The incompressibility of asymmetric nuclear matter $K_{\infty }$ is studied analytically within the framework of the relativistic mean field theory and the nonrelativistic Skyrme Hartree-Fock model. We investigate also the relation between $K_{\infty }$ of asymmetric nuclear matter and the surface diffuseness by using the extended Thomas Fermi approximation. The self-consistent relativistic and nonrelativistic mean field calculations are performed for Sn isotopes, taking into account the pairing correlation, in order to extract the asymmetry parameter $(N$ $-Z)/A$ dependences of the surface diffuseness a and the central density $\rho \mathrm{}(r=0\mathrm{}).$ Clear correlations are found between the incompressibility $K_{\infty }$ of asymmetric nuclear matter and the extracted surface diffuseness $a,$ and also between $K_{\infty }$ and the extracted central density $\rho \mathrm{}(r=0\mathrm{}).$

The scattering of dressed nucleons in nuclear matter is studied. By casting the conventional asymptotic analysis of scattering in free space in the language of the two-body propagator, it becomes possible to develop modifications of this analysis due to the dressing of the scattering nucleons in the medium. While the scattering energy singles out a unique (on-shell) momentum characterizing the relative wave function of free or mean-field nucleons, this uniqueness is no longer maintained for dressed nucleons. The resulting distribution of momenta in the relative wave function leads to a localization in coordinate space of the influence of the scattering process which can be expressed as a healing of the wave function to the noninteracting one. An analytic approximation to the noninteracting propagator of the dressed nucleons is utilized to illustrate these points. The localization of the scattered wave implies that the particles no longer “remember” their scattering event beyond some finite distance. This feature suggests that the strict notion of a cross section in the medium is a tenuous concept. Approximate expressions are developed to characterize the strength of the interaction in the medium in terms of phase shifts and cross sections to facilitate comparisons with results of calculations involving mean-field nucleons.

In order to understand the origin of one-body dissipation in nuclei, we analyze the behavior of a gas of classical particles moving in a two-dimensional cavity with nuclear dimensions. This “nuclear” billiard has multipole-deformed walls which undergo periodic shape oscillations. We demonstrate that a single-particle Hamiltonian containing coupling terms between the particle motion and the collective coordinate induces a chaotic dynamics for any multipolarity, independently of the geometry of the billiard. If the coupling terms are switched off, the “wall formula” predictions are recovered. We discuss the dissipative behavior of the wall motion and its relation to the order-to-chaos transition in the dynamics of the microscopic degrees of freedom.

The decay properties of proton-rich nuclei with $Z=13\mathrm{}$–20 are investigated using measured binding energies of the analog neutron-rich nuclei and Coulomb energy shifts deduced from a parametrization of measured Coulomb displacement energies. Calculated binding energies and particle separation energies are compared to measurements and previous predictions where these are available. The positions of the one-proton and diproton drip lines are determined. Nuclides predicted to be proton stable but unstable to two-proton emission include ${}^{22}\mathrm{Si},$ ${}^{31}\mathrm{Ar},$ and ${}^{34}\mathrm{Ca}.$

The ${}^{17}\mathrm{O}{(n}_{\mathrm{th}},\alpha {)}^{14}\mathrm{C}$ reaction cross section was determined at the high flux reactor of the ILL in Grenoble relative to the known ${}^{14}\mathrm{N}{(n}_{\mathrm{th}}{,p)}^{14}\mathrm{C}$ cross section. For the flux calibration measurements, ${}^{14}{\mathrm{N}}_2$ from the air was used. The ${}^{17}\mathrm{O}(n,\alpha )$ measurements were performed with several highly enriched oxygen gas samples. This resulted in a precise value of $(244\mathrm{}\pm 7)$ mb for the ${}^{17}\mathrm{O}{(n}_{\mathrm{th}},\alpha {)}^{14}\mathrm{C}$ cross section.

The differential cross section of Delbrück scattering is measured on a bismuth germanate $\left({\mathrm{Bi}}_4{\mathrm{Ge}}_3{\mathrm{O}}_{12}\right)$ target at photon energies 140–450 MeV and scattering angles 2.6–16.6 mrad. A good agreement with the theoretical results, obtained exactly in a Coulomb field, is found.

Isomeric ratios in $(n,\gamma )$ and $(\gamma ,n)$ reactions in Eu isotopes were measured. Thermal neutrons and bremsstrahlung photons in the giant dipole resonance energy range of 13–22 MeV were used to excite the isomeric states. The isomeric levels $0^{-}$ and $8^{-}$ were excited in the isotopes ${}^{150}\mathrm{Eu},{}^{152}\mathrm{Eu},$ and ${}^{154}\mathrm{Eu}.$ The cross section for the reaction $(\gamma ,n)$ leading to the high-spin isomeric state $8^{-}$ on ${}^{152}{\mathrm{Eu}}^{m2\mathrm{}}$ isotope was measured in the giant-dipole-resonance region by the activation method. Experimental values of the isomeric cross section ratios were compared with the theoretical values. The influence of the nuclei quadropole deformation on the isomeric ratio was described.

We discuss the stability of fragments formed in central heavy ion collisions at intermediate energies using a quantum molecular dynamics model as an event generator. To address the question of stability of fragments, we employ three different methods of clusterization. (i) The standard minimum spanning tree (MST) method which is based on simple spatial correlations. (ii) A modified version of MST where we first identify the prefragments using MST and then check the binding energy of each fragment explicitly. If any fragment fails to meet the binding energy check, all nucleons of that prefragment are treated as free nucleons. (iii) Our newly advanced algorithm based on energy minimization criteria. This algorithm finds the most bound fragment structure using the simulated annealing technique. Our analysis shows that the fragments created with the MST method are not stable even at $200\mathrm{fm}/c$ and an additional binding energy check helps (to a great extent) to discard the unbound fragments and, as a result, the modified MST (with binding energy check) identifies the fragments quite early.

In this paper we study the energy spectra and related parallel momentum distributions of the neutrons from the breakup of ${}^{11}\mathrm{Be}.$ Earlier papers on transfer to the continuum reactions have shown that the breakup amplitude reduces to a simple eikonal approximation in the limit of weakly bound projectiles. The aim is to establish a reliable method to obtain information on the structure of the halo from the experimental results which depend on the reaction mechanism. Theoretical results for the widths of the parallel momentum distributions and for the total breakup cross section are compared to recent experimental data.

We discuss the effects of coupling of the relative motion to nuclear collective excitations which have a finite lifetime on heavy-ion fusion reactions at energies near and below the Coulomb barrier. Both spreading and escape widths are explicitly taken into account in the exit doorway model. The coupled-channels equations are numerically solved to show that the finite resonance width always hinders fusion cross sections at sub-barrier energies irrespective of the relative importance between the spreading and the escape widths. We also show that the structure of fusion barrier distribution is smeared due to the spreading of the strength of the doorway state.

A recently constructed strangeness-including statistical bootstrap model (SSBM), which defines the limits of the hadronic phase and provides for a phase beyond, is further extended so as to include a factor ${\gamma }_s$ that describes strangeness suppression. The model is then used to analyze the multiplicity data from collision experiments in which the colliding entities form isospin symmetric systems, the primary focus being on $S+S$ interactions (NA35 Collaboration). An optimal set of thermodynamical variables is extracted through a fit to both the inclusive $4\pi$ and midrapidity data. The assumption that the measured particles originate from a thermally and partial-chemically equilibrated source described by the SSBM is satisfactorily established. The proximity of the thermodynamical variables extracted from the $S+S$ data to the limits of the hadronic phase is systematically investigated. Finally, experimental data from $p+\overline{p}$ collisions (UA5 Collaboration) are similarly analyzed.

We extend our early analyses of the dilepton and photon emission rates from a hadronic gas to account for strange mesons using a density expansion. The emission rates are reduced to vacuum correlation functions using three-flavor chiral reduction formulas, and the latter are assessed in terms of empirical data. Using a fire- ball, we compare our results to the low and intermediate mass dilepton data available from CERN. Our results suggest that a baryon free hadronic gas does not account for the excess of low mass dielectrons observed at CERES but does well in accounting for the intermediate dimuons at HELIOS. The same observations apply to the recent low and high $p_t$ dielectron rates from CERES.

We show results from an analysis performed to test the resolving power of a two-dimensional ${\chi }^2$ method proposed previously when applied to the case of kaon interferometry, where no significant contribution from long-lived resonances is expected. For that purpose, use is made of the preliminary E859 $K^{+}{K}^{+}$ interferometry data from Si+Au collisions at $14.6A\mathrm{GeV}/c.\mathrm{}$ Although less sensitivity is achieved in the present case, this analysis seems to favor scenarios with no resonance formation at the AGS energy range. The possible compatibility of data with zero decoupling proper time interval, conjectured by the three-dimensional experimental analysis, is also investigated and is ruled out when considering more realistic dynamical models with expanding sources. Furthermore, these results strongly emphasize that the static Gaussian parametrization cannot be trusted under more realistic conditions, leading to a distorted or even wrong interpretation of the source parameters.

We carry out a study of intermediate-mass (between 1 and 2.5 GeV) dilepton spectra from hadronic interactions in heavy-ion collisions. The processes considered are $\pi \overrightarrow{\pi }l\overline{l},$ $\pi \overrightarrow{\rho }l\overline{l},$ $\pi a_1\to l\overline{l},$ $\pi \overrightarrow{\omega }l\overline{l},$ $K\overline{K}\to l\overline{l},$ and $K{K}^{*}+\mathrm{c}.\mathrm{c}.\mathrm{}\to l\overline{l}.$ The elementary cross sections for those are obtained from chiral Lagrangians involving pseudoscalar, vector, and axial-vector mesons. The respective electromagnetic form factors are determined by fitting to experimental data for the reverse processes of $e^{+}{e}^{-}\to \hspace{0.5em}\mathrm{hadrons}.$ Based on this input we calculate cross sections and thermal dilepton emission rates and compare our results with those from other approaches. Finally we use these elementary cross sections with a relativistic transport model and calculate dilepton spectra in $S+W$ collisions at SPS energies. The comparison of our results with experimental data from the HELIOS-3 Collaboration indicates the importance of the secondary hadronic contributions to the intermediate-mass dilepton spectra.

The interaction mediated by irreducible pion and gluon exchange between constituent quarks is calculated and shown to have a strong tensor component, which tends to cancel the pion exchange tensor interaction between quarks. Its spin-spin component is somewhat weaker than the pion exchange spin-spin interaction, while its central and spin-orbit components are small in comparison to the corresponding single gluon exchange interactions. The combination of the $\pi -$gluon exchange interaction with the single pion exchange interaction and a weak gluon exchange interaction between constituent quarks has the qualitative features required for understanding the hyperfine splittings of the spectra of the nucleon and the $\Delta$ resonances.

Vector mesons show up in the electromagnetic current-current correlator. QCD sum rules provide a constraint on hadronic models for this correlator. This constraint is discussed for the case of finite nuclear density concerning the longitudinal as well as the transverse part of the current-current correlator at finite three-momentum.

The scale of a phenomenologically successful charge-symmetry-violating nucleon-nucleon interaction, that attributed to meson exchange with a $\Delta I=1\mathrm{}$ ρ-ω transition, is set by the Coleman-Glashow SU(2)-breaking tadpole mechanism. A single tadpole scale has been obtained from symmetry arguments, electromagnetic meson and baryon measured mass splittings, and the observed isospin-violating $(\Delta I=1)$ decay $\overrightarrow{\omega }{\pi }^{+}{\pi }^{-}$. The hadronic realization of this tadpole mechanism lies in the $I=1\mathrm{}$ $a_0$ scalar meson. We show that measured hadronic and two-photon widths of the $a_0$ meson, with the aid of the vector meson dominance model, recover the universal Coleman-Glashow tadpole scale.

In this paper we reconcile two contradictory statements about deep inelastic scattering in manifestly covariant theories: (i) the scattering must be gauge invariant, even in the deep inelastic limit, and (ii) the pole term (which is not gauge invariant in a covariant theory) dominates the scattering amplitude in the deep inelastic limit. An “intermediate” answer is found to be true. We show that, at all energies, the gauge-dependent part of the pole term cancels the gauge-dependent part of the rescattering term, so that both the pole and rescattering terms can be redefined separately in a gauge-invariant fashion. The resulting, redefined pole term is then shown to dominate the scattering in the deep inelastic limit. Details are worked out for a simple example in $1+1$ dimensions.

Parity nonconservation was studied for 23 $p$-wave resonances in ${}^{113}\mathrm{Cd}$ up to $E_n=500\mathrm{}\mathrm{eV}$ at the LANSCE pulsed neutron source using a longitudinally polarized neutron beam and the time-of-flight method. The helicity dependence of the total neutron capture cross section was measured with an enriched ${}^{113}\mathrm{Cd}$ target and with a target of natural cadmium. Parity violating effects were observed for several resonances in ${}^{113}\mathrm{Cd}$ and ${}^{111}\mathrm{Cd}.$ A root-mean-square value of the parity nonconserving matrix element $M_{J=1\mathrm{}}{=2.9\mathrm{}}_{-0.9}^{+1.3\mathrm{}}\mathrm{meV}$ was obtained for the spin $J=1\mathrm{}$ levels in the compound nucleus ${}^{114}\mathrm{Cd}.$ This result from the $3p$-peak region of the neutron strength function is compared with the parity violation results for nuclei from the $4p$-peak region.

Recent studies of heavy ion fragmentation led to the conjecture that the hot and dense compound nuclei formed in the reaction do not decay into just any possible mass partition, but that some decay channels tend to be selected during breakup. We verify this conjecture by means of an extensive analysis of several distributions of decay probabilities. This simplifies the study of nuclear fragmentation tremendously.