$K$-vacancy fractions have been measured for Si ions moving in nickel at velocities between $3.9v_0$ and $9.0v_0$. The observed fractions, 2-23%, provide strong evidence that transient magnetic fields for ions moving in magnetized materials are caused mainly by bound, polarized electrons. A polarization close to 0.13 suffices to explain measured transient fields, and it is argued that the polarization can be due to a combination of spin-exchange interactions and capture-loss processes.

We have observed the expected sixfold valley degeneracy in the inversion layer on Si(111). This observation suggests that the twofold valley degeneracy, observed in previous experiments, cannot be an intrinsic effect due to the intervalley charge-density-wave state proposed by Kelly and Falicov.

The corrections to the low-temperature Seebeck coefficient of dilute alloys caused by the electron-phonon renormalization of the impurity scattering vertex are found to cancel completely those other corrections due to the electron-phonon renormalization of the electron energy, velocity, and relaxation time in a model of weak $s$-wave scatterers, Debye phonons, and free electrons in the limit of large valence. For normal valences the electron-phonon corrections are reduced by a partial cancellation to a few percent of some recently predicted values.

Hot-electron kinetics and distribution in pure AgCl and AgBr at crossed electric and magnetic fields have been studied at 4.2 K up to $E_x=3.4\mathrm{}$ kV/cm and $H_z=58\mathrm{}$ kOe by detecting a response current $Q_z$ to a perturbing electric field $E_z$ in the transient condition. The results of measurements on $Q_z(E_x,H_z)$ established the pictures of an ideal streaming motion of electrons in the range $\frac{c{E}_x}{H_z}>V_{\mathrm{LO}}$ (where $\frac{1}{2}{m}^{*}{V_{\mathrm{LO}}}^2\equiv \hslash {\omega }_{\mathrm{LO}}$) and of a population inversion of hot electrons in the range $\frac{c{E}_x}{H_z}<V_{\mathrm{LO}}$.

Zero-field Cu NMR of the first and fourth nearest neighbors of Mn in spin-glass Cu-Mn(1%) have been detected for $T\lesssim \frac{T_g}{5}$. The observed enhancement of rf field and signal intensity, associated with domain rotation, increases with the remanent magnetization and vanishes if the sample is zero-field cooled. A new description of the remanent properties of spin-glasses with no independent magnetic domains after zero-field cooling is proposed.

The specific heat of the diluted simple-cubic antiferromagnetic system ${\mathrm{Co}}_p{\mathrm{Zn}}_{1-p}{\left({\mathrm{C}}_5{\mathrm{H}}_5\mathrm{NO}\right)}_6{\left(\mathrm{Cl}{\mathrm{O}}_4\right)}_2$ has been studied for $0.11<~p<~1$. It is shown that for $p=p_c=0.31\mathrm{}$ (the percolation threshold for the simple-cubic lattice) the specific-heat anomaly is excellently described by the prediction for a linear-chain antiferromagnet.

The production, focusing, and numerical simulation of a 0.5-TW proton beam is reported. This beam is produced with a spherical, magnetically insulated, ion diode fed symmetrically by the dual-pulse-line Proto I generator. The ions are accelerated with electric fields due to a virtual cathode supported by magnetic field surfaces. Approximately 75% of the diode electrical power is delivered to ions and 25% of the ion beam is focused upon thin, 1-cm-diam, 1-cm-long conical targets to produce the first experimental ion-driven implosions.

A method is presented for generating stationary, axisymmetric, asymptotically flat, vacuum solutions of Einstein's equation with an arbitrary number of mass and angularmomentum parameters. As an example, a two-parameter asympotically flat solution, generalizing extreme Kerr, is generated from flat space. It is conjectured that the method, applied to the general static metric, can be used to generate all stationary, axisymmetric, asymptotically flat metrics.

The Foldy-Wouthuysen transformations are not always unitary within the space of solutions of the Dirac equation with boundary conditions. Therefore, imprecise nonrelativistic limits can be obtained for particular interactions if these transformations are always used. This assertion is confirmed by considering the case of plane electromagnetic waves and by comparing with the result given by an exact (closed-form) unitary transformation.

The production of the $\Upsilon$ family in proton-nucleus collisions is clarified by a sixfold increase in statistics. Constraining $\Upsilon$,${\Upsilon }^{\prime }$ masses to those observed at DORIS we find the statistical significance of the ${\Upsilon }^{\prime \prime }$ to be 11 standard deviations. The dependence of $\Upsilon$ production on $p_t$, $y$, and $s$ is presented. Limits for other resonance production in the mass range 4-18 GeV are determined.

Conversion electrons from the decay of a spin isomer in the secondary minimum of ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$ have been measured. They are interpreted as transitions feeding and depopulating a rotational band built on the fission isomeric ground state with spin $\frac{5}{2}$. Rotational parameters of $A=3.36\mathrm{}\pm 0.10$ keV and $B=4\mathrm{}\pm 3$ eV have been deduced. The observed upper limit on the $\frac{M1\mathrm{}}{E2\mathrm{}}$ mixing ratio of 1.4 suggests an antiparallel coupling between orbital angular momentum and spin vectors for the wave function of the fission isomer.

Yrast states of ${}_{}{}^{160}{}_{}{}^{}\mathrm{Yb}$ with spins up to $30\hslash$ were identified in the reaction ${}_{}{}^{148}{}_{}{}^{}\mathrm{Sm}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$,$4n\gamma$). In addition to an initial backbend at $I=12\mathrm{}\hslash$, a second backbend occurs at $I=28\mathrm{}\hslash$. This result is discussed in terms of recently proposed explanations of the backbending effect.

Large-amplitude, spatially modulated coherent high-frequency waves produce a change in the plasma equilibrium. The nonresonant wave-particle interaction is investigated and the local, time-independent Vlasov distribution function is found for the one-dimensional case to all orders in the electric field amplitude. For a critical value of the electric field amplitude at a fixed temperature, the distribution function exhibits "double hump" but the Penrose criterion shows that it is stable.

Electron solitary holes were observed in a magnetized collisionless plasma. These holes were identified as Bernstein-Green-Kruskal equilibria, thus being purely kinetic phenomena. The electron hole does not damp even though its velocity is close to the electron thermal velocity. Two holes attract each other like particles of negative mass, and coalesce when their relative velocity is small.

A discussion of phase transitions in two-dimensional ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ is presented. A new type of phase transition is proposed, in which "islands of reversed $\overrightarrow{\mathrm{l}}$" spontaneously nucleate, leading to an Ising-like transition. It is shown that such transitions may need to be taken into account, possibly competing with the well-know Kosterlitz-Thouless transition. Consequences of both types of transition are discussed.

We report the diffraction of He atoms at the Si(111) 7×7 reconstructed surface. The atom diffraction patterns consist of numerous sharp peaks filling out the seventh-order net observed by low-energy electron diffraction (LEED). In contrast to low-energy electron diffraction, the diffraction intensities in this seventh-order net are determined by only the outermost exposed layer of silicon atoms. These results should be sufficient to allow a semiclassical scattering calculation to test critically the various structural models which have been proposed for this reconstruction.

The coherent $\alpha -{\alpha }^{\prime }$ phase transition of H in Nb has been studied in several sample shapes. The samples were loaded in situ with the critical hydrogen concentration of 0.31 H/Nb above $T_c=171\mathrm{}°$C and slowly cooled. Below $T_c$ a coherent macroscopic spinodal decomposition takes place. By x-ray scattering and examination of the relaxed crystals, the spatial arrangement of the phases was determined. The macroscopic modes so revealed depend sensitively upon sample shape through the fulfillment of the elastic boundary condition.

Range profiles for 300- and 475-eV ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ ions implanted in situ in tungsten at 60, 61, 80, 90 K were measured, directly and absolutely, employing an atom-probe field-ion microscope. A mean range ($\overline{x}$) of 40 ± 4 Å and a parent standard deviation ($\sigma$) of 20 to 36 Å was obtained for 300-eV ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$; values of $\overline{x}$ and $\sigma$ of 56 ± 6 Å and 37 to 42 Å, respectively, were determined for 475-eV ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$. The existence of an isolated and immobile interstitial ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ atom was established and an enthalpy change of migration of 0.24 and 0.32 eV was determined.

A new model for polymer gelation is presented that predicts new effects that can not be derived from the conventional theory of Flory and Stockmayer. An exact solution is obtained for the Bethe lattice, and is related to recent experimental results of Tanaka. Under certain conditions, the gelation curve terminates at the consolute point; at this point, both connectivity and concentration fluctuations are critical, just as in the random magnet at the percolation threshold.

We report measurements of the laser excitation thresholds for the onset of electron-hole—droplet luminescence in Si in the temperature range 2.5-19.3 K. The results are consistent with finite-lifetime nucleation theory. Fits to the data determine a surface tension ≲1.1×${10}^{-2\mathrm{}}$ erg/${\mathrm{cm}}^2$ and a sticking fraction ≲5%.