The surface energy for several simple metals is calculated self-consistently with use of a single variational parameter whose optimal value depends on the crystal structure and the surface plane considered. The calculation clearly demonstrates the strong dependence of the electron-density profile at the metal-vacuum interface on the discreteness of the ionic density. The method is as simple numerically as the usual jellium calculations and can probably be applied readily to more complex surface problems.

The electronic structure of the (001) ideal surface of niobium is calculated using a self-consistent pseudopotential method. Surface states are identified and analyzed throughout the two-dimensional Brillouin zone. Charge densities and the local density of states near the surface are presented and discussed. Our calculations predict strong surface features in the density of states in the range 0-2 eV above the Fermi energy. Occupied surface states are also discussed.

Luminescence excitation spectroscopy of donor-acceptor pair recombination in GaP is reported. We observe $s$ and $p$ excited states of C, Mg, and Zn acceptors, and deduce acceptor binding energies and Luttinger valence-band parameters (${\gamma }_1=4.04\mathrm{}$, ${\gamma }_2=0.53\mathrm{}$, and ${\gamma }_3=1.26\mathrm{}$). Directly obtained information on the interaction between donors and acceptors characterizes the acceptor state and confirms observation of the $1S_{\frac{1}{2}}$ level.

Dual-parameter measurements of the positron annihilation energy and time spectra in neutron-induced voids in Mo show that the mean lifetime does not decrease monotonically with increasing momentum of the center of mass of the positron-electron pair. At intermediate values of the momentum, there is a minimum in the mean lifetime which deepens with increasing void size; this effect may be due to positronium formation and trapping in the voids.

We have studied in the gigahertz range the ultrasonic attenuation by electron-hole droplets in Ge as function of their size. A broad bump is attributed to the resonant excitation of nonresolved capillary modes. From a detailed analysis of the line shape we derive a value of 3× ${10}^{-4\mathrm{}}$ erg/${\mathrm{cm}}^2$ for the surface tension of droplets. This is the first mechanical measurement of this quantity.

Enhancement of the critical current of clean point contacts made of bulk superconducting aluminum is measured when the contacts are in a 1-10 GHz microwave field. This enhancement interferes with the ac Josephson effect.

A renormalization-group method is developed to study critical phenomena in a disordered system. The method bases its considerations on a generalized probability distribution which incorporates both thermodynamic and configurational averaging. Special attention is paid to the higher-order critical phenomena that occur at the percolation limit. A crossover scaling theory describes this region. The equation of the critical line is obtained for the Ising model.

We report the results of the application of the quark-confining string to the $\psi$ spectrum. The model is defined by a relativisticallly invariant action of quarks and color gauge fields. In the Schrödinger limit, where light quarks are neglected, this model (with two parameters) reduced to the charmonium model (with a linearly rising potential) plus additional vibrational levels. In the $e^{+}{e}^{-}$ channel, the first vibrational levels come at about 4.0 and 4.4 GeV.

We have searched in the mass range $1.8<M<\mathrm{}2.5\mathrm{}$ GeV for narrow resonances produced by antiprotons and pions of momentum 12.4-15.0 GeV/c interacting in a carbon target. We present upper limits on the production cross section times branching ratio for charmed mesons decaying into two charged particles.

We derive expressions for the Wilson coefficient functions in terms of moments of $W_{1,2}$ treating target-mass effects exactly. An analysis of existing electroproduction data indicates that scaling in the Wilson sense sets in for $Q^2$ as low as 2-3 ${\mathrm{GeV}}^2$. The effective charge ${\alpha }_s\left(Q^2\right)$ appears to be small and may have $Q^2$ dependence only within experimental errors. We consider these results as evidence that the underlying theory of strong interactions is a field theory.

The new isotope ${}_{}{}^{184}{}_{}{}^{}\mathrm{Tl}$ has been identified with $T_{\frac{1}{2}}=11\mathrm{}\pm 1$ sec and the levels in ${}_{}{}^{184}{}_{}{}^{}\mathrm{Hg}$ investigated from its decay. The $0^{+}$ band head of a deformed band was found to drop to 375 keV in agreement with theoretical predictions. The mean life of the 375-keV $0^{+}$ level was measured to be 0.9 ± 0.3 nsec which is a factor of 10 faster than theoretically predicted for a shape-isomeric $E2\mathrm{}$ transition.

The $E2\mathrm{}$ giant-resonance region in $\mathrm{sd}$-shell nuclei was studied by inelastic scattering of 106-, 120-, 145-, and 172.5-MeV $\alpha$ particles. Strong excitation in this region was observed for all investigated nuclei (${}_{}{}^{24,25,26}{}_{}{}^{}\mathrm{Mg}$ and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$) at the higher incident energies. At lower incident energies, the tail of the giant resonance tends to be obscured by another broad distribution. In the $E2\mathrm{}$ giant-resonance region, there is more fine structure in the Mg isotopes than in ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$.

Peripheral collisions between ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ are investigated at a laboratory energy of 315 MeV. The relative cross sections are remarkably similar to published cross sections measured at 33.6-GeV laboratory energy. They are compared with statistical models involving dinuclear systems and projectile fragmentation.

The $\alpha$-proton elastic scattering has been measured with $\alpha$ particles at equivalent incident proton energies of 438, 648, and 1036 MeV. A structure is observed at the position where a second minimum is expected in the differential cross section. Comparison with improved versions of the Glauber model are presented.

The dissipation of angular momentum during the particle-emission and photon-emission stages of de-excitation of ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ and Se has been determined from measurements of the average multiplicity $〈N_{\gamma }〉$ and the average energy $〈E_{\gamma }〉$ of the continuum $\gamma$ rays, emitted in coincidence with the heavy recoiling evaporation residues produced in reactions induced by ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ projectiles. The energy and angular momentum dissipated in $\gamma$-ray emission is independent of projectile energy but increases with atomic number of the residual nucleus.

A simple model is proposed for the emission of nucleons with velocities intermediate between those of the target and projectile. In this model, the nucleons which are mutually swept out from the target and projectile form a hot quasiequilibrated fireball which decays as an ideal gas. The overall features of the proton-inclusive spectra from 250- and 400-MeV/nucleon ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ ions and 400-MeV/nucleon ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ ions interacting with uranium are fitted without any adjustable parameters.

Total cross sections for the knockout reactions ${}_{}{}^7{}_{}{}^{}\mathrm{Li}({\pi }^{-},{\pi }^{-}n){}_{}{}^6{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^7{}_{}{}^{}\mathrm{Li}({\pi }^{+},{\pi }^{+}n){}_{}{}^6{}_{}{}^{}\mathrm{Li}$ to 3.56-MeV $0^{+}$ $T=1\mathrm{}$ state have been measured at ten energies between 50 and 290 MeV by detecting the direct $\gamma$ de-excitation. As found in previous work, the ratio $\frac{\sigma ({\pi }^{-},{\pi }^{-}n)}{\sigma ({\pi }^{+},{\pi }^{+}n)}$ on the (3,3) resonance is significantly less than the value of 3 expected from free pion-nucleon results.

$L$-subshell ionization cross-section ratios for heavy elements induced by protons, $\alpha \text{'}s$, carbon ions, and oxygen ions in the range 0.5 to 6.0 MeV/amu have been investigated. The resulting ratios of $\frac{{\sigma }_{L_1}}{{\sigma }_{L_2}}$ and $\frac{{\sigma }_{L_3}}{{\sigma }_{L_2}}$ show large deviations from the plane-wave-Born-approximation, semiclassical-approximation, and binary-encounter-approximation predictions below 2 MeV/amu. These deviations are more pronounced for higher projectile charges.

We have measured large orientations for Ar II states excited by 300-keV ${\mathrm{Ar}}^{+}$ impact on solid Cu surfaces at grazing incidence. We report circulary polarized light fractions of up to 76% and interpret the excitation mechanism as an orbital-angular-momentum effect. As an application of this new excitation scheme, a zero-field level-crossing experiment is presented.

We present a completely classical analysis of the small-signal regime of a free-electron laser. It is explicitly shown that the amplification is due to stimulated scattering produced by a bunching of the electron distribution.