We report the first observation by neutron inelastic scattering of a collective elementary excitation in a metallic actinide compound. The excitation is longitudinally polarized with respect to the direction of the magnetic moment, has a dispersion of 6.7 THz Å, and has a most unusual temperature dependence. Present models for the electronic structure of this and similar materials are inadequate to account for the dynamical behavior we have observed.

Sharp luminescence lines from indirect-free-exciton decay are observed in selenium. These permit for the first time an unambiguous identification of the indirect gap. A unique feature of the band structure and symmetry is the existence of two almost degenerate types of excitons with different wave vectors, leading to a superposition of two different indirect-exciton luminescence spectra.

Using a new experimental technique based on the hysteresis effect, the spatial distribution of a localized packet of electron-hole drops in a spatially uniform free-exciton gas near threshold is measured for times ∼${10}^4$ sec. No significant motion is found, determining an upper limit $D\lesssim {10}^{-9\mathrm{}}$ ${\mathrm{cm}}^2$ ${\sec }^{-1\mathrm{}}$ to the drop diffusion constant. These results require that drops bind to crystal defects; for electrical impurities we estimate the binding energy $B\gtrsim 5$ meV.

Time constants of the processes causing the microwave enhancement of the critical current in superconducting Al films have been determined by measuring the response to an amplitude-modulated microwave signal. The dominant time constant corresponds to the quasiparticle-recombination time, while for $\frac{T}{T_c}<0.9\mathrm{}$ a second time constant similar to the inelastic scattering time is also found. These observations confirm the results of Chang and Scalapino that increased recombination is more important than redistribution in enhancing the energy gap.

It is shown that changes in the angle-resolved spectra of a Cu(111) surface brought about by oxidation can be largely explained in terms of an increase in the breakdown of the conservation of the component of the momentum perpendicular to the surface in the photoionization matrix element of the wave function of the bulk.

Clear experimental evidence is given for the first observation of a spontaneous magnetization in a mixed-valent rare-earth compound at low temperatures. The magnetic susceptibility, the magnetization, the magnetostriction, and the electrical conductivity of Tm${\mathrm{Se}}_{0.83}$${\mathrm{Te}}_{0.17}$ reveal a transition to a magnetically ordered state with a net magnetic moment below 5.5 K. This is in quantitative agreement with Varma's recent predictions based on a microscopic model for mixed-valent systems.

The Hamiltonian of the massive Thirring model is explicitly diagonalized by formulating a Bethe Ansatz for the eigenstates. A general method for computing the energy spectrum is presented.

The arbitrary $n$-point Green's functions of spontaneously broken gauge supersymmetry are shown to be ultraviolet finite to arbitrary loop order for $N>~2$ (where $4N$ is the number of Fermi coordinates) when the spontaneous breaking preserves global supersymmetry.

We report further evidence for fractional charge of $\sim \frac{1}{3}e$ on niobium spheres. With a modified apparatus in which we can determine all of the background dipole forces we have measured fractional charges of $(0.304\mathrm{}\pm 0.040)e$ and $(0.345\mathrm{}\pm 0.035)e$.

We present measurements of the production symmetric high-mass hadron and pion pairs by protons of 200, 300, and 400 GeV, incident on a beryllium target. The two-particle invariant cross section for pion production can be described by the function $\frac{E_1{E}_2{d}^6\sigma }{d{p_1}^{3}d{p_2}^3}=(1.7\mathrm{}\times {10}^{-28\mathrm{}}){p_t}^{-8.4\mathrm{}}{(1-x_t)}^{14}$ ${\mathrm{cm}}^2$/Ge${\mathrm{V}}^4$ (where $p_t$ is the mean $p_t$ of the two hadrons). Functions of the same form have been used in describing single-pion inclusive production. Equality of the exponents of $p_t$ in the two processes is observed, confirming the role of smearing contributions to single-hadron cross sections.

Analysis of 5180 $\overline{\nu }$ interactions shows a variation with energy of the inelasticity ($y$) distributions over the range 10 to 220 GeV and a dependence on the scaling variable $x$. From these data are obtained the approximate $x$ dependence of the sea quarks and a limit on the strength of right-handed coupling between the $u$ quark and a massive $b$ quark.

We have observed fission induced by transfer to ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ from ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ projectiles at sub-Coulomb energies. The cross sections for the stronger reactions are in qualitative agreement with simple theoretical estimates. They are of the same magnitude as those found earlier by bombardment with Kr and Xe where the $Q$ windows are considerably less favorable. In those cases, transfer involving Coulomb excitation is proposed as an explanation.

We examine changes in light-particle emission from high-spin states in nuclei arising from a deformation dependence of the transmission coefficients. These changes are large enough to have measurable influences upon decay-product characteristics; consequently, the use in statistical models of transmission coefficients representative of spherical nuclei is probably inadequate.

Differential cross sections for the reaction ${}_{}{}^3{}_{}{}^{}\mathrm{He}$(${\pi }^{-}$,${\pi }^0$)${}_{}{}^3{}_{}{}^{}\mathrm{H}$ at energies of 200, 250, 275, and 290 MeV over the angular region $80°\lesssim {\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}\lesssim 150°$ are presented. Comparison is made with theoretical predictions based on Glauber theory and optical-potential calculations. Neither approach gives a satisfactory description of the data; in particular, the observed energy dependence is much smaller than the theoretical predictions.

The spectrum of fast backward nucleons emitted in nucleon-nucleus scattering is correlated with the inclusive fast-neutron spectra from $\mu$ capture and radiative $\pi$ capture by using a universal, phenomenological nuclear recoil function. Agreement with experiment, where available, is good.

The $L_{2,3}{M}_{4,5}{M}_{4,5}$ Auger spectrum of selenium in a variety of compounds has been measured following near-threshold photoionization of the $2p_{\frac{1}{2}}$ level by monochromatic Al $K{\alpha }_{1,2}$ radiation. The energy difference between the $L_2{M}_{4,5}{M}_{4,5}$ and the $L_3{M}_{4,5}{M}_{4,5}$ Auger peaks was observed to increase by as much as 1.1±0.1 eV as the $2p_{\frac{1}{2}}$ binding energy approached to within 1.1 eV of the ionization threshold. The energy shifts are compared with the predictions of a semiclassical analysis by Niehaus which takes into consideration the influence of the Coulomb field of the slow photoelectron on the Auger process.

I derive reduced equations of motion for molecular multiphoton processes by constructing a set of relevant operators and adopting the Mori projection-operator technique. The intramolecular dephasing processes which play a dominant role in the quasicontinuum are properly incorporated by utilizing the representation of exact molecular states. The resulting equations include dephasing operators expressed in terms of intramolecular dipole correlation functions, and interpolate between the coherent and incoherent driving limits.

Transitions, driven by a C${\mathrm{O}}_2$ laser, between the $7{}_{}{}^1{}_{}{}^{}S$ state and $n=9\mathrm{}$ manifold of states in He have been observed by monitoring the optical emission from the $7{}_{}{}^1{}_{}{}^{}S$ state. In addition to the normally expected $\Delta L=1\mathrm{}$ transition to the ${}_{}{}^1{}_{}{}^{}P$ state, clearly resolved transitions have also been observed to the even-parity states with $L=2, 4, 6, \mathrm{and} 8$. The high-$L$—state transitions are observed because of a combination of diamagnetic Zeeman and motional Stark-effect mixing. A theory has been developed which describes the line shapes of these forbidden transitions.

We report the experimental observations of resonance charge transfer from a photoexcited donor state in sodium to excited acceptor states in protons and other rare-gas ions. This reaction is followed by rapid decay of the excited acceptor states with the emission of intense spontaneous radiation in the vuv.

We use a new computational model to investigate the absorption of a focused beam of circularly polarized laser light, including the ponderomotive force. We find, in agreement with recent experiments, that at high intensity large craters can form due to the variation of the ponderomotive force across the focal region. The critical surface becomes concave and the walls of the crater refract the incident light so that resonant absorption can be greatly enhanced.