Inverted population distribution between $\Lambda$-doublet states of OH produced in the reaction H + N${\mathrm{O}}_2$ → OH + NO has been observed in a beam maser and in a molecular-beam electric-resonance spectrometer. The observed inversions are of the order of 4-6% for the ${}_{}{}^2{}_{}{}^{}\Pi _{\frac{3}{2}}^{}{}_{}{}^{}$, $J=\frac{3}{2}, \frac{5}{2}, \frac{7}{2}$, and the ${}_{}{}^2{}_{}{}^{}\Pi _{\frac{1}{2}}^{}{}_{}{}^{}$, $J=\frac{1}{2}$ states, and less than 1% for the ${}_{}{}^2{}_{}{}^{}\Pi _{\frac{1}{2}}^{}{}_{}{}^{}$, $J=\frac{3}{2}, \frac{5}{2}, \frac{7}{2}, \mathrm{and} \frac{9}{2}$ states.

We report the observation of near-infrared Dicke superradiant pulses. The active medium (atomic Na vapor) is optically pumped in the $5S_{\frac{1}{2}}$ state and superradiates on transitions cascading down from this level at 3.41, 2.21, and 9.10 μm. The superradiant character of the emission is checked by studying variations of pulse heights and delays versus initial population inversion density.

Spectral line profiles from impurity ions in a small theta pinch have been measured and are interpreted as ion-velocity distribution functions. For antiparallel driving and bias fields, the ions attain a Maxwellian distribution corresponding to a perpendicular temperature of 3-4 keV in a time short compared to particle self-collision times. Thermalization is less rapid for parallel magnetic fields.

It is shown that energy loss in tokamaks due to cross field diffusion caused by the dissipative trapped-electron drift instability is compensated in part by the heating associated with this mode. Thus the energy loss rate presently predicted for tokamaks in the parameter range of this mode may be substantially overestimated.

Parametric excitation of the equilibrium surface ripples of a drifting, magnetically confined, nonneutral plasma is investigated by passing it through a spatially periodic magnetic field. Resonances are observed at $2{\Omega }_0$, ${\Omega }_0$, and $\frac{{\Omega }_0}{2}$ (${\Omega }_0$ is the natural frequency for the ripple). The ripple amplitude of the equilibrium surface is measured as a function of the phase angle of the excitation, the number of pump periods, and the magnitude of the magnetic field perturbations.

Detailed experimental studies of the nonlinear evolution of an electron-beam-plasma instability reveal trapping of unstable electron-plasma waves by ion-acoustic modes as well as scattering of beam electrons.

A quasilinear model is developed describing the time evolution of a mirror-confined plasma which is unstable to the drift-cyclotron loss-cone mode. Good correlation is obtained with experiments with and without an external stream of cold plasma.

The ${}_{}{}^{111}{}_{}{}^{}\mathrm{Cd}$ hyperfine quadrupole interaction due to the effect of radiation damage was studied following the reaction ${}_{}{}^{109}{}_{}{}^{}\mathrm{Ag}(\alpha , 2n){}_{}{}^{111}{}_{}{}^{}\mathrm{In}$ In in silver at 80 K. A strong dose-rate dependence is observed, which is related to interactions between recoil-damage cascades.

Extension of analyses of low-energy-electron-diffraction intensities to encompass structure determination of low-index semiconductor surfaces reveals that GaAs(110) is reconstructed. The As atoms protrude from the surface whereas the Ga atoms are displaced inward such that no nearest-neighbor bond lengths are altered.

${}_{}{}^{161}{}_{}{}^{}\mathrm{Dy}$ Mössbauer spectra show that the dysprosium moments in amorphous Dy${\mathrm{Co}}_{3.4}$ are strongly coupled to the local crystal field axes. The magnetic structure is one in which the cobalt "sublattice" is strongly ferromagnetic, and the dysprosium moments are almost randomly distributed in directions between antiparallel and perpendicular to the cobalt.

This paper presents a new and generally covariant approach to quantum field theory in curved space-time. Previously unknown expressions are obtained for particle creation amplitudes in oscillating gravitational fields. These expressions illuminate the physical origin of the particle creation.

The shape of the large, random clusters, occurring near percolation threshold $c_0$, is shown to be such that the mean cluster boundary-to-bulk ratio $\frac{〈b〉}{〈n〉}$ gives $c_0$. A Monte Carlo calculation yields that the cluster size distribution is proportional to a Gaussian in $\frac{b}{n}$ which is independent of concentration and narrows to a $\delta$ function as $n\to \infty$; the asymptotic behavior gives $c_0$ and the critical exponents.

The Froissart-Martin bound on the total cross section is improved by taking into account the multiplicity distribution of secondary particles, in addition to the unitarity, analyticity, and polynomial boundedness of the scattering amplitude in the Martin ellipse.

The nonleptonic decays of hyperons are analyzed in weak-interaction models with right-handed currents. By taking into account the corrections to current-algebra results arising from the $K^{*}$-pole contributions, a reasonable fit to both the $s$- and $p$-wave decay amplitudes is obtained with right-handed charmed current of the ${\left(\overline{\chi }d\right)}_R$ type.

We have used the polarized proton beam at the Argonne zero-gradient synchrotron to measure left-right asymmetries in the processes $p_{\mathrm{pol}}+p\to {\pi }^{\pm }\pm X$ at $p_0=6\mathrm{} \mathrm{and} 11.8$ Gev/c and $x\equiv \frac{{p_l}^{*}}{p_{max}}=0.1\mathrm{} \mathrm{to} 0.9$. For both pion charges, the asymmetries show considerable but different structure in $u$, the square of the four-momentum transfer between the incident proton and the outgoing pion. The data suggest that pions produced at large $x$ in $\mathrm{pp}$ collisions result from a baryon-exchange process.

Direct muon production in the forward direction in 300-GeV proton-uranium collisions has been measured at Fermilab. The measurements were made for muons with $P_{\perp }$ less than 400 MeV/c and with momenta of 90 and 150 GeV/c. The values for the $\frac{\mu }{\pi }$ ratios are $\frac{{\mu }^{-}}{{\pi }^{-}}=(1.56\mathrm{}\pm 0.40)\times {10}^{-4\mathrm{}}$ and $\frac{{\mu }^{+}}{{\pi }^{+}}=(4.7\mathrm{}\pm 1.1)\times {10}^{-5\mathrm{}}$ at 90 GeV/c; and $\frac{{\mu }^{-}}{{\pi }^{-}}=(3.8\mathrm{}\pm 2.1)\times {10}^{-5\mathrm{}}$ at 150 GeV/c. The ratio $\frac{{\mu }^{+}}{{\mu }^{-}}$ at 90 GeV/c is 1.05 ± 0.1. The signal is too large to be accounted for by known processes.

In an exposure of the Fermilab 15-ft hydrogen bubble chamber to a broad-band $\overline{\nu }$ beam, we have observed 106 $\overline{\nu }p\to {\mu }^{+}X$ events with a mean incident energy of 23 GeV. The experimental distributions agree well with the predictions of the quark-parton model. No anomaly is observed in strange-particle production.

We have observed the reaction $\nu +N\to \mu +\mu +\mathrm{hadrons}$ at high energies. The approximate rate for these events is ∼1% of that for the reaction $\nu +N\to {\mu }^{-}+\mathrm{hadrons}$, at $E_{\nu }\sim 150$ GeV.

The photon spectrum from the pion-capture reaction ${\pi }^{-}+{}_{}{}^3{}_{}{}^{}\mathrm{H}\to 3n+\gamma$ was measured with a high-resolution pair spectrometer. The measured branching ratio $\frac{({\pi }^{-}+{}_{}{}^3{}_{}{}^{}\mathrm{H}\to 3n+\gamma )}{({\pi }^{-}+{}_{}{}^3{}_{}{}^{}\mathrm{H}\to 3n+\gamma or 3n)}$ is (4.5 ± 0.8)%. The shape of the photon spectrum is in satisfactory agreement with theoretical calculations which include final-state interactions among the three neutrons. No evidence for a bound trineutron is found.

I have calculated ultraviolet photoionization cross sections for ${\mathrm{N}}_2$ and CO in the gas phase and the differential cross sections for oriented molecules. The gas-phase results agree well with recent data and display shape resonances, predicted by Dehmer and Dill, about 1 Ry above threshold for certain levels. For oriented molecules I find distinctive angular distributions which could be used to identify levels or determine the bond geometry of molecules adsorbed at surfaces.