This paper presents energy spectra of $\alpha$ particles emitted following the bombardment of ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{92}{}_{}{}^{}\mathrm{Mo}$, ${}_{}{}^{94}{}_{}{}^{}\mathrm{Mo}$, and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ with 120-MeV electrons, together with $\alpha$-particle angular distributions from ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ and ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Ni}$ for $E_{\alpha }=30\mathrm{} \mathrm{and} 50$ MeV. The data are compared with preequilibrium exciton-model and statistical-model calculations. It is concluded that few-step processes are dominant in the production of $\alpha$ particles with energies above 20 MeV.

A rotation of the angular correlation of deexcitation $\gamma$ rays from ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$ was observed in a tilted foil geometry. The signs and magnitudes of the magnetic moments of the $2_1^{+}$ level of ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$ and of the $3_1^{-}$ level of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ were determined to be $g=-0.28\mathrm{}\pm 0.11$ and $g=+0.52\mathrm{}\pm 0.18$, respectively. The experiment demonstrates that polarization of deeply bound electronic configurations can be appreciable and that this technique can be used as a quantitative measure of magnetic moments of picosecond nuclear levels.

The analyzing power of proton-proton scattering has been measured at 6.14 MeV in the angular range $7.5<~{\theta }_{\mathrm{lab}}<~20°$ with an accuracy of ±3×${10}^{-4\mathrm{}}$. Phase shifts are deduced from an analysis of the cross-section and polarization data. The spin-orbit and tensor $P$-wave phase-shift combinations are determined in a model-independent way to be ${\Delta }_{\mathrm{LS}}=0.139\mathrm{}°\pm 0.31°$ and ${\Delta }_T=-0.488\mathrm{}°\pm 0.023°$.

Evidence for the dissociation of relativistic ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ ions into the channels ${}_{}{}^3{}_{}{}^{}\mathrm{H}$+${}_{}{}^2{}_{}{}^{}\mathrm{H}$+$p$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ +${}_{}{}^2{}_{}{}^{}\mathrm{H}$+$n$ is presented. The number of events in each of these secondary channels is approximately 20% of the number of events in the channel ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$→${}_{}{}^4{}_{}{}^{}\mathrm{He}$+${}_{}{}^2{}_{}{}^{}\mathrm{H}$. Possible mechanisms for populating the secondary channels are discussed.

The interacting-boson-approximation model has recently been extended to odd-$A$ nuclei. The first extensive test of the new model gives good agreement for unique-parity levels in ${}_{}{}^{109}{}_{}{}^{}\mathrm{Pd}$, where the particle-rotor model cannot reproduce empirical results.

A method is outlined for performing finite-range distorted-wave Born-approximation calculations for pickup reactions in which the ejectile is unbound with respect to the transferred particle.

Superradiance and transient maser action have been obtained at millimeter wavelengths with alkali Rydberg atoms as the active medium. The emission was detected by monitoring the evolution of Rydberg-state populations using field ionization. Because of the strong Rydberg-atom-radiation-field coupling, the number of radiators at threshold is far smaller than in conventional masers. The estimated radiated energy is extremely low, 10 to ${10}^3$ eV. Applications for spectroscopy and microwave detectors are considered.

Electrostatic collisionless drift waves in a sheared magnetic field have been studied extensively with use of particle-code simulations. When the shear is strong, we have found that the plasma is dominated by spatially uncorrelated small-amplitude oscillations with frequencies close to those prescribed by the local dispersion relation. With a weaker shear, spatially correlated large-amplitude waves with a well-defined frequency have been observed. Theoretically predicted eigenmodes are not the dominant feature of the fluctuation spectrum.

Laser-plasma interaction physics including absorption, plasma formation, heating, plasma expansion, and energy transport, are examined for 3-nsec Nd-laser irradiances between ${10}^{12}$ and ${10}^{15}$ W/${\mathrm{cm}}^2$. Efficient energy deposition and conditions favorable to ablative acceleration are found at ${10}^{12}$-${10}^{13}$ W/${\mathrm{cm}}^2$, whereas reduced absorption, hot electrons, and fast ions are seen at 7×${10}^{14}$ W/${\mathrm{cm}}^2$. Suitability of the observed physics to pellet fusion is discussed.

Expressions are derived for the transition radiation fields due to the particles of a plasma, in the presence of an intense electromagnetic beam. Radiation is caused by the nonlinear modifications of the plasma dielectric constant, and can be observed if the plasma is slightly nonneutral.

Electron-energy deposition in thin Au foils irradiated by a tightly pinched electron beam has been studied on the Proto I accelerator (1.1 MV, 300 kA, 25 nsec). X-ray diode measurements indicate front surface temperatures of 15-20 eV, in agreement with calculations assuming deposition rates of ≳5x${10}^{13}$ W/g. These results are consistent with magnetically enhanced deposition due to self-beam fields (enhancement ∼3-5).

We have resolved the inconsistency between low-energy electron diffraction (LEED) and ultraviolet photoemission spectroscopy (UPS) analyses concerning the orientation of molecular CO when chemisorbed in a $c(2\mathrm{}\times 2)$ structure on the Ni(001) surface. Dynamical analysis of new LEED data indicates that CO stands perpendicular to the Ni surface with the C atom on top of a Ni atom; preliminary results for the Ni-C and C-O separations are 1.72 and 1.15 Å, respectively.

The $\mathrm{Cu}\mathrm{}\left(100\right)c(2\mathrm{}\times 2)$-CO and $\mathrm{Ni}\mathrm{}\left(100\right)c(2\mathrm{}\times 2)$-CO structures have been examined by dynamical low-energy electron diffraction intensity analysis using the (00), (½½) and (10) beams measured at 80 K (Cu) and 120 K (Ni) substrate temperatures. The analysis is compatible with a vertical terminal-CO arrangement, Cu-C and C-O bond lengths of 1.90 ± 0.10 and 1.15 ± 0.10 Å, respectively, for Cu/CO, and Ni-C and CO bond lengths of 1.80 ± 0.10 and 1.10 ± 0.10 Å, respectively, for Ni/CO.

The expansion of self-avoiding chains is studied through a progressive elimination of loops, resembling the renormalization group. The exponents for the mean square extension and for the number of walks are estimated in dimensionality $d=4-\epsilon , 3, \mathrm{and} 2$.

The temperature dependence (0.35 K to 6 K) of the low-temperature specific heat of the linear chain mercury compound, ${\mathrm{Hg}}_{3-\delta }\mathrm{As}{\mathrm{F}}_6$ is reported. The one- to three-dimensional crossover in the low-temperature lattice specific heat due to the phase-ordered incommensurate Hg chains is observed. The results are analyzed with use of Tarasov's phenomenological theory for the specific heat of the weakly interacting one-dimensional chains. The specific-heat results yield a value for the phason mode energy, $\frac{\Delta }{k_{\mathrm{B}}}=1.75\mathrm{}$ K.

This paper reports He diffraction from clean and hydrogen-saturated Ni(110) at 100 K. The clean surface can be described by a sinusoidal corrugation of amplitude 0.05 Å in the [001] azimuth. The hydrogen-saturated surface requires an additional corrugation of amplitude 0.23 Å on each second maximum of the basic corrugation. Possible adsorption structures consistent with this corrugation function are discussed.

The orientational ordering phase transition in solid hydrogen has been studied as a function of para concentration and pressure up to 6 kbar. Measurements are consistent with the $\mathrm{Pa}3\mathrm{}$ structure for all densities and high ortho concentration. The density dependence of the critical temperature is consistent with that for the electric quadrupole-quadrupole interaction. When doped with $p$-${\mathrm{H}}_2$, with increasing density the critical concentration decreases anomalously below the zero-pressure value of 0.56.

We have observed in Pr${\mathrm{Cu}}_6$ a sharp peak in the heat capacity and rapid change in the magnetization at 2.5 mK consistent with the occurrence of nuclear magnetic ordering below that temperature. Applying magnetic fields greater than 100 G rounds the transition. The behavior observed is similar to ferromagnetism in electronic systems, but other structures showing weak "ferromagnetism" are not ruled out.

The theory of high-field superconductivity contains two parameters, one of which, the spin-orbit scattering rate, previously has been treated as a variable in fitting the theory to the experimental data. We have made critical-field measurements on thin-film super-conductors and have simultaneously determined both parameters from an independent spin-polarized tunneling measurement, allowing for the first time a test of the theory with no adjustable parameters. A significant lack of agreement was found.

We present (a) a general formulation of the electron-hole interaction which takes into account both screened electron-hole attraction and its exchange counterpart, giving rise to the excitonic and local-field effects, respectively; (b) a quantitative calculation of absorption and modulation spectrum in Si, which demonstrates the dominant role played by the continuum-exciton effect on the main optical absorption of a covalent semiconductor; and (c) a model analysis of the continuum-excitonic effect on the optical excitations of semiconductors in general.