The result of few-particle ground-state calculation employing a two-particle nonlocal potential supporting a continuum bound state in addition to a negative-energy bound state has occasionally revealed unusually strong attraction in producing a very strongly bound ground state. In the presence of the continuum bound state the difference of phase shift between zero and infinite energies has an extra jump of π as in the presence of an additional bound state. The wave function of the continuum bound state is identical with that of a strongly bound negative-energy state, which leads us to postulate a pseudo bound state in the two-particle system in order to explain the unexpected attraction. The role of the Pauli forbidden states is expected to be similar to these pseudo states.

Using our previously developed crossing and duality consistent model for kaon photoproduction and radiative capture, we investigate the kaon electroproduction processes p(e,e’${\mathit{K}}^{+}$)Y for Y=Λ, ${\mathrm{\Sigma }}^0$, and Λ(1405). Because there is no electroproduction data near threshold, consistency requires extending the energy range of our photoproduction model parametrization from an upper bound of ${\mathit{E}}_{\gamma }^{\mathrm{lab}}$=1.4 to 2.2 GeV. We find that baryon resonances with spin greater than 1/2 are necessary to describe the higher energy photoproduction data (1.4≤${\mathit{E}}_{\gamma }^{\mathrm{lab}}$≤2.2 GeV). We also extend our use of duality by representing these higher-spin s- and u-channel baryon resonances with the low-lying t-channel vector, ${\mathit{K}}^{\mathrm{*}}$(890), and pseudovector, ${\mathit{K}}_1$(1270), mesons. Using this extended crossing and duality consistent model, we obtain reasonable agreement with the data for both photoproduction and electroproduction processes.

The influence of relativity on the triton binding energy is investigated. The relativistic three-dimensional version of the Bethe-Salpeter equation proposed by Blankenbecler and Sugar (BbS) is used. Relativistic (nonseparable) one-boson-exchange potentials (constructed in the BbS framework) are employed for the two-nucleon interaction. In a 34-channel Faddeev calculation, it is found that relativistic effects increase the triton binding energy by about 0.2 MeV. Including charge dependence (besides relativity), the final triton binding energy predictions are 8.33 and 8.16 MeV for the Bonn A and B potentials, respectively.

The ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$${(}^{30}$Si,5n${)}^{179}$Os reaction has been used to study rotational bands at high spin by means of extensive gamma-ray coincidence measurements. The new α=-1/2 signature partner of the 1/$2^{\mathrm{-}}$[521] band has been found up to spin 31/$2^{\mathrm{-}}$ and the previously known α=+1/2 partner extended up to spin 45/$2^{\mathrm{-}}$. The α=-1/2 and α=+1/2 components of the previously known 7/$2^{\mathrm{-}}$[514] and the 9/$2^{+}$[624] bands were extended up to spins 63/$2^{\mathrm{-}}$, 53/$2^{\mathrm{-}}$ and 63/$2^{+}$,61/$2^{+}$, respectively. The two components of the newly found band 5/$2^{\mathrm{-}}$[512] have been established up to spins 59/$2^{\mathrm{-}}$ and 65/$2^{\mathrm{-}}$. In addition, two other new bands were found, one of them with spins up to 61/$2^{+}$ decays to the 9/$2^{+}$[624] band. Configurations have been proposed by comparing the signature splittings and the B(M1)/B(E2) ratios with the theoretical predictions. The latter points to rather strong Coriolis interaction between the 5/$2^{\mathrm{-}}$[512] and 7/$2^{\mathrm{-}}$[514] bands. The first band crossing observed in nine out of the ten bands is most probably due to the alignment of a pair of ${\mathit{i}}_{13/2}$ neutrons, on the basis of a comparison of experimental Routhians with the cranking shell model calculations. In the three positive-parity sequences and in the α=+1/2 signature of the 5/$2^{\mathrm{-}}$[512] band, second band crossings are also observed that are suggested to be caused by an alignment of two ${\mathit{h}}_{9/2}$ protons.

Differential cross sections for electron scattering from ${}_{}{}^{86}{}_{}{}^{}\mathrm{Sr}$ have been measured for excited states below 3.5 MeV over a range of effective momentum transfer of 0.4 to 2.8 ${\mathrm{fm}}^{\mathrm{-}1}$. The elastic scattering data have been analyzed to reconstruct the ground-state charge distribution. The inelastic scattering data have been analyzed to extract transition charge densities. Interpretation of the underlying nuclear structure is given in the framework of a self-consistent finite Fermi system theory.

We identify two electric isovector giant resonances at ${\mathit{E}}_{\mathit{x}}$=28 and 33 MeV in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, and at ${\mathit{E}}_{\mathit{x}}$=27 and 31 MeV in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, distinguishing them from a continuum background in the ${(}^7$Li${,}^7$Be) reaction at ${\mathit{E}}_{\mathit{L}}$=26 MeV/nucleon and ${\mathrm{\theta }}_{\mathit{L}}$=0°. The shape of the underlying continuum is determined from a comparison of ΔS=0 and ΔS=1 energy spectra deduced with a ${}_{}{}^7{}_{}{}^{}\gamma$ coincidence method. The excitation energies of these resonances are consistent with those of the isovector giant quadrupole and monopole resonances previously observed by the electron scattering and the (${\mathrm{\pi }}^{\pm }$,${\mathrm{\pi }}^0$) reaction, respectively, though the widths presently observed are much narrower.

High-spin states in ${}_{}{}^{43}{}_{}{}^{}\mathrm{K}$ were studied using the ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$${(}^{36}$S,pnγ${)}^{43}$K reaction. Threefold (p${\gamma }_1$${\gamma }_2$) coincidence data and γ-ray intensity ratios were used to establish a decay scheme and identify negative- and positive-parity yrast decay chains. The 15/$2^{\mathrm{-}}$ yrast state is relatively poorly aligned prior to decay. Energies of positive-parity levels predicted by Johnstone are in good agreement with experiment.

The temperature-dependent Hartree-Fock approach is extended to the relativistic quantum-field-theory framework; exchange of σ, ω, ρ, and π mesons and photons are included. Application is made to two spherical nuclei, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$. Temperature dependences of excitation energies, single-particle spectra, charge densities, and entropies are evaluated and compared to corresponding nonrelativistic calculations. We find a considerably larger thermal response for these nuclei when compared to the nonrelativistic results.

The ${}_{}{}^{184–200}{}_{}{}^{}\mathrm{Hg}$ isotopes are studied in the interacting-boson-approximation-plus-fermion-pair model. In general, energy levels up to I=22 can be reproduced quite well. In the low excitation energy region both the shape evolution and the ($8^{+}$,${10}^{+}$,${12}^{+}$) triplet structure can be reproduced. The ($8^{+}$,${10}^{+}$,${12}^{+}$) triplet structure can be understood as the saturation of isospin 1 fermion-pair interaction at the high spin end. The termination of triplet structure at I=12 strongly supports the (${\mathit{i}}_{13/2}$${)}^2$ band crossing. Striking agreements between the observed energy gaps of (${14}_1^{+}$,${12}_1^{+}$) and ($2_1^{+}$,$0_1^{+}$) states are considered as an indication of weak coupling between the boson core and the fermion pair. The B(E2,I→I-2) are calculated and the spin dependence of the B(E2) values can be reproduced qualitatively. However, the detailed mass dependence is not correctly reproduced.

Spectral functions are calculated from mean fields calculated both by Brueckner and by Botermans-Malfliet Green’s function methods. Similarities and differences between the two methods are illustrated. Results are shown at normal nuclear matter density and zero temperature. Calculations are made by the separable phase-shift technique that was introduced earlier including the single-particle strength up to ∼1700 MeV with (usually) less than 1% of the total strength missing. It is found that ∼5% of the single particle strength lies above 500 MeV. Mean removal (centroid) energies of nucleons and occupation numbers are calculated by energy averaging over the spectral functions. The averages are also done in the extended quasiparticle approximation for the spectral function discussed in an earlier paper showing good agreement with the ‘‘exact’’ results. It is in fact shown that this approximation yields the same result for centroid energies as does Koltun’s work which was based on an analysis of the linked cluster expansion. The total energy is calculated by Koltun’s sum rule which involves an integration over the calculated (correlated) occupation numbers. The result compares favorably with the Brueckner energy which involves an integration over model (uncorrelated) occupation numbers.

We have evaluated the nucleon self-energy in a model that has proper analytical properties, satisfies the low density theorem and provides values of Im Σ for high densities comparable to those of realistic microscopic approaches. The model, however, relies only upon the NN experimental cross sections and the empirical spin-isospin interaction, which induces an important polarization of the medium. The results obtained for the spectral functions, occupation numbers, and effective masses are quite reasonable. The model does not give the absolute value of the nucleon self-energy but only differences with respect to the Fermi energy. On the other hand, it provides an easy and efficient way of evaluating many of the nucleon properties in the nuclear medium.

The spectral properties of the eigenvalues of realistic nuclear Hamiltonians for light nuclei are studied and compared with the predictions of the Gaussian orthogonal ensemble and with experimental data. The consequences of isospin-nonconserving forces on the generic behavior of nuclear levels are also investigated.

We have studied neutron-deficient even-mass platinum isotopes in the framework of the relativistic mean-field theory. The ground-state properties of nuclei have been calculated in the σωρ model with the nonlinear scalar self-interaction of the σ meson. The charge radii, binding energies, and deformation properties have been obtained in the relativistic Hartree approximation with deformed basis. Solutions have been obtained for both the prolate as well as oblate shapes. A comparison of the calculated properties has been made with data from recent measurements on these nuclei performed at the ISOLDE project at CERN. It has been shown that the isotopic shift measurements reveal an oblate shape for all even platinum isotopes, in contrast with some existing theoretical calculations which indicate prolate shape for highly neutron-deficient isotopes.

An algebraic method for the description of giant dipole resonances built on discrete excited states of both spherical and deformed nuclei is presented within the framework of the interacting boson model. Applications to lanthanide and actinide isotopes are discussed and the effect of γ deformation is also investigated.

Expressions are derived for the E0 transition strengths for the symmetric and antisymmetric β-vibrational bandhead states to the ground state for O(6)-like nuclei. These E0 transitions are the only ones allowed to the ground state, and we predict them to be of similar magnitude. The isomer shifts for these β-vibrational states are also discussed, as well as the isotope shifts for the ground states. We propose the Ba isotopes around A≊132 as possible candidates for observing these E0 decays.

We report variational calculations of the ground state of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ with realistic two- and three-nucleon interactions. The trial wave function is constructed from pair- and triplet-correlation operators acting on a product of single-particle determinants. These operators include central, spin, isospin, tensor, spin-orbit, and three-nucleon potential components. Expectation values are evaluated with a cluster expansion for the noncentral correlations; terms in the expansion are evaluated exactly using Monte Carlo integration. The optimal trial function is obtained by minimizing the energy through the four-body cluster level. Results are reported for the ground-state binding energy, nucleon density and momentum distributions, charge form factor, and longitudinal structure function. They are also compared with the available results for few-body nuclei and nuclear matter with the same interactions.

We present initial results in the calculation of nuclear ground state properties in a relativistic Hartree approximation. Our model consists of Skyrme-type interactions in four-, six-, and eight-fermion point couplings in a manifestly nonrenormalizable Lagrangian, which also contains derivative terms to simulate the finite ranges of the mesonic interactions. A self-consistent procedure has been developed to solve the model equations for several nuclei simultaneously by use of a generalized nonlinear least-squares adjustment algorithm. With this procedure we determine the nine coupling constants of our model so as to reproduce measured ground state binding energies, rms charge radii, and spin-orbit splittings of selected closed major shell and closed subshell nuclei in nondeformed regions. The coupling constants obtained in this way predict these same observables for a much larger set of closed shell spherical nuclei to good accuracy and also predict these quantities for similar nuclei far outside the valley of beta stability. Finally, they yield properties of saturated nuclear matter in agreement with recent relativistic mean meson field approaches.

Magnetic dipole spin excitations of deformed nuclei are studied in a schematic random-phase approximation (RPA) approach using a projected single-particle basis. The comparison of the present results with those obtained by conventional but more realistic RPA calculations supports the validity of the approach used here.

The model-space Brueckner-Hartree-Fock (BHF) approach of nuclear matter is extended to asymmetric nuclear matter. The energy per nucleon of bulk nuclear matter is calculated over a wide range of density and asymmetry parameter with both the Reid soft-core and the Paris nucleon-nucleon interactions. The results are compared to those calculated by using the usual BHF approach.

Relativistic Thomas-Fermi calculations for finite nuclei including quantum corrections up to second order in ħ, i.e., Wigner-Kirkwood and exchange corrections, have been performed. A linear σ-ω model is used, in case of exchange-corrected calculations extended by π-nucleon and tensor ρ-nucleon contributions. A detailed discussion of the outcome shows that the inclusion of quantum corrections improves the description of the nuclear surface and the classical forbidden region in comparison to the standard relativistic Thomas-Fermi model. Furthermore, special attention is devoted to the investigation of the spin-orbit interaction and the influence of the σ-meson mass on nuclear properties.