various values of the deformation parameter.Translated from Izvestiya VUZ. Fizika, No. 5, pp. 16–22, May, 1971.     

Polarized structure functions of nucleons and nuclei

We determine the quark distributions and structure functions for both unpolarized and polarized DIS of leptons on nucleons and nuclei. The scalar and vector mean fields in the nucleus modify the motions of the quarks inside the nucleons. By taking into account this medium modification, we are able to reproduce the experimental data on the unpolarized EMC effect, and to make predictions for the polarized EMC effect. We discuss examples of nuclei where the polarized EMC effect could be measured. We finally present an extension of our model to describe fragmentation functions.     

有限核中核子间的短程关联

The short-range correlation between nucleons in finite nuclei is investigated in high energy protonnucleus and α-nucleus elastic scattering in the framework of Glauber multiple scattering theory without any free parameters. The effects on the p-^4He and ^4He-^12C elastic scattering, and in particular on the proton elastic scattering off hallo-like nuclei, ^6,8He, are estimated. Our calculations show that the short-range correlations play an important role in reproducing experimental data and could be also thought of as being possible origin and nature of halo-like phenomena in the nuclear structure. More accurate calculations along this line are needed.     

Inelastic interactions of fast nucleons with nuclei and fission of nuclei

The cross section for the fission of actinide nuclei that is induced by fast neutrons is considered as a fraction of the cross section for inelastic nucleon interaction with nuclei. In turn, inelastic nucleon interaction with a nucleus is treated as scattering on intranuclear nucleons. It is shown that this interaction model describes satisfactorily the cross section for the inelastic interaction of 60- to 2200-MeV nucleons for a broad set of nuclei and that the energy dependence of the cross section for the fission of actinide nuclei that is induced by 400- to 1000–MeV protons replicates the energy dependence of the cross section for inelastic interactions with respective nuclei. From the model used, it follows that the cross sections for proton-nucleus interactions exceed cross sections for respective neutron-nucleus interactions in the energy range extending up to 550 MeV; at higher energies neutron cross sections are larger than proton cross sections.     

Short range correlations between nucleons in finite nuclei

The short-range correlation between nucleons in finite nuclei is investigated in high energy protonnucleus and α-nucleus elastic scattering in the framework of Glauber multiple scattering theory without any free parameters. The effects on the p-4He and 4He-12C elastic scattering, and in particular on the proton elastic scattering off hallo-like nuclei, 6,8He, are estimated. Our calculations show that the short-range correlations play an important role in reproducing experimental data and could be also thought of as being possible origin and nature of halo-like phenomena in the nuclear structure. More accurate calculations along this line are needed.     

Semileptonic electroweak interactions with nucleons and nuclei

The basic formalism needed to describe parity-violating electron scattering from nucleons and nuclei is presented and the experiments anticipated in the next few years discussed. The underlying structure of the relevant leptonic and hadronic tensors is developed in some detail for both parity-conserving and -violating situations to highlight the new physics that becomes accessible in the latter case. When applying the basic formalism to specific (practical) examples, the theme of determining the strangeness content of the nucleon is stressed.Lectures given at the Indian-Summer School on Electron Scattering from Nucleous and Nuclei, Prague (The Czech Republic), September 1994.This work is supported in part by funds provided by the U. S. Department of Energy (D.O.E.) under cooperative agreement #DE-FC02-94ER40818.     

The exchange of effective mesons between nucleons in nuclei

A study is made of the nuclear matter G-matrix. A method is developed which allows the determination of a local G-operator. This method is applied to analyse the correlations of the G-matrix, i.e. G without the bare interaction V, in terms of meson-exchange-type interactions. For a strong potential (REID) these effective mesons have masses which exceed 800 MeV implying very short-ranged correlations. For a weaker potential these correlations are somewhat longer ranged. The dominant feature of these G-operator correlations is found to be a strong scalar isoscalar attractive interaction which provides the binding of the nuclear system. By comparing with exact results for Landau parameters and binding energies it is shown that the approximation made with this local operator is excellent. A weak density dependence of the correlations is found and the structure of the Landau parameter ? is discussed. Finally it is proposed that this G-operator is a suitable object to study finite nuclei.     

Effects of neutron skin on the excitation of isovector modes of neutron-rich nuclei

The existence of a neutron skin in neutron-rich nuclei is discussed in connection with the excitation of isovector dipole and quadrupole giant modes via isoscalar nuclear probes. In the case of large neutron excess, important contributions are obtained from the nuclear excitation, which may even become predominant according to proper kinematical conditions. At variance with the usual situation encountered in inelastic processes, constructive interference can be found between nuclear and Coulomb contributions.     

Photoexcitation of baryon resonances on nucleons and nuclei

Photoproduction of η-mesons off the proton, the deuteron and other light nuclei, and off heavy nuclei has been studied in detail during the last decade at the electron accelerators MAMI in Mainz, ELSA in Bonn, ERSF in Grenoble, CEBAF in Newport News, at KEK, and at Tohoku. The physics topics range from the detailed investigation of the properties of known nucleon resonances (in particular S ₁₁(1535)), over the search of new states, to the in-medium properties of baryon resonances, and the possible formation of η-nucleus (quasi)bound states (η-mesic nuclei). It is thus an excellent example for the different aspects of the photoexcitation of nucleon resonances. Here we report new preliminary results from the CBELSA/TAPS experiment for this reaction at higher incident photon energies for the deuteron and heavy nuclei.     

On the possibility of spin-, isospin- and spin-isospin-quadrupole collective excitation modes in nuclei

The spin-, isospin- and spin-isospin quadrupole modes in spherical open shell nuclei are studied through a modified surface delta interaction model.     

The interaction of kaons with nucleons and nuclei

This paper reviews the essential requirements for observing stimulated emission of recoilles gamma radiation, categorizes and discusses the difficulties attending various proposals for creating an ultrashort-wave radiation source based on the Mössbauer effect.     

The swelling of nucleons in nuclei and the Roper resonance

Conditions where some swelling of the nucleon occurs, and, in particular the relation of this effect with the attractive character of the force acting on it, are studied. It is found that short range repulsive correlations can turn the swelling into a shrinking, in spite of a globally attractive interaction, whereas repulsive velocity dependent forces can lead to some swelling. The role of the Roper resonance in this nucleon change of size is considered in some detail.     

The role of the distribution of nucleons in finite nuclei

The total energy of many-nucleon system is expressed as a functional E[ _p(r), _n(r)] of the proton and neutron densities _p(r) and _n(r), respectively. The distribution(r) of nucleons in the nucleus, which is essential to determine the energy functional, is chosen. The energy density formalism is applied to finite nuclei, and then the binding energies per nucleon together with the mean square radii, for some medium and heavy nuclei, are obtained. Finally the achieved results are compared with the corresponding experimental values.