High-momentum components of proton momentum distributions in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ have been studied from 300 to 500 MeV/c with the ($e,e^{\prime }p$) reaction. Cross sections were measured with 180 keV excitation-energy resolution for transitions to the low-lying ${\mathrm{½}}^{+}$, ${\frac{3}{2}}^{+}$, ${\frac{11}{2}}^{-}$, ${\frac{5}{2}}^{+}$, and ${\frac{7}{2}}^{+}$ states in ${}_{}{}^{207}{}_{}{}^{}\mathrm{Tl}$. The data are compared to distorted-wave impulse-approximation calculations with mean-field wave functions and with wave functions that include nucleon-nucleon correlations. The data are substantially larger than mean-field predictions. The observed excess strength at low excitation energy appears to be mainly due to long-range correlations and not to short-range and tensor correlations.

Event shapes for Au + Au collisions at 11.4 GeV/c per nucleon were studied over nearly the full solid angle with the E877 apparatus. The analysis was performed by Fourier expansion of azimuthal distributions of the transverse energy ($E_T$) measured in different pseudorapidity intervals. For semicentral collisions a pronounced event anisotropy is identified with a clear forward-backward anticorrelation. In the forward pseudorapidity interval up to 9% of the $E_T$ is in a directed component. The signal decreases for peripheral and very central collisions.

We calculate the low-momentum $N-N$ effective potential obtained in the one-boson exchange approximation, inside a nuclear plasma at finite temperature, as described by the relativistic $\sigma -\omega$ model. We analyze the screening effects on the attractive part of the potential in the intermediate range as density or temperature increases. In the long range the potential shows Friedel-type oscillations instead of the usual exponential damping. These oscillations arise from the sharp edge of the Fermi surface and should be encountered in any realistic model of nuclear matter.

The Eurogam-1 array has been used to study $\gamma$ rays emitted following the spontaneous fission of a ${}_{}{}^{248}{}_{}{}^{}\mathrm{Cm}$ source. Yrast level schemes for the neutron-rich nuclei ${}_{}{}^{152,154,156}{}_{}{}^{}\mathrm{Nd}$ have been constructed. The stopping of the Nd fragments in the source material leads to Doppler-broadened line shapes for those states that have lifetimes comparable to the stopping time. This paper describes the first measurements of lifetimes of medium-spin states in very neutron-rich nuclei obtained from the analysis of these line shapes. The transition quadrupole moments for the yrast states in the spin range $\mathrm{}(10-16)\mathrm{}\hslash$ have been deduced to be 5.88 ± 0.08 e b (${}_{}{}^{152}{}_{}{}^{}\mathrm{Nd}$), 5.75 ± 0.10 e b (${}_{}{}^{154}{}_{}{}^{}\mathrm{Nd}$), and 5.33 ± 0.16 e b (${}_{}{}^{156}{}_{}{}^{}\mathrm{Nd}$).

The angular momenta and parities of the low-lying states of ${}_{}{}^{132}{}_{}{}^{}\mathrm{Sn}$ have been firmly determined through studies of the $\beta$ decay of ${}_{}{}^{132}{}_{}{}^{}\mathrm{In}$. The lowest lying state with a negative parity is shown to have a collective octupole character. Several particle-hole multiplets have been identified, including the lowest lying proton excitation. More than about 20% of the theoretically estimated bound states of ${}_{}{}^{132}{}_{}{}^{}\mathrm{Sn}$ have been identified.

Experiment E858 at the Brookhaven National Laboratory Alternating Gradient Synchrotron has recently reported the detection of two antideuterons produced in $14.6A$ GeV/c Si + Au collisions. The data were interpreted as implying antideuteron production rates about an order of magnitude below expectations. We use an extended RQMD model to demonstrate that the antideuteron yields are readily explained in a dynamical scenario that includes collective expansion and strong antinucleon absorption.

The preliminary results for the single-photon spectrum obtained by the WA80 collaboration are analyzed. The data are well described by a scenario where a thermalized quark-gluon plasma is formed initially, which expands, cools, hadronizes, and undergoes a freeze-out. It is also seen that the data do not seem to favor the scenario where the matter is initially formed in a hot hadronic phase, which cools and undergoes freeze-out and does not involve a phase transition.

We point out a simple relation between the nuclear vertex constant (NVC) and the overall normalization of the astrophysical $S$ factor. Using predicted values of the NVC for the virtual decay of ${}_{}{}^8{}_{}{}^{}\mathrm{B}\to {}_{}{}^7{}_{}{}^{}\mathrm{Be}+p$ we find $S_{17}\mathrm{}\left(0\right)\mathrm{}\approx 17.6$ eVb for ${}_{}{}^7{}_{}{}^{}\mathrm{Be}{(p,\gamma )}^8\mathrm{B}$ reactions, consistent with the low values extrapolated from direct capture measurements by Filippone et al. and by Vaughn et al. New possibilities, using proton transfer reactions, to measure the astrophysical $S$ factor indirectly are proposed.

A dynamical model has been developed to study the evolution of a quark-gluon system towards equilibrium with the gluons equilibrating prior to the quarks and the quarks executing random Brownian motion in the gluonic heat bath. We estimate the thermalization times for various quark flavors and heavy flavor production rates within this model.

Recent interpretations of $K^{\pi }=4^{+}$ bands as double-$\gamma$ phonons in even-even nuclei of the deformed rare earth region are shown to be in serious conflict with single-nucleon-transfer results and other data. The main argument for the double-$\gamma$-phonon interpretation, the existence of large $B\left(E2\mathrm{}\right)\mathrm{}$ values connecting the $K^{\pi }=4^{+}$ bands with gamma bands, and all other available data, including $E4\mathrm{}$ strengths, single-nucleon-transfer results, allowed $\beta$ decays, etc., are explained if the $4^{+}$ bands are predominantly hexadecapole vibrations, or $g$-boson structures.

We study intrinsic aspects of quadrupole collectivity with conserved isospin in the framework of the interacting boson model (IBM-3) of nuclei. A geometric visualization is achieved by means of a novel type of intrinsic states which are deformed in angular momentum yet have well-defined isospin. The energy surface of the general IBM-3 Hamiltonian is derived, and normal modes are identified for prolate deformations.

Extending the field of spectroscopy to very neutron-rich heavy nuclei has been impaired by reaction $Q$ values that consistently favor the formation of the lighter isotopes. Radioactive beams offer a chance to overcome this difficulty. We carry out a systematic study of cross sections for multinucleon transfer processes in order to determine the actual neutron excess in the projectiles that is needed to revert the aforementioned tendency. This identification, supplemented by quantitative predictions for the production yields, provide concrete guidelines for the selection of reaction partners and bombarding conditions.

We study the behavior of a finite classical system in the instability region. The equation of state of such a system resembles that of nuclear matter. Through a study of mass distributions, scaled factorial moments, and anomalous fractal dimensions, we provide evidence of the presence of critical behavior of our system. Such behavior can be understood by use of the droplet model of the liquid-gas phase transition.

An exclusive study of the hard photon production in the reaction ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$+${}_{}{}^{51}{}_{}{}^{}\mathrm{V}$ at 44 MeV/nucleon has been carried on with the $4\pi$ multidetector MEDEA. An anticorrelation effect in the emission of very energetic photons and protons has been observed for the first time. This is a strong indication for the first-chance $n-p$ bremsstrahlung production mechanism.

Inelastic proton scattering to the first excited $2^{+}$ state of the doubly magic ${}_{}{}^{56}{}_{}{}^{}\mathrm{Ni}$ nucleus was investigated in inverse kinematics, using a secondary beam of radioactive ${}_{}{}^{56}{}_{}{}^{}\mathrm{Ni}$ nuclei. At an incident energy of 101 MeV/nucleon, a value $B(E2,0^{+}\to 2^{+})=600\mathrm{}\pm 120 e^2$ ${\mathrm{fm}}^4$ was measured. This result completes the set of experimental data for the first excited $2^{+}$ states in the $1f-2p$ shell with a closed shell of neutrons or protons. These data are compared to recent shell-model calculations.

Using reverse kinematics, we have studied the breakup of $1.0A$ GeV gold nuclei incident on a carbon target. The detector system permitted exclusive event reconstruction of nearly all charged reaction products. The moments of the resulting charged fragment distribution provide strong evidence that nuclear matter possesses a critical point observable in finite nuclei. We have determined values for the critical exponents $\gamma$, $\beta$, and $\tau$. These values are close to those for liquid-gas systems and clearly different than those for 3D percolation and the liquid-gas mean field limit.

By colliding ultrarelativistic ions, one achieves energy densities close to the critical value for the formation of a quark-gluon plasma. We introduce a percolation approach to model the final stage ($\tau >1\mathrm{}$ fm/c) of ion-ion collisions, the initial stage being treated by well-established methods, based on strings and Pomerons. The percolation approach amounts to finding high density domains, and treating them as quark-matter droplets. In this way, we have a realistic, microscopic, and Monte Carlo-based model which allows for the formation of quark matter. We find that even at CERN SPS energies large quark-matter droplets are formed—at a low rate though. Large quark-matter droplets are formed due to geometrical fluctuation, but not in the average event.

High resolution $\gamma -\gamma$ and $\gamma -\gamma -\gamma$ coincidences in the spontaneous fission of ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ were measured. Relative yields and neutron multiplicities from zero up to 10 were extracted directly for the first time in fission for the Zr-Ce and Mo-Ba correlated fragment pairs. The 0, 8, and the new 10 neutron emission yields for Mo-Ba are significantly larger than those reported previously for total ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ spontaneous fission. Our results demonstrate that the use of this high resolution $\gamma -\gamma -\gamma$ coincidence technique can provide important, previously inaccessible data on fission.

We evaluate the contribution to the nucleon-nucleon interaction due to correlated $\pi \rho$ exchange by means of dispersion-theoretic methods based on a realistic meson-exchange model for the interaction between a $\pi$ and a $\rho$ meson. This process has a substantial effect; in the pionic channel it counterbalances the suppression of the one-pion-exchange potential due to a realistic, soft $\pi \mathrm{NN}$ form factor.

Measurements have been made of ${\pi }^{+}$ absorption on ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ at $T_{\pi +}=118,162, \mathrm{and} 239$ MeV using the Large Acceptance Detector System. The nearly $4\pi$ solid angle coverage of this detector minimizes uncertainties associated with extrapolations over unmeasured regions of phase space. The total absorption cross section is reported. In addition, the total cross section is divided into components in which only two or all three nucleons play a significant role in the process. These are the first direct measurements of the total and three nucleon absorption cross sections.