The anisotropy in the quenching radiation of H atoms in the metastable $2s$ state has been studied with the aim of developing a new method for Lamb-shift measurements in hydrogenic ions. The extrapolated value of the anisotropy at zero field strength is 0.1392 ± 0.0015, in good agreement with the theoretical prediction 0.139 04 based on the accepted value of the Lamb shift and a consideration of hyperfine coupling effects. Our anisotropy corresponds to a Lamb shift of 1059 ± 13 MHz.

We report an improved experimental upper limit for $D$, the triple-correlation coefficient in polarized-neutron decay. A nonzero value for this coefficient implies a breakdown of $T$ invariance. We find that $D=-(1.1\mathrm{}\pm 1.7)\times {10}^{-3\mathrm{}}$, consistent with $T$ invariance.

Coulomb-nuclear interference in high-energy charged-hadron-deuteron collisions is treated exactly within the framework of Glauber theory. Charge-distribution effects are included. Applications are made to $\mathrm{pd}$ measurements below 70 GeV to extract ${\rho }_n$, the ratio of real to imaginary parts of the proton-neutron forward elastic scattering amplitude. An alternative and earier analysis is shown to yield comparable values for ${\rho }_n$. Both results for ${\rho }_n$ differ significantly from an earlier analysis.

High-energy hadron-hadron collisions are viewed as proceeding by a strong short-range "quark-quark" interaction, generating a "spark" in the form of a self-interacting meson field, which yields observable mesons only after the incident particles have passed. This picture leads to the possibility of rare events with high multiplicity. There is a definite contradiction to Gottfried's recent model of multiple production in nuclei, but little practical distinction for beams below 1 TeV.

A beam of slow positrons in the few-eV region is directed at bakable solid targets in a vacuum of (2-4) × ${10}^{-8\mathrm{}}$ Torr. Measurements of the $\frac{2\gamma }{3\gamma }$ annihilation-yield ratio indicate the conversion of the incident positrons into positronium. The conversion efficiency depends on the target material and incident positron energy, varying from less than 25% at 300 K to 40-85% at 900 K.

The relative x-ray yields corresponding to $\mathrm{KL}$ and $K$ ionized atoms have been measured for elements ranging from $\mathrm{V} \mathrm{}(Z=23\mathrm{})\mathrm{}$ to $\mathrm{Ni} \mathrm{}(Z=28\mathrm{})\mathrm{}$ at incident electron energies of 20 keV and 2 MeV. The intensity ratios of $K\alpha$ satellite to diagram lines at 2 MeV are found to be lower by a factor ∼ 0.6 than those measured at 20 keV. These results cannot be understood solely in terms of electron shakeoff. It is suggested that the observed energy dependence is due to a competing multiple Coulomb-ionization mechanism.

The $S$ and $D$ partial-wave cross sections for photoionization from the $3{}_{}{}^1{}_{}{}^{}P$, $4{}_{}{}^1{}_{}{}^{}P$, $3{}_{}{}^3{}_{}{}^{}P$, and $4{}_{}{}^3{}_{}{}^{}P$ states of helium are calculated for ejected-electron energies from 2.04 to 13.6 eV. It is shown that the $S$ and $D$ contributions may be combined to obtain the total cross section for arbitrary polarization states of the excited helium atoms and of the ionizing radiation. Good agreement is obtained with a recent experimental determination in which polarized $\mathrm{He}\left(n{}_{}{}^{1,3}{}_{}{}^{}P\right)$ atoms were excited and subsequently ionized by linearly polarized laser light.

Strong transient oscillations have been observed in proton-carbon-13 cross-polarization experiments in a ferrocene single crystal. These oscillations are in contrast with the usually observed exponential behavior of cross polarization. They are manifestations of coherence effects caused by the dipolar coupling of the carbon-13 to the directly bound proton. A simple model is described which explains the observations.

We have measured a change in specific volume of (0.5 ± 0.2) × ${10}^{-4\mathrm{}}$ ${\mathrm{cm}}^3$/g at the nematic-smectic-$A$ transition of $\mathrm{N}-p-\mathrm{cyanobenzylidene}-p-\mathrm{octyloxyaniline}$. The order of this transition has recently been subject to dispute. On the basis of our data, we conclude unambiguously that it is of first order as is expected from theoretical analysis.

A deviation from the Ornstein-Zernike theory of critical scattering has been observed in a neutron-diffraction study of neon near its critical point. The critical exponent $\eta$ was determined to have the value ${0.11}_{-0.02\mathrm{}}^{+0.03\mathrm{}}$.

A self-consistent version of the $\frac{1}{n}$ expansion is used to calculate the critical exponent $\eta \mathrm{}(n,d)\mathrm{}$ for an $n$-component Ginzburg-Landau field with spatial dimensionality $d$. The result is exact to first order in $\frac{1}{n}$ but also includes a partial summation of graphs to all orders in $\frac{1}{n}$. This leads to a bounding of $\eta$ for small $n$, in contrast to the simple $\frac{1}{n}$ expansion. Results are $\eta \mathrm{}(3,3)\mathrm{}\simeq 0.079$, $\eta \mathrm{}(2,3)\mathrm{}\simeq 0.11$, and $\eta \mathrm{}(1,3)\mathrm{}\simeq 0.177$. For $d=2\mathrm{}$ the theory leads to the conjecture that $\eta$ vanishes for large values of $n$.

The Lorentz gas approximation to the Boltzmann collision integral for a weakly ionized gas is generalized to the case of a flowing gas, and the electron distribution function for such a gas in a time-varying electric field is derived. Several limiting cases are discussed. The results are applicable to problems of shock waves, gas lasers, and plasma-microwave interactions.

We present an analytic solution for the resonant oscillations of a cold, inhomogeneous, one-dimensional plasma under the influence of a sinusoidal applied field. The model approximates the response to obliquely incident electromagnetic radiation. Energy can be absorbed collisionlessly through either electron wave breaking or ion bunching, when the driven field is strong or weak, respectively. The two regimes are distinguished by $e{E}_L\gtrless \frac{0.02L{m}^2{\omega }^2}{M}$, where $L$ is the plasma scale length and $E_L$ the longitudinal driver. In the weak-driver case, ions with keV emergies can be produced in the resonance region.

Atoms adsorbed on a metal surface acquire an induced dipole moment. An argument is presented which leads to a new mechanism responsible for these induced dipole moments.

The temperature dependence of the longitudinal sound velocity has been measured in vitreous silica between 0.28 and 4.2 K and at frequencies between 30 and 150 MHz. With decreasing temperature the sound velocity does not increase monotonically towards its value at $T=0\mathrm{}$ K, but reaches a maximum around 2 K and decreases steadily at lower temperatures. This new result, unique for a pure dielectric solid, gives further evidence for the existence of two-level systems in glasses.

We have investigated the role of thermal and electronic effects in threshold switching in an amorphous semiconductor of memory composition. Evidence is presented to show that switching is a bulk field effect, and that, if thermal effects are discounted or eliminated, the switching field is independent of pulse width for pulses longer than 1 nsec. This was the shortest pulse width measured. Short-pulse (1.5 nsec) measurements indicate that a previously unreported conduction region is established at the critical switching field.

We give semiempirical tight-binding calculations of dangling- and back-bond surface bands and resonances for unreconstructed relaxed Si and Ge (111) surfaces. For Si at high-symmetry points these are in very good agreement with those of Appelbaum and Hamann. Comparison of the results with the energy-loss-spectroscopy data of Rowe and Ibach suggests that the observed back-bond resonances are associated primarily with minima in the back-bond surface bands.

Anomalous behavior of the proton spin-lattice and spin-spin relaxation times in the intercalation complex Ta${\mathrm{S}}_2$:${\mathrm{NH}}_3$ is shown to result from the two-dimensional aspects of the motion of the intercalated ammonia molecules.

The molecular-field approximation (MFA) and the random-phase approximation (RPA) are shown to be unreliable in predicting the types of order in cubic Heisenberg magnets that include second-neighbor exchange. Anomalies in the Padé-approximant critical temperatures are found and traced to instabilities in the RPA and MFA. These instabilities lead to new types of order involving canted and perpendicular alignment of the spins.

A nonresonant mechanism, magnetization directional softness, is proposed to explain anomalous resonancelike ultrasonic absorption effects which have been observed in ferromagnetic metals by the present and by previous investigators. Magnetoelastic dispersion data are presented which provide independent evidence for this nonresonant mechanism. We assert that neither the present nor previous ultrasonic absorption measurements in bulk metals correspond to acoustic ferromagnetic resonance.