Theoretical calculations have thus far been used to interpret the soft-x-ray spectra of several alkali halides in terms of band structures alone, excluding the possibility that core excitons are formed below the band edge. By independently determining the threshold for band transitions from x-ray photoemission spectroscopy and optical-gap data, we conclude that these spectra are in fact almost entirely excitonic in nature.

Fluctuations of valence-electron density are expected to occur in the wake of a fast charged particle moving through condensed matter. Electrons can be trapped into wakeriding states by the potential minima associated with domains of electron-density depletion with binding energies ranging from ∼ 10 ev behind protons to several hundred eV behind highly charged heavy ions. Observable phenomena possibly linked to wake-riding states are discussed.

The resistivity of one-dimensional metals is calculated for two models in which impurity scattering is the only mechanism for dissipating momentum. In the first model, impurity scattering is added to the Fröhlich Hamiltonian. In the fluctuation regime above an incommensurate Peierls transition it is found that the resistivity is enhanced. For a general two-body interaction Hamiltonian it is found that charge-density-wave fluctuations predominate over Cooper-pair fluctuations leading to enhanced resistivity.

The forward-angle oscillations recently observed in heavy-ion transfer reactions are explained as the Young interference pattern of a refractive two-slit "optical system" in $l$ space, and a new phenomenon is predicted.

From a bubble-chamber experiment, we studied the $\overline{p}d\to p_s\overline{p}p{\pi }^{-}, p_s\overline{p}p{\pi }^{-}{\pi }^0, p_s\overline{n}p{\pi }^{-}{\pi }^{-}$ reactions at 5.55 GeV/c in order to see whether a $\Delta -\Delta$ component of the deuteron wave function can be observed in our data. This was achieved by searching for spectator $\Delta \to p_s\pi$ systems. We observed significant production of $\Delta \to p_s\pi$, a fraction of which is emitted in the backward laboratory hemisphere. The meaning of this high $\Delta \to p_s\pi$ production rate is discussed.

As a test of soft-pion theorems in nuclei, we measured near threshold the ratio of positive-pion photoproduction cross sections on ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ and on protons. If the total cross section of the reaction $\gamma +p\to {\pi }^{+}+n$ is expressed as ${\sigma }_p=a_p\frac{q}{k}$, our result for the reaction $\gamma +{}_{}{}^6{}_{}{}^{}\mathrm{Li}\to {\pi }^{+}+{}_{}{}^6{}_{}{}^{}\mathrm{He}_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{}{}_{}{}^{}$ is ${\sigma }_{\mathrm{Li}}=(0.073\mathrm{}\pm 0.002)a_p\frac{q}{k}\frac{\frac{12.5}{q}}{\exp \left(\frac{12.5}{q}\right)-1\mathrm{}},$ where $q$ is the pion and $k$ the photon c.m. momenta expressed in units of MeV/c. This result is considerably lower than the existing theoretical predictions.

The $Q$ values for (${}_{}{}^3{}_{}{}^{}\mathrm{He}$, $t$) reactions on ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$, ${}_{}{}^{34}{}_{}{}^{}\mathrm{S}$, ${}_{}{}^{42}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{46}{}_{}{}^{}\mathrm{Ti}$, ${}_{}{}^{50}{}_{}{}^{}\mathrm{Cr}$, and ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$ have been measured relative to that for ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}({}_{}{}^3{}_{}{}^{}\mathrm{He}, t){}_{}{}^{27}{}_{}{}^{}\mathrm{Si}$. The results lead to significant deviations from $\stackrel{\mathrm{̇}}{\mathrm{p}}$reviously accepted values for the $\beta$-decay end-point energies of ${}_{}{}^{42}{}_{}{}^{}\mathrm{Sc}$, ${}_{}{}^{46}{}_{}{}^{}\mathrm{V}$, and ${}_{}{}^{54}{}_{}{}^{}\mathrm{Co}$. The new $\mathrm{ft}$ values for these transitions now agree with other known superallowed transitions ($A<\mathrm{}40\mathrm{}$); only the decay of ${}_{}{}^{50}{}_{}{}^{}\mathrm{Mn}$ remains anomalous. A limit is also set on the $Z^2{\alpha }^2$ radiative correction term.

By the introduction of a chemical potential for an absolutely conserved fermion quantum number, we determine the onset of a phase transition in a general renormalizable, finite-temperature field theory with spontaneously broken symmetries. We also briefly investigate the possible physical existence of such a phase transition in black holes and in the early universe.

We have measured the single-photon cross section in the reaction $p+p\to \gamma +\mathrm{anything}$ for incident proton momenta from 50 to 400 GeV/c and lab angles of 80, 100, and 120 mrad. It is shown that in the range $p_{\perp }=0.3\mathrm{} \mathrm{to} 4.3$ GeV/c, the derived ${\pi }^0$ invariant cross section can be factorized into a product of two functions, one in $p_{\perp }$ and the other in a new scaling variable $x_R=\frac{p^{*}}{{p_{max}}^{*}}$, where $p^{*}$ is the total c.m. momentum of the ${\pi }^0$.

We show that over a very wide range of c.m. angles, energies, and transverse momenta, the invariant cross sections for inclusive production of hadrons in $\mathrm{pp}$ collisions show a very simple behavior when expressed in terms of a new radial scaling variable $x_R\equiv \frac{p^{*}}{{p_{max}}^{*}}$, where $p^{*}$ is the total c.m. momentum of the hadron.

We show that implementation via unitarity and analyticity of quantum mechanical constraints due to pair final-state interactions in three-body states leads to the simplest form of linear scattering integral equations usually used for the three-body problem. This form of the separable interaction equation is therefore the minimal equation compatible with these general constraints of quantum mechanics.

We report measurements of $s-p$, $f-g$, and $g-h$ transitions in electronically excited states of ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ observed via electric dipole resonances on a fast helium ion beam.

Normalized differential and integral electron-impact cross sections for elastic scattering and for the excitation of the ${}_{}{}^2{}_{}{}^{}D_{\frac{5}{2}}^{}{}_{}{}^{}$, ${}_{}{}^2{}_{}{}^{}D_{\frac{3}{2}}^{}{}_{}{}^{}$, and ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2},\frac{1}{2}}^{}{}_{}{}^{}$ levels of atomic copper have been determined at 20 and 60 eV. An unexpectedly large cross section was found for the excitation of the ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2},\frac{1}{2}}^{}{}_{}{}^{}$ levels, which at certain angular and energy ranges surpasses the cross section for elastic scattering. The integral cross sections in units of ${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ are elastic, 91.0 and 59.0; ${}_{}{}^2{}_{}{}^{}D_{\frac{5}{2}}^{}{}_{}{}^{}$, 1.85 and 0.36; ${}_{}{}^2{}_{}{}^{}D_{\frac{3}{2}}^{}{}_{}{}^{}$, 1.26 and 0.26; ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2},\frac{1}{2}}^{}{}_{}{}^{}$, 77.2 and 36.5, at 20 and 60 eV, respectively.

Nonresonant stimulated anti-Stokes Raman scattering from an inverted population in atomic iodine has been observed. The population inversion was achieved by flash photolysis of trifluoromethyliodide. A gain of $e^7$ was measured for a laser probe pulse at the anti-Stokes wavelength passing through the inverted iodine coincident with a laser pump pulse. This result is in good agreement with theoretical predictions.

We have measured relative x-ray-production cross sections for Ca $K\alpha$ satellite and hypersatellite transitions produced from 24.0- to 48.0-MeV oxygen bombardment of thick targets. All cross-section ratios as functions of projectile energy for initial defect configurations $K^k{L}^l$, where $k=1, 2$ and $l=0, 1, 2, 3, 4$, are in qualitative agreement with configuration-space binary-encounter-approximation predictions.

In a Mössbauer source experiment the $\beta$ decay produces a large initial population of the excited electronic levels of the Mössbauer source atom. It is shown that this causes such excited levels to contribute more prominently in the source experiment than in the corresponding absorber experiment. These contributions can provide a particularly sensitive method for studying relaxation rates among the excited electronic levels. A detailed discussion and model calculations are given for dilute paramagnetic $4f$ impurities in a metal.

A stability criterion for localized modes in an axisymmetric torodial plasma is derived from the kinetic energy principle, taking account of trapped particles. This criterion predicts greater stability than the Mercier criterion.

Perturbation analysis of the stability of ablative, laser-driven implosions of homogeneous spherical pellets shows stability of the ablation surface, a necessary condition for achieving the high densities required for laser fusion. This conclusion is supported by physical arguments.

The nonlinear frequency shift of a strong electromagnetic wave in a plasma, due to weak relativistic effects and the $\overrightarrow{\mathrm{v}}\times \overrightarrow{\mathrm{B}}$ force, can cause modulation and self-focusing instabilities. These processes are explored, and their relation to self-focusing driven by the ponderomotive force is described.

A theoretical treatment is presented of the quasiparticle-recombination dynamics of a nonequilibrium superconductor. The microwave reflectivity of a superconducting film in the presence of external pair breaking is calculated. It is shown how microwave experiments may permit the separation of the effective recombination time into its intrinsic and recombination-phonon components.