Nucleon-exchange effects are examined in the case where one of the nuclei involved exhibits properties of considerable clustering. The results, obtained by analyzing the exponential parts of the exchange-normalization kernel function in a three-cluster resonating-group formulation, indicate that, as in the case of no target clustering, the one-exchange and core-exchange terms are still the terms which make the dominant contribution. The characteristics of the one-exchange term are found to be rather insensitive to the clustering nature of the target nucleus. The core-exchange term, on the other hand, may acquire a rather long range compared to the direct potential when the degree of clustering is appreciable.

The effect of the polarization potential in proton-deuteron scattering is studied numerically at low incident proton energies in a two-body model. Inclusion of this potential in this problem leads to a very small change in the ‘‘nuclear’’ phase shifts and hence its effect can be neglected for all practical purposes at low energies in contradiction to some recent conjectures.

A phenomenological algebraic approach to nuclear isovector excitations is discussed within the framework of the interacting boson model. Analytic formulae are obtained for isospin splittings and excitation strengths of the giant dipole resonance in deformed nuclei. An application of the formalism to ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$ is presented, where both schematic and realistic calculations have been performed.

The time-dependent Schrödinger equation is solved for NN scattering in the case of a one-boson-exchange potential. The method works in momentum space with a complex contour to damp the oscillations which build up for large times. Since we abandon a partial wave decomposition, the treatment is well suited for high energies. The behavior of various observables is displayed as a function of time. As a side effect, we gain some quantitative insight into how the stationary scattering process is approached.

The cross section for the ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$(γ,2n) reaction has been studied from 20 to 28 MeV. The cross section remains near zero for 3 MeV above threshold, then rises sharply at about 24 MeV, to a maximum value of 1.7 mb. The shape is explained in terms of the density of $T_{>}$ states in ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ at the relevant excitation energy.

A radioactive ${}_{}{}^{226}{}_{}{}^{}\mathrm{Ra}$ ($t_{1/2}$=1600 yr) target was used to study the ${}_{}{}^{226}{}_{}{}^{}\mathrm{Ra}$(α,t${)}^{227}$Ac and ${}_{}{}^{226}{}_{}{}^{}\mathrm{Ra}$${(}^3$He,d${)}^{227}$Ac reactions at an incident energy of 30 MeV for both the α and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ particles. These measurements have confirmed most levels observed in earlier decay-scheme studies, and give evidence for 11 additional levels. Several of the new levels were used in the tentative assignment of two $K^{\pi }$${=(5/2\mathrm{}}^{\pm }$ bands. The experimental data are compared with results from the Nilsson model and a nonadiabatic, rigid, reflection-asymmetric rotor (octupole) model. Although the order and spacing of levels in this mass region can be explained better by models that include an octupole deformation, the spectroscopic strengths in ${}_{}{}^{227}{}_{}{}^{}\mathrm{Ac}$ are in better agreement with those calculated for the reflection-symmetric potential.

The cross sections for the elastic and inelastic scattering of alpha particles from ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ have been measured at 50.5 MeV for angles up to 92° in steps of 1°. An optical model analysis of the elastic scattering data has been made, starting with the parameters predicted from systematics and consistent with those determined at higher energies. The large angular range combined with the relatively small errors in the measurement restrict the real potential to just three discrete families. A nearside-farside decomposition of the data clearly reveals the Fraunhofer diffraction pattern superimposed on the large background of Fresnel diffraction. The inelastic scattering data have been analyzed in terms of the collective model using the distorted wave Born approximation, for which the distorted waves were generated by the optical model analysis of the elastic scattering data. The values of the deformation lengths (βR) obtained are compared with those reported in the literature.

A microscopic description of the recent data on the inelastic electron scattering form factors for the $0^{+}$→$2^{+}$ as well as $0^{+}$→$4^{+}$ transitions in some doubly even Ti, Cr, Fe, Ni, and Zn isotopes is attempted in terms of the projected Hartree-Fock-Bogoliubov wave functions resulting from realistic effective interactions operating in the 2p-1f shell. It turns out that the available form factor data out to about 2.5 ${\mathrm{fm}}^{\mathrm{-}1}$ can be reproduced in most of the cases in a fairly satisfactory manner in terms of reasonable values of effective charges. It is seen that the empirical transition charge densities in Ni and Zn isotopes extracted from the form factor data via the Fourier-Bessel analysis play a decisive role vis-à-vis the choice of a model of core-polarization contributions.

The shape evolution of ${}_{}{}^{160}{}_{}{}^{}\mathrm{Er}$ at high excitation energies was studied by measuring the giant dipole resonance following the heavy ion fusion reaction ${}_{}{}^{19}{}_{}{}^{}$F${+}^{141}$Pr at excitation energies of 59.2, 61.2, 74.3, and 90.3 MeV. The data analysis yields prolate, oblate, and triaxial solutions and without theoretical systematics none of them can be ruled out. Detailed comparison with theoretical predictions favor the prolate solution with a deformation decreasing from β=0.28 at 59.2 MeV to 0.24 at 90.3 MeV. No phase transition from a prolate to an oblate deformation was found in the temperature range (T∼1.1–1.5 MeV) covered by this experiment.

Pion yields are computed from the pion and delta populations found in a field theoretic description of hot dense matter. Two different prescriptions for the initial conditions are considered and the results of a quasihydrodynamic expansion are also studied. It is found that the yield and the slope of pion yield as a function of energy, which are functions of the chemical freeze-out density, might possibly provide a means of determining that density. However, the dependence on the compression modulus of the corresponding cold matter is found to be very low in this model.

Streamer chamber data for collisions of Ar + KCl and Ar + ${\mathrm{BaI}}_2$ at 1.2 GeV/nucleon are compared with microscopic model predictions based on the Vlasov-Uehling-Uhlenbeck equation, for various density-dependent nuclear equations of state. Multiplicity distributions and inclusive rapidity and transverse momentum spectra are in good agreement. Rapidity spectra show evidence of being useful in determining whether the model uses the correct cross sections for binary collisions in the nuclear medium, and whether momentum-dependent interactions are correctly incorporated. Sideward flow results do not favor the same nuclear stiffness parameter at all multiplicities.

We use a phenomenological equation of state to describe the phase transition between a hot and dense hadron resonance gas and a quark-gluon plasma. Our analysis covers the entire temperature-baryon density plane. The consequences for the phase diagram of strangeness conservation during nuclear collisions are analyzed. The flavor composition of the quark plasma and an equilibrated hadron resonance gas is studied and compared along the phase transition surface. We emphasize the need to compare systems with equal total baryon number and entropy contents in order to be consistent with the dynamics of the hadronization process and to obtain results relevant to nuclear collisions. From our results we conclude that the flavor composition of the hadronization debris from a quark-gluon plasma formed in a nuclear collision is probably hard to distinguish from that of a chemically equilibrated hadron gas, although in both cases the production level of strange and nonstrange antibaryons will be much higher than observed in proton-proton collisions.

Using a schematic hydrodynamic description of relativistic heavy-ion collisions in the regime of complete nuclear stopping, we study the freeze-out and strange particle energy spectra from a hadronized quark-gluon plasma. We argue that characteristic changes in the slopes of the ${\mathrm{K}}^{+}$ and ${\mathrm{K}}^{\mathrm{-}}$ meson energy spectra are a signature for the quark-gluon plasma phase transition.

Equilibrium solutions of bubbles and drops in superheated and supercooled nuclear matter are studied. The existence of such objects is shown to depend on several factors including Coulomb energy, surface tension, hydrodynamic stability, and fissility. We suggest conditions under which such objects might be formed in the laboratory.

An investigation of the collective structures in the doubly-odd nucleus ${}_{}{}^{132}{}_{}{}^{}\mathrm{Pr}$ has been undertaken with the ${}_{}{}^{117}{}_{}{}^{}\mathrm{Sn}$${(}^{19}$F,4n${)}^{132}$Pr reaction. Two distinct rotational structures showing both signature components have been established. One band, with no signature splitting, is built on a near-prolate π$h_{11/2}$⊗ν$g_{7/2}$ structure. The second band, with a small signature splitting, involves the π$h_{11/2}$⊗ν$h_{11/2}$ configuration with a triaxial shape. A comparison with recent results for the ${}_{}{}^{130}{}_{}{}^{}\mathrm{La}$ isotone has been made. A third band structure of large signature splitting (doubly decoupled) was observed showing only one signature component. This band structure is believed to involve the β-driving ν$i_{13/2}$${\left[660\right](1/2\mathrm{}}^{+}$ orbital.

We discuss the evidence of dynamical mean field effects in medium energy peripheral fragmentation through the excitation of collective motions, mostly of isoscalar giant quadrupole resonance type, in the colliding ions before fragmentation. From an analysis of the dissipative tail in the fragment energy spectra we deduce the mean number of excited phonons at the moment of fragmentation. Since giant resonances have a very peculiar structure in momentum space we can establish a definite correlation between the dissipative part of the energy spectra and the behavior of parallel and orthogonal momentum widths of emitted fragments. Everything can be consistently evaluated without free parameters, and we finally get a thorough understanding of several unexplained features of projectile fragmentation in medium energy heavy-ion collisions. Detailed analysis of the reactions ${}_{}{}^{40}{}_{}{}^{}$${,}^{\mathrm{nat}}$Ti at 44 MeV/nucleon is shown.

We present measurements of the spallation cross sections of carbon, oxygen, and iron in helium and hydrogen, at beam energies from 540 to 1600 MeV/nucleon, performed by exposing liquid helium, ${\mathrm{CH}}_2$, and C targets. Charge changing cross sections are reported for fragments down to Ne for Fe+α and Fe+p reactions, and down to B for O+α, O+p, C+α, and C+p reactions. α- to p-induced cross section ratios (${\sigma }_{\alpha }$/${\sigma }_{\mathrm{p}}$) are determined at the same energy per nucleon. From these measurements an empirical formula for the ${\sigma }_{\alpha }$/${\sigma }_{\mathrm{p}}$ ratios is derived, and is found in good agreement with available isotopic cross sections data from radioactivity and radiochemical techniques. These results are applied to the propagation of heavy charged cosmic rays in an interstellar medium with an helium to hydrogen abundance ratio of 0.10. It is shown that the Sc–Mn/Fe ratio prediction is decreased relative to the B/C ratio when compared to propagation calculations in a pure hydrogen interstellar medium.

The theory of sub-Coulomb transfer of one neutron is extended to include the deformation and orientation effects of the colliding heavy ions. Both the deformation and orientation degrees of freedom are treated by classical equations of motions. In these calculations the center-to-center and surface-to-surface distances at closest approach are determined, on which the transfer cross section is assumed to depend. Also, an analytical expression for the center-to-center distance is derived. Application is made to the recent data of the one-neutron transfer in ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ collisions at 5.05–6.07 MeV/nucleon. Deformation effects are shown to be important for central collisions.

Angular distributions of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^{12}$C, ${\alpha }_0$${)}^{20}$Ne reaction have been measured from $E_{\mathrm{c}.\mathrm{m}.\mathrm{}=5.2\mathrm{}}$ to 5.8 MeV in 20 keV steps. At $E_{\mathrm{c}.\mathrm{m}.\mathrm{}=5.435\mathrm{}}$ MeV a $6^{+}$ state is reported.

A new method is presented for the stochastic solution of tunneling problems in quantum many-body systems. The primary practical problem of trapping in local minima of the action is overcome by extending the standard implementation of the Metropolis algorithm to include collective updates motivated by semiclassical instanton solutions. We demonstrate the accuracy of our method in the case of tunneling in one degree of freedom and apply it to a model many-fermion system in one spatial dimension which undergoes spontaneous symmetric fission.