Using the Bonn B nucleon-nucleon potential and the Tucson-Melbourne family of π-π, π-ρ, and ρ-ρ three-nucleon forces we solved the 3N Faddeev equation below and above the deuteron breakup threshold. For different elastic scattering and breakup observables we looked for the effects caused by adding consecutively the above 3N forces. The largest effects were found for the π-π three-nucleon force. The influence of π-ρ exchange was generally found to be smaller than π-π and it acts in opposite direction. The effect of the ρ-ρ three-nucleon force was found to be always negligible. Adding π-ρ and ρ-ρ three-nucleon forces does not explain the analyzing power puzzle in the low energy nucleon-deuteron elastic scattering.

A general procedure for constructing instant form, one particle exchange models for two particle systems is developed. The procedure entails the construction of a mass operator which when used in conjunction with a free spin operator and a free Newton-Wigner position operator leads to an exactly Poincaré invariant model. The method is applied to a simple model for s-wave pion-nucleon scattering. This model is derived from a quantum field theory which describes the interaction between pions, nucleons, and sigma mesons through the virtual processes N?N+π, π?π+σ, and N?N+σ. The instant form version of this exchange model is compared with a front form version that was constructed previously. With the procedures used to ensure Poincaré invariance, the instant form two-particle potentials are of the same form as the front form potentials; however, the pion-nucleon propagators that appear in the two-particle Lippmann-Schwinger equations are not the same. The instant form and front form models are fit to the same s-wave pion-nucleon phase shifts, and the resulting parameters are compared.

The ${}_{\mathrm{}63}{}^{139}{}_{}{}^{}\mathrm{Eu}_{76}^{}{}_{}{}^{}$ nucleus has been investigated by γ-γ coincidence measurements employing the ${}_{}{}^{92}{}_{}{}^{}\mathrm{Mo}$${(}^{50}$Cr,3p) reaction at 220 MeV with both backed and thin self-supporting targets. The high-spin properties have been followed up to a spin of 47/2. The π${\mathit{h}}_{11/2}$ yrast band and its unfavored signature partner both exhibit backbends due to ${\mathit{h}}_{11/2}$ proton alignment. The two signatures of a π${\mathit{g}}_{7/2}$(${\mathit{d}}_{5/2}$) band above the ${\mathit{h}}_{11/2}$ proton alignment were also identified. Interpretations of other structures are discussed.

Spectra of two-step γ-ray cascades following the thermal-neutron capture in the ${}_{}{}^{162}{}_{}{}^{}\mathrm{Dy}$ target were measured. Based on a rigorous modeling procedure, the experimental results are compared with their various theoretical predictions. A satisfactory agreement is reached for the E1 strength function described by the Brink-Axel model and the M1 strength function containing a resonance component at ${\mathit{E}}_{\gamma }$≊3 MeV. A possible interpretation of this component in terms of the M1 scissors resonance is discussed.

The near-yrast spectrum of the N=84 isotope ${}_{}{}^{144}{}_{}{}^{}\mathrm{Nd}$ has been studied using the ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}$${(}^{18}$O,4n) reaction at a lab energy of 85 MeV and the techniques of γ-ray spectroscopy. Sixteen new states and 23 new γ rays were placed in the level scheme. Most of the yrast and near-yrast negative-parity states have been interpreted in terms of empirical shell-model configurations. However, the interpretation of a sequence of states from J=17–24 in terms of the ${\mathit{h}}_{11/2}^3$${\mathit{g}}_{7/2}^{\mathrm{-}1}$${\mathit{d}}_{5/2}^{\mathrm{-}6}$ proton configuration is problematic because the observed energies cannot be satisfactorily reproduced with empirical shell-model calculations.

Superdeformation in ${}_{}{}^{146}{}_{}{}^{}\mathrm{Gd}$ has been studied using the EUROGAM I spectrometer at the NSF Daresbury. The two known superdeformed (SD) bands in ${}_{}{}^{146}{}_{}{}^{}\mathrm{Gd}$ have been extended to 15 transitions. All transitions within each band were clearly observed in coincidence among each other and accurate γ-ray energies were determined. The association of both bands to ${}_{}{}^{146}{}_{}{}^{}\mathrm{Gd}$ has been unambiguously confirmed. In addition a band with energies corresponding to the first known SD band in ${}_{}{}^{147}{}_{}{}^{}\mathrm{Gd}$ was also observed. Several methods to search for new SD bands were applied.

The ‘‘identical’’ bands in superdeformed mercury, thallium, and lead nuclei are interpreted as examples of orbital angular momentum rotors with the weak spin-orbit coupling of pseudo-SU(3) symmetries and supersymmetries.

A measurement of low-lying states in ${}_{}{}^9{}_{}{}^{}\mathrm{B}$ was conducted using the ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$${(}^6$Li,t${)}^9$B reaction at a beam energy of 56 MeV. The particles resulting from the decay of ${}_{}{}^9{}_{}{}^{}\mathrm{B}$ into ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$ + p were detected with position sensitive detectors, and relative energy spectra were obtained from the data using the technique of resonant particle decay spectroscopy. This technique provided a very low background, and the ability to separate the ${}_{}{}^9{}_{}{}^{}\mathrm{B}$ states that decay by ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$ + p from those that decay by ${}_{}{}^5{}_{}{}^{}\mathrm{Li}$ + α. Results show that a significant portion of the measured spectrum below ≊ 1.5 MeV cannot be explained by the known states which suggests that these counts arise from the mirror of the 1.68 MeV 1/$2^{+}$ state of ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$. It was also shown that the recently observed 1/$2^{\mathrm{-}}$ state decays via the p${+}^8$Be channel.

High-spin states in ${}_{}{}^{177}{}_{}{}^{}\mathrm{Ta}$ were produced using the ${}_{}{}^{170}{}_{}{}^{}\mathrm{Er}$${(}^{11}$B, 4n) reaction at 55 and 60 MeV. Considerable extensions have been made to the previously known level scheme, and new structures have been found. B(M1)/B(E2) ratios have been extracted for strongly coupled bands. The behavior of the different rotational cascades, in particular the anomalous crossing frequency observed in the [541]1/$2^{\mathrm{-}}$ proton ${\mathit{h}}_{9/2}$ band and the occurrence of ‘‘identical bands,’’ is discussed. Comparisons are made with projected shell model calculations.

With prompt γ-ray and x-ray spectroscopy on fission fragments, several new transitions in ${}_{}{}^{109,111}{}_{}{}^{}\mathrm{Ru}$ have been identified. Angular correlation analysis of several of the new transitions yield evidence of a stretched E2 band structure. Qualitative Nilsson model arguments, systematics, and triaxial rotor+particle calculations support our hypothesis that the observed band is built on the unique parity ν${\mathit{h}}_{11/2}$ orbital.

The levels ${\mathrm{in}}^{108,110,112}$Ru have been investigated in the spontaneous fission of ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ using γ-γ-γ-, γ-γ-, x-x-, x-γ-, and x-γ-γ-coincidence techniques. The levels up to ${16}^{+}$ and $9^{+}$ in the yrast bands and γ-vibrational bands have been identified with very little energy staggering in ${}_{}{}^{108,110,112}{}_{}{}^{}\mathrm{Ru}$. The ground bands in ${}_{}{}^{108,110}{}_{}{}^{}\mathrm{Ru}$ have identical γ-ray transition energies up to $8^{+}$. These are the lightest observed even-even nuclei with extended identical ground bands. Calculations in a collective model which includes rotations and vibrations reproduce the level energies and γ band branching ratios above the $3^{+}$ state rather well, while rigid triaxial rotor model calculations reproduce the branching ratios for the $2^{+}$ and $3^{+}$ states.

The decays of seniority isomers in the N=82 nuclei ${}_{}{}^{150}{}_{}{}^{}\mathrm{Er}$ and ${}_{}{}^{152}{}_{}{}^{}\mathrm{Yb}$ and in their respective N=81 isotopes ${}_{}{}^{149}{}_{}{}^{}\mathrm{Er}$ and ${}_{}{}^{151}{}_{}{}^{}\mathrm{Yb}$ were studied following mass separation by the Argonne Fragment Mass Analyzer. Conversion electrons were detected with Si p-i-n diodes operated at room temperature. The low-energy isomeric transitions in ${}_{}{}^{151,152}{}_{}{}^{}\mathrm{Yb}$ have been observed for the first time in the electron spectra. Multipolarity assignments were made for many of the decay γ rays of the four nuclei.

The ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$${(}^3$He,t${)}^{120}$Sb charge-exchange reaction has been investigated at E${(}^3$He) = 200 MeV and θ≊0° to study neutron decay from the isobaric analog state at ${\mathit{E}}_{\mathit{x}}$=10.20 MeV in ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sb}$. The low-energy neutrons (average energy ∼0.85 MeV) were detected in coincidence with tritons observed in the focal plane of a high-resolution magnet spectrometer. Four small deuterated NE230 scintillation detectors were mounted at distances of 9.5 cm from the target resulting in an overall neutron detection efficiency including solid angle of ≳1%. This efficiency was obtained by combining the measured dependence on neutron energy with a calculated neutron evaporation spectrum. From the measured ratio of coincidence to singles events a branching ratio of ≳86% was deduced for neutron decay. The observation of isospin-violating neutron decay with a branching ratio close to 100% is in agreement with the expectation that the escape width (${\mathrm{\Gamma }}^{\mathrm{\uparrow }}$) of the isobaric analog state in ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sb}$ is small compared to its spreading width (${\mathrm{\Gamma }}^{\mathrm{\downarrow }}$). Triton spectra measured in coincidence with γ rays from the deexcitation of the final nucleus display pronounced structures related to the thresholds for neutron emission, in agreement with the characteristics of calculated evaporation spectra.

A relativistic hadronic model for nuclear matter and finite nuclei, which incorporates nonlinear chiral symmetry and broken scale invariance, is presented and applied at the one-baryon-loop level to finite nuclei. The model contains an effective light scalar field that is responsible for the midrange nucleon-nucleon attraction and which has anomalous scaling behavior. One-loop vacuum contributions in this background scalar field at finite density are constrained by low-energy theorems that reflect the broken scale invariance of quantum chromodynamics. A mean-field energy functional for nuclear matter and nuclei is derived that contains small powers of the fields and their derivatives, and the validity of this truncation is discussed. Good fits to the bulk properties of finite nuclei and single-particle spectra are obtained.

Recently measured B(E2;$0_1^{+}$→$2_1^{+}$) values for the light xenon (Z=54) isotopes show a marked increase in deformation as the neutron numbers approach the midshell value of N=66. At first sight, this behavior is anomalous because the $2_1^{+}$ level energies are nearly the same for these isotopes. Moreover, this increase is not readily explained by several nuclear models that assign single shells to valence protons and neutrons. In particular, the single-shell asymptotic Nilsson model with current parameters seriously underpredicts the B(E2;$0_1^{+}$→$2_1^{+}$) values for ${}_{}{}^{118}{}_{}{}^{}\mathrm{Xe}_{64}^{}{}_{}{}^{}$, ${}_{}{}^{120}{}_{}{}^{}\mathrm{Xe}_{66}^{}{}_{}{}^{}$, and ${}_{}{}^{122}{}_{}{}^{}\mathrm{Xe}_{68}^{}{}_{}{}^{}$. On the other hand, several modern multishell models correctly predict these values. We examine the latter results more closely to find ways in which the single-shell asymptotic Nilsson model can be revised to correctly reproduce the measurements. We also show that the B(E2;$0_1^{+}$→$2_1^{+}$) values for lighter (N<66) barium isotopes, when they are measured, will test the predictive power of existing systematics and modeling of quadrupole deformations in nuclei.

We construct finite Dyson boson-fermion mappings of general collective algebras extended by single-fermion operators. A key element in the construction is the implementation of a similarity transformation which transforms boson-fermion images obtained directly from the supercoherent state method. In addition to the general construction, we give detailed applications to SO(2N), SU(l+1), SO(5), and SO(8) algebras.

Band-crossing phenomena in the high-spin region of deformed nuclei are studied in this paper. The power of modern computers for large-matrix diagonalization (up to 17 527×17 527) is exploited in a multinucleon-plus-rotor model. The interesting test case of ${}_{}{}^{154}{}_{}{}^{}\mathrm{Gd}$ is treated in this paper. Though a small basis set of 9–18 Nilsson orbitals is used, the strict angular momentum and particle number conservation guarantees superior orthogonal microscopic wave functions for nucleon transfer calculations. This method takes account of pairing correlations among the valence particles and shows the effects of quadrupole pairing and the usually neglected j⋅j recoil terms.

The F-spin mixing and M1 properties of the low-lying bands in the neutron-proton interacting boson model (IBM-2) are studied. Application of the intrinsic state formalism in the leading order in 1/N and of the perturbative approach makes it possible to obtain analytical expressions in which a dependence on F-spin breaking terms is clearly exhibited. A simple explanation of many features observed in numerical studies is given. Comparison between the IBM-2 results and the treatment of M1 properties with the extended M1 operator in the IBM-1 approach is discussed.

A comparative study of the liquid-drop model (LDM) type expansions of energy E and compression modulus ${\mathit{K}}_{\mathit{A}}$ is made within the energy density formalism using Skyrme interactions. As compared to the energy expansion, it is found that, in the pure bulk mode of density vibration, the LDM expansion of ${\mathit{K}}_{\mathit{A}}$ shows an anomalous convergence behavior due to pair effect. A least-squares-fit analysis is done to estimate the minimum error one would expect, even with synthetic data due to the inherent nature of the LDM expansion of ${\mathit{K}}_{\mathit{A}}$ as well as the narrow range of accessible mass number A, in the values of the various coefficients. The dependence of the higher-order coefficients like curvature and Gauss curvature on the coupling ${\mathrm{\beta }}_{\mathit{c}}$ between the bulk and surface parts of the monopole vibrations is analytically studied. It is shown that the ${\mathit{K}}_{\mathit{A}}$ expansion including the dynamical effect (A dependence of ${\mathrm{\beta }}_{\mathit{c}}$) shows an ‘‘upturn’’ behavior below mass number about 120, suggesting the inapplicability of the LDM expansion of ${\mathit{K}}_{\mathit{A}}$ over this mass region.

Landau theory of phase transitions is used to determine the shape evolution of even-even s-d shell nuclei with temperature and spin. Further in this study, the most important statistical thermal shape fluctuations are also incorporated. The constants appearing in the Landau expression for the free energy are determined by using the free energy surfaces at ω=0 calculated by the finite temperature Strutinsky and summation methods. The pairing effect is included at ground state but shown to be of minor importance in shape determination. It is seen that the averaged shapes for the above nuclei at different temperatures and spins are mostly triaxial which are quite different from the most probable shapes, prolate or oblate. Only these averaged shapes can be seen through the study of giant dipole resonance decays of highly excited states.