A systematic study of the pairing correlations derived from various particle-number projection methods is performed in an exactly soluble cranked-deformed shell model Hamiltonian. It is shown that most of the approximate particle-number projection methods including the method of Lipkin and Nogami, which is used quite extensively in nuclear structure studies, break down in the weak pairing limit. The results obtained from the recently formulated number-projected Hartree-Fock-Bogoliubov (PHFB) equations, on the other hand, are in complete agreement with the exact solutions of the model Hamiltonian. The pairing energy calculated from the PHFB method is shown to be finite in all the studied limits.

A new version of the Liège intranuclear cascade (INC) model is proposed for the description of spallation reactions. Compared to the previous version, it incorporates new features: (i) it can accommodate a diffuse nuclear surface, (ii) the treatment of the Pauli blocking effect is improved, removing unphysical features linked with the use of statistical blocking factors, (iii) collisions between moving spectator nucleons are explicitly suppressed, (iv) pion dynamics is improved, especially concerning the delta lifetime, (v) it can accommodate light ions as incoming projecticles, (vi) the remnant angular momentum is included in the output of the model. Another important feature is the self-consistent determination of the stopping time, i.e., the time at which the INC calculation is terminated and coupled to evaporation. The predictions of the model, used with the Schmidt evaporation code, are tested against a large body of experimental data, in the 200-MeV–2-GeV range for incident energy per nucleon, including total reaction cross sections, neutron, proton, pion, and composite double differential cross sections, particle multiplicities, residue mass and charge distributions, and residue recoil velocity distributions. Good agreement is generally obtained without additional varying parameters. It is shown that the introduction of a diffuse surface considerably improves the description of the total reaction cross sections, of the intensity of the quasielastic peak in proton and neutron double differential cross sections and of the residue production yield for isotopes close to the target. High energy neutron spectra are found to be sensitive to details of the deuteron structure in deuteron-induced reactions. The shape of the fragmentation peaks in residue mass spectra is shown to be closely related to the shape of the distribution of the excitation energy left after the cascade stage. The longitudinal residue recoil velocity and its fluctuations display typical random-walk characterics, which are interpreted as a direct consequence of the independence of successive binary collisions occurring during the cascade process and therefore provide a strong support of the basic hypotheses of the INC model. Small but systematic discrepancies between model predictions and experiment are identified and possible further improvements to reduce them are discussed. The influence of the evaporation model is investigated. A comparison with similar approaches is presented.

The NA44 experiment has measured single-particle inclusive spectra for charged pions, kaons, and protons as a function of transverse mass near midrapidity in $158A\mathrm{GeV}/c$ Pb+Pb collisions. From the particle mass dependence of the observed $m_T$ distributions, we are able to deduce a value of about 120 MeV for the temperature at thermal freeze-out. From the observed ratios of the rapidity densities, we find values of the chemical potentials for light and strange quarks and a chemical freeze-out temperature of approximately 140 MeV.

We use a light-cone approach to solve the Schwinger-Dyson equation for the quark propagator in Minkowski space. We show how this method can be used to solve the equation beyond the spacelike region, to which one is usually restricted with the Euclidean-space approach. We work in the Landau gauge, use an infrared-enhanced model for the gluon propagator, and include instanton effects to get both confinement and vacuum condensates. With our models reasonable fits to known quantities are obtained, resulting in a light-cone quark propagator that can be used for hadronic physics at all momentum transfers.

The simplest version of a class of toy models for QCD is presented. It is a Lipkin-type model, for the quark-antiquark sector, and, for the gluon sector, gluon pairs with spin zero are treated as elementary bosons. The model restricts to mesons with spin zero and to few baryonic states. The corresponding energy spectrum is discussed. We show that ground state correlations are essential to describe physical properties of the spectrum at low energies. Quantum phase transitions are described in an effective manner, by using coherent states. The appearance of a Goldstone boson for large values of the interaction strength is discussed, as related to a collective state. The formalism is extended to consider finite temperatures. The partition function is calculated, in an approximate way, showing the convenience of the use of coherent states. The energy density, heat capacity, and transitions from the hadronic phase to the quark-gluon plasma are calculated.

Stability of nuclei beyond the drip lines in the presence of an enveloping gas of nucleons and electrons, as prevailing in the inner crust of a neutron star, is studied in the temperature-dependent Thomas-Fermi framework. A limiting asymmetry in the isospin space beyond which nuclei cannot exist emerges from the calculations. The ambient conditions such as temperature, baryon density, and neutrino concentration under which these exotic nuclear systems can be formed are studied in some detail.

The ${}^{15}\mathrm{O}(\alpha ,\gamma {)}^{19}\mathrm{Ne}$ reaction is generally considered as a potential breakout reaction from the hot CNO cycle. Under nova conditions, the reaction rate is dominated by a single sub-Coulomb resonance at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=504\mathrm{}\mathrm{keV}$ which corresponds to a ${}^{19}\mathrm{Ne}$ excitation energy of $E_R=4.033\mathrm{}\mathrm{MeV}.$ Results from a ${d(}^{18}\mathrm{Ne}{,}^{19}\mathrm{Ne})p$ experiment show that states of astrophysical interest are populated in this reaction. An upper limit for the $\alpha$-branching ratio of the 4.033 MeV state was identified and branching ratios for other states in ${}^{19}\mathrm{Ne}$ were found to be in good agreement with stable beam based results.

Anomalous negative heat capacities have been claimed as indicators of first-order phase transitions in finite systems in general, and for nuclear systems in particular. A thermodynamic approach allowing for all Q-value terms is used to evaluate heat capacities in finite van der Waals fluids and finite lattice systems in the coexistence region. Fictitious large effects and negative heat capacities are observed in lattice systems when periodic boundary conditions are introduced. Small anomalous effects are predicted for small drops and for finite lattice systems. A straightforward application of the analysis to nuclei shows that negative heat capacities cannot be observed for $A>\mathrm{}60.\mathrm{}$

Presently, the most accurate values of the free neutron beta-decay lifetime result from measurements using fluid-coated ultacold neutron (UCN) storage bottles. The purpose of this work is to investigate the temperature-dependent UCN loss rate from these storage systems. To verify that the surface properites of fomblin films are the same as the bulk properties, we present experimental measurements of the properties of a liquid “fomblin” surface obtained by the quasielastic scattering of laser light. The properties include the surface tension and viscosity as functions of temperature. The results are compared to measurements of the bulk fluid properties. We then calculate the upscattering rate of UCNs from thermally excited surface capillary waves on the liquid surface and compare the results to experimental measurements of the UCN lifetime in fomblin-fluid-walled UCN storage bottles, and show that the excess storage loss rate for UCN energies near the fomblin potential can be explained. The rapid temperature dependence of the fomblin storage lifetime is explained by our analysis.

Local optical model calculations have been carried out for elastic, inelastic, total, and reaction cross sections of ${\mathrm{K}}^{+}$ from ${}^2\mathrm{H},$ ${}^6\mathrm{Li},$ ${}^{12}\mathrm{C},$ and ${}^{40}\mathrm{Ca}$ at kaon laboratory momenta ranging from 488 to $800\mathrm{MeV}/c.\mathrm{}$ Zero-range distorted-wave Born approximation calculations have been carried out for elastic and inelastic scattering of $K^{+}$ leading to the lowest $3^{+}$ state in ${}^6\mathrm{Li}$ and $2^{+}$ and $3^{-}$ states in ${}^{12}\mathrm{C}.$ Local optical potential is also used to estimate quadrupole noncentral contributions to elastic ${\mathrm{K}}^{+}$ scattering from the $1^{+}$ ground state of ${}^6\mathrm{Li},$ and these are found to be very small. Deformation lengths extracted from inelastic scattering are similar to those deduced from other works. Our calculations adequately reproduced the kaon scattering data.

Heavy quarks are copiously produced in ultraperipheral heavy ion collisions. In the strong electromagnetic fields, $c\overline{c}$ and $b\overline{b}$ are produced by photonuclear and two-photon interactions. Hadroproduction can also occur in grazing interactions. We calculate the total cross sections and the quark transverse momentum and rapidity distributions, as well as the $Q\overline{Q}$ invariant mass spectra from the three production channels. We consider $\mathrm{AA}$ and $\mathrm{pA}$ collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider. We discuss techniques for separating the three processes and describe how the $\mathrm{AA}$ to $\mathrm{pA}$ production ratios might be measured accurately enough to study nuclear shadowing.

We study the behavior of the pion dispersion relation in a pion medium at finite density and temperature. We introduce a pion chemical potential to describe the finite pion number density and argue that such description is valid during the hadronic phase of a relativistic heavy-ion collision between chemical and thermal freeze-out. We make use of an effective Lagrangian that explicitly respects chiral symmetry through the enforcement of the chiral Ward identities. The pion dispersion relation is computed through the computation of the pion self-energy in a nonperturbative fashion by giving an approximate solution to the Schwinger-Dyson equation for this self-energy. The dispersion relation is described in terms of a density and temperature dependent mass and an index of refraction which is also temperature, density, as well as momentum dependent. The index of refraction is larger than unity for all values of the momentum for finite $\mu$ and T. We conclude by exploring some of the possible consequences for the propagation of pions through the boundary between the medium and vacuum.

Fission fragment angular distributions have been measured for the fusion of ${}^{16}\mathrm{O}$ with deformed ${}^{181}\mathrm{Ta}$ target, in the energy range 90 MeV to 110 MeV. Combining with the existing data of evaporation residue and fission cross sections in the literature, the fusion cross sections have been determined in the range $1.1<~{E/V}_B<~\mathrm{1.6.}$ Detailed statistical model analysis of the entire data set has been performed and it has been shown that fission fragment anisotropies calculated are in good agreement with the experimental data. Even at the lowest energy studied, ${(E=1.1V}_B)$ as there is good agreement between the data and the calculation, it can be concluded that the quasifission effect is negligible at this energy.

We examine the effects of pseudoscalar and pseudovector coupling of the $\pi$ and $\eta$ mesons in one-boson exchange models of the $\mathrm{NN}$ interaction using two approaches: time-ordered perturbation theory unitarized with the relativistic Lippmann-Schwinger equation, and a reduced Bethe-Salpeter approach using the Thompson equation. Contact terms in the one-boson exchange amplitudes in time-ordered perturbation theory lead naturally to the introduction of s-channel nucleonic cutoffs for the interaction, which strongly suppresses the far off-shell behavior of the amplitudes in both approaches. Differences between the resulting $\mathrm{NN}$ predictions of the various models are found to be small, and particularly so when coupling constants of the other mesons are readjusted within reasonable limits.

We investigate the three-nucleon system with a realistic nucleon-nucleon potential and the Tucson-Melbourne (TM) two-pion exchange three-body interaction using a translationally invariant harmonic oscillator basis. In the calculations, the no-core shell-model two-body effective interaction replaces the nucleon-nucleon potential, while the three-nucleon interaction is added without any renormalization. We study the convergence of the approach by changing the basis size. Also the dependence of the binding energies on the TM cutoff parameter $\Lambda$ is examined. The results show promise for the construction of three-body effective interactions including a three-nucleon interaction, for use in future ab initio no-core shell-model nuclear structure calculations for $A>\mathrm{}3\mathrm{}$ systems.

High-spin states in doubly odd ${}^{166}\mathrm{Tm}$ were investigated by means of in-beam $\gamma$-ray spectroscopy techniques using the multidetector array GASP. Excited states of ${}^{166}\mathrm{Tm}$ were populated using the ${}^{160}\mathrm{Gd}{(}^{11}\mathrm{B},5n)$ reaction at a beam energy of 61 MeV. Known rotational bands have been extended to higher spins and their configurations have been discussed. Alignments, band crossing frequencies, and electromagnetic properties have been analyzed in the framework of the cranking model. Signature inversion in the $\pi h_{9/2}\otimes \nu i_{13/2}$ structure is discussed. Calculations in the framework of the particle rotor model with $p-n$ interaction included have been able to reproduce the inversion. $E1\mathrm{}$ decay modes were observed in competition with $E2\mathrm{}$ intraband transitions.

The inclusive $\alpha$-particle spectra from ${}^{16}\mathrm{O}{+}^{89}\mathrm{Y},$ ${}^{12}\mathrm{C}{+}^{93}\mathrm{Nb},$ and ${}^{16}\mathrm{O}{+}^{93}\mathrm{Nb}$ reactions around 6–7 MeV/nucleon incident energy (laboratory) have been studied. These spectra have been fitted very well using an algebraic expression for the statistical emission of particles from the compound nucleus and subsequent daughter nuclei. We do not find any statistically significant oscillations in the remaining spectra after subtracting out the contributions due to initial and sequential emissions from the compound nuclei, thus showing no direct evidence for the existence of $\alpha$ particles as independent particles in the nuclei.

The quasielastic ${(e,e}^{\prime }p)$ reaction was studied on targets of deuterium, carbon, and iron up to a value of momentum transfer $Q^2$ of $8.1(\mathrm{GeV}{/c)}^2.$ A nuclear transparency was determined by comparing the data to calculations in the plane-wave impulse approximation. The dependence of the nuclear transparency on $Q^2$ and the mass number A was investigated in a search for the onset of the color transparency phenomenon. We find no evidence for the onset of color transparency within our range of $Q^2.$ A fit to the world’s nuclear transparency data reflects the energy dependence of the free-proton–nucleon cross section.

The experimental data on hadron yields and ratios in central lead-lead and gold-gold collisions at $158A\mathrm{GeV}/c$ (SPS) and $\sqrt{s}=130A\mathrm{GeV}$ (RHIC), respectively, are analyzed within a two-source statistical model of an ideal hadron gas. A comparison with the standard thermal model is given. The two sources, which can reach the chemical and thermal equilibrium separately and may have different temperatures, particle and strangeness densities, and other thermodynamic characteristics, represent the expanding system of colliding heavy ions, where the hot central fireball is embedded in a larger but cooler fireball. The volume of the central source increases with rising bombarding energy. Results of the two-source model fit to RHIC experimental data at midrapidity coincide with the results of the one-source thermal model fit, indicating the formation of an extended fireball, which is three times larger than the corresponding core at SPS.

The nucleon axial vector form factor is investigated in a light-cone quark spectator diquark model, in which Melosh rotations are applied to both the quark and vector diquark. This model gives a very good description of available experimental data and the results have very little dependence on the parameters of the model. The relation between the nucleon axial constant and the anomalous magnetic moment of nucleons is also discussed.