Multifragmentation has been measured for ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$${+}^{197}$Au collisions at E/A=100, 250, and 400 MeV. The mean fragment multiplicity increases monotonically with the charged particle multiplicity at E/A=100 MeV, but decreases for central collisions with incident energy, consistent with the onset of nuclear vaporization. Molecular dynamics calculations follow some trends but underpredict the observed fragment multiplicities. Including the statistical decay of excited residues improves the agreement for peripheral collisions but worsens it for central collisions.

In an extended mean field theory, we find a large class of bound multistrange objects, formed from combinations of {p,n,Λ,${\mathrm{\Xi }}^0$,${\mathrm{\Xi }}^{\mathrm{-}}$} baryons, which are stable against strong decay. We predict a maximal binding energy per baryon of ${\mathit{E}}_{\mathit{B}}$/A≊-21 MeV, strangeness per baryon ${\mathit{f}}_{\mathit{s}}$≊1.2, charge per baryon ${\mathit{f}}_{\mathit{q}}$≊-0.1 to 0, and baryon density 2.5–3 times that of ordinary nuclei. For A≥6, we obtain stable combinations involving only {Λ,${\mathrm{\Xi }}^0$,${\mathrm{\Xi }}^{\mathrm{-}}$} hyperons.

Azimuthal correlations of pions are studied with the quantum molecular dynamics model. Pions are preferentially emitted perpendicular to the reaction plane. Our analysis shows that this anisotropy is dominated by pion absorption on the spectator matter in the reaction plane. Pions emitted perpendicular to the reaction plane undergo less rescattering than those emitted in the reaction plane and might therefore be more sensitive to the early hot and dense reaction phase.

We present data on collective flow of neutrons in collisons of ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ + ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ at 400 MeV/nucleon. The azimuthal distribution about the beam axis is investigated with respect to the reaction plane as determined from light charged particles. The ‘‘squeezeout’’ of neutrons, perpendicular to the reaction plane, is observed for the first time. Quantitative agreement to a high level of accuracy is found between the behavior of neutrons and hydrogen ions.

One- and two-step Coulomb excitation cross sections of the double-phonon giant dipole resonance are calculated in a semiclassical formalism. The contribution of nuclear interaction is shown to be small. The multipole sum rules are used to evaluate corresponding nuclear matrix elements; the widths of final and intermediate states are taken into account. The recent experimental data re discussed and compared to our calculations.

The four-nucleon Yakubovsky equations are solved precisely for various realistic NN interactions. The resulting binding energies underbind the α particle by about 1 to 5 MeV. The one-boson-exchange NN potentials with smallest deuteron d-state probabilities provide the strongest binding. Within the group of NN-force models used the 3N and 4N binding energies are strongly correlated. The probabilities to find two nucleons at a distance r are compared to each other in the deuteron, the triton, and the α particle.

Nuclear resonance fluorescence experiments are reported to search for enhanced M1 scissors mode states in the deformed odd-mass nucleus ${}_{}{}^{163}{}_{}{}^{}\mathrm{Dy}$. A concentration of dipole strengths near 3 MeV excitation energy is found, which fits nicely into the systematics observed for M1 excitations in the neighboring even-even Dy isotopes. The observed strength distribution and the decay branching ratios are discussed in the context of the interacting boson-fermion model.

No evidence for the neutrinoless double-β decay of ${}_{}{}^{100}{}_{}{}^{}\mathrm{Mo}$ has been found in a search using a segmented Si(Li) detector with source foils enriched to 97% ${}_{}{}^{100}{}_{}{}^{}\mathrm{Mo}$. After 0.2664 mole years of exposure, we report a 1σ lower limit on the half-life for the ${\mathit{J}}^{\mathit{P}}$=$0^{+}$→$0^{+}$ transition of 0.44×${10}^{23}$ years.

The azimuthal angle distributions of neutral pions at midrapidity from Au+Au reactions at 1 GeV/nucleon incident energy have been measured. An enhanced emission of ${\mathrm{\pi }}^0$’s perpendicular to the reaction plane is observed. The azimuthal asymmetry is dependent on the ${\mathrm{\pi }}^0$ momentum: the ${\mathrm{\pi }}^0$ spectrum perpendicular to the reaction plane is harder than in the reaction plane. The strength of the observed asymmetry appears to be more pronounced for ${\mathrm{\pi }}^0$ than for charged particles and neutrons.

The polarization transfer observable ${\mathit{D}}_{\mathit{L}\mathit{L}}$(0°) has been measured for ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(p→,n→)2p, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(p→,n→${)}^{12}$N, and ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$(p→,n→${)}^{14}$N reactions with beam energies of 318 and 494 MeV. The deuterium results are in close agreement with free NN scattering constrained to the Δ${\mathit{J}}^{\mathrm{\pi }}$=$1^{+}$ channel. The results for the carbon targets, however, are systematically more negative than those for deuterium, which suggests a difference between the free and effective nucleon-nucleon interactions. Such a medium modification of the spin-dependent interaction may have important implications for intepretation of other intermediate-energy scattering experiments.

Eight superdeformed rotational bands have been observed in the ${}_{}{}^{149}{}_{}{}^{}\mathrm{Gd}$ nucleus. Several excited bands have partners in neighboring nuclei which differ by up to four nucleons, with nearly identical dynamic moments of inertia and quantized γ-ray phasing. These observations cannot be easily explained by theoretical models including an intrinsic scaling with mass of the moment of inertia. A paired backbend and an interaction due to an accidental degeneracy between two superdeformed levels have also been observed.

The quantum equation of motion of the density operator in the Wigner representation is solved using a stochastic approach. Nuclear ground states and an asymmetric nucleus-nucleus collision below the Coulomb barrier are studied. Quantum effects are shown to cause significant differences in comparison to results obtained from the classical Vlasov equation.

Triple differential cross sections ${\mathit{d}}^3$σ/${\mathit{dp}}^3$ for charged pions produced in symmetric heavy-ion collisions were measured with the KaoS magnetic spectrometer at the heavy-ion synchrotron facility SIS at GSI. The correlations between the momentum vectors of charged pions and the reaction plane in ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$${+}^{197}$Au collisions at an incident energy of 1 GeV/nucleon were determined. We observe, for the first time, an azimuthally anisotropic distribution of pions, with enhanced emission perpendicular to the reaction plane. The anisotropy is most pronounced for pions of high transverse momentum in semicentral collisions.

A superdeformed band has been observed for the first time in an Au isotope. The reaction used was ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$ + ${}_{}{}^{186}{}_{}{}^{}\mathrm{W}$, demonstrating that very light ions can be used to populate superdeformed (SD) bands at high angular momentum. The band is assigned to ${}_{}{}^{191}{}_{}{}^{}\mathrm{Au}$. The γ-ray energies are at the quarter-point energies of the ${}_{}{}^{192}{}_{}{}^{}\mathrm{Hg}$ SD band, indicating that it is ‘‘identical’’ to that of ${}_{}{}^{192}{}_{}{}^{}$ Hg.

A new analysis of yrast energies in collective medium and heavy even-even nuclei shows two startling results. First, although these nuclei exhibit widely varying structure [the ratio E($4_1^{+}$)/E($2_1^{+}$) ranges from ∼2.0 to ∼3.33], they show a universal behavior of an anharmonic vibrator with nearly constant anharmonicity in which the multiphonon interactions are independent of the internal structure of the vibration. Second, the transition from anharmonic vibrator to rotor can be described by critical phase transitional behavior. These results suggest a reexamination of very basic ideas of structural evolution in finite-body nuclear systems.

A ridge structure consisting of stretched E2 transitions and extending from ħω≃0.6 to 0.75 MeV has been found in a proton-selected γ-γ matrix in the reaction ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$${(}^{37}$Cl, xn${)}^{152,153}$Dy at 187 MeV. The ridge spacing corresponds to a dynamic moment of inertia, ${\mathit{scrI}}^{\mathrm{}\left(2\right)\mathrm{}}$, of about 130${\mathrm{ħ}}^2$ ${\mathrm{MeV}}^{\mathrm{-}1}$ and suggests the existence of a hyperdeformed prolate shape with a quadrupole deformation ${\mathrm{\beta }}_2$≥0.9. Furthermore, a cascade of 10 discrete transitions with an average energy spacing of 30±3 keV has been found. This result is consistent with calculations indicating conditions favorable to hyperdeformed structures.

All currently available data on the pionic double charge exchange reaction (${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^{\mathrm{-}}$) on nuclei exhibit a very peculiar energy dependence near ${\mathit{T}}_{\mathrm{\pi }}$=50 MeV, while the angular distributions behave quite regularly. We demonstrate that these features find their natural explanation by a narrow resonance in the πNN subsystem with ${\mathit{J}}^{\mathit{P}}$=$0^{\mathrm{-}}$ and a mass of 2.065 GeV.

We discuss two different approximation schemes for the self-consistent solution of the relativistic Brueckner-Hartree-Fock equation for finite nuclei. The results obtained by the two methods are very similar. Employing a realistic one-boson-exhange potential (Bonn A), the predictions for energies and radii of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ come out in substantially better agreement with experiment as compared to nonrelativistic approaches. As a by-product of our study, it turns out that the Fock exchange terms, ignored in a previous investigation, are not negligible.

A new technique, based on relative measurements of the longitudinal polarization (P) of positrons emitted in two opoosite directions with respect to the nuclear polarization (R=${\mathit{P}}^{\mathrm{-}}$/${\mathit{P}}^{+}$), is used to provide constraints on extensions of the standard model (${\mathit{R}}_0$). The first result, i.e., R/${\mathit{R}}_0$=0.926±0.041, was obtained with ${}_{}{}^{107}{}_{}{}^{}\mathrm{In}$. Interpreted in the framework of left-right symmetric models and assuming no mixing, it provides a 90% C.L. lower limit of 225 GeV/${\mathit{c}}^2$ for the mass of a possible right-handed charged W gauge boson, reducing the mass range allowed by other semileptonic experiments.

A method to calculate the mean squared matrix element of the weak interaction between compound states is developed. The result is expressed in terms of matrix elements of the nucleon-nucleon strong and weak interactions times the Fermi distribution functions at finite temperature. Numerical calculations for ${}_{}{}^{233}{}_{}{}^{}\mathrm{Th}$ are in agreement with recent measurements of parity nonconservation effects in neutron capture. In fact, our calculations prove that the factor of dynamical enhancement (ratio of compound-nucleus effect to single-particle one) really exceeds 100, thus making it unnecessary to assume a value of the weak constant bigger than standard one (g≃${10}^8$ε∼1–4).