The dipole transition densities as well as the radial pattern of partial widths for bound states embedded in the continuum, which are excited in the photonuclear reaction processes ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(γ,n) and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(γ,p), are investigated in the framework of the continuum shell model for radii up to 11 fm. The ${\mathit{d}}_{3/2}$ nucleons in the resonance states of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ are loosely bound. Their extension well beyond the nuclear surface is taken into account in a straightforward manner. The interaction of the incoming photon with the nucleons of the target nucleus takes place mainly in the surface region at about 3 fm. The surface character is caused, above all, by geometrical effects. The nucleons emitted originate mainly from the interior of the nucleus due to the strong correlations of the nucleons. By this, the shell-model approach is justified in spite of the large radial extension of the ${\mathit{d}}_{3/2}$ nucleons.

The static-path approximation is applied to the real-time response function of a nucleus at finite temperature. This approximation is shown to become accurate in the high-temperature limit for an appropriately energy-smoothed strength function. An additional local approximation to overlap integrals yields the familiar adiabatic approximation. These two approximations are compared with exact results for the Lipkin model. For a sufficiently large ratio of two-body interaction to single-particle energy, the static-path approximation accurately describes the exact strength function. For parameters characteristic of nuclear shape transitions, the static-path approximation is not reliable and the adiabatic approximation is qualitatively in error.

Assuming the ηN interaction is dominated by the ${\mathit{N}}^{\mathrm{*}}$(1535) excitation we evaluate an η-nucleus optical potential that takes into account the free decay modes of the ${\mathit{N}}^{\mathrm{*}}$ plus its many-body decay modes up to one-particle-hole excitation. The potential is able to generate bound states in light and heavy nuclei but provides large widths for these states. The results are highly sensitive to the value of Re${\mathrm{\Sigma }}_{\mathit{N}}^{\mathrm{*}}$. In general, the widths are larger than the separation between the levels, although for Re${\mathrm{\Sigma }}_{\mathit{N}}^{\mathrm{*}}$ sufficiently repulsive a few narrow states can be found. In connection with a recent experiment our results suggest a potential for the ${\mathit{N}}^{\mathrm{*}}$ more attractive than for nucleons.

Excitation functions of fragments produced in the ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$${+}^{64}$Ni reaction have been measured in the incident energy range ${\mathit{E}}_{\mathrm{lab}}$=142 to 150 MeV at ${\mathrm{\theta }}_{\mathrm{lab}}$=10°, 20°, 35.7°, 40°, 44.3°, and 50°. Angular distributions and excitation functions were analyzed in the framework of the Strutinsky transfer reaction model and the Kun dissipative reaction statistical model, respectively. The role of the dinuclear configuration of the intermediate system in determining the features of both the angular distributions and the cross-section coherence widths was evidenced.

The ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(γ,n) reaction cross section has been measured with tagged photons with energies ranging from 31.2 to 102 MeV, for neutron emission angles of 45°, 60°, 75°, 90°, and 135°. Exclusive differential cross sections for the ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(γ,n) and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(γ,p) reactions are found to be of a similar magnitude, but are not well predicted by recent random-phase-approximation and relativistic direct knock-out calculations. A quasideuteron model calculation with spin-orbit splitting of single-particle shells and an improved nucleon transparency correction is found to be consistent with the data. However, it is shown that this does not establish that the photoabsorption matrix element for the deuteron is necessarily similar to that of a correlated np-pair in nuclear matter. This result is generalized to question the predicted sensitivity to short-range correlations for photonuclear reactions calculated within the Gottfried factorization.

We have measured the cross section for neutron radiative capture by ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ at thermal neutron energy as 45.4±3.0 mb. We have compared this value, and the available fast-neutron-capture cross-section data on ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$, with direct- and valence-capture theory. The mechanism of direct capture involving simple neutron-orbital transitions within a potential well can adequately account for the magnitude of the thermal-neutron-capture cross sections and the shape of the fast-neutron-capture cross sections. We recommend that the capture cross sections from the theoretical calculation, instead of those from a recent measurement, be used for nuclear astrophysics calculations. If the fast-neutron-capture data are normalized at 25 keV to the theoretical value, the magnetic-dipole (M1) radiation width of the 255-keV p-wave resonance can be deduced. It is in agreement with the value calculated from a valence theory for M1 capture, thus lending support for this neutron-capture mechanism as an important one, at least for light nuclei. We also find some evidence from our analysis of the total cross-section data for a possible energy dependence of the potential required to describe the almost pure single-particle s-wave resonances underlying the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ cross section.

Charged-particle emission has been studied in ten heavy-ion reactions spanning composite systems of 16≤Z≤64. By means of reversed kinematics, high-quality energy spectra were obtained for proton and alpha evaporation from compound nuclei with temperatures ∼1.5–3.5 MeV and spins up to ∼70ħ. In some cases, deuteron and triton spectra were recorded as well. Statistical model calculations for spherical nuclei require systematically low emission barriers to reproduce the data. For the lighter systems, the effective spins (or moments of inertia) must be modified as well, whereas for the heavier systems this effect is of less importance. The roles of multistep particle emission and competition in the model calculations are assessed and found to be inadequate to explain the observed discrepancies. Calculations that model statically deformed nuclear emitters suggest that large deformations may be present, but they do not give a satisfactory overall picture. The very low proton energies in particular seem to indicate an extended density profile. Such an effect, together with the requirements for cluster preformation, may explain the observed low barriers for ${}_{}{}^1{}_{}{}^{}\mathrm{H}$${/}^4$He and the increasing mean energies found for the series ${}_{}{}^1{}_{}{}^{}\mathrm{H}$, ${}_{}{}^2{}_{}{}^{}\mathrm{H}$, ${}_{}{}^3{}_{}{}^{}\mathrm{H}$, respectively.

Assuming that the elastic scattering between heavy ions, at energies just above the Coulomb barrier, is dominated by the physical phenomenon of reflection at the nuclear surface, it is possible to formulate a new model of heavy ion scattering which appears to be able to account both for the energy and angular dependence of the experimental differential cross sections. The model, named the reflective model, is based on suitable modifications of the scattering function for the scattering of charged particles by an impenetrable charged sphere and is an extension to quantum mechanics of a similar classical model previously formulated. In its simpler formulation the reflective model depends on two parameters: the first parameter is the radius of the reflecting region and the second gives a measure of the probability that the reflection phenomenon occurs when the surfaces of two nuclei come in contact. The analysis of the experimental angular distributions indicates that the radius parameter follows the usual law of nuclear radii and that the reflective parameter depends weakly on the energy and on the particular pair of nuclei in collision. The two-parameter version of the model violates the unitarity bound, but the introduction of two additional parameters, which physically control the importance of the diffractive contribution, allows one to avoid this difficulty and to obtain a better agreement with the experimental results. In contrast with the optical model case, the parameters of the reflective model are rather well determined by the analyses of the experimental results, and this seems to provide an indication that they describe some real properties of the interaction between nuclei.

Particle emission after electroexcitation of a nucleus is studied in the quasielastic region of the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(e,e’p${)}^3$H reaction. The calculations are performed using a meson-exchange potential. The displacement observed in the experimental spectral functions appears to be due to the mean-field scattering mainly. The rescattering processes lead to the splitting between the longitudinal and transverse spectral functions in agreement with the trend of the Saclay data. The related damping of the longitudinal spectral function originates from the coupling between (e,e’p) and (e,e’n) channels.

We calculate the effects of Pauli-blocking in the quasideuteron model of hard photon absorption. Our approach is based upon phase-space considerations and uses Fermi-gas state densities that conserve linear momentum. The Pauli-blocking function that we obtain differs from Levinger’s phenomenological exponential factor and yields nuclear photoabsorption cross sections that are in good agreement with experimental data for photon energies up to the pion threshold. The temperature dependence of the nuclear photoabsorption cross section in the quasideuteron regime is also investigated. The model that we use to describe nuclear photoabsorption is particularly suited for application to preequilibrium models of hard photon emission.

We study the transition from fusion-fission phenomena at about 20 MeV/nucleon multifragmentation at 100–200 MeV/nucleon in the reaction ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{80}$Br employing the quantum molecular dynamics model. The time evolution of the density and mass distribution, the charged-particle multiplicity, and spectra as well as angular distributions of light particles are investigated. The results exhibit the transition of the disassembly mechanism, but no sharp change is found. The results are in good agreement with recently measured 4π data.

Exclusive-type experimental data on the emission of projectile helium fragments from the interactions of ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ nuclei in the emulsion at 1.88A GeV (the dependence of angular distribution and mean multiplicity on the number of shower particles) are presented and discussed. The angular distribution is interpreted by simple superposition of well-known processes without assuming the existence of fireballs. In this paper, we present an interpretation on production of He fragments: A ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ fragment is produced in a pickup process of a p-n pair by scattered p-n pair, and a ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ fragment is produced by recombining a p-n pair and a proton that are scattered into small phase volume.

Multiplicity and angular distributions of shower, grey, and black particles produced in the interactions of ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ at 200A GeV, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ at 200 and 60A GeV, and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ at ∼140A GeV in emulsion are compared with the predictions of a Monte Carlo code which takes into account the internuclear cascading. The correlations between the various parameters belonging to the same or to the different kinds of particles are discussed. The data on shower and grey particles from all the beams are well described by the code. However, the black prong data show a significant departure from this model.

Corrected scaled factorial moments are calculated for the multiplicity distributions in one- (pseudorapidity and azimuthal angle) and two-dimensional (the product of pseudorapidity and azimuthal angle) phase spaces. An intermittency power-law growth is observed in the central collisions of ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ at 200A GeV, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ at 60A GeV, and He at ≊140A GeV, while for ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ at 14.5A GeV it is observed for inclusive interactions in nuclear emulsion. The effect is much pronounced for higher dimensions. The data for the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ beam at 200A GeV satisfy the condition for two phases occurring together.

An instability, known as Kelvin-Helmholtz instability (shear instability), well known in fluid theory and plasma physics is studied in heavy-ion collisions to study the process of entropy generation. The source of this instability is the transverse gradient of longitudinal velocity which is quite likely to arise when the collisions are somewhat peripheral (noncentral). Relativistic equations describing this instability are derived here. A set of coupled partial differential equations in three dependent and three independent variables are obtained. It is difficult to solve them analytically. In order to get a qualitative idea, we have solved the nonrelativistic version of the above equations with some approximations. We find that in the boost-invariant unperturbed state the growth rate of this instability competes with damping due to the boost-invariant expansion of the unperturbed system. We also analyze low-energy nuclear collisions, where there is no boost invariance, using a simple equilibrium flow with shear.

Nuclear spectral functions computed with realistic nuclear forces are used to compute mean separation energies and to estimate the binding corrections to lepton-nucleus deep inelastic scattering. The separation energies are large and significant binding effects are obtained.

We extend the standard relativistic mean-field treatment of dense nuclear matter to make it consistent with the anomalous trace of the energy-momentum tensor of QCD. This is accomplished by introducing a field for scalar gluonium and coupling it to nucleons and to scalar and vector mesons. Only the gluonium potential, proportional to the bag constant, breaks scale invariance. A physically sensible, first-order, phase transition to quark matter occurs at high baryon density.

The color-dielectric model has been used to study the behavior of nucleons in the nuclear medium. Assuming that the nuclear medium generates a background color-dielectric field and a scalar density of quarks, the equations of motion of the quark and the color-dielectric field are solved in the presence of the background fields. The properties of the nucleon in the nuclear medium are then calculated from these solutions. The calculations show that the nucleon swells in the nuclear medium and the quark eigenenergy decreases. It is found that when the nuclear density is more than 0.08 ${\mathrm{fm}}^{\mathrm{-}3}$, bound quark states do not exist, thus implying that the nucleon dissolves into quark matter.

We report a new measurement of the rate of spontaneous emission of monoenergetic Ne nuclear clusters from ${}_{}{}^{232}{}_{}{}^{}\mathrm{U}$, which results in a revision of rates previously reported for Ne radioactivity of ${}_{}{}^{232}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$, and ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$. The Ne emission rate goes up a factor of 4.6 for ${}_{}{}^{232}{}_{}{}^{}\mathrm{U}$, goes down a factor of 4.8 for ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$, and may have been marginally detected (1.9σ) for ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$.

Different deformations for the two bands built above the (π${\mathit{h}}_{11/2}$${)}^2$ ${10}^{+}$ and the (ν${\mathit{h}}_{11/2}$${)}^{\mathrm{-}2}$ ${10}^{+}$ states in ${}_{}{}^{140}{}_{}{}^{}\mathrm{Sm}$ have been determined from lifetime measurements using the reaction ${}_{}{}^{106}{}_{}{}^{}\mathrm{Pd}$${(}^{37}$Cl,p2n${)}^{140}$Sm at 143 MeV. The β values derived for the N=78 and N=80 core nuclei, coexisting in ${}_{}{}^{140}{}_{}{}^{}\mathrm{Sm}$, complete the systematics of nuclear deformation from N=72 to 80.