We present new calculations of the $\alpha$ particle which are based on the most modern nucleon-nucleon interactions alone and combined with the Tucson-Melbourne or the Urbana IX three-nucleon interaction. Results for the binding energies and some properties of the wave function are given. On that phenomenological level little room is left for the action of a possible four-nucleon force.

Isotopic distributions for light particles and intermediate mass fragments have been measured for ${}^{112}\mathrm{Sn}{+}^{112}\mathrm{Sn}$, ${}^{112}\mathrm{Sn}{+}^{124}\mathrm{Sn}$, ${}^{124}\mathrm{Sn}{+}^{112}\mathrm{Sn}$, and ${}^{124}\mathrm{Sn}{+}^{124}\mathrm{Sn}$ collisions at $E/A=50\mathrm{}\mathrm{MeV}$. Isotope, isotone, and isobar yield ratios are utilized to estimate the isotopic composition of the gas phase at freeze-out. Analyses within the equilibrium limit imply that the gas phase is enriched in neutrons relative to the liquid phase represented by bound nuclei. These observations suggest that neutron diffusion is commensurate with or more rapid than fragment production.

The $N_p{N}_n$ scheme, which has been extensively applied to even-even nuclei, is found to be a very good benchmark for odd-even, even-odd, and doubly-odd nuclei as well. There are no apparent shifts in the correlations for these four classes of nuclei. The compact correlations highlight the deviant behavior of the $Z=78\mathrm{}$ nuclei and are used to deduce effective valence proton numbers near $Z=64\mathrm{}$ as well as to study the evolution of the $Z=64\mathrm{}$ subshell gap.

A candidate for a soft dipole resonance, a dipole oscillation mode between a core cluster and a neutron skin, was observed at $E_x=4\mathrm{}\pm 1\mathrm{MeV}$ and with a width of $4\pm 1\mathrm{MeV}$ in ${}^6\mathrm{He}$ via the ${}^6\mathrm{Li}({}^7\mathrm{Li},{}^7\mathrm{Be})$ reaction at an incident energy of $65A\mathrm{MeV}$ and forward scattering angles including $0°$. Its cross section is deduced to be $\sigma \left(0°\right)=0.9\mathrm{}\pm 0.2\mathrm{mb}/\mathrm{sr}$. This value is comparable to that of the giant dipole resonance simultaneously measured.

Partial cross sections and corresponding momentum distributions have been studied in the one-neutron knockout reaction ( ${}^{12}\mathrm{Be}{,}^{11}\mathrm{Be}+\gamma$) on a ${}^9\mathrm{Be}$ target at 78 MeV/nucleon. The resulting spectroscopic factors for the only two bound states of ${}^{11}\mathrm{Be}$ are $0.42\pm 0.06$ ( $1/2^{+}$) and $0.37\pm 0.06$ ( $1/2^{-}$), where the errors are experimental only. This result shows that $N=8\mathrm{}$ is not a good closed shell in the neutron-rich ${}^{12}\mathrm{Be}$ and that the last neutron pair is two-thirds in the ( ${1s}^2{+0d}^2$) intruder configuration.

Movitated by the on-going $\gamma$-ray experiments at the Alternating Gradient Synchrotron at Brookhaven National Laboratory, we discuss the energy splittings of the ${5/2}_1^{+}-{3/2}_1^{+}$ doublet in ${}_{\Lambda }^9\mathrm{Be}$ and the ${3/2}_1^{-}-{1/2}_1^{-}$ doublet in ${}_{\Lambda }^{13}\mathrm{C}$ for which the $\Lambda N$ spin-orbit ( $\mathrm{LS}$) and antisymmetric spin-orbit ( $\mathrm{ALS}$) forces are relevant. In the microscopic $2\alpha +\Lambda$ ( $3\alpha +\Lambda$) model for ${}_{\Lambda }^9\mathrm{Be}$ ( ${}_{\Lambda }^{13}\mathrm{C}$), all the available Nijmegen one-boson-exchange (OBE) model $\Lambda N$ interactions lead to a wide range of splittings of $0.08–0.20\mathrm{MeV}$ in ${}_{\Lambda }^9\mathrm{Be}$ and $0.39–0.96\mathrm{MeV}$ in ${}_{\Lambda }^{13}\mathrm{C}$. On the other hand, if we use information from quark-model $\Lambda N$ interactions which have generally large $\mathrm{ALS}$ force, the splittings become about half of the smallest OBE model prediction.

The doubly magic nuclei ${}^{40}\mathrm{Ca}$ and ${}^{48}\mathrm{Ca}$ have been studied in high resolution photon scattering experiments. We have derived absolute dipole and quadrupole excitation strengths up to 10 MeV. Evidence was found for a two-phonon quadrupole-octupole state in ${}^{48}\mathrm{Ca}$. At higher energies in contrast to ${}^{40}\mathrm{Ca}$, a concentration of dipole strength is observed in ${}^{48}\mathrm{Ca}$ which is discussed in terms of a pygmy resonance originating from the large neutron excess.

The emission pattern of charged pions has been measured in $\mathrm{Au}+\mathrm{Au}$ collisions at 1 GeV/nucleon incident energy. In peripheral collisions and at target rapidities, high-energy pions are emitted preferentially towards the target spectator matter. In contrast, low-energy pions are emitted predominantly in the opposite direction. The corresponding azimuthal anisotropy is explained by the interaction of pions with projectile and target spectator matter. This interaction with the spectator matter causes an effective shadowing which varies with time during the reaction. Our observations show that high-energy pions stem from the early stage of the collision whereas low-energy pions freeze out later.

We study the emission of two protons from nuclei where this is the only decay channel. A three-body model is developed. We compare the “diproton” model with the three-body calculations. We present exploratory studies of the ${}^{19}\mathrm{Mg}$ and ${}^{48}\mathrm{Ni}$ ground states, which are good candidates for two-proton radioactivity. The two-proton width for the ${}^{17}\mathrm{Ne}{3/2}^{-}$ state is also estimated. Our calculations give substantially lower values for the width than predicted by the diproton model, but larger than from direct decay to the continuum.

We study the behavior of shell effects, like pairing correlations and shape deformations, with the excitation energy in atomic nuclei. The analysis is carried out with the finite temperature Hartree-Fock-Bogoliubov method and a finite range density dependent force. For the first time, properties associated with the octupole and hexadecupole deformation and with the superdeformation as a function of the excitation energy are studied. Calculations for the well quadrupole deformed ${}^{164}\mathrm{Er}$ and ${}^{162}\mathrm{Dy}$, superdeformed ${}^{152}\mathrm{Dy}$, octupole deformed ${}^{224}\mathrm{Ra}$, and spherical ${}^{118}\mathrm{Sn}$ nuclei are shown. We find, in particular, the level density of superdeformed states to be 4 orders of magnitude smaller than for normal deformed ones.

The neutron and proton density distributions obtained in constrained Hartree-Fock-Bogolyubov calculations with the Gogny force along the fission paths of ${}^{232}\mathrm{Th}$, ${}^{236}\mathrm{U}$, ${}^{238}\mathrm{U}$, and ${}^{240}\mathrm{Pu}$ are analyzed. Significant differences in the multipole deformations of neutron and proton densities are found. The effect on potential energy surfaces and on barrier heights is studied under an additional constraint by imposing similar spatial distributions to neutrons and protons, as assumed in macroscopic-microscopic models.

The astrophysical factor for the proton weak capture on ${}^3\mathrm{He}$ is calculated with correlated hyperspherical harmonic wave functions corresponding to a realistic Hamiltonian consisting of the Argonne $v_{18}$ two-nucleon and Urbana-IX three-nucleon interactions. The nuclear weak current has vector and axial-vector components with one- and many-body terms. All possible transitions connecting any of the $p{}^3\mathrm{He}$ $S$- and $P$-wave channels to ${}^4\mathrm{He}$ are considered. The $S$ factor at a $p{}^3\mathrm{He}$ center-of-mass energy of $10\mathrm{keV}$ is predicted to be $10.1\times {10}^{-20\mathrm{}}\mathrm{keV}\mathrm{b}$, a factor of $\simeq 4.5$ larger than the value adopted in the standard solar model. The $P$-wave transitions are found to contribute about $40\%$ of the calculated $S$ factor.

Using a large-acceptance germanium detector array (Hyperball), we have observed a spin-flip $M1\mathrm{}$ $\gamma$ transition between the ground-state spin doublet of ${}_{\Lambda }^7\mathrm{Li}$ ( ${\frac{3}{2}}^{+}\to {\frac{1}{2}}^{+}$). The observed energy of $691.7\pm 0.6\left(\mathrm{stat}\right)\pm 1.0\left(\mathrm{syst}\right)$ keV provides crucial information on the strength of the spin-spin interaction between a $\Lambda$ and a nucleon. This is the first observation of well-identified hypernuclear $\gamma$ transitions using germanium detectors.

Spectra of the $E2\mathrm{}$ quasicontinuum $\gamma$ rays feeding different spin regions of the ${}^{154}\mathrm{Dy}$ yrast line have been extracted. These are compared with corresponding theoretical spectra obtained by numerical simulations based on temperature-dependent Hartree-Fock theory, with thermal shape fluctuations. In this manner, different regions of the spin-energy plane can be examined. The results support the predictions of a smeared-out phase transition at high spin above the yrast line.

Excitation-energy-gated two-fragment correlation functions have been studied between $E^{*}/A=(2–9)A\mathrm{MeV}$ for equilibriumlike sources formed in $8–10\mathrm{GeV}/c$ ${\pi }^{-}$ and ${p+}^{197}\mathrm{Au}$ reactions. Comparison with an $N$-body Coulomb-trajectory code shows an order of magnitude decrease in the fragment emission time in the interval $E^{*}/A=(2–5)A\mathrm{MeV}$, followed by a nearly constant breakup time at higher excitation energy. The decrease in emission time is strongly correlated with the onset of multifragmentation and thermally induced radial expansion, consistent with a transition from surface-dominated to bulk emission expected for spinodal decomposition.

We obtain properties of ${}^{12}\mathrm{C}$ in the ab initio no-core nuclear shell model. The effective Hamiltonians are derived microscopically from the realistic CD Bonn and the Argonne $\mathrm{V}{8}^{\prime }$ nucleon-nucleon $\left(\mathrm{NN}\right)$ potentials as a function of the finite harmonic oscillator basis space. Binding energies, excitation spectra, and electromagnetic properties are presented for model spaces up to $5ħ\Omega$. The favorable comparison with available data is a consequence of the underlying $\mathrm{NN}$ interaction rather than a phenomenological fit.

It is shown that the rotating mean field of triaxial nuclei can break the chiral symmetry. Two nearly degenerate $\Delta I=1\mathrm{}$ rotational bands originate from the left-handed and right-handed solutions.

Spallation residues produced in 1 GeV per nucleon ${}^{208}\mathrm{Pb}$ on proton reactions have been studied using the Fragment Separator facility at GSI. Isotopic production cross sections of elements from ${}_{61}\mathrm{Pm}$ to ${}_{82}\mathrm{Pb}$ have been measured down to 0.1 mb with a high accuracy. The recoil kinetic energies of the produced fragments were also determined. The obtained cross sections agree with most of the few existing gamma-spectroscopic data. The data are compared with different intranuclear-cascade and evaporation-fission models. Drastic deviations were found for a standard code used in technical applications.

Total photofission cross sections for ${}^{238}\mathrm{U}$, ${}^{235}\mathrm{U}$, ${}^{233}\mathrm{U}$, ${}^{237}\mathrm{Np}$, ${}^{232}\mathrm{Th}$, and ${}^{\mathrm{nat}}\mathrm{Pb}$ have been measured simultaneously, using tagged photons in the energy range $E_{\gamma }=0.17\mathrm{}–3.84\mathrm{GeV}$. This was the first experiment performed using the Photon Tagging Facility in Hall B at Jefferson Lab. Our results show that the photofission cross section for ${}^{238}\mathrm{U}$ relative to that for ${}^{237}\mathrm{Np}$ is about $80\%$ over the entire energy range, implying the presence of important processes which compete with fission. If we assume that for ${}^{237}\mathrm{Np}$ the photofission probability is equal to unity, we observe a significant shadowing effect, starting below 1.5 GeV.

We describe a strategy for attacking the canonical nuclear structure problem—bound-state properties of a system of point nucleons interacting via a two-body potential—which involves an expansion in the number of particles scattering at high momenta, but is otherwise exact. The required self-consistent solutions of the Bloch-Horowitz equation for effective interactions and operators are obtained by an efficient Green's function method based on the Lanczos algorithm. We carry out this program for the simplest nuclei, $d$ and ${}^3\mathrm{He}$, in order to explore the consequences of reformulating the shell model as a controlled effective theory.