The statistics of on-resonance measurements of the deformation effect cross section ${\sigma }_{02}$ in unpolarized neutron transmission through an aligned ${}^{165}\mathrm{Ho}$ target is discussed. Under the standard Porter-Thomas assumption about reduced partial width amplitudes, the sign of ${\sigma }_{02}$ is random at $s$-wave resonances with $d$-wave admixtures. Motivated by the observation of sign correlations in epithermal parity-violation studies, conditions under which a doorway state will give rise to ${\sigma }_{02}$’s of nonrandom sign are identified. Oblate shape isomers lying at excitation energies in the isolated resonance regime could meet these conditions.

Quantum molecular dynamics is applied to study the ground state properties of nuclear matter at subsaturation densities. Clustering effects are observed to soften the equation of state at these densities. The structure of nuclear matter at subsaturation density shows some exotic shapes with variation of the density.

Isoscalar and isovector density vibrations in a slab with sharp edges are studied in a nonlinear hydrodynamic approach. The frequency shift of the $N$-phonon excitation due to nonlinear terms is obtained. The frequencies of one- and two-phonon vibrations calculated in the nonlinear hydrodynamic theory are reduced by $\approx$5–30 % for isoscalar and by $\approx$1–8 % for isovector resonances as compared to the linear approximation. The frequency shift is a function of both the slab thickness and the parameters of the nucleon-nucleon interaction. Experimental data on the frequency shift of the $N$-phonon states due to the nonlinear terms in the case $N>~2$ may be used for selecting of the set of nucleon-nucleon interaction parameters.

The interacting boson model with broken pairs has been extended to include mixed proton-neutron configurations in the fermion model space. The extended version of the model has been used to describe high-spin bands in the transitional nucleus ${}^{136}$Nd. Model calculations reproduce ten bands of positive and negative parity states, including the two dipole high-spin structures based on the $(\pi h_{11/2}{)}^2$ $(\nu h_{11/2}{)}^2$ configuration.

Nuclear structure of ${}^{97}\mathrm{Y}$ is described in the interacting boson fermion plus broken pair model, including quasiproton and quasiproton-two-quasineutron configurations in the basis states. In particular, the yrast bands and the decay of the ${27/2}^{-}$ high-spin isomer are accounted for in this approach.

Neutron-proton pairing correlations are studied within the context of two solvable models, one based on the algebra SO(5) and the other on the algebra SO(8). In both of these models, particles interact in $L=0\mathrm{}$ pairs only. Boson-mapping techniques are applied to these models and shown to provide a convenient methodological tool both for solving such problems and for gaining useful insight into general features of pairing. We first focus on the SO(5) model, which involves generalized $T=1\mathrm{}$ pairing. Neither boson mean-field methods nor fermion-pair approximations are able to describe in detail neutron-proton pairing in this model. The analysis suggests, however, that the boson Hamiltonian obtained from a mapping of the fermion Hamiltonian contains a pairing force between bosons, pointing to the importance of boson-boson (or equivalently four-fermion) correlations with isospin $T=0\mathrm{}$ and spin $S=0\mathrm{}$. These correlations are investigated by carrying out a second boson mapping. Closed forms for the fermion wave functions are given in terms of the fermion-pair operators. Similar techniques are applied—albeit in less detail—to the SO(8) model, involving a competition between $T=1\mathrm{}$ and $T=0\mathrm{}$ pairing. Conclusions similar to those of the SO(5) analysis are reached regarding the importance of four-particle correlations in systems involving neutron-proton pairing.

We determine in an extended Brueckner-Hartree-Fock formalism self-consistent single-particle potentials of nucleons, lambda, and sigma hyperons for a system consisting of symmetric nuclear matter and lambda hyperons of uniform densities ${\rho }_N$ and ${\rho }_{\Lambda },$ respectively. The binding energy per baryon of this system is discussed and its maximum strangeness content preserving binding is evaluated. The results are used to introduce a hyperonic symmetry energy term in a generalized mass formula for multistrange hypernuclei.

The lowest order constrained variational method is used to calculate the properties of asymmetrical nuclear matter with the new charge-independent breaking, Argonne $V_{18}$ ${(AV}_{18}),$ as well as Argonne $V_{14}$ ${(AV}_{14})$ potentials, for a wide range of density and proton to neutron ratio. The new ${\mathrm{AV}}_{18}$ potential, unlike ${\mathrm{AV}}_{14}$ and Δ-Reid interactions, overbinds nuclear matter at a saturation density of about $0.31{\mathrm{fm}}^{\mathrm{-}3}$ which agrees well with the variational method based on hypernetted chain summation techniques. It is shown that it is not a good approximation to use the result of nuclear and neutron matter to get the equation of state of asymmetrical nuclear matter with an empirical parabolic approximation. Finally, various properties of asymmetrical nuclear matter such as incompressibility, symmetry energy, etc., are given and a comparison is made with the other many-body techniques.

Fusion and quasielastic excitation functions were measured for ${}^{40}\mathrm{Ca}{+}^{46,48,50}\mathrm{Ti}$ at energies close to the Coulomb barrier. The interest in these systems lies in the opposite target-mass dependence of surface vibration couplings and neutron-transfer couplings. The cross sections were measured at small energy steps and with high precision, so that the structure in the excitation functions (barrier distributions) could be revealed through a differentiation process. The subbarrier fusion data show a larger enhancement with increasing target mass number, which clearly indicates the importance of transfer couplings. The agreement between the fusion and quasielastic barrier distributions is quite good. Simplified coupled-channel calculations were performed to reproduce the fusion data. A very good agreement is obtained by coupling to low lying excited states ${(2\mathrm{}}^{+}$ and $3^{-})$ and to the most positive neutron-transfer $Q$ value (two-neutron projectile pickup channel).

Compound-nucleus fusion and binary-reaction mechanisms have been investigated for the ${}^{35}$Cl+${}^{24}$Mg system at an incident beam energy of E${}_{\mathrm{lab}}$= 282 MeV. Charge distributions, inclusive energy spectra, and angular distributions have been obtained for the evaporation residues and the binary fragments. Angle-integrated cross sections have been determined for evaporation residues from both the complete and incomplete fusion mechanisms. Energy spectra for binary fragment channels near the entrance-channel mass partition are characterized by an inelastic contribution that is in addition to a fully energy damped component. The fully damped component which is observed in all the binary mass channels can be associated with decay times that are comparable to, or longer than, the rotation period. The observed mass-dependent cross sections for the fully damped component are well reproduced by the fission transition-state model, suggesting a fusion followed by fission origin. The present data cannot, however, rule out the possibility that a long-lived orbiting mechanism accounts for part or all of this yield.

Excitation functions and recoil range distributions for radioactive products formed in the reactions of ${}^{12}\mathrm{C}$ on ${}^{89}\mathrm{Y}$ have been measured using catcher foil technique followed by gamma-ray spectrometry. The alpha emission products show higher cross sections than that predicted for complete fusion. Recoil range distributions of evaporation residues indicate incomplete momentum transfer events. Detailed Monte Carlo simulation of the shapes of recoil range distributions for these processes have been carried out using PACE2 code to extract the contributions of incomplete fusion in the individual channels. From the relative yields of incomplete fusion products the excitation energy and angular momentum of the incompletely fused composite nucleus have been deduced. The values agree well with the break-up fusion model of the incomplete fusion.

Inclusive spectra of different ejectiles and coincidence spectra of $\alpha$ particles with various nuclides emerging from the collisions of ${}^{12}\mathrm{C}$ ions of energy 344.5 MeV with a ${}^{12}\mathrm{C}$ target have been measured. A large fraction of the observed cross section is contained in the continuous part of the inclusive spectra. In the coincidence data the excitation of states of intermediate nuclei is observed which indicates the sequential mechanism of the reaction. Calculations performed with a simple phenomenological model of such processes reproduce well the shape and magnitude of both inclusive and coincidence spectra. The contribution of various reaction mechanisms to the total reaction cross section is estimated.

A high-statistics exclusive study of the multifragmentation of $1A$ GeV gold on carbon has been performed. Particles with $Z<~2$ show evidence of emission in a first prompt stage as well as in a second equilibrium stage whereas fragments with $Z>~3$ appear to be emitted essentially only in the second stage. Two methods for the separation of the $Z<~2$ particles into the two stages are given and they are in agreement. The yields for each stage are determined as a function of the event charged particle multiplicity $m$. The mass, nuclear charge, excitation energy per nucleon, and temperature of the remnant left after the first stage and their fluctuations have been determined as a function of $m$. The expansion of the remnant to fragment freeze-out is examined. The freeze-out temperature is determined from double isotope ratios as a function of $m$ and isentropic trajectories are obtained in the temperature-density plane. The caloric curve shows a monotonic increase with excitation energy. Some of the energy is in the form of radial flow. Overall, the results are consistent with a previous statistical analysis of the data which suggests that, over a certain range of excitation energies, multifragmentation involves a continuous phase transition.

An analysis of low-energy charged pion-nucleon data from recent ${\pi }^{\pm }p$ experiments is presented. From the scattering lengths and the Goldberger-Miyazawa-Oehme (GMO) sum rule we find a value of the pion-nucleon coupling constant of $f^2=0.0756\mathrm{}\pm 0.0007$. We also find, contrary to most previous analyses, that the scattering volumes for the $P_{31}$ and $P_{13}$ partial waves are equal, within errors, corresponding to a symmetry found in the Hamiltonian of many theories. For the potential models used, the amplitudes are extrapolated into the subthreshold region to estimate the value of the $\Sigma$ term. Off-shell amplitudes are also provided.

We describe giant resonances as the collective coordinates of a harmonic oscillator with dissipative coupling. Using a quantum master equation, the energy and width of the first two levels are obtained as functions of temperature and of the dissipative coupling strength. On this basis, we evaluate the ratio of the two spectral linewidths. The result agrees with available experimental data. We evaluate transition matrix elements among particle excitations belonging to the environment and find a weak dependence on temperature.

We calculate the elastic nucleon-nucleon cross section in symmetric nuclear matter at finite temperature by determining the nonrelativistic in-medium scattering matrix with a realistic nucleon-nucleon potential. We define average in-medium cross sections depending on density and temperature and provide simple parametrizations for the use in numerical simulations of heavy-ion collisions. The effect of hole-hole propagation in the nuclear medium is found to be small.

We examine ${}^{12}\mathrm{C}$ fragmentation in ${p+}^{12}\mathrm{C},$ $\alpha {+}^{12}\mathrm{C},$ and ${}^{14}{\mathrm{N}+}^{12}\mathrm{C}$ reactions using antisymmetrized molecular dynamics. We compare ${}^{12}\mathrm{C}$ fragmentation among the above three kinds of reactions and find that the alpha-clustering effect in ${}^{12}\mathrm{C}$ fragmentation depends on the projectile and also on the incident energy. In proton induced reactions ${}^4\mathrm{He}$ fragments are scarcely produced at the early stage of the reaction in a wide range of incident energy. On the other hand, in $\alpha$ and ${}^{14}\mathrm{N}$ induced reactions many ${}^4\mathrm{He}$ fragments are produced during the dynamical stage at a lower incident energy but fewer ${}^4\mathrm{He}$ fragments are produced with increasing incident energy. We indicate that this abundance of ${}^4\mathrm{He}$ fragments at a lower incident energy in $\alpha$ and ${}^{14}\mathrm{N}$ induced reactions is due to the excitation of ${}^{12}\mathrm{C}$ to states with an excitation energy of 7–15 MeV which have the alpha-cluster structure. We see that the upper limit of the incident energy which gives rise to the dynamical production of ${}^4\mathrm{He}$ fragments is lower in the $\alpha$ induced reaction than in the ${}^{14}\mathrm{N}$ induced reaction. We show that the excitation to the clustering states is caused by the mean field from the projectile and that nucleon-nucleon collisions work to destroy this excitation. We will see that the disappearance of the excitation to the clustering states at high incident energies is partly due to the weakened effect of the mean field of the projectile and partly due to the strengthened effect of nucleon-nucleon collision processes.

Similarities between models of fragmenting nuclei and disordered systems in condensed matter suggest corresponding methods. Several theoretical models of fragmentation investigated in this fashion show marked differences, indicating possible new methods for distinguishing models using yield data. Applying nuclear methods to disordered systems also yields interesting results.

We establish, within the framework of the statistical multifragmentation model, the connection between the caloric curve and the analysis of conditional moments. In particular, we show that the conditional moments of fragment charge distributions peak at the region where the curve temperature versus excitation energy shows a plateau assumed to be a signature of a phase transition. Furthermore, we show that the slopes of the moments at the peak are not influenced by secondary decay after the first breakup of the nucleus.

Experiment NA44 has measured proton and antiproton distributions at midrapidity in sulphur and proton collisions with nuclear targets at 200 and $450\mathrm{GeV}/c$ per nucleon respectively. The inverse slopes of transverse mass distributions increase with system size for both protons and antiprotons but are slightly lower for antiprotons. This could happen if antiprotons are annihilated in the nuclear medium. The antiproton yield increases with system size and centrality and is largest at midrapidity. The proton yield also increases with system size and centrality, but decreases from backward rapidity to midrapidity. The stopping of protons at these energies lies between the full stopping and nuclear transparency scenarios. The data are in reasonable agreement with RQMD predictions except for the antiproton yields from sulphur-nucleus collisions.