The Dirac-Brueckner-Hartree-Fock approximation is extended to the calculation of finite nuclei. As an example, the ground-state properties of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ are studied using modern versions of the one-boson-exchange model for the nucleon-nucleon interaction. The Dirac effect yields a significant increase for the radius of the charge distribution and a moderate gain in binding energy. This improves the agreement with the experimental data considerably, but does not remove the discrepancy between theory and experiment completely.

We study the response to an electromagnetic probe of a simple system of two scalar particles (‘‘nucleons’’) bound to form a scalar ‘‘deuteron.’’ The use of a covariant separable interaction allows for an elementary solution of the Bethe-Salpeter equation for both the bound state and for the scattering amplitude. Knowledge of the scattering amplitude allows for an exact treatment of the final state interactions within the limitations of the model. We present results for structure functions and sum rules for a large range of momentum transfer. We also present a systematic study of y scaling and discuss the role of the final state interactions in our model. As noted by other authors, we see that y scaling is well satisfied at the quasielastic peak; however, significant deviations from such scaling behavior are seen in our results as one moves away from the quasielastic peak to the region of large, negative y. We also discuss the influence of final state interactions in modifying sum rules which are well satisfied in the plane wave Born approximation at all ${\mathit{Q}}^2$.

A study of fragmentation of the low energy octupole state is performed in order to study the dependence of this fragmentation on quadrupole deformation, determine the limitations of surveys of $3_1^{\mathrm{-}}$ states, and search for exceptional cases of fragmentation. A regular dependence of fragmentation on the deformation parameter ${\mathrm{\beta }}_2$ is found, and it is demonstrated that the large degree of fragmentation observed in ${}_{}{}^{194,196,198}{}_{}{}^{}\mathrm{Pt}$ is indeed unique.

A relativistic random-phase approximation (RPA) description of discrete excitations in closed-shell nuclei is presented using a spectral approach, with emphasis on the nature and importance of self-consistency. A functional derivation of self-consistent RPA equations is given, based on a nonrelativistic formalism, and its generalization is discussed. Vacuum polarization is neglected, but consistency demands configuration spaces that include both particle-hole pairs and pairs formed from occupied states and negative-energy states, which ensures current conservation and the decoupling of the spurious state. Results in the Walecka (σ-ω) model for various isoscalar states in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, are given, including electron scattering form factors.

A geometric interpretation of the interacting boson model (IBM) is studied within a framework of the coherent-state method. Effects of the angular momentum projection in the description of shape transitions and in the procedure of resolution of the IBM Hamiltonian into the intrinsic and collective parts are investigated. The projection may be crucial in obtaining a reasonable geometric picture of the IBM. The geometric interpretation of the O(6) limit of the IBM is discussed.

A fermion mapping of boson-fermion pairs is proposed. The mapping is applied to an exactly solvable two-level test model and shown to be useful for treating strong boson-fermion correlations in quantum systems.

The coexistence of normal and intruder states is described within the framework of the proton-neutron interacting boson model. It is shown that the excitation energy of the intruding configuration and the structure of both the normal and intruding configurations can be described without large differences between the strength of the neutron-proton quadrupole force used for either. Detailed comparison is made for ${}_{}{}^{114}{}_{}{}^{}\mathrm{Cd}$.

The ability of nonrelativistic physics to correctly describe saturation in systems where relativistic effects are important is studied. A fully relativistic model system of nucleons interacting via weakly coupled mesons is utilized, for which perturbative methods can be used to generate results for the energy density of the uniform system and the two-body scattering cross section. The energy of the uniform system derived from the relativistic model is then compared with that obtained from performing a nonrelativistic calculation using a nonlocal two-body potential that exactly fits the two-body scattering cross section obtained from the relativistic model. The nonrelativistic and relativistic calculations differ, and the reasons for their difference are discussed. The differences can be reconciled by adding nonlocal many-body potentials to the nonrelativistic model.

An empirical effective interaction for the A=4–16 p-shell nuclei in the complete (0+2)ħω model space is presented, which also reproduces the predominant 2ħω intruder states. The results are not spoiled by the mixing catastrophe. The inclusion of 2ħω states also leads to a new feature not encountered before in smaller model spaces, i.e., the appearance of radially excited states. The latter can be observed experimentally in certain cases.

Several observables for the A=4–16 p-shell nuclei, resulting from a calculation in the complete (0+2)ħω model space, are presented. It is shown that the 2ħω admixtures are substantial. The calculated values of these observables are compared with the experimental data. Not only can the properties of many intruder states be reproduced correctly, but also the description of predominantly 0ħω states is often improved considerably.

A formalism is developed in order to describe, within the Glauber model, the scattering processes between heavy ions in situations involving several coupled channels. The approach is based on a suitable truncation of the number of nuclear states which can be excited at each microscopic nucleon-nucleon collision. The set of coupled equations for the S-matrix elements of the conventional reaction theory is replaced by simple matrix relations, only involving the nucleon-nucleon scattering amplitude and the nuclear densities and transition densities. This method avoids the difficulties arising from the combinatorial aspects of the multiple scattering theories, the slow convergence of the series, and the problems of center-of-mass correlations. We discuss some specific examples of multichannel collisions where the multiple-scattering series can be summed to give analytic expressions for the scattering amplitude. We finally explicate the formalism for the perturbative treatment of mutual excitation and charge-exchange processes.

The thermal Green’s functions are used to derive the thermal random phase approximation (TRPA) in open shell systems. The TRPA in the Sn isotopes is studied for a separable quadrupole interaction as a function of the temperature. The matrix elements of quadrupole particle-hole and two-particle operators as well as their energy-weighted sum rules are evaluated. The most noticeable features introduced by the temperature dependence are the big changes that happen when the superconductivity disappears.

The ratio of the yields for the isomer (${\mathit{J}}^{\mathrm{\pi }}$=11/$2^{\mathrm{-}}$,${\mathit{t}}_{1/2}$=34.4 h) and ground state (3/$2^{+}$, 9.0 h) of ${}_{}{}^{137}{}_{}{}^{}\mathrm{Ce}$ populated in the reactions ${}_{}{}^{128}{}_{}{}^{}\mathrm{Te}$${(}^{12}$C,3n), ${}_{}{}^{133}{}_{}{}^{}\mathrm{Cs}$${(}^7$Li,3n), ${}_{}{}^{136}{}_{}{}^{}\mathrm{Ba}$${(}^3$He,2n), ${}_{}{}^{136}{}_{}{}^{}\mathrm{Ba}$${(}^4$He,3n), and ${}_{}{}^{137}{}_{}{}^{}\mathrm{Ba}$${(}^3$He,3n) were measured from energies above the Coulomb barrier to energies typically 20–30% below the barrier by observing the delayed x- and γ-ray emission. In the first three reactions we observed an approximately constant value for the isomer ratio at energies far below the barrier. This indicates an approximately constant average angular momentum at low bombarding energies. We analyze isomer ratios and cross sections using a coupled-channels model for the fusion and a statistical model for the decay of the compound nucleus. Absolute values of the angular momentum J¯ in the entrance channel are deduced from the isomer ratio. The values of J¯ exhibit the behavior predicted for low energies and the expected variation with the reduced mass of the entrance channel.

Light charged-particle emission and neutron emission have been measured for the fusion-evaporation and fusion-fission channels in the ${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$${+}^{100}$Mo reaction at 550 and 655 MeV bombarding energies. Temperatures, emission barriers, and multiplicities for the particles detected in coincidence with evaporation residues and fission fragments have been determined. For the evaporation residue data, the ‘‘first-chance’’ spectra of particles emitted from the compound nucleus have been isolated and the same initial temperature for the different evaporated particles has been extracted. The inverse level density parameter K=A/a reaches a value of 13.8±0.7 MeV at ${\mathit{E}}_{\mathrm{th}}$≃236 MeV. A decrease of the apparent emission barriers for the charged-particle emission at high excitation energy suggests dynamical effects on the de-excitation process. Analysis of the fissionlike events shows a saturation of light particle emission from the fission fragments. Using the average energies and multiplicities of the emitted neutrons, and charged particles, it has been found that for both initial excitation energies, 251 and 293 MeV, scission occurs at an excitation energy ≃140 MeV. For both fusion evaporation and fusion fission, the light charged particles are preferentially emitted during the early part of the de-excitation cascade. Statistical models and dynamical calculations have been used in an attempt to interpret the experimental data.

The spectral function for p-n pairs in the ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ ground state (i.e., the distribution in p-n relative momentum ħk for pairs whose c.m. is at rest in the laboratory) was measured for k ranging from 0.6 to 1.5 ${\mathrm{fm}}^{\mathrm{-}1}$, using the ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$(p,pα)pn reaction at 200 MeV. These and earlier 120 MeV ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$(α,2α)pn measurements show that, when k increases from 0.1 to 1.5 ${\mathrm{fm}}^{\mathrm{-}1}$, this function decreases by 4 orders of magnitude and is predicted within a factor of 2 by the plane-wave impulse approximation. The asymmetry for the ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$(p,pα)pn reaction induced with polarized protons was measured at 56° c.m. and found to have the same bombarding-energy dependence as that for p-α elastic scattering. The d-α cluster probability of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, determined by the ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$(p,pα)d reaction, was consistent with that found in other intermediate-energy experiments.

We have measured the angular and mass distributions of the fragments from photofission of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ using tagged photons with energies between 11 and 16 MeV. The fission fragments were detected by a 4π arrangement of position-sensitive parallel-plate avalanche counters. Anisotropic angular distributions have been observed for the first time in the energy range where second-chance fission becomes energetically possible. A consistent assignment of ${\mathit{J}}^{\mathrm{\pi }}$ and K for the fission channels in ${}_{}{}^{237}{}_{}{}^{}\mathrm{U}$ has been deduced from a combined analysis of (γ,nf) and (e,e’f) data. A clear relationship between the anisotropies and the fragment mass asymmetry has also been established. This correlation, together with the energy dependence of the angular distribution parameters, points to a possible interpretation of the results in terms of a recent theoretical model incorporating multiple exit channels in fission.

The original sum-rule model worked out by Wilczyński et al. and successfully used for a global description of complete and incomplete fusion reactions has been extended by a term accounting for dissipative processes of the dinuclear system on its way to fusion. When applying to light- and heavy-ion collisions with various targets at energies in the transitional region, the new term proves to be rather essential for reproducing the element distributions of the fragments emitted from rather asymmetric systems.

A number of recent experiments reveal the emission of hard photons in heavy-ion interactions. Assuming that these photons originate in single proton-neutron bremsstrahlung processes that add incoherently, their spectra are satisfactorily reproduced, at incident energies up to ≊70 MeV/nucleon, in both the case of asymmetric and symmetric systems, by calculations based on a system of master equations. The cross section for the elementary np→n’p’γ process is that, recently proposed by Nakayama and Bertsch, which includes convection, magnetic and exchange contributions. The initial energy distribution of the excited particles and holes is assumed to be that corresponding to two shifted Fermi spheres in momentum space.

Expressions are developed for the differential electroexcitation cross section and the polarization of the scattered electrons in polarized electron scattering from oriented nuclei. These expressions are derived for a mixed multipole transition using the distorted-wave method. The effect of the Coulomb distortion is discussed for electric dipole transition of unoriented ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ using 20 MeV partially polarized electrons.

Relativistic effects in two-body Coulomb collisions are investigated within a classical context. Special emphasis is given to heavy-ion collisions at intermediate energies. It is found that such corrections may be responsible for a 10–20 % increase of the elastic cross sections for a fixed scattering angle and kinetic energy. Comparisons with other methods are also made and some useful simple parametrizations of the cross sections are obtained. The separate contributions from kinematic and retardation corrections are also studied.