We present evidence for the existence of an intermediate state observed in the decay sequence $\psi \mathrm{}\left(3684\right)\mathrm{}\to \psi \mathrm{}\left(3095\right)\mathrm{}\gamma \gamma$. The mass of the state is either 3500 ± 10 or 3270 ± 10 MeV. The branching fraction of the sequence is (3.6 ± 0.7)%.

The crystal blocking effect was used to study the time distribution of 5-MeV protons elastically scattered from a germanium crystal. The time delay associated with compound-elastic scattering is estimated and used to separate the direct and compound-nuclear contributions to the elastic cross section.

We measured the static electric quadrupole moment ($Q_{2^{+}}$) and $B(E2, {0_1}^{+}\to {2_1}^{+})$ of the first excited state of ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ at 1.98 MeV. The values obtained were $(-0.19\mathrm{}\pm 0.02 \mathrm{b})e$ (for the positive sign of the interference term involving the $2_2^{+}$ state) and $(0.0048\mathrm{}\pm 0.0002 {\mathrm{b}}^2)e^2$ for $Q_{2^{+}}$ and $B(E2, {0_1}^{+}\to {2_1}^{+})$, respectively. For these values the ratio $\frac{\left|Q_{2^{+}}\right|}{{\left[B\right(E2, {0_1}^{+}\to {2_1}^{+}\left)\right]}^{\frac{1}{2}}}$ is about 3, whereas for no other nucleus does it exceed unity by more than 30%.

A triple-coincidence, five-parameter technique was employed to search for two-photon emission in the decay of the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(6.05-MeV) state. Data were event-recorded and analyzed in parallel with events associated with decay of the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(6.13-MeV) and the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(7.12-MeV) states. Our measured branching ratio is $\frac{N_{\gamma \gamma }}{N_{\pi }}=(2.5\mathrm{}\pm 1.1)\times {10}^{-4\mathrm{}}$.

Spontaneously generated magnetic fields can substantially reduce the thermal conductivity in pellet atmospheres and give rise to localized hot spots, which may lead to the ablation of anomalously fast ions.

Measurement of hard x-rays produced in normal ORMAK discharges provides direct evidence that runaway electrons can be produced at early times and can be contained stably during the whole discharge time, thereby attaining energies of the order of 10 MeV. This class of high-energy runaway electrons complements and extends previous information on runaways in toroidal discharges and can have some distinct consequences on the operation of future tokamak devices.

High-current, relativistic, electron streams with low energy of transverse motion under-go very tight pinching in high-density matter. Power flux densities of ${10}^{16}$ W/${\mathrm{cm}}^2$ are realizable from modest electron streams, 50-100 kA at several MV, interacting with solids. Both cylindrical and spherical self-generated interaction geometries obtain from conditions realizable by use of dielectric-rod cathodes.

I report the first observation of C${\mathrm{O}}_2$-laser-induced x-ray emission from gaseous targets. By varying the gas pressure, the plasma density of the target was tuned through resonance at the critical density. The x-ray emission rose quickly from zero at the critical pressure, and reached a peak when the plasma was slightly overdense. Because of the resonant enhancement, a C${\mathrm{O}}_2$-laser pulse of only 0.1 J was sufficient for this experiment.

The propagation of ion-acoustic waves (IAW) in a double-electron-temperature plasma is investigated both experimentally and theoretically. It is found that the presence of even a small fraction of the lower-electron-temperature component can dominate the behavior of the waves. The results have important implications both for the use of IAW as a diagnostic tool for measuring electron temperature and for the interpretation of turbulent IAW spectra.

A study of the temperature dependence of the absorption coefficient in amorphous dielectrics below 10 ${\mathrm{cm}}^{-1\mathrm{}}$ has enabled us to identify two level configurations from thermal population changes. We also find that the anomalous low-frequency modes in glasses consist of widely spaced manifolds of energy levels.

The first steps in the oxidation of GaAs(110) are examined through shifts in the As and Ga $3d$ levels as a function of oxygen exposure. We observe a large chemical shift in the As $3d$ levels (about 4 eV) while the Ga $3d$ levels were shifted by less than 1 eV. This gives direct evidence for oxygen bonding to arsenic at the GaAs(110) surface, and illustrates the change in chemical character which can take place in atoms at the surfaces of compounds.

The conductivity of electrons in the inversion layer of silicon has been measured from 0 to 40 ${\mathrm{cm}}^{-1\mathrm{}}$ at 1.2°K in the metallic and localized regimes. The correlation between $\sigma \mathrm{}\left(T\right)\mathrm{}$ and $\sigma \left(\omega \right)$ in the localized regime suggests that the drop in conductivity at low electron concentrations is caused by the appearance of a gap at the Fermi level.

The Li $K$ absorption edge was measured with yield spectroscopy at liquid-nitrogen temperature. The broad feature hitherto considered to be the edge is shown to be a combination of a sharp absorption edge corresponding to a 0.17-eV-wide Li $K$ core level and a rising density of states at the Fermi level.

Energy transfer of bound excitons in GaP: N is investigated by time-resolved, resonant-excitation spectroscopy and by studies of below-band-gap excitation spectra. Exciton tunneling is found to dominate over dipole-dipole interactions because of the large spatial extent of the exciton wave function. This is the first definitive observation of exciton tunneling in a semiconductor.

A chemical-bond theory of the magnetic susceptibility of tetrahedral semiconductors is presented. Starting from a Hall-Weaire-type Hamiltonian, we derive an expression for the susceptibility, whose diamagnetic and paramagnetic contributions are written in terms of gauge-invariant physical quantities. Our analysis confirms a recently postulated model for the susceptibility. Theory and experiment are in good agreement.

The magnetic susceptibility of an intrinsic tetrahedrally coordinated semiconductor is calculated using a tight-binding basis and approximations appropriate to the bond-orbital model. The susceptibility associated with the valence electrons is found to separate into a diamagnetic Langevin component and a paramagnetic Van Vleck component, both of which are found to be proportional to the square of the bond length, and nearly cancel in the homopolar semiconductors. The Langevin term is found to be approximately independent of polarity while the paramagnetic component varies with polarity, ${\alpha }_p$, as ${(1-{{\alpha }_p}^2)}^{\frac{3}{2}}$.

In situ electron-spin-resonance measurements have been performed on silicon crystals cleaved under ultrahigh-vacuum conditions. Our observations are in conflict with existing publications which report a surface signal ($g=2.0055\mathrm{}$) corresponding to a spin density of the order of ${10}^{14}$/${\mathrm{cm}}^2$. No signal which could be ascribed to the cleaved surface was detected although the minimum detectable surface spin density was less than ${10}^{13}$/${\mathrm{cm}}^2$. In view of this result we comment on the origin of the ESR observed in powders and amorphous films.

The $g=2.0055\mathrm{}$ EPR signal from a silicon crystal well cleaved in situ in ultrahigh vacuum at low temperatures is sensitive to gases and can be as low as (3 ± 2) × ${10}^{12}$ spins ${\mathrm{cm}}^{-2\mathrm{}}$, which is more than an order of magnitude lower than reported previously for a single crystal or crushed powers. The signal is now believed to arise mainly not from electrons at ordinary surfaces but ones trapped in atomic mismatch regions in the bases of microcracks.

Multiphoton-induced directional emission of halogen atoms and ions from fcc KCl, KBr, and NaCl single crystals has been observed in the [110] and [211] direction during interaction of the crystals with strong ruby laser pulses. Nonradiative decay of self-trapped excitons and subsequent replacement collision chains seem to account for this effect. Some difficulties remain with the mechanism for the previously unobserved [211] emission.

The emission of neutral halogen atoms from alkali halide crystals in [211] directions is explained in terms of defocusing of the usual [110] momentum produced by ionization and a short sequence of momentum transfers to a surface halogen. No replacement sequences are involved in the process.