We have studied the level properties of the N=39 nucleus ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ge}$ by gamma-ray spectroscopy following the beta decay of ${}_{}{}^{71}{}_{}{}^{}\mathrm{As}$, for which we measure a half-life of 65.30±0.07 h. When we calculated the level structure of ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ge}$ within the framework of the interacting boson fermion model, we found good agreement with the experimentally determined level properties. Some evidence was found for the occurrence of levels built on the coexisting ${}_{}{}^{70}{}_{}{}^{}\mathrm{core}$ intruder state.

The Fermi surface anomaly consists in a variation, localized in the vicinity of the Fermi energy, of the energy derivative of the real part of the nuclear mean field. A quantitative analysis of this anomaly is performed in the framework of the relativistic Brueckner-Hartree-Fock approximation to the mean field in symmetric nuclear matter. The investigation is based on dispersion relations that connect the imaginary to the real part of the Lorentz components of the mean field; its main input is the imaginary part of the relativistic mean field recently calculated by ter Haar and Malfliet from a one-boson-exchange nucleon-nucleon interaction. It is found that the Fermi surface anomaly is very nearly the same as in the nonrelativistic Brueckner-Hartree-Fock approximation. However, the physical origin of the anomaly is quite different in the two cases. Relatedly, the predicted depletion of the Fermi sea is much smaller in the relativistic than in the nonrelativistic description. As a consequence, the rearrangement and renormalization corrections are much smaller in the relativistic than in the nonrelativistic case.

We derive a stability condition for the Thomas-Fermi solution of a finite nucleus where the underlying force has a finite range. The stability condition can be cast in the form of an eigenvalue equation; these eigenvalues must be all positive. The lowest eigenmodes correspond closely to vibration modes. The relationship of this time-independent formulation to the time-dependent Vlasov equation with self-consistent potential is established.

High-spin states in the odd-neutron ${}_{}{}^{131}{}_{}{}^{}\mathrm{Ba}$ nucleus have been populated following the ${}_{}{}^{122}{}_{}{}^{}\mathrm{Sn}$${(}^{13}$C,4n) reaction. Several rotational bands were established using γ-γ coincidence techniques. The yrast band, built on a ν$h_{11/2}$ orbital, has a relatively large signature splitting (∼160 keV). Cranking calculations suggest a significant triaxial shape with γ≪0° for this configuration. A pair of $h_{11/2}$ protons align at a rotational frequency ħω∼0.43 MeV and drive the nucleus towards a near-prolate shape (γ≥0°), which is manifest by the observation of a ΔI=1 band with strong dipole transitions and a small signature inversion. At a similar frequency, pairs of $h_{11/2}$ neutrons align and drive the nucleus to near-oblate (γ∼-60°) shapes, resulting in the observation of decoupled ΔI=2 bands.

A simple analytic expression is reported for U(6) matrix elements in the totally symmetric irreducible representations relevant to the interacting boson model. With respect to the SU(3) symmetry-adapted basis, the U(6) generators are given explicitly as SU(3) reduced matrix elements. The two-body Hamiltonian is expressed as a linear combination of SU(3) tensor operators. In particular, the Casimir invariants of the SU(5), O(6), and O(5) algebras are given in terms of SU(3) tensors. By using 9-(λμ) coefficients, the SU(3) tensor method is extended to the proton-neutron interacting boson model.

A model is formulated for a system of several valence nucleons coupled to a core. Single-particle orbits in this model can be determined consistently with underlying potentials between the core and the valence nucleon. A continuum spectrum for the single-particle state is taken into account through its discretization. A very simple system, the He isotopes, is used to show the feasibility of the model.

The self-consistent relativistic Fermi-sea particle formalism in the quantum hadrodynamics is discussed in terms of properties of conserving approximations. The relativistic Dirac-Hartree-Fock approximation (σ, ω, ρ, and π), for example, is examined from the point of view of the Hugenholtz–Van-Hove theorem and thermodynamics as a check for internal consistency. These two conditions sufficient for constructing conserving approximations are strict constraints on modification and simplification of the Fermi-sea particle approximations and should be used in order to define consistent quasiparticle approximations. It is shown that the pion vertex and retardation which enters through exchange corrections prevent conserving properties to be maintained in the Dirac-Hartree-Fock approximation, and this suggests a careful analysis of self-consistency in the relativistic formalism when correlation effects are considered. The relativistic Fermi-sea particle approximations can be defined uniquely when both constraints are incorporated into self-consistency of the approximations.

Electric transition strengths are calculated in a relativistic model. It is found that for electric transitions there is, in addition to the spin-orbit current, an extra medium-induced current coming from the Darwin term in the Hamiltonian. A medium-modified transition strength is defined and the effects of both medium-induced currents are studied. The application for the first $3^{\mathrm{-}}$ excitation in ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ yields unrealistic results. However, when vacuum polarization corrections are included the resulting B(E3) value comes close to the nonrelativistic shell-model one.

The formation of band patterns in odd-odd nuclei is investigated in the SU(3) limit of the interacting boson-fermion-fermion model. For two holes (particles) coupled to the SU(3) prolate (oblate) core, we study the algebraic K-representation basis which is the analog of the strong-coupling basis of the geometrical model. In the case of a particle and a hole coupled to the SU(3) core, we derive a new algebraic basis which, in the limit of the large boson number, becomes equivalent to the semi- decoupling basis of the particle-rotor model. For a simple demonstration case which was proposed in the first part of this work, the interacting boson-fermion-fermion-model Hamiltonian is explicitly diagonalized in these algebraic bases and all bands, which derive their parentage from the (2N,0) representation of the SU(3) boson core, are identified. Electromagnetic properties of low-lying bands are calculated and compared to the predictions of the geometrical model of Bohr and Mottelson. We also present an illustrative calculation for the realistic case (πh(11/2,νi 13) / 2 ) and identify several low-lying bands.

A ${}_{}{}^{60}{}_{}{}^{}\mathrm{Co}$ source has been used to photoactivate the 396 keV isomeric level ($T_{1/2}$∼48.6 min) of ${}_{}{}^{111}{}_{}{}^{}\mathrm{Cd}$. Our results confirm the existence of nonresonant contributions.

Spectroscopic information about ${}_{}{}^{127}{}_{}{}^{}\mathrm{Xe}$ is obtained by studying $\gamma$ rays following the $\beta$ decay of ${}_{}{}^{127}{}_{}{}^{}\mathrm{Cs}$. The results are of interest for determining the efficiency of a proposed ${}_{}{}^{127}{}_{}{}^{}\mathrm{I}$-based $\nu$ detector.

Previous observation of heavy-ion emission from ${}_{}{}^{226}{}_{}{}^{}\mathrm{Ra}$ has been confirmed. Charge and energy of the emitted fragment were measured using thin ${}_{}{}^{226}{}_{}{}^{}\mathrm{Ra}$ sources and polycarbonate track-recording films. Decay by ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ emission could be identified unambiguously. The track-detector was calibrated with tandem-accelerated ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ ions and tested by observing the ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ emission from ${}_{}{}^{223}{}_{}{}^{}\mathrm{Ra}$ yielding a branching ratio of (5.0±1.0)×${10}^{\mathrm{-}10}$. In the case of ${}_{}{}^{226}{}_{}{}^{}\mathrm{Ra}$ our result for the ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$/α ratio is (2.3±0.8)×${10}^{\mathrm{-}11}$. Estimates of partial half-lives of Ra isotopes for ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ emission are discussed.

Using a pairing-plus-quadrupole-model interaction Hamiltonian in a variation-after-exact-angular-momentum-projection approach we have calculated g factors of ${}_{}{}^{158}{}_{}{}^{}\mathrm{Er}$ for the low-spin yrast states with I=2–8. We find that g factors decrease very slowly with the increase of spin ($g_8$=0.86$g_2$) even though shape parameters (β,${\Delta }_n$,${\Delta }_p$) change appreciably as a function of angular momentum. This is in contrast to a rapid fall predicted in the cranked Hartree-Fock-Bogoliubov approach which happens because of a too early (I<8) strong rotation alignment of neutron $i_{13/2}$ orbitals.

A recent proton scattering experiment performed with 500 MeV protons has demonstrated a systematic quenching of the isovector spin-dipole strength. This report describes two mechanisms which can each contribute to the quenching: the effect of 2p-2h ground-state correlations and the spreading width that arises from the coupling of 1p-1h to 2p-2h excitations. The contributions from both effects bring theory within the range of experimental observation and indicate that these effects should be included in future calculations in which the origin of inhibition of spin-dependent excitations needs to be understood.

The specific heat has been calculated in the canonical ensemble for several light nuclei, using the experimental discrete spectrum and continuum. In each case, a prominent structure is present at low temperatures which results from the increased density of states associated with thermal excitation to the continuum; we associate this structure with the phase transition seen in earlier work in which the effects of the continuum were ignored. The phase transition is also predicted by finite-temperature mean-field calculations and is a general feature of all nuclei.

It is shown that the nondynamical violation of the isospin and Wigner SU(4) symmetries, induced by the Hartree-Fock-BCS approximation, can be circumvented by using the quasiparticle random-phase approximation. The suppression mechanism for the ββ-decay transition rates, proposed by Vogel and Zirnbauer, is found to be closely related to the restoration of SU(4) symmetry. It is suggested that the extreme sensitivity of the ββ-decay amplitude on the proton-neutron coupling is a consequence of the explicit violation of the SU(4) symmetry and therefore an artifact of the model. A prescription is given for fixing this interaction strength within the quasiparticle random-phase approximation itself, which in this way acquires predicting power on both single and double β-decay lifetimes.

New data for the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(${\pi }^{+}$,2p) reaction at $T_{\pi }$=165 MeV are presented. Significant differences with previously published data are discussed. It is found that below 20 MeV excitation approximately 14% of the total absorption cross section is due to a two-nucleon mechanism. Evidence for direct two-nucleon absorption at higher excitation energy is also presented. Including estimates for final state interactions, the present results suggest that about 50% of the abosrption cross section is due to two-nucleon processes.

The nucleus ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ has been studied with the (n,n’γ) reaction and lifetimes of many states have been extracted from the observed Doppler shifts of the deexciting γ rays. A large number of fast E1 transitions have been observed and have led to the identification of possible members of the octupole-octupole and the quadrupole-octupole multiplets. Substantial fragmentation of the two-phonon octupole strength is indicated.

Neutrons emitted by targetlike fragments after the inelastic reactions of 154 MeV ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ on ${}_{}{}^{100}{}_{}{}^{}\mathrm{Mo}$ have been measured. Neutron energy spectra and multiplicities have been derived as a function of the dissipated energy for targetlike fragment mass bins $A_{\mathrm{TL}}$=96–98, 101–103, and 104–106 and have been compared with the results of a Monte Carlo simulation which performs statistical model calculations of the targetlike fragment decay, with different assumptions on the partition of the excitation energy between the reaction partners. The partition following an equal temperature hypothesis better describes the experimental data but a sizable influence of the exit channel is found on the experimental neutron multiplicity.