Measurements of the β anisotropy of the mirror nuclei ${}_{}{}^{15}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{17}{}_{}{}^{}\mathrm{F}$, using on-line isotope separation and low-temperature nuclear orientation, are reported for the first time. Results of this novel approach are discussed in connection with the study of weak interactions in nuclei.

The leading T-conserving P-nonconserving (PNC) electromagnetic coupling to the nucleon or nucleus is known as the anapole moment. We evaluate the pion-cloud contribution to the nucleon anapole moment, and the enhancements in nuclei associated with meson-exchange currents and with the mixing of the nuclear ground state with opposite-parity excited states. We find that the anapole moment becomes the dominant PNC spin-dependent coupling in heavy nuclei.

An effective theory for low-energy nuclear interactions is proposed, based on results obtained from the 1/$N_c$ expansion of quantum chromodynamics. The Lagrangian is local in the meson sector, but in the baryon sector it is nonlocal both in the meson-baryon Yukawa coupling and in the baryon propagators. It satisfies an important consequence of the 1/$N_c$ expansion, the suppression of baryon loops. Our findings are then shown to support the traditional approaches in nuclear physics and, more especially, the relativistic nuclear many-body theories at baryon-tree level.

Cross sections were determined in the Δ(1232) excitation region for the reactions ${}_{}{}^3{}_{}{}^{}\mathrm{H}$(γ,p)pn and ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(γ,p)n at several photon energies and proton emission angles. Inclusive proton spectra were measured with a magnetic spectrometer, using quasimonochromatic $e^{+}$-annihilation photons. The ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ data can be mainly accounted for by predictions assuming photon absorption by a pair of nucleons, except in the high-momentum part of the proton spectra. They clearly indicate the need for additional contributions, such as three-body absorption mechanisms.

Microsecond isomers in the very proton-rich N=82 nuclei ${}_{}{}^{153}{}_{}{}^{}\mathrm{Lu}$ and ${}_{}{}^{154}{}_{}{}^{}\mathrm{Hf}$ have been identified by γ-ray spectroscopy following mass analysis of ${}_{}{}^{102}{}_{}{}^{}\mathrm{Pd}$ +245 MeV ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$ reaction products using the Daresbury Recoil Separator. The decays of the isomers, interpreted as (π$h_{11/2}$${)}^n$ states, are characterized. Examination of reduced E2 transition rates between (π$h_{11/2}$${)}^n$ states in the N=82 isotones indicates that the half-filling of the π$h_{11/2}$ subshell occurs just below Z=71.

The A dependence of the (e,e’p) reaction in the quasifree region has been measured at an average $Q^2$ of 0.33 (GeV/c${)}^2$ for targets of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, and ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$. The outgoing proton kinetic energy was 180±30 MeV. By comparing the ratio of (e,e’p) coincidence to (e,e’) singles yields, average proton transmissions are obtained for each target. The resulting ‘‘mean free path’’ or, more precisely, the attenuation length for protons in the nucleus is significantly longer than expectations based on the free nucleon-nucleon cross section.

Cross sections for the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${\mathrm{\pi }}^{\pm }$,${\mathrm{\pi }}^{\pm }$’p${)}^{11}$B reaction have been measured and compared with the results of distorted-wave impulse-approximation calculations that employ the vactirozation approximation for quasifree scattering. Near the giant dipole resonance of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ the calculations underestimate the cross sections for (${\pi }^{\mathrm{-}}$,${\pi }^{\mathrm{-}}$’p). The angular distributions for (${\pi }^{+}$,${\pi }^{+}$’p) and (${\pi }^{\mathrm{-}}$,${\pi }^{\mathrm{-}}$’p) are different and indicate that in this region there is interference between direct decay and semidirect decay.

The triple-differential cross sections for elastic breakup of 156-MeV ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ measured at larger relative momenta of the outgoing α-particle and deuteron fragments exhibit conspicuous double-peaked structures in the momentum-transfer dependence. The origin of these features is explored, sensitively revealing interference and off-shell scattering effects in the fragment-target interaction. Elastic breakup data of 56-MeV deuterons and 90-MeV ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ are reanalyzed in view of these effects on the basis of the prior-form distorted-wave Born-approximation theory.

Nucleon-nucleus optical potentials are calculated using full off-shell nucleon-nucleon free t matrices based on the Paris potential. Applications to proton scattering from ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ at 200 and 300 MeV are presented. Significant differences are found between observables calculated using full-folding potentials and tρ approximations to them, demonstrating the importance of an accurate treatment of off-shell effects. The agreement between calculated and measured observables improves substantially using the full-folding model.

Compton polarimeters have been used to measure the linear polarization of resonantly scattered photons. In the deformed nucleus ${}_{}{}^{150}{}_{}{}^{}\mathrm{Nd}$ the first direct and model-independent evidence has been obtained that in a cluster of enhanced dipole excitations near 3 MeV the three strongest transitions are of the same, positive parity.

We have measured the polarizations and the differential cross sections of the produced Λ’s at backward angles (70°<${\theta }_{\mathrm{lab}<145\mathrm{}\mathrm{°}}$) using a large-aperture spectrometer. The angular range is kinematically not accessible in interactions of the incident pions with free nucleons. The calculated polarizations in terms of superposition of an elementary process incorporating Fermi motion of nucleons in the nucleus are opposite in sign to the observed ones, while a quark-parton model of Λ production with a Thomas precession effect reproduces both the polarizations and the cross sections well.

The dependence of multifragment-emission processes upon linear momentum transfer to the target residue is determined for ${}_{}{}^{36}{}_{}{}^{}\mathrm{induced}$ reactions on ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ at E/A=35 MeV. Significantly more intermediate-mass fragments are emitted in central collisions. Multiplicity distributions for intermediate-mass fragments emitted behind the grazing angle resemble Poisson distributions and are consistent with a stochastic production process. Exit channels with up to five intermediate-mass fragments and two fission fragments were observed.

Differential and absolute cross sections for the coherent reaction ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(γ,${\pi }^0$${)}^{40}$Ca g.s., as well as for the incoherent reaction ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(γ,${\mathrm{\pi }}^0$${)}^{40}$Ca(g.s.), have been measured with monochromatic photons in the threshold region ($E_{\gamma }$=157–169 MeV). The differential cross section for the coherent process exhibits a diffraction minimum due to the nuclear mass form factor while the incoherent cross section is rather structureless. The cross sections are in good agreement with recent distorted-wave impulse-approximation calculations.

The first observation of superdeformation in the mass region A≃190 is reported. A rotational band of twelve transitions with an average energy spacing of 37 keV, an average moment of inertia ${\mathrm{scrF}}^{\mathrm{}\left(2\right)\mathrm{}}$ of 110 ${ħ}^2$ ${\mathrm{MeV}}^{\mathrm{-}1}$, and an average quadrupole moment of 18±3 e b has been observed in ${}_{}{}^{191}{}_{}{}^{}\mathrm{Hg}$; this band persists at low rotational frequency. These results are in excellent agreement with a calculation that predicts an ellipsoidal axis ratio of 1.65:1 for the superdeformed shape in this nucleus.

We explain ‘‘intermittency’’ in recent data, using a simple model in which pions are emitted from quark-gluon-plasma droplets. We find that droplets with a temperature near the QCD phase transition temperature that emit 10–15 pions, with a droplet volume of 5–10 ${\mathrm{fm}}^3$, reproduce the observations very well.

The problem of signature inversion is studied by using a model of particles coupled to a rotor. We have assumed an axially symmetric equilibrium deformation and taken into account the γ vibration around it. The calculated signature dependence is found inverted in agreement with the experimental data if we adopt a set of moments of inertia which favor the rotation around the shortest axis, but not if we employ the set of the irrotational-flow model.

A new method of fast-timing measurements using β-γ-γ coincidences with ${\mathrm{BaF}}_2$ and plastic detectors has been used to measure a number of lifetimes for low-lying states in ${}_{}{}^{116}{}_{}{}^{}$,118,120Cd in the range of 10–100 ps. The results are discussed in terms of the vibrational and intruder structure of these nuclei.

The Landau theory of shape transitions in hot rotating nuclei is applied to even-even rare-earth nuclei from cerium to hafnium. The parameters of the Landau expansion are extracted from microscopic calculations based on the Nilsson-Strutinsky procedure, and are shown to follow simple systematics. In particular, the systematics of the critical temperature and the critical angular momentum of the shape transitions as functions of neutron and proton number are investigated. Simple rules are provided for the behavior of these quantities.

It is shown that one-nucleon-loop calculations of the vacuum contributions to the effective potential for hadronic field theories with point nucleon fields are not compatible with large-${\mathrm{N}}_{\mathrm{c}}$ QCD. One expects that nucleon substructure will lead to a suppression of such effects of at least order ${\mathrm{N}}_{\mathrm{c}}^{1\mathrm{-}\mathrm{d}}$, where d is the dimension of space-time. Issues of the self-consistency of the large-${\mathrm{N}}_{\mathrm{c}}$ QCD are discussed.

A new mechanism for producing J/ψ’s in a quark-gluon plasma is explored. A cc¯ pair created in the hard part of a hadronic collision need not be initially formed as a color singlet to result in a charmonium state if a plasma is also present. Instead, a color-octet pair can subsequently scatter off of the plasma to lose its color. It is shown that if a hot plasma is formed in a relativistic heavy-ion collider, then a substantial enhancement of the J/ψ production rate might be expected from this mechanism. Thus this production mechanism acts to counteract the decrease in cross section arising from Debye screening of the color-binding force in the plasma.