A photon scattering experiment has been performed on the odd-A nucleus ${}_{}{}^{143}{}_{}{}^{}\mathrm{Nd}$. Strong dipole excitations have been detected in the energy region around 3.2 MeV. This is near the expected position of the two-phonon ($2^{+}$⊗$3^{\mathrm{-}}$) multiplet in the even-even neighboring nucleus ${}_{}{}^{142}{}_{}{}^{}\mathrm{Nd}$. The summed dipole strength between 2.8 and 3.6 MeV in ${}_{}{}^{143}{}_{}{}^{}\mathrm{Nd}$ is in agreement with the sum rule for weak particle coupling to the core nucleus ${}_{}{}^{142}{}_{}{}^{}\mathrm{Nd}$. Model calculations in a harmonic approximation are in a very good agreement with the experiment and they suggest a two-phonon ($2^{+}$⊗$3^{\mathrm{-}}$) particle structure of the excitations in ${}_{}{}^{143}{}_{}{}^{}\mathrm{Nd}$.

Two-way decay has been observed between superdeformed bands in ${}_{}{}^{193}{}_{}{}^{}\mathrm{Hg}$. It is proposed the decays have M1 multipolarity and connect signature partner bands. Candidates for the two-way gamma decays connecting superdeformed bands are observed for the first time.

The rotational spectrum of ${}_{}{}^{168}{}_{}{}^{}\mathrm{Yb}$ is calclated by diagonalizing different effective interactions within the basis of unperturbed rotational bands provided by the cranked shell model. A transition between order and chaos taking place in the energy region between 1 and 2 MeV above the yrast line is observed, associated with the onset of rotational damping. It can be related to the higher multipole components of the force acting among the unperturbed rotational bands.

The spin-orbit splitting of the ${\mathit{p}}_{1/2}$ and ${\mathit{p}}_{3/2}$ hole states in ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ is studied with realistic nuclear forces and the variational cluster Monte Carlo method. The results show that the two-nucleon L⋅S forces give approximately half of the observed splitting, while the other half comes from pion exchange interactions between three or more nucleons. The observed splitting is fairly well reproduced by these calculations based on nonrelativistic nuclear many-body theory.

Proton-proton correlations at small relative momenta were measured for ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$${+}^{197}$Au reactions at E/A=200 MeV. Comparing the correlation functions to predictions based on single-particle phase space distributions from microscopic Boltzmann-Uehling-Uhlenbeck and quantum-molecular-dynamics (QMD) simulations, no satisfactory agreement could be established. Calculations utilizing two-particle emission probabilities predicted by the QMD model differ significantly from the single-particle calculations and are much closer to the experimental observations at E/A=200 MeV, potentially signaling the importance of the two-particle density for the proton-proton correlation function.

Perturbative analysis of parton kinetics for high energy nuclear collisions shows that thermal equilibration of gluons happens very fast, while quark production is much slower. A simple ‘‘minimal model’’ is proposed which includes only incoming quarks and antiquarks. We have found that a smaller quark number is more than compensated by the fact, that they are imbedded into the hotter glue. Predicted yield of dileptons and photons in the interesting kinematic region are larger than considered before, and are quite observable at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider.

Recently measured properties of the prescission particle emission from heavy-ion induced fission of systems with A∼200 were analyzed using the statistical model. Simultaneous fits to prescission neutron, proton, and α-particle multiplicities and mean kinetic energies can be obtained when the deformation dependence of both the particle transmission coefficients and particle binding energies are taken into account. The experimental data are consistent with a total fission time scale of (30±10)×${10}^{\mathrm{-}21}$ s, with more than half of this time being spent beyond the saddle point.

We show that the differences between the Plastic Ball and DIOGENE experiments on sideward flow make it possible to asses independently, within the transport description of collisions, the effect of density dependence and momentum dependence of the nucleon optical potential. We estimate that the nuclear compressibility K lies between 180 and 235 MeV.

The spectrum of low energy beta-delayed alpha-particle emission of ${}_{}{}^{16}{}_{}{}^{}\mathrm{N}$ was measured with high sensitivity; e.g., at ${\mathit{E}}_{\mathrm{\alpha }}^{\mathit{L}}$≊1 MeV, a sensitivity for a beta-decay branching ratio in the range of ${10}^{\mathrm{-}9}$ (to ${10}^{\mathrm{-}10}$) was achieved. We used previous theoretical work of Ji, Filippone, Humblet, and Koonin to extract from these data the astrophysical p-wave S factor for the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ (α,γ${)}^{16}$O capture reaction, and find ${\mathit{S}}_{\mathit{E}1}$(300)=95±6(stat)±28(syst) keV b. This result is crucial, for example, for understanding the last stages of a massive star before a supernova.

The mass distributions from the sequential decay of the compound nuclei formed by the ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$${+}^9$Be and ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$${+}^{10}$B reactions at ${\mathit{E}}_{\mathrm{lab}}$≃11A MeV show no evidence of nuclear structure effects. We thus conclude that hot composite systems as light as ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ and ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ can behave like liquid droplets with no remnant shell effects.

We compute the radiation of lepton pairs by the quarks during a central collision between gold nuclei at energy of the Brookhaven Relativistic Heavy Ion Collider (√s =200A GeV) within the parton cascade model. The distribution of radiated pairs evolves smoothly from the initial Drell-Yan type reactions all the way towards equilibrium radiation. Contributions from reactions involving secondary partons dominate the Drell-Yan yield by at least a factor of 5 even at an invariant mass of 8 GeV. Therefore, experiments can test the evolution of partons towards thermal equilibrium at these energies.

We present Z distributions for fragments with 1≤Z≤12 from central collisions of ${}_{}{}^{40}{}_{}{}^{}$ Ar${+}^{45}$Sc at incident energies ranging from 35 to 115 MeV/nucleon. We find that the Z distributions can be described by a power law or an exponential and steepen with increasing incident energy. Over the range of incident energies studied, the average number of intermediate mass fragments decreases while the average number of particles increases. When combined with previous results for the charge distributions, a minimum is observed in the extracted power-law parameter.

Using a chemically purified sample of ${}_{}{}^{55}{}_{}{}^{}\mathrm{Fe}$ and a coaxial Ge detector, we collected a high-statistics internal-bremsstrahlung photon spectrum, and conducted a local search for departures from a smooth shape near the end point. We find no evidence for emission of a neutrino in the mass range 5–25 keV. In particular, a 17 keV neutrino with ${\sin }^2$θ=0.008 is excluded at the 7σ level.

We have measured antiproton production cross sections as functions of centrality in collisions of 14.6 GeV/c per nucleon ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ ions with targets of Al, Cu, and Pb. For all targets, the antiproton yields increase linearly with the number of projectile nucleons that have interacted, and show little target dependence. We discuss the implications of this result on the production and absorption of antiprotons within the nuclear medium.

The nuclear response of a medium-mass nucleus ${(}^{136}$Xe) to electromagnetic excitation in a near-relativistic heavy-ion collision was investigated in the ${\mathrm{reaction}}^{136}$Xe(0.7A GeV)+Pb. From an exclusive measurement of the neutron decay of the excited ${}_{}{}^{136}{}_{}{}^{}\mathrm{Xe}$ projectiles, strong excitations of giant resonances and, in particular, of the double isovector giant dipole resonance were identified. A resonance energy of 28.3±0.7 MeV, a width of 6.3±1.6 MeV, and a total cross section of 215±50 mb were found for the double giant dipole resonance.

A new framework, the variational shell model, is proposed to describe the structure of neutron-rich unstable nuclei. An application to ${}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$ is presented. Contrary to the failure of the spherical Hartree-Fock model, the anomalous 1/$2^{+}$ ground state and its neutron halo are reproduced with the Skyrme (SIII) interaction. This state is bound due to dynamical coupling between the core and the loosely bound neutron, which oscillates between the 2${\mathit{s}}_{1/2}$ and the 1${\mathit{d}}_{5/2}$ orbits.

By a realistic dynamical microscopic reaction approach to ${}_{}{}^5{}_{}{}^{}\mathrm{He}$ we reproduce the empirical positions of the two S matrix poles associated with the 3/$2^{+}$ resonance, and unambiguously prove that it arises from the t+d channel. The picture is not coherent though, unless the presently adopted α+n phase shift, extracted partly from α+p scattering data, is assumed to be incorrect. It is pointed out that the analog resonance in ${}_{}{}^5{}_{}{}^{}\mathrm{Li}$ behaves very differently because the shadow pole is located on another Riemann sheet.

Experimental particle yield ratios from 14.6A-GeV/${\mathit{c}}^{28}$Si interactions with nuclei at intermediate impact parameters are correlated with the orientation of the transverse momentum of projectile fragments. The ${\mathrm{\pi }}^{\pm }$/p ratio increases and the (d+t)/p ratio decreases when fragments are deflected toward the observing spectrometer. Asymmetries are confined to the target rapidity region. Assuming a spectator participant model, these results suggest the presence of significant rescattering of particles with dependences on the collision geometry.

A new method for the study of time reversal violation is described. It consists of measurements of the forward-backward asymmetry in individual gamma-ray transitions resulting from unpolarized neutron capture in p-wave resonances. An experiment with a ${}_{}{}^{113}{}_{}{}^{}\mathrm{Cd}$ target performed at the Dubna pulsed neutron source has been analyzed and a limit on the time reversal odd, parity even interaction extracted. The possibility of experiments using the powerful pulsed neutron source at Los Alamos are considered.

A new probe of dynamical effects in heavy-ion induced fission is proposed. This is the ‘‘long-lifetime’’ tail of the time distribution of fission events, or the so-called long-lifetime fission component (LLFC). The excess of LLFC over its standard statistical-model value is calculated by taking into account dissipation and fluctuations of the collective nuclear motion. The magnitude of this excess is shown to be much larger and its dependence upon the reduced friction parameter to be much stronger than those of the corresponding excess of the pre-scission neutron multiplicity which is at present a commonly used probe of dynamical effects in heavy-ion induced fission. Experiments for measuring LLFC are proposed which can provide decisive information about the strength of nuclear friction for compact configurations in nuclear fission.