The low-spin structure of ${}_{}{}^{126}{}_{}{}^{}\mathrm{Xe}$ has been investigated following the decay of 1.6-min $1^{+}$ ${}_{}{}^{126}{}_{}{}^{}\mathrm{Cs}$. Gamma-ray singles, gamma-gamma coincidences, and conversion-electron spectra have been measured. Several new levels have been identified and some new spins and parities have been suggested. The structure of ${}_{}{}^{126}{}_{}{}^{}\mathrm{Xe}$ and adjacent Xe nuclides has been investigated through interacting boson model-2 (IBM-2) calculations. The results of these calculations are discussed along with a number of other calculations of the structure of even-even Xe nuclides. Both these IBM-2 calculations and the total Routhian surface calculations suggest notable changes in structure for ${}_{}{}^{130}{}_{}{}^{}\mathrm{Xe}$.

We have studied the primary and secondary γ rays (33 in ${}_{}{}^{25}{}_{}{}^{}\mathrm{Mg}$, 212 in ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$, and 35 in ${}_{}{}^{27}{}_{}{}^{}\mathrm{Mg}$) following thermal-neutron capture by the stable ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$, ${}_{}{}^{25}{}_{}{}^{}\mathrm{Mg}$, and ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$ isotopes. Almost all of these γ rays have been incorporated into the corresponding level schemes consisting of 9 excited levels in ${}_{}{}^{25}{}_{}{}^{}\mathrm{Mg}$, 55 in ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$, and 10 in ${}_{}{}^{27}{}_{}{}^{}\mathrm{Mg}$. In each case, the observed γ rays account for nearly 100% of all captures. The measured neutron separation energies for ${}_{}{}^{25}{}_{}{}^{}\mathrm{Mg}$, ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$, and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Mg}$ are, respectively, 7330.65±0.05, 11 093.18±0.05, and 6443.40±0.05 keV. The measured thermal-neutron capture cross sections for ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$, ${}_{}{}^{25}{}_{}{}^{}\mathrm{Mg}$, and ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$ are, respectively, 54.1±1.3, 200±3, and 39.0±0.8 mb. In all three cases, primary electric-dipole (E1) transitions account for the bulk of the total capture cross section. We have calculated these E1 partial cross sections using direct-capture theory. We have also speculated on the mechanism responsible for the magnetic-dipole (M1) transitions which are quite strong in ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$.

α groups and γ-ray transitions have been observed from nuclides produced in the bombardment of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ with ${}_{}{}^{127}{}_{}{}^{}\mathrm{I}$. Two weak α groups were assigned to ${}_{}{}^{162,163}{}_{}{}^{}\mathrm{Ta}$ based on their measured half-lives and excitation functions. With an unambiguous assignment of these two α groups the absolute masses of nuclides in two long α chains, for which ${}_{}{}^{162,163}{}_{}{}^{}\mathrm{Ta}$ form links, can now be deduced with confidence. Absolute masses are thus obtained for some nuclides very far from stability, including ones that are not bound against ground-state proton emission. The simultaneous observation of α groups and γ rays from other nuclides produced in this bombardment also permitted the determination of the upper limits of six new α branching ratios.

States in ${}_{}{}^{145}{}_{}{}^{}\mathrm{Pm}$ were studied in the reaction ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}$${(}^{19}$F,4n) at a beam energy of 75 MeV using techniques of in-beam γ-ray and conversion electron spectroscopy. Measurements were made of γ-γ coincidences, γ-ray angular distributions, conversion electrons, and excitation functions between 70 and 85 MeV. The reduced B(E3) transition strength for the 795 keV (11/$2^{\mathrm{-}}$→5/$2_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{+}$) transition was determined to be 7.8(18) Weisskopf units, supporting the interpretation of the 11/$2^{\mathrm{-}}$ state as a ${\mathit{h}}_{11/2}$ proton state. A negative-parity sequence built on the 11/$2^{\mathrm{-}}$ state as well as eleven new states above the 1503 keV 15/$2^{+}$ state were found. A weak coupling model can explain the structure of the deduced decay scheme up to an energy of 2.5 MeV.

Differential cross sections were measured for the ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$(n,n’γ) reactions at incident energies between 4.8 and 8.0 MeV. Excitation energies, spins, level lifetimes, γ-ray branching ratios, and γ-ray production cross sections were determined. Members of the doublet at 4.50 MeV are clearly identified and assigned spins of $4^{+}$ and $3^{\mathrm{-}}$. Inelastic neutron scattering cross sections were inferred from the γ-ray branching ratios and production cross sections. The inferred cross sections are in excellent agreement with those measured in a separate neutron detection experiment, and with a recent vibrational model coupled-channels analysis of the ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$(n,n’) data. Comparison of level excitations produced by neutrons and other hadrons with electomagnetic strengths shows very different mixtures of neutron and proton particle-hole amplitudes for different levels.

The double-charge-exchange (DCX) reaction with Ca isotopes as targets is studied by employing the interacting-boson approximation (IBA). A comparison between the IBA and the shell-model results shows that IBA is a good approximation of the shell model in describing the DCX reactions.

A generalized Inglis formula is derived for the dynamic inertia tensor scr${\mathbf{I}}^{\mathrm{}\left(2\right)\mathrm{}}$. This formula is valid at high spins. It also describes rotations about nonprincipal axes. If the rotation axis is parallel to a principal axis, then the formula determines how the nucleus responds to a perturbation away from the principal axis.

We have calculated nucleon spectral functions and momentum distributions for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and infinite nuclear matter in a relativistic mean-field approximation to the Walecka model. In spite of the mean-field nature of the ground state we have observed fragmentation of single-particle strength and partial occupancy of single-particle orbits. A substantial amount of single-particle strength was found at very high excitation energy due to particle-antiparticle mixing. This mixing was also responsible for the high-momentum tail seen in the calculation of nucleon momentum distributions. We argued that these findings are a general consequence of the relativistic formalism and should remain valid even in more sophisticated treatments of the ground state.

Isospin fluctuations and triaxial deformation are incorporated in the statistical theory of hot nuclei, and various nuclear parameters are extracted as functions of isospin, temperature, and deformation for nuclei around Zr. Shape changes are observed with changes in isospin and temperature. Above a particular temperature the shape is found to remain unchanged for all isospins. Constant entropy lines are drawn and yrast traps are observed. The yrast traps at the low entropy values indicate the neutron-proton shell closure for the systems considered. A shift in the yrast minima towards lower isospin is predicted with increase in entropy. At higher entropy values yrast minima are found to disappear. The neutron-proton asymmetry parameter calculated for A=90, 92, 94, and 96 is found to depend strongly on deformation and isospin at low temperatures. For all these nuclei the asymmetry parameter is found to be a maximum for isospins corresponding to stable neutron-proton combination. The single-particle level-density parameter for A=90 extracted as a function of temperature for various isospins shows a minimum at a total isospin of τ=5, indicating the higher stability of this isospin state. At higher temperatures the empirical value of a≊A/10 is reproduced.

We study the fluctuations in the spectrum and the E2 transition intensities of the low-lying collective states in heavy nuclei. Using the interacting boson model we investigate the transition from rotational nuclei to γ-unstable nuclei. Near those two limits the system exhibits regular behavior but in the transition region we observe the onset of chaos where both the level statistics and the intensities statistics are described by the Gaussian orthogonal ensemble of random matrices. The systematics of the onset of chaos within different spin/parity classes are investigated. The quantal results agree with the classical mean-field analysis.

We examine the phenomenon of proton emission from the ground states of heavy nuclei, using a model of charged particle emission which has previously given a good description of unhindered s-wave alpha and exotic decays in heavy nuclei. We have extended the model formalism by including an angular momentum term, because the emitted proton seldom comes from an s orbital. Using a realistic proton-nucleus potential, obtained from proton-nucleus scattering, we calculate partial half-lives and find generally good agreement with the currently available experimental measurements.

The properties of nuclear matter are studied in the framework of quantum hadrodynamics. Assuming an ω-meson field, periodic in space, a self-consistent set of equations is derived in the mean-field approximation for the description of nucleons interacting via σ-meson and ω-meson fields. Solutions of these self-consistent equations have been found: The baryon density is constant in space, however, the baryon current density is periodic. This high density phase of nuclear matter can be produced by anisotropic external pressure, occurring, e.g., in relativistic heavy ion reactions. The self-consistent fields developing beyond the instability limit have a special screw symmetry. In the presence of such an ω field, the energy spectrum of the relativistic nucleons exhibits allowed and forbidden bands, similar to the energy spectrum of the electrons in solids.

A theoretical calculation of the partial lifetime of the fission isomer in ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ decaying via electric quadrupole radiation to the lowest $2^{+}$ state is presented and compared to experiment. This is a fully microscopic nuclear structure calculation using the constrained Hartree-Fock-Bogoliubov method, where the only input is the finite-ranged D1S interaction. The low-lying collective states are obtained via the Gaussian overlap approximation of the generator coordinate method. Rotational symmetry is restored within the rotor approximation. The computation of the transition rates provides an upper limit on the γ-decay lifetime of the isomer, since only axial quadrupole deformations are considered.

The diffusion coefficient for quadrupolar shape changes is derived in a model based on the mixing of static Hartree-Fock configurations by the residual interaction. The model correctly predicts the width of single-particle configurations. We find a diffusion rate depending on temperature as ${\mathit{T}}^3$, consistent with at least one other theoretical estimate. However, our diffusion rate is an order of magnitude lower than two values extracted from data.

Two-shell-model interactions are constructed in the model space of the five proton and six neutron orbits just above the double shell closure at ${}_{}{}^{132}{}_{}{}^{}\mathrm{Sn}$. One interaction uses the two-body matrix elements calculated by Kuo and Herling for use near ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. For the other, the proton-proton two-body matrix elements are replaced with effective ones of Kruse and Wildenthal and selected proton-neutron matrix elements were varied in order to better reproduce the known energy spectra of ${}_{}{}^{134}{}_{}{}^{}\mathrm{Sb}$. The main difficulty in this construction is the determination of the neutron single-particle energies. This determination was done by comparison of theoretical and experimental (d,p) spectroscopic factors for the N=83, Z=54, 56, and 58 isotones. The ΔJ≠0 first-forbidden ${\mathrm{\beta }}^{\mathrm{-}}$ decays of ${}_{}{}^{133}{}_{}{}^{}\mathrm{Sn}$(7/$2^{\mathrm{-}}$), ${}_{}{}^{134}{}_{}{}^{}\mathrm{Sn}$($0^{+}$), ${}_{}{}^{134}{}_{}{}^{}\mathrm{Sb}$($0^{\mathrm{-}}$), and ${}_{}{}^{134}{}_{}{}^{}\mathrm{Sb}$($7^{\mathrm{-}}$) were considered in order to exemplify the application of these interactions.

Azimuthal distributions of helium ions have been measured in coincidence with high-energy protons in reactions induced by ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ at 94 MeV/nucleon on ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$. Helium ions have been detected in a large area multidetector. Protons have been observed at 90°. Mean multiplicities of light charged particles (H and He) are found slightly dependent on the target mass. Strong azimuthal asymmetries whose intensity is larger for the Al target and vanishes with the increasing of the target mass are observed in the He distributions. Experimental data are discussed in the framework of the participant-spectator picture of a modified fireball model, taking into account intermediate energy corrections. In this framework the behavior of the azimuthal asymmetries, as a function of the target mass, indicates a strong final-state interaction between participant and spectator fragments. Such a result is found in agreement with interaction time predictions of a microscopical calculation based on the Boltzmann-Nordheim-Vlasov equation.

Nuclear pion production has been studied by means of the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(p,d${\mathrm{\pi }}^{+}$${)}^{11}$B at an incident energy of 223 MeV, which is considerably below the threshold for a free N-N process. The shape and absolute cross section of the experimental energy-sharing distribution are in remarkable agreement with the prediction of a distorted-wave impulse approximation theory. This shows that the reaction mechanism is quasifree pion production, which is related to the elementary reaction p+p→${\mathrm{\pi }}^{+}$+d.

New measurements of beam-velocity fragment yields from ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ projectiles at energies of 50 and 70 MeV/nucleon show that the yields of fragments with Z>1 are remarkably independent of beam energy from 20 MeV/nucleon to 200 GeV/nucleon. The yields of ${}_{}{}^2{}_{}{}^{}\mathrm{H}$${+}^3$H increase by a factor of only 1.7 between 50 and 2000 MeV/nucleon. Statistical decay of primary fragments accounts reasonably well for the measured fragment and coincidence channel cross sections, and for the fragment momentum distributions from ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ projectiles at energies from 70 MeV/nucleon to 200 GeV/nucleon and from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ projectiles at 2 GeV/nucleon.

The ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$(α,α’) reaction was studied at ${\mathit{E}}_{\mathrm{\alpha }}$=50 MeV. The angular distribution of the continuum region near the ${}_{}{}^6{}_{}{}^{}\mathrm{\alpha }$+d breakup threshold (1.475 MeV) was measured for ${\mathrm{\theta }}_{\mathrm{lab}}$=7°–40°. The data were analyzed in terms of plane-wave and distorted-wave impulse approximation calculations. To study the possible effects of recombination of the breakup clusters in the exit channel, distorted-wave Born approximation calculations were also performed.

Singles ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(${\mathrm{\pi }}^{+}$,p) and coincidence ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(${\mathrm{\pi }}^{+}$,2p${)}^{14}$N measurements have been made at ${\mathit{T}}_{\mathrm{\pi }}$=115 MeV over an extended range of the phase space of the two final-state protons. The coincidence measurements have a missing-mass resolution of 4 MeV. The direct two-nucleon absorption cross section extracted from the data is 58±8 mb. After corrections for final-state interactions, it was found that the two-nucleon ${\mathrm{\pi }}^{+}$+np→pp process accounts for about 76% of the total absorption cross section, and thus is the dominant absorption mechanism. Evidence for absorption on s-p pairs is seen as a broad bump near 32 MeV of excitation. At backward angles the inclusive ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(${\mathrm{\pi }}^{+}$,p) spectra show a distinct absorption peak, an important feature not previously observed. Comparisons of distorted wave impulse approximation calculations to both the coincidence data and inclusive data are presented.