We study a ring-diagram approach for nuclear matter where the particle-particle and hole-hole ring diagrams are calculated to all orders via a random-phase-approximation equation. This equation is found to have complex eigenvalues within a small temperature-density region, and our results suggest that this occurrence of complex eigenvalues may be a useful signal for nuclear-matter phase transitions. With a slightly modified Gogny interaction, our ring-diagram nuclear-matter calculations give ${\rho }_0=0.17\mathrm{}{\mathrm{fm}}^{-3\mathrm{}}$, $\frac{E_0}{A}=-15.9\mathrm{}$ MeV, $K=127\mathrm{}$ MeV, and the liquid-gas critical temperature $T_c=7.6\mathrm{}$ MeV.

Several rotational-band structures have recently been observed in mass $A\simeq 130$ nuclei, built on multiquasiparticle states of enhanced quadrupole deformatin, the so-called superdeformed states $\beta \simeq 0.4$. In ${}_{}{}^{137}{}_{}{}^{}\mathrm{Sm}$, a decoupled band built on the ${\mathrm{vi}}_{\frac{13}{2}}\mathrm{}\left[660\right]\mathrm{}{\frac{1}{2}}^{+}$ single-quasineutron orbital, intruding from two oscillator shells above with a predicted $\beta \simeq 0.35$, was observed to low spin and excitation energy. The role of this $\beta$-driving ${\mathrm{vi}}_{\frac{13}{2}}$ orbital, which showed a 50% enhanced moment of inertia, is discussed in terms of the superdeformation in this mass region.

States in ${}_{}{}^{154}{}_{}{}^{}\mathrm{Dy}$ have been located up to $I^{\pi }={48}^{+}$ and their lifetimes measured. Marked structural changes occur along the yrast line with a transition from prolate to oblate shape, followed by an unexpected return to moderate collectivity at the highest spins. Structural changes with increasing energy above the yrast line are also observed.

We investigate the utility of the $K^{+}$ meson as a probe of effective-size modifications ("swelling") of nucleons in the nuclear medium. The $K^{+}$-nucleus elastic and total cross sections are found to be sensitive to the density-dependent effective masses of the vector mesons ($\rho ,\omega$) whose exchange is responsible for the dominant part of the low-energy $K^{+}$-nucleon interaction. This density dependence is estimated in several ways and used to construct a $K^{+}$-nucleus optical potential. Such a model is consistent with the $K^{+}+{}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ data at 800 Mev/c, and provides a physical picture of the "swelling" mechanism in terms of the medium modifications of the meson cloud of the nucleon.

We measured the differences in $R=\frac{{\sigma }_L}{{\sigma }_T}$ and the cross-section ratio $\frac{{\sigma }^A}{{\sigma }^D}$ in deep-inelastic electron scattering from D, Fe, and Au nuclei in the kinematic range $0.2\le x\le 0.5$ and $1\le Q^2\le 5$ ${(\mathrm{G}\mathrm{e}\mathrm{v}/\mathit{c})}^2$. Our results for $R^A-R^D$ are consistent with zero for all $x$ and $Q^2$, indicating that possible contributions to $R$ from nuclear higher-twist effects and spin-0 constituents in nuclei are not different from those in nucleons. The European Muon Collaboration effect is reconfirmed, and the low-$x$ data from all recent experiments, at all $Q^2$, are now in agreement.

A search for nuclear-bound states of the $\eta$ meson has been carried out. Targets of lithium, carbon, oxygen, and aluminum were placed in a ${\pi }^{+}$ beam at 800 MeV/c. A predicted $\eta$ bound state in ${}_{}{}^{15}{}_{}{}^{}\mathrm{O}_{}^{*}{}_{}{}^{}\left(E_x\approx 540 \mathrm{MeV}\right)$ with a width of ≅ 9 MeV was not observed. A bound state of a size ⅓ of the predicted cross section would have been seen in this experiment at a confidence level of $3\sigma \mathrm{}(P>\mathrm{}0.9987\mathrm{})\mathrm{}$.

Projectile fragmentations of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^8{}_{}{}^{}\mathrm{He}$, and ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ have been measured at 0.79 GeV/nucleon. Production cross sections and momentum distributions of the produced isotopes ($Z\ge 2$) are measured inclusively. Transverse-momentum distributions of ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$ from the fragmentation of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ show two Gaussian components of different widths. The width of the wide component is consistent with the values observed in the fragmentation of stable nuclei, whereas the other component shows an extremely narrow width reflecting the weak binding of the two outer neutrons in the ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ nucleus.

The neutron decay of the giant monopole resonance region between 13 and 15 MeV in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ is analyzed in terms of collective and statistical doorway states. The direct escape widths of the giant monopole resonance populating the lowest five valence hole states of ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$ are determined, and compared with the results obtained from complex collective states. This comparison discriminates sharply between different model Hamiltonians which predict similar energies and collectivities for the resonance.

We report the application of a new nonoptical detection scheme in laser spectroscopy on ion beams of on-line isotope separators. The method consists of ground-state depopulation by optical pumping in collinear laser-ion-beam interaction, state-selective neutralization, and charge-state-separated fast-atom counting. Strontium isotope-shift measurements are extended into the strongly deformed region of the neutron-rich isotopes up to ${}_{}{}^{100}{}_{}{}^{}\mathrm{Sr}$. The radii are generally well described by the droplet model including empirical deformatins obtained from $B\left(E2\mathrm{}\right)\mathrm{}$ values.

We have studied the $\beta$ decays of ${}_{}{}^{60}{}_{}{}^{}\mathrm{Co}$ at times $\lesssim {10}^{-4\mathrm{}}{t}_{\frac{1}{2}}$ and those of ${}_{}{}^{56}{}_{}{}^{}\mathrm{Mn}$ over the interval $0.3t_{\frac{1}{2}}\le t\le 45t_{\frac{1}{2}}$ to search for proposed deviations from the exponential decay law at short and long times, respectively. Over all time periods examined, our data are consistent with purely exponential behavior. From these measurements, stringent limits are derived on the amplitudes of possible deviations from the exponential decay law.

The theoretical estimates of the $P$-conserving $T$-invariance violation in neutron transmission are reexamined. It is shown that the previously omitted factors of dynamical enhancement caused by the $T$-nonconserving interaction of the two closely lying resonances might sum up to an overall amplification of the effect by 3-5 orders of magnitude.

It is shown within the Hartree-Fock method with the Skyrme force that the quadrupole-quadrupole neutron-proton interaction gives the leading term in the nuclear deformation energy. The quadrupole-quadrupole coupling constants are derived and shown to agree with those obtained within the simple harmonic-oscillator model.

Using a thin stack of glass detectors to measure $\frac{Z}{\beta }$ of forward-projected fast fragments from interactions of 900-MeV/nucleon ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ nuclei, we measure a cross section of 35 ± 8 mb for charge pickup ($\Delta Z=+1\mathrm{}$) from Au to Hg, and we infer a mean velocity downshift $\delta \beta \approx -0.004\mathrm{}$ and a mean momentum downshift $\delta p_{\parallel }\approx -6\mathrm{}$ GeV/c for Au to Hg, 2 orders of magnitude larger than observed for charge pickup by light nuclei. Implications of this result are discussed.

In deformed Hartree-Fock calculations with Skyrme interactions, a near degeneracy of the intrinsic state energies of $n$-particle, $n$-hole ($n\mathrm{p}-n\mathrm{h}$) deformed states with differing $n$ has been obtained. For example, in ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ the 8p-8h intrinsic state energy is close to but even lower than that of the 4p-4h deformed state. Whether there is an underlying symmetry to explain this near degeneracy has yet to be determined.

The production of the $\frac{J}{\psi }$ resonance in 125-GeV/c $\overline{p}$ and ${\phi }^{-}$ interactions with Be, Cu, and W targets has been measured. The cross section per nucleon for $\frac{J}{\psi }$ production is suppressed in W interactions relative to the lighter targets, especially at large values of Feynman $x$, which is opposite to the expectation from the various explanations of the European Muon Collaboration effect. Models incorporating modifications of the gluon structure functions in heavy targets show qualitative agreement with the data.

The apparent characteristic temperature observed in the fragmentation of highly excited nuclei is studied by calculations using a simple model consisting of an expanding and emitting source. A characteristic temperature for emission, nearly independent of the initial temperature, is found in the calculations, and the underlying physics is interpreted. This temperature is consistent with the values found in experiments which seem independent of bombarding energy.

At moderate temperatures in nuclei (≅0.5 MeV), there is evidence for damping effects in the rotational behavior. Instead of normal rotational bands, each state can emit any one of a distribution of $\gamma$-ray energies whose FWHM is called the damping width. At higher temperatures, there are expected to be motional narrowing effects, where the damping widths decrease with further increases in temperature. We do not find such a narrowing in the experimental damping widths.

This paper reports the first demonstration of nuclear orientation of radon atoms. The method employed was spin exchange with potassium atoms polarized by optical pumping. The radon isotopes were produced at the ISOLDE isotope separator of CERN. The nuclear alignment of ${}_{}{}^{209}{}_{}{}^{}\mathrm{Rn}$ and ${}_{}{}^{223}{}_{}{}^{}\mathrm{Rn}$ has been measured by observation of $\gamma$-ray anisotropies and the magnetic dipole moment for ${}_{}{}^{209}{}_{}{}^{}\mathrm{Rn}$ has been measured by the nuclear-magnetic-resonance method to be $\left|\mu \mathrm{}\right|=0.83881\left(39\mathrm{}\right)\mathrm{}{\mu }_N$.

The coincidence cross section for the two-body breakup of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ has been determined up to recoil momenta of 350 MeV/c with the ($e,e^{\prime }p$) reaction. The momentum probability distribution for the $t+p$ final state deduced from the cross section is compared to theoretical predictions that include correlations. A substantial deviation from the impulse approximation is observed, which cannot fully be explained by final-state interaction effects and contributions due to charge exchange.

We report the results of an experimental search for double-$\beta$ decay of ${}_{}{}^{100}{}_{}{}^{}\mathrm{Mo}$. No evidence is found for the decay mode with majoron emission, yielding a half-life limit of 3.3×${10}^{20}$ yr with 90% confidence. We also obtain a lower limit for the two-neutrino mode of 3.8×${10}^{18}$ yr.