The longitudinal relaxation rate of ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$ nuclear spins slows down substantially in an external magnetic field of about 100 G. From an analysis of the magnetic slowing down and of the dependence of the zero-field relaxation rates on the third-body pressure, the authors have deduced the magnitudes of the spin-rotation and spin-exchange interactions in the ${\mathrm{Rb}}^{129}$Xe molecule, as well as the formation and breakup rates of RbXe in ${\mathrm{N}}_2$ gas and the dissociation constant of RbXe. The magnetic slowing down shows directly that binary collisions contribute no more than a few percent to the relaxation rates.

The bifurcations to periodic and chaotic states in an all-optical bistable system proposed by Ikeda et al. have been observed. A single-mode optical fiber was used as a nonlinear medium in a ring cavity. The incident beam was the second harmonic of a pulse train from an actively mode-locked and $Q$-switched yttrium-aluminum-garnet laser whose cavity length was equal to one-half that of the ring cavity. The bifurcation to period-two state was clearly observed at a certain level of the incident power, and further increase in power resulted in a chaotic state.

The innovation of adding a beam prebunching section at the input to the cavity of a millimeter-wave gyrotron oscillator has yielded outstanding improvements in mode control and device efficiency. These results constitute a technological breakthrough which greatly improves prospects of developing gyrotrons with megawatt average power ratings as will be required for bulk heating of plasma in controlled thermonuclear reactors.

High-frequency acoustic phonons in an ${\mathrm{Al}}_2$${\mathrm{O}}_3$ crystal at low temperature were generated at one frequency (891 GHz) by excitation of ${\mathrm{V}}^{4+}$ impurity ions with a far-infrared laser, and detected at another frequency (874 GHz) by fluorescence from ${\mathrm{Cr}}^{3+}$ ions. A strong detector signal was observed, giving evidence that inelastic phonon scattering occurred. The dependence on magnetic field and temperature indicated that the effect was due to Raman scattering of phonons by spin states.

The 7 × 7 reconstruction on Si(111) was observed in real space by scanning tunneling microscopy. The experiment strongly favors a modified adatom model with 12 adatoms per unit cell and an inhomogeneously relaxed underlying top layer.

Stage-1 Eu-intercalated graphite Eu${\mathrm{C}}_6$ was studied by Mössbauer and $L$-edge spectroscopy. Isomer shift and $L_{\mathrm{III}}$-edge position results indicate the divalent state for Eu. Below 40 K, Eu${\mathrm{C}}_6$ orders antiferromagnetically with the Eu spins oriented perpendicular to $\overrightarrow{\mathrm{c}}$ and a magnetic hyperfine field saturating at - 10.7 T. The large electric field gradient at the Eu site (-1.4×${10}^{18}$ V/${\mathrm{cm}}^2$), with axis parallel to $\overrightarrow{\mathrm{c}}$, is consistent with the structure of Eu${\mathrm{C}}_6$ and a partial charge transfer from Eu to the C planes.

Direct evidence has been obtained for electron tunneling between sputtered ${\mathrm{Cs}}^{+}$ ions and the solid surfaces from which they originate. Strong neutralization of the ${\mathrm{Cs}}^{+}$ ions is observed whenever the tunneling channel is opened by changing the surface work function so that a crossing of the Fermi level by the Cs $6s$ level occurs. A tunneling model which takes the spatial dependences of the position and the width of the atomic level into account explains the data successfully.

The free energy of bcc, fcc, and hcp iron has been calculated as a function of temperature and pressure within the single-site spin-fluctuation theory of band magnetism, which has been developed recently by Hubbard and Hasegawa. The simple theory can account for the occurrence of the $\alpha$, $\gamma$, $\delta$, and $\epsilon$ phases in the $T-P$ phase diagram of iron, the phase transitions being driven by the magnetic contributions to the free energy.

A four-dimensional system of nonlinear difference equations describing the evolution of the general relativistic "mixmaster" cosmological model is studied. The evolution splits into two parts: one given by a (chaotic) generalized Baker's transformation and the other by a (systematic) change of scales. The chaotic degrees of freedom are studied in detail: Their evolution may be described by a two-sided shift and the invariant measure for these variables is found. Strong ergodic properties (mixing, nonzero entropy) are deduced.

The Bogoliubov-Valatin variational method is used to show analytically that the chiral-invariant vacuum is unstable for a color, fourth-component vector linear potential. The physical origin of the instability is the fermion self-energy, which is negative and overcomes the positive potential energy, destabilizing the vacuum by pair condensation.

The mean free path of a nucleon for two colliding nuclei has been calculated in terms of the imaginary part of the optical potential and the $k$ effective mass. The energy range 10-30 MeV/nucleon appears to be optimum for mean free paths in the range 3-4 fm.

Precise observation of the ratio $\frac{P_{\mathrm{F}}}{P_{\mathrm{GT}}}$ of beta polarizations for Fermi and Gamow-Teller decays can provide stringent constraints on electroweak models. The result of a first measurement, with a Bhabha polarimeter of novel design, is $\frac{P_{\mathrm{F}}}{P_{\mathrm{GT}}}=0.986\mathrm{}\pm 0.038$. Resulting bounds, being comparable to those from existing muon polarization experiments, are limited by statistics. Precision of order ${10}^{-3\mathrm{}}$ or better may be anticipated with an extended system.

Three-body dynamics for the ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ ground states are used for the first time to investigate the shell structure of these nuclei. Shell orbital probabilities, configuration-space single-particle orbital densities, and two-particle wave-function amplitudes in $j-j$ coupling are calculated. The predicted orbital probabilities differ significantly from shell-model values except for those with core excitation. The need in shell models for core excitation may actually reflect required three-body dynamical effects.

High-transverse-energy events produced in proton-nucleus collisions at 400 GeV/c were studied with use of the Fermilab multiparticle spectrometer. The cross sections for such interactions increase more rapidly than the atomic mass number for both small- and large-acceptance data. The nuclear events are less planar than the corresponding high-transverse-energy $\mathrm{pp}$ events.

Electron scattering data have been used to obtain transition charge densities for the low-lying $E2\mathrm{}$ transitions in ${}_{}{}^{88}{}_{}{}^{}\mathrm{Sr}$, ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$, and ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$. These charge densities show a characteristic shape indicative of their microscopic constituency, modified by core-polarization effects. A good description of transitions in the even-even nuclei is obtained by using the measured single-particle transitions in ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$ as effective densities.

The tensor analyzing power $T_{20}$ for $d-p$ elastic scattering at or near ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}=180\mathrm{}°$ has been measured at sixteen deuteron beam energies between 0.3 and 2.3 GeV. In marked disagreement with earlier work, large negative values ($\left|T_{20}\right|>\mathrm{}0.6\mathrm{}$) are found at all energies in this range, with a dip to $T_{20}=-1.25\mathrm{}$ at $T_d=0.5\mathrm{}$ GeV. The present results are compared with various model calculations.

Kinematic shifts of $\alpha$ particles from the $\beta$-delayed particle decay of ${}_{}{}^{20}{}_{}{}^{}\mathrm{Na}$ were measured in a coincidence experiment. $\beta -\nu -\alpha$ triple correlation coefficients were determined. Limits on isospin mixing amplitudes were deduced for states in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$. The vector weak-coupling constant was deduced from the superallowed $J^{\pi }=2^{+}\to 2^{+}$ $\beta$ decay of ${}_{}{}^{20}{}_{}{}^{}\mathrm{Na}$ to be ${G_V}^{\prime }=(1.365\mathrm{}\pm 0.037)\times {10}^{-49\mathrm{}}$ erg ${\mathrm{cm}}^3$.

Secondary ions ${\left[{\left(\mathrm{CsI}\right)}_n\mathrm{Cs}\right]}^{+}$, with $n$ up to ∼ 40, were produced by 8-keV ${\mathrm{Cs}}^{+}$ bombardment of CsI. The yield of clusters decreased smoothly with $n$ when observed in a time-of-flight mass spectrometer at effective times ∼ 0.2 μs after emission. Clusters with $n>\mathrm{}7\mathrm{}$ were found to be metastable, with lifetimes ≪ 100 μs. A large anomaly in the population of the disintegration products was measured at ∼ 70 μs after emission, $n=13\mathrm{}$ clusters being favored and $n=14\mathrm{} \mathrm{and} 15$ suppressed.

A quantum action variable is defined in the context of a quantum Hamilton-Jacobi theory. The action variable can be used to find the exact bound-state energy levels of a quantum system without solving an equation of motion for the system wave functions.

The impact-parameter dependence of the quasimolecular $K$ x rays emitted in collisions of 10-MeV ${\mathrm{Cl}}^{16+}$ with Ar has been measured. The coincidence spectra show a clear impact-parameter-dependent structure. The results are in good agreement with dynamical calculations which take into account the interference between the $1s\sigma$ decay amplitudes in the incoming and the outgoing halves of the trajectory.