The cross sections for the ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$(n,p${)}^{58}$${\mathrm{Co}}^{\mathit{m},\mathit{g}}$ reactions were measured in the neutron energy range 2.1–14.8 MeV using the activation technique in combination with high-resolution gamma-ray spectroscopy. Neutrons were produced via the ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(d,n${)}^3$He and ${}_{}{}^3{}_{}{}^{}\mathrm{H}$(d,n${)}^4$He reactions using solid TiD, TiT, and deuterium gas targets. The isomeric cross section ratio was determined in the 5.38–12.2 MeV range and at 14.8 MeV neutron energy. Statistical model calculations taking into account precompound effects were performed for the formation of the isomeric and ground states of the ${}_{}{}^{58}{}_{}{}^{}\mathrm{Co}$. The calculational results based on the ‘‘back-shifted’’ level density model agree well with the measured excitation functions and render possible the selection of the most probable values of isomeric cross section ratios among the discrepant data obtained around 2 and 14 MeV neutron energies.

We critically examine, in selected 1p-shell nuclei, the theoretical procedure of determining nuclear transition matrix elements, by fits to low-energy electromagnetic and weak observables. We systematically study various fitting strategies using the latest database, and obtain a set of optimal one-body matrix elements. The onset of inadequacies of these sets in describing a given nuclear electroweak observable usually signals the breakdown of the 1p-shell model and/or importance of the two-body corrections. We compare the particle-hole conjugate nuclei ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, and obtain effective amplitudes. We also study the mass-12 case and find a set of effective one-body amplitudes. The difference in the ${\mathit{p}}_{1/2}$ and ${\mathit{p}}_{3/2}$ radial wave functions plays an important role in our fits.

We investigate pion photoproduction in the A=6, 12, and 14 nuclei, using the effective one-body amplitudes determined from a fit to the low-momentum transfer electroweak observables. This reaction provides an independent test of the reliability of the one-body effective amplitudes in a process well described in the impulse approximation.

We derive double polarization observables for the photodisintegration of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ with an incident polarized photon beam. In particular we study the effect of the ground state α-particle D wave on these observables in a simple nuclear model. We find that in general the double polarization observables offer no clear advantage to the corresponding variables studied in the single polarization ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(γ,d→${)}^2$H reaction. However, the photon asymmetry Σ appears as a promising observable for the study of ground state effects.

The influence of the dense nuclear medium on the process of photon bremsstrahlung in nuclear collisions at low excitation energies is investigated. The in-medium nucleon-nucleon scattering T matrix is incorporated in the calculations of photon bremsstrahlung cross section for nucleon-nucleus and nucleus-nucleus scattering cases. Calculations are performed in the soft photon approximation. It is shown that the Pauli blocking of intermediate scattering states and quasiparticle energy shifts due to the mean field interaction essentially suppress the photon bremsstrahlung cross section for temperatures T≤10 MeV and densities n≤${\mathit{n}}_{\mathit{s}}$ (${\mathit{n}}_{\mathit{s}}$ being the nuclear saturation density). In the case of nucleus-nucleus collisions, when the photons are emitted from the thermalized zone, a temperature and density dependent reduction factor for the bremsstrahlung rate is calculated. It implies a typical bremsstrahlung rate which is ∼15% of that in the free scattering case.

It is shown that preequilibrium fission can give rise to a large anisotropy at sub-barrier energies for the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{232}$Th and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${+}^{236}$U reactions, since the transmission coefficient is several times larger for target orientation angles around 180° in comparison with angles around 90°. At higher energies the effect dilutes, since the transition probability becomes of approximately equal magnitude for all orientations.

Recent estimates of the p-wave multipoles for p(γ,${\mathrm{\pi }}^0$) near threshold [J. C. Bergstrom, Phys. Rev. C 50, 2979 (1994)] are compared with new low-energy theorems (LETs) derived from heavy-baryon chiral perturbation theory. Very good agreement is obtained with the LET for the combination ${\mathit{M}}_{1+}$-${\mathit{M}}_{1\mathrm{-}}$, but a marked discrepancy exists with the LET for ${\mathit{E}}_{1+}$. Comparison is also made with an explicit (model-dependent) evaluation of the multipoles which incorporates the off-shell behavior of the Δ(1232) resonance in a generalized covariant form. Excellent agreement is observed for the multipole ${\mathit{M}}_{1\mathrm{-}}$ including the isospin components, but again a substantial discrepancy exists with ${\mathit{E}}_{1+}$. An experimental test of the conflicting ${\mathit{E}}_{1+}$ results is suggested.

The theory of the elastic scattering of a nucleon from a nucleus is presented in the form of a spectator expansion of the optical potential. Particular attention is paid to the treatment of the free projectile-nucleus propagator when the coupling of the struck target nucleon to the residual target must be taken into consideration. First order calculations within this framework are shown for neutron total cross sections and for proton scattering for a number of target nuclides at a variety of energies. The calculated values of these observables are in very good agreement with measurement.

The extraction of source radii from heavy-ion collisions using coalescence models is explored. A new prescription is presented which considers nucleosynthesis via the coalescence of fragments which is, in particular, more appropriate for intermediate-energy collisions than the previous nucleon coalescence prescriptions. This fragment coalescence model provides an avenue for viewing the breakup stage of heavy-ion reactions that yields valuable complimentary information to two-nucleon and two-fragment correlation measurements. This model was applied to recent experimental data on central 55 and 115 MeV/nucleon ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$${+}^{45}$Sc collisions studied at midrapidity. Source radii are presented versus the transverse velocity for six different coalescence channels leading to charge one, two, and three fragments. Particular attention is paid to the temperature input in the model, as the extracted radii depend significantly on this parameter. A means of extracting the temperature from experimental data using the present model is described. Comparisons to the two temperature-dependent nucleon coalescence models will also be discussed.

A flow analysis on symmetric and asymmetric reactions from 100 to 400 MeV/nucleon is performed in the framework of the semiclassical Landau-Vlasov approach. In this energy range our results present two different trends. At lower energies it is governed by the momentum dependence of the nuclear optical potential, whereas at higher energies its density dependence plays a crucial role leading to a rather pronounced sensitivity to the incompressibility modulus. The nonlocality of the nuclear interaction is relevant for asymmetric colliding systems. With an incompressibility modulus in the vicinity of 200 MeV, an excellent quantitative description of the flow behavior with incident energy and impact parameter or the system mass is provided.

The preequilibrium cross sections for the direct excitation of collective states, including giant resonances, in the continuum region, are calculated and combined with the multistep direct, multistep compound, and compound nucleus cross sections to give a complete analysis of neutron scattering by niobium. These collective cross sections we calculated in the framework of DWBA. A good description of neutron emission spectra and angular distributions has been obtained at incident energies 14.1, 20, and 25.7 MeV.

We present the transverse energy distributions, dσ/${\mathit{dE}}_{\mathit{T}}$ and ${\mathit{dE}}_{\mathit{T}}$/dη, and the charged particle multiplicity distributions, dσ/${\mathit{dN}}_{\mathit{c}}$ and ${\mathit{dN}}_{\mathit{c}}$/dη, produced in p+Al and p+Pb collisions at 14.6 GeV/c. The data exhibit a weak correlation between these global variables. While a significant increase of the mean multiplicity with the mass of the target is observed, the transverse energy distributions show little target dependence. The ${\mathit{dE}}_{\mathit{T}}$/dη distribution shifts backward as the mass of the target increases, indicating the presence of rescattering. The data are compared to the predictions of the relativistic quantum molecular dynamic model (RQMD) and Fritiof event generators. RQMD reproduces well the main features of the data while Fritiof predicts too forward peaked transverse energy and particle multiplicity pseudorapidity distributions.

We present the detail of a newly developed relativistic transport model (ART 1.0) for high energy heavy-ion collisions. Using this model, we first study the general collision dynamics between heavy ions at the AGS energies. We then show that in central collisions there exists a large volume of sufficiently long-lived superdense hadronic matter whose local baryon and energy densities exceed the critical densities for the hadronic matter to quark-gluon plasma transition. The size and lifetime of this matter are found to depend strongly on the equation of state. We also investigate the degree and time scale of thermalization as well as the radial flow during the expansion of the superdense hadronic matter. The flow velocity profile and the temperature of the hadronic matter at freeze-out are extracted. The transverse momentum and rapidity distributions of protons, pions, and kaons calculated with and without the mean field are compared with each other and also with the preliminary data from the E866/E802 Collaboration to search for experimental observables that are sensitive to the equation of state. It is found that these inclusive, single particle observables depend weakly on the equation of state. The difference between results obtained with and without the nuclear mean field is only about 20%. The baryon transverse collective flow in the reaction plane is also analyzed. It is shown that both the flow parameter and the strength of the ‘‘bounce-off’’ effect are very sensitive to the equation of state. In particular, a soft equation of state with a compressibility of 200 MeV results in an increase of the flow parameter by a factor of 2.5 compared to the cascade case without the mean field. This large effect makes it possible to distinguish the predictions from different theoretical models and to detect the signatures of the quark-gluon plasma which is expected to significantly soften the equation of state.

Considering energy conservation, the multipion correlation function effects on the pion’s multiplicity distribution is discussed. It is shown that energy constraint can change the pion multiplicity distribution behavior. A pion laser could exist if the total energy of the pions is very large.

Ratios of strange antibaryons to baryons in the reaction S + Pb at 200A GeV beam energy have been computed using a new version of the Fritiof event generator, Luciae, with collective string interaction and rescattering. Theoretical ratios of Λ¯/Λ, ${\mathrm{\Xi }}^{\mathrm{-}}$/Λ, Ξ${\mathrm{¯}}^{\mathrm{-}}$/Λ¯, and Ξ${\mathrm{¯}}^{\mathrm{-}}$/${\mathrm{\Xi }}^{\mathrm{-}}$ are comparable with experimental data within the range of the deviation among the data of different collaborations. It seems to indicate that the ratios of production of strange antibaryons to baryons might be explained within a hadronic scenario.

A relativistic mean-field model of nuclear matter with arbitrary proton fraction is studied at finite temperature. An analysis is performed of the liquid-gas phase transition in a system with two conserved charges (baryon number and isospin) using the stability conditions on the free energy, the conservation laws, and Gibbs’ criteria for phase equilibrium. For a binary system with two phases, the coexistence surface (binodal) is two dimensional. The Maxwell construction through the phase-separation region is discussed, and it is shown that the stable configuration can be determined uniquely at every density. Moreover, because of the greater dimensionality of the binodal surface, the liquid-gas phase transition is continuous (second order by Ehrenfest’s definition), rather than discontinuous (first order), as in familiar one-component systems. Using a mean-field equation of state calibrated to the properties of nuclear matter and finite nuclei, various phase-separation scenarios are considered. The model is then applied to the liquid-gas phase transition that may occur in the warm, dilute matter produced in energetic heavy-ion collisions. In asymmetric matter, instabilities that produce a liquid-gas phase separation arise from fluctuations in the proton concentration (chemical instability), rather than from fluctuations in the baryon density (mechanical instability).

In this paper we present an analysis of our ${}_{}{}^{32}{}_{}{}^{}\mathrm{induced}$ interaction data at 200A GeV in terms of factorial correlators. The correlated moments are found to increase with decreasing bin-bin separation, D. This increase follows a power law within the region D≤1. Bin-size independence of the factorial correlators is observed for the values of D=0.4 and D=0.8. Our data are consistent with the dimension-independent scaling relation proposed by Seixas, which gives a way out of the ‘‘intermittent’’-‘‘nonintermittent’’ ambiguity.

The Compton scattering cross section on the proton has been measured at laboratory angles of 90° and 135° using tagged photons in the energy range 70–100 MeV and simultaneously using untagged photons in the range 100–148 MeV. With the aid of dispersion relations, these cross sections were used to extract the electric and magnetic polarizabilities, α¯ and β¯ respectively, of the proton. We find α¯+β¯=(15.0 ±2.9±1.1±0.4)×${10}^{\mathrm{-}4}$ ${\mathrm{fm}}^3$, in agreement with a model-independent dispersion sum rule, and α¯ -β¯ =(10.8±1.1±1.4±1.0)×${10}^{\mathrm{-}4}$ ${\mathrm{fm}}^3$, where the errors shown are statistical, systematic, and model-dependent, respectively. A comparison with previous experiments is given and global values for the polarizabilities are extracted.

We present a covariant formulation of the Salpeter equation for qq¯ states in order to calculate bound-state transitions between mesons. The corresponding Bethe-Salpeter amplitudes are reconstructed from equal-time amplitudes which were obtained in a previous paper by solving the Salpeter equation for a confining plus an instanton-induced interaction. This method is applied to calculate electromagnetic form factors and decay widths of low-lying pseudoscalar and vector mesons, including predictions for CEBAF experiments. We also describe the momentum transfer dependence for the processes ${\mathrm{\pi }}^0$,η,${\mathrm{\eta }}^{\prime }$→γ${\gamma }^{\mathrm{*}}$.

We present the results of energy-dependent and single-energy partial-wave analyses of πN elastic scattering data with laboratory kinetic energies below 2.1 GeV. Resonance structures have been extracted using Breit-Wigner fits, speed plots, and a complex plane mapping of the associated poles and zeros. This is the first set of resonance parameters from a VPI analysis constrained by fixed-t dispersion relations. We have searched our solutions for structures which may have been missed in our previous analyses, finding candidates in the ${\mathit{S}}_{11}$ and ${\mathit{F}}_{15}$ partial-wave amplitudes. Our results are compared with those found by the Karlsruhe, Carnegie-Mellon–Berkeley, and Kent State groups.