Consistent shell model parameters for the rocksalt structure alkali halides

A set of shell model parameters for the rocksalt structure alkali halides is presented in which the shell charges and polarization force constants are taken to be crystal independent properties. The high and low frequency dielectric constants and the transverse optic frequencies for the whole family of crystals are reproduced with high accuracy.     

Consistent cluster model description of the electromagnetic properties of lithium and beryllium nuclei

We calculate the electromagnetic properties of lithium and beryllium nuclei within a resonating group model using bare charges and g-factors. For ⁶Li we give results for reduced transition strengths and explain the tiny quadrupole moment. For ⁷Li and ⁷Be we compute electromagnetic moments and transitions between bound states. Furthermore we reproduce the existing data on the radiative captures ³He(α, γ)⁷Be and ³H(α, γ)⁷Li. In the ⁷Li case the calculations indicate an increase of the astrophysical S- factor for decreasing energy which might have astrophysical consequences. We show that closed channels do not influence results on the astrophysical S-factor at low energy. Finally we demonstrate that the polarisability of ⁷Li originates from the virtual break-up at low energies. In this case, the ⁶Li + n channels contribute appreciably.     

On the three-alpha model for12C

For the 3α-model of¹²C two simple cases are discussed. In the first case a potential is introduced which has a strong minimum when the three α-particles are at the corners of an equilateral triangle. Only small vibrations around this equilibrium positions are allowed. This model does not give the desired level sequence. In the second case this potential is dropped and one finds surprisingly good agreement with the experimental level sequence.     

New model interaction potential for the description of charged particle motion in matter

A new model interaction potential, in the form of a screened Coulomb potential, is proposed. Analytical expressions are derived for the stopping power of ions in elastic collisions. A program is written for Monte Carlo calculations of the ion ranges in an amorphous substance, taking inelastic losses into account in the continuous-slowing approximation and taking elastic collisions into account in the approximation of the new model interaction potential. The ranges of Cu and Rb ions in C and B targets are calculated. The results of the calculations are in good agreement with experiment.     

Neutrino-12C scattering in the Ab initio shell model with a realistic three-body interaction

We investigate cross sections for neutrino-12C exclusive scattering and for muon capture on 12C using wave functions obtained in the ab initio no-core shell model. In our parameter-free calculations with basis spaces up to the 6 variant Planck's over 2pi Omega we show that realistic nucleon-nucleon interactions, like, e.g., the CD-Bonn, underpredict the experimental cross sections by more than a factor of 2. By including a realistic three-body interaction, Tucson-Melbourne TM'(99), the cross sections are enhanced significantly and a much better agreement with experiment is achieved. At the same time, the TM'(99) interaction improves the calculated level ordering in 12C. The comparison between the CD-Bonn and the three-body calculations provides strong confirmation for the need to include a realistic three-body interaction to account for the spin-orbit strength in p-shell nuclei.     

Modified Glauber model for the total reaction cross-section of 12C + 12C collisions

Glauber's theory has been adopted to calculate the total heavy-ion reaction cross-sections at high energies. At relatively low energies, Glauber's total reaction cross-section has been modified in order to take into account the Coulomb field effect and is called modified Glauber model I. In addition to the Coulomb field effect, the nuclear effect has also been taken into account in the Glauber model and is called modified Glauber model II. An analytical expression for the transparency function for heavy-ion reactions, involving the nuclear densities of the colliding ions and the nucleon-nucleon cross- section, has been obtained within the framework of the modified Glauber models I and II. The transparency and the total reaction cross-sections of the ¹²C + ¹²C collisions are calculated at different bombarding energies. The obtained results are in good agreement with the experimental data and with previous theoretical calculations. Received: 26 January 2001 / Accepted: 15 October 2001     

Magnetic dipole excitation mode according to the collective model with separate neutron and proton deformations

The collective model with separate neutron and proton deformations is developed. The collective motion of individual neutron and proton surfaces is reduced to the motion of the mass surface and the neutron skin. The strong coupling scheme of the neutron skin vibrations to the mass-surface motion is applied for well-deformed nuclei. The magnetic dipole excitation mode, which was discovered experimentally, is explained as theK = 1 one-phonon neutron skin vibration in a deformed nucleus. Some estimates of parameters of the model are performed. Finally, the model is confronted with the two-rotor model and the interacting boson model (IBM-2).     

Microscopic description of nuclear π + production in 12C

The cross section for the process (p, π⁺) is calculated in the framework of the Jastrow model. It is shown that in contrast to the pure independent particle model the experimental data for ¹²C at E_p = 185 MeV can be reproduced quantitatively.     

A collective model description of the low lying and giant dipole resonant properties of40,42,44,46Ca

Zeitschrift für Physik A Hadrons and nuclei - The low lying and giant dipole resonant properties of the even-even calcium isotopes are calculated within the framework of the Gneuss-Greiner...     

Vacuum renormalization of the chiral-sigma model and the structure of neutron stars

Vacuum renormalization corrections are calculated for normal nuclear matter and neutron star matter in the chiral-sigma model. The theory is generalized to include hyperons in equilibrium with nucleons and leptons. The equations of state corresponding to two compression moduli, a “stiff” and “soft” one for nuclear matter, are studied. It is shown that fully one half the mass of a neutron star at the limiting mass is composed of matter at less than twice nuclear density. Neutron star masses are therefore moderately sensitive to the properties of matter near saturation and to the domain of the hyperons, but dominated by neither. The predictions for the two equations of state are compared with observed neutron star masses, and only the stiffer is compatible.