The weak $4_2^{+}$→$2_3^{+}$ transition in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ was observed with a branching ratio (0.30±0.08)%, using the ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}(\alpha ,\gamma ){}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ radiative-capture reaction at $E_{\alpha }=1.14\mathrm{}$ MeV. The corresponding $B(E2:4_2^{+}\to 2_3^{+})=5.7\mathrm{}\pm 1.9$ Weisskopf unis appears noncollective, and serves as a crucial test of microscopic models predicting collective band structures and enhanced $E1\mathrm{}$ decays in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$; it is smaller by a factor of 3-8 than predictions of such models, and cannot be reproduced by the well-established coexistence model for ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, suggesting that our understanding of collective motion in light nuclei is incomplete. We review recent suggestions for extending coexistence models.

The method of scaled factorial moments is used to study short-range fluctuations in the pseudorapidity distributions of particles produced in high-energy interactions in nuclear emulsion. An intermittent behavior of the fluctuations is clearly observed in both proton (200 and 800 GeV) and oxygen (60 and 200 GeV/nucleon) beam interactions in emulsion.

The observed differences in kinetic and chemical temperatures in heavy-ion reactions is addressed by means of a computer simulation. Focusing on ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ nuclei emitted at wide angles, we find that the chemical temperatures show no strong variation with laboratory bombarding energy between 35 and 100 MeV/nucleon. Further, the chemical temperature is found to be in the 3—4-MeV range, much lower than the kinetic temperature and consistent with experiment. The difference in the two temperatures is established after a fairly short time scale roughly corresponding to the breakup time of the reaction region.

The evolution of the $\gamma$ quasicontinuum spectrum with neutron number has been investigated in the sequence of isotopes ${}_{}{}^{152,154,156}{}_{}{}^{}\mathrm{Dy}$. The three nuclei display a pronounced collective $E2\mathrm{}$ component. In ${}_{}{}^{154}{}_{}{}^{}\mathrm{Dy}$ this component shows a splitting into two distinct parts, signifying a structural change along the $\gamma$ cascade above the yrast line. The $E2\mathrm{}$ and statistical components are reproduced in simple $\gamma$-cascade calculations; in ${}_{}{}^{152}{}_{}{}^{}\mathrm{Dy}$ and ${}_{}{}^{156}{}_{}{}^{}\mathrm{Dy}$ only rotational bands are included, whereas in ${}_{}{}^{154}{}_{}{}^{}\mathrm{Dy}$ additional vibration-like transitions are required to reproduce the two $E2\mathrm{}$ peaks.

Using the relativistic light-cone description of the two-nucleon system we argue that experimental confirmation of the recently observed structure in the deuteron magnetic form factor at $Q^2\approx 2$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ would provide new independent evidence in favor of the dominant role of nucleonic degrees of freedom in the deuteron.

The longitudinal response function for quasielastic electron scattering from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ at a momentum transfer $q=550\mathrm{}$ MeV is calculated in a relativistic random-phase approximation (RPA). The particle-hole response is calculated exactly in the finite system, while vacuum-polarization effects are included in a local-density approximation. The RPA result with vacuum polarization is about 25% below the Hartree response and comparable to Saclay data.

We present the first quantitative study of the final-state-interaction effect in the missing-energy spectrum measured in a coincidence ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(e, e^{\prime }p)$ experiment in the dip region. It is found that the calculated cross section for the two-body type of final-state interaction is very small compared with the data. Furthermore, it decreases with increasing missing energy; this qualitative behavior does not agree with the data. From a qualitative investigation, the presence of the many-body mechanism involving more than two nucleons is suggested.

The cross sections for the fusion reaction ${}_{}{}^{128}{}_{}{}^{}\mathrm{Te}({}_{}{}^{12}{}_{}{}^{}\mathrm{C}, 3n){}_{}{}^{137}{}_{}{}^{}\mathrm{Ce}$ were measured from $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=34.5\mathrm{} \mathrm{to} 50$ MeV by observing the decay of the ground ($J^{\pi }={\frac{3}{2}}^{+}$, $t_{\frac{1}{2}}=9.0\mathrm{}$ h) and isomeric (${\frac{11}{2}}^{-}$, 34.4 h) states in ${}_{}{}^{137}{}_{}{}^{}\mathrm{Ce}$. The isomer ratio decreases rapidly from a value of ≃34 at 47 MeV to an essentially constant value of ≃1.5 below 38 MeV. This confirms the prediction of an approximately constant value for the average angular momentum for fusion of heavy ions at energies well below the fusion barrier.

The mass splits in the fission decays of giant $E1\mathrm{}$, $\frac{E2\mathrm{}}{E0\mathrm{}}$, and $E3\mathrm{}$ multipole resonances have been studied in ${}_{}{}^{235,238}{}_{}{}^{}\mathrm{U}(e, e^{\prime }f)$ coincidence experiments. The fission width ratios $\frac{{\Gamma }_S}{{\Gamma }_A}$ have been determined as functions of excitation energy for separated multipoles. The isoscalar gaint $E2\mathrm{}$ resonances show a larger symmetric contribution than the $E1\mathrm{}$ and $E3\mathrm{}$ resonances.

A parameter-free method is proposed for the analysis of transfer reactions leading to an unbound three-body final state. The three-body dynamics are treated in the adiabatic approximation. The technique is applied successfully to new data for the ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}({}_{}{}^3{}_{}{}^{}\mathrm{He}, pp){}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ reaction.

The excitation of the isovector giant dipole resonance by inelastic scattering of 120-MeV $\alpha$ particles has been studied with the ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}(\alpha , {\alpha }^{\prime }, \gamma ){}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ reaction for $0°\le {\theta }_{{\alpha }^{\prime }}\le 3°$. The $\gamma$-decay branching ratio to the ground state, extracted from the coincidence data, indicates that not more than (12±4)% of the observed singles resonance cross section around 13.6 MeV in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ can be due to isovector dipole excitation.

The potential-energy-surface concept of the generalized collective model is given a shell-model interpretation. For deformation less than the equilibrium value, $\beta <{\beta }_0$, the shape of the potential is related to intrashell dynamics while the sharp rise for $\beta >{\beta }_0$ is shown to be an intershell phenomenon that depends on competition between major shell excitation energies and the binding energy of the residual interaction. The exclusion principle plays an essential role in the argument. Results for ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ illustrate the necessity of an open-shell picture.

In the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(e, e^{\prime }d){}_{}{}^{10}{}_{}{}^{}\mathrm{B}$ the lowest-lying $T=1\mathrm{}$ state in ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$ is found to be as strongly excited as the $T=0\mathrm{}$ ground state of ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$, although the transition to the $T=1\mathrm{}$ state is isospin forbidden for direct deuteron knockout. A mechanism integration of a $p-n$ pair in a relative $T=1\mathrm{}$ state into a deuteron is proposed to explain this result. This new proposed mechanism is consistent with both the observed purely transverse character of the transition and the momentum-transfer dependence of the cross section.

We calculate angular correlations between coincident electron-positron pairs emitted in heavy-ion collisions with nuclear time delay. Special attention is directed to a comparison of supercritical and subcritical systems, where angular correlations of pairs produced in collisions of bare U nuclei are found to alter their sign for nuclear delay times of the order of 2 × ${10}^{-21\mathrm{}}$ s. This effect is shown to occur exclusively in supercritical systems, where spontaneous positron creation is active.

We propose a unified theory of nuclear level densities, encompassing both spherical and deformed nuclei, using the static-path approximation. The theory appears numerically tractable for a pairing-plus-quadrupole Hamiltonian.

Two-proton correlations were measured as a function of the total energy and relative momentum of the protons. The correlation is analyzed for different orientations of the relative momentum, which allows information on the size and lifetime of the emission source to be extracted. The most energetic particles are emitted from a short-lived source of compound-nucleus dimensions while the lower-energy protons appear to be emitted from a source considerably larger than the compound nucleus.

We have measured the differential cross section for two-body deuteron photodisintegration at ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}=90\mathrm{}°$ and for photon energies between 0.8 and 1.6 GeV. At energies above ≃ 1.2 GeV, the data appear to obey a simple scaling law predicted by constituent-counting rules assuming parton degrees of freedom for the deuteron and nucleons. Agreement with model calculations based on meson exchange or "reduced nuclear amplitudes" is discussed.

We perform an analysis of exclusive heavy-ion reactions around 100 MeV/nucleon in terms of multipole moments of the momentum distribution of nucleons. Numerical calculations based on the Boltzmann-Uehling-Uhlenbeck theory are presented and compared to an approximate scaling function. We find that nuclei completely stop each other even at 100 MeV/nucleon, if $A_P+A_T>200\mathrm{}$ in symmetrical central collisions. We propose that the mass dependence of the quadrupole momentum tensor can be used to determine the nuclear compressibility.

Local deviations from the Grodzins systematics for the product $E\left(2^{+}\right)B\left(E 2\right)$ are observed in several light Ra-Th nuclei. We note an abrupt increase to 5.5% of the isoscalar $E 2$ energy-weighted sum rule, almost a factor of 2 above the value typically found near shell closures and equal to the value found in the very deformed actinides. This indicates mixing of a low-lying deformed state into the ground state of the light Ra-Th nuclei, as expected for a low-lying cluster state. Evidence for mixing of a deformed state is also present in the rms radii and binding energies of these nuclei.

We have studied the fragmentation of 6.4-TeV ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ nuclei in Pb, Cu, and Al targets. For Pb, the electromagnetic spallation cross sections are larger than the nuclear cross sections. For Pb and Cu the electromagnetic cross sections decrease with projectile charge loss $\Delta Z$ as $\sim \exp \left(0.6\mathrm{}\Delta Z\right)$ and show a dependence on target charge consistent with $\sim Z_T^{1.8}$ as predicted by theory.