H or D implantation of $6H$ SiC produces new luminescence spectra at 1.3°K. A striking difference between the H and D spectra are strong lines with energy displacements of 369 and 274 meV for H and D, respectively, energies that are recognized as those of the CH and CD bond-stretching modes. Annealing to 800°C increases the luminescence intensity, apparently by promoting the diffusion of H or D to a vacant Si site, where it forms a bond with one of the neighboring C atoms.

Interlayer bonding splits the $z^2$ band of the $2H$ polytypes of layered metal dichalcogenides. In group-$\mathrm{V}A$ compounds hole surfaces may appear at the Fermi level, leading to two-carrier conduction. The low-temperature reversal of the Hall effect may be due to a shift of the Fermi energy which removes the holes. Intercalation fills the band structure to a level where such a transition would not occur.

Second-order resonant optical nonlinearity due to conduction-electron spins has been observed by difference-frequency generation of far-infrared radiation (90.1 ${\mathrm{cm}}^{-1\mathrm{}}$) in $n-\mathrm{I}\mathrm{n}\mathrm{S}\mathrm{b}$ at 15°K $n=2.2\mathrm{}\times {10}^{15}$ ${\mathrm{cm}}^{-3\mathrm{}}$). When the spin-resonance frequency is tuned to the difference frequency, the measured effective nonlinear coefficient for a linewidth of 114 G is 5.4 times larger than the conventional second-order nonlinear coefficient $d_{14}$.

The spin-flip Raman interaction causes a nonlinear spin-resonance process in semi-conductor crystals. This mechanism is responsible for a large, resonant coefficient for difference-frequency generation in InSb.

We have investigated the energy-momentum relationship for optical polarons by taking into consideration the phonon-cross-exchange diagrams. Our result is similar to that of the improved Tamm-Dancoff method, except that the whole curve shifts downward. Therefore, the ground-state energy is lower than the upper bound obtained by the variational method.

This paper examines the possibility of observing effects arising from stimulated emission in the radiative recombination from electron-hole liquid in semiconductors. It is concluded that the optical gain arising from such stimulated emission in Ge would be too small for direct observation. A technique is proposed which still allows confirmation of stimulated emission by indirect means.

An analysis is made of the possible structural transformations in the self-consistent phonon approximation, in a mean-field approximation, and in an exactly solvable model. The character of the transition is found to depend both on the theoretical treatment and on the parameters used in the model Hamiltonians.

The half-life of ${}_{}{}^{10}{}_{}{}^{}\mathrm{Be}$ has been measured to be (1.5 ± 0.3) × ${10}^6$ yr, a value in significant disagreement with the previously accepted value of (2.7 ± 0.4) × ${10}^6$ yr. We discuss several implications of the revised half-life.

Isospin mixing between the 12.71-MeV, $1^{+}$, $T=0\mathrm{}$ and 15.11-MeV, $1^{+}$, $T=1\mathrm{}$ levels in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ is measured utilizing two different direct reactions. A consistent value (${\beta }^2\sim 0.01$) is obtained from both the isospin-forbidden reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(d,d^{\prime }){}_{}{}^{12}{}_{}{}^{}\mathrm{C}_{}^{*}{}_{}{}^{}$ and the comparison of the yields in the analog reactions ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}\mathrm{}(d,t)\mathrm{}{}_{}{}^{12}{}_{}{}^{}\mathrm{C}_{}^{*}{}_{}{}^{}$ (15.11 MeV) and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}\mathrm{}(d,h)\mathrm{}{}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ (0.00 MeV). This mixing implies a charge-dependent matrix element between these two levels of approximately 250 keV.

A study of the reaction ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}(\gamma ,n)$ near threshold suggests that a doorway state with $J^{\pi }={\frac{3}{2}}^{-}$ common to the channels ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}+n$ and ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}+\gamma$ lies near 750 keV. We observe experimentally Lane's prediction of a significant nonresonant background cross section associated with strong partial-width correlations.

It is argued that at some density, estimated at about 1 baryon/${\mathrm{F}}^3$, superdense nuclear matter will make a transition to a phase of approximately equal numbers of protons, neutrons, and ${\pi }^{-}$ particles, the latter condensed in one or two plane-wave states of momentum $\approx 170 \frac{\mathrm{MeV}}{c}$. These conclusions are based on the conventional theory of the pionnucleon interaction.

Sawyer has proposed a variational ground state for superdense nuclear matter which contains a coherent admixture of approximately equal numbers of protons, neutrons, and ${\pi }^{-}$ particles. Here we investigate this problem by introducing a self-consistent mean ${\pi }^{-}$ field. We find that at a critical baryon density the normal ground state becomes unstable with respect to the formation of an infinitesimal ${\pi }^{-}$ condensate.

In theories with spontaneously broken gauge symmetries, various masses, or mass differences may vanish in zeroth order as a consequence of the representation content of the fields appearing in the Lagrangian. These masses or mass differences can then be calculated as finite higher-order effects. The mechanism for cancelation of divergences in second-order fermion masses is described explicitly. The weak interactions play an essential role in canceling infinities in electromagnetic masses.

We consider the mean-spherical-model (MSM) equation for systems composed of radially symmetric particles. It is shown that for all densities less than close packing no physically satisfactory solidlike (i.e., nonradial) solutions exist to the MSM equation. The Percus-Yevick equation for hard-core particles (i.e., hard disks in two dimensions and hard spheres in three dimensions) is a special case of the MSM equation.

Electromagnetic waves propagating along a dc magnetic field are shown to excite parametrically decay, purely growing, modulational and beat wave instabilities. Particular attention is given to whistler parametric instabilities, including a discussion of their nonlinear development and saturation.

Large-amplitude electron plasma waves in a bounded plasma are observed to steepen and to form shock waves with trailing wave trains. For larger-amplitude shocks, however, the trailing wave trains are found to disappear.

500-keV, 10-kA electron beams are injected into a magnetic mirror trap of Astron geometry without wall resistors. When using ${\mathrm{H}}_2$ and pressures of several hundred millitorr in the tank, we observe ring-shaped electron layers exhibiting field changes $\rho =\frac{\delta B}{B_{\mathrm{vac}}}$ of up to 120% in the trap center and lifetimes of up to 20 μsec. With the exception of a fast final "dump" when the $\rho$ of the layer has decreased to small values, we observe a smooth decay of the layer, roughly compatible with scattering of the fast electrons in the background gas.

We have measured the reflectivity of liquid Hg-In alloys at near normal incidence from 0.14 to 4.0 μm. Our results deviate from the predictions of the Drude free-electron model. We attribute this to an unusual two-peaked density-of-states profile in liquid In and to concentration gradients of the components in a layer at the surface of the alloy.

Voltage, current, and x-ray measurements have been made on a 700-keV, 50-kA electron-beam generator using a small dielectric rod cathode. The beam is very tightly pinched, and current densities exceeding previously published values are verified.

We have observed a pronounced anisotropy of critical neutron scattering at the 27-K phase transition of solid heavy methane. The anisotropy is due to orientational fluctuations of mainly two-dimensional character. We develop a formalism to treat neutron scattering from orientational fluctuations. Agreement with experiment is reasonable.