Table of contents

It is shown that, with the choice beta =-7 fm⁷ the formula for the eigen-shape P_e=5 alpha +2 alpha ²(A_s²(1+ eta ²))^-1-6a_t^-1-2r₀ alpha ²-2 beta alpha ⁸/2r₀³ alpha ⁴ gives a good value for P_e for each of the potential models considered. In this expression, alpha ² is the deuteron binding energy (in fm^-2), A_s the asymptotic amplitude of S-state wavefunction, eta the asymptotic D- to S-state ratio, a_t the triplet scattering length and r₀ the effective range for neutron-proton scattering in the ³S₁-³D₁ state.

A cluster model of ²³Na, developed by Kabir and Buck (1990), as a composite of ¹¹B and ¹²C is used to calculate the ²³Na-target interaction potentials by folding the cluster wavefunction with the cluster-target interaction potentials. Coupled channels calculations are carried out for the quasi-elastic scattering of polarized ²³Na from ²⁰⁸Pb at 170 MeV and compared with recent experiments. Quantitative agreement with experiment is obtained when the interaction is adjusted by a single overall normalization constant.

The gamma decay of excited states in the neutron deficient isotopes ⁸⁷Tc and ⁸⁸Tc has been observed for the first time. The fusion-evaporation reaction ⁵⁸Ni(³²S, p2n)⁸⁷Tc and ⁵⁸Ni(³²S, pn)⁸⁸Tc at 110 MeV, ⁴⁰Ca(⁵⁰Cr, p2n)⁸⁷Tc and ⁴⁰Ca(⁵⁰Cr, pn)⁸⁸Tc at 170 MeV and ⁵⁸Ni(³⁶Ar, alpha pn)⁸⁸Tc at 145 MeV beam energy were used. Unambiguous identification of these nuclei which are populated with less than 1 mb cross section was achieved with coincidences between the gamma radiation and the evaporation residues detected in a recoil mass separator. From gamma gamma coincidence data, a decay scheme of 11 transitions was constructed for ⁸⁸Tc, the ground state of which is suggested to have I^pi =7^- or 8⁺. Two transitions identified in ⁸⁷Tc follow the pattern of a g_9/2 one-quasiparticle band.

The authors review the various string models proposed to describe hadrons and their interactions. QCD and QCD-inspired phenomenological models motivated the development of a rather large variety of string models. Among others the Polyakov model, the Friedberg-Lee model, the MIT flux tube model, semirelativistic string models of hadrons and massive strings are discussed in detail. To correctly describe the dynamical aspects of the hadron-hadron interaction, especially of high-energy heavy-ion collisions, ideas from these models are proposed to be combined into a semiclassical unified string-flux tube model. Special emphasis is given to the dynamical string model recently developed on the basis of such a unified string-flux tube model.

Simple observations are made about both the current masses and the constituent masses of the lighter quarks. The latest values of the decay constants f pi , f_K, and f_D of the pseudoscalar mesons suggest that the current-quark mass ratio 2s/(u+d) of the mass of strange quark to the average mass of the up and down quarks is closer to 14 than to 26 as is usually assumed. Such heavier masses for m_u and m_d are also implied by a model in which the masses of the first family of fermions arise from their electric and chromoelectric fields rather than from the Higgs mechanism. Since constituent-quark masses incorporate some of the energy of the interaction, which is different for mesons and baryons, it might be useful to consider two sets of constituent-quark masses, one for mesons and one for baryons. Plausible quark mass values in MeV are u=303, d=307, s=490 and c=1668 for the meson constituents and U=326, D=328, S=510 and C=1726 for the baryon constituents.

The binding energies of the 1s, 1p_3/2, 1p_1/2 states of the Lambda particle in hypernuclei, the corresponding root mean square radii of the orbits of the Lambda particle and also the spacings Delta _sp obtained relativistically using potentials of the form U_+or-(r)=-D_+or- (cosh²(r/R))^-1 are compared with the non-relativistic results (without spin-orbit term). Though there are some differences, mainly in the excited states, this study shows that one may still have confidence in the non-relativistic calculations. The relativistic binding energies obtained are also compared with those obtained using Woods-Saxon potentials and Gaussian ones. It is observed that in the ground state and for the lighter hypernuclei the binding energies obtained with the potential considered here are in very good agreement with the experimental ones. It is also observed that the RMS radii as a function of A¹3/ show a rather hyperbolic behaviour for the lighter hypernuclei which turns into a linear behaviour for the heavier hypernuclei.

In a simplified model the authors follow the evolution of the originally non-thermal momentum distribution in order to clarify the reason for too good an agreement between models with thermal equilibrium and detected spectra. The result is that the final entropy deficiency may indeed be quite substantial at 800 MeV/nucleon beam energy for smaller nuclei, but the detected energy distribution is not very sensitive to this deviation. Therefore energy spectra do not give too direct a check of equilibration in this energy range.

The so-called 'cosh' or symmetrized Woods-Saxon potential which has been used in nuclear physics is discussed and certain comments are made regarding its form factor, depth and radius. A rough estimate of its parameters is also attempted by using various possibilities. This is done either by considering a number of individual nuclei or by least-squares fitting. The potential depth parameter V₀, apart from being state dependent, varies also with the mass number of the nucleus. Comments on relevant limitations and inaccuracies are made and the state dependence of V₀ is also discussed in relation with the concept of an effective nucleon mass.

A method is proposed to perform canonical mean field calculations at finite temperature. This method can easily be extended to include particular diagonal two-body correlations. The approach is illustrated in an exactly soluble model and exhibits definitive advantages over the conventional finite temperature Hartree-Fock approximation.

The results of a recent relativistic Dirac-Brueckner calculation of nuclear matter are fitted to different versions of the relativistic mean-field model. It is shown that the non-linear mean-field model and the linear model with a density-dependent scalar meson mass describe well the binding energy of nuclear matter over a wide range of nuclear densities. The scalar and vector components of the self-energy, however, are not individually reproduced correctly in the whole fitted window. Nevertheless, the parameterization, which may be considered to be equivalent to the relativistic G-matrix in the range of normal nuclear densities, is found.

The effects of the Lambda n interaction on cross sections and Lambda polarization in the reaction ( gamma +d to K⁺+ Lambda ⁰+n) are investigated in the spirit of the impulse approximation for three different potential models which have quite different scattering lengths and effective ranges. The authors find the interaction causes a significant enhancement of the cross section for the exclusive process d( gamma , K⁺ Lambda ⁰)n for selected kinematics near threshold, and not so significant an enhancement for the inclusive process d( gamma , K⁺) Lambda ⁰n. The produced Lambda tends to be depolarized and the polarization is sensitive to the potentials considered. The authors suggest that this reaction be used to extract information on the Lambda-neutron interaction by experiments being proposed for the new accelerators.

The authors obtain cross sections for the reaction nu _e+¹³C to ¹³N_(gs)+e^- and nu _mu +¹³C to ¹³N_(gs)+ mu ^- from threshold to several hundred MeV. They obtain the vector current form factors from electron scattering data and the axial current form factors from beta decay data and arguments based on an impulse approximation result. The behaviour of the form factors is discussed in detail.