Measurements of the initial frequency dependence (dispersion) of the velocity of sound in gaseous helium-argon mixtures are in good agreement with predictions based on the linearized Boltzmann equations. The dispersion shows a pronounced dependence on mole fraction, and this effect can probably be exploited to determine the interaction between different noble-gas atoms.

The resonant frequency of a quartz crystal oscillating in the thickness-shear mode changes by virtue of the mass loading due to any type of film laid down on its surfaces. For a helium film only the normal fraction remains rigidly coupled to the substrate motion. Adsorption isotherms of ${\mathrm{He}}^4$ measured with this technique show clear departures from conventional nonsuperfluid behavior. We attribute this effect to the onset and presence of superfluidity in the film.

We have developed a technique for introducing a variety of impurity atomic ions into liquid helium and measuring their mobility. We find that, in contrast with predictions of the "snowball" model of Atkins, the ion mobility depends on the atomic number of the core ion in a way that cannot be explained simply in terms of the mass of the ion. The relative mobility of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$ ions has been measured and is consistent with existing theories.

Appearance potential spectra from Ni/Cu alloys reveal that in no case do $d$ holes enter the sites of Cu atoms, but on the other hand that $d$ holes at Ni sites exist even at Cu contents of more than 55%. The derived densities of states at the Fermi level are in very good agreement with results of Stocks, Williams, and Faulkner, calculated on the basis of the coherent potential approximation.

Structure in the secondary-electron emission spectrum of amorphous Ge films is interpreted as due to features in the density of conduction states, the magnitude of which is shown to be sensitive to disorder effects determined by substrate deposition and annealing temperatures. Activation energies for the reordering processes are determined for deposition and annealing temperatures from 20 to 500°C. The results provide evidence for density-of-states features associated with a random-network, metastable phase.

We measured diffuse x-ray scattering from the displacement field of point defects in KBr single crystals. From these results absolute values for the double-force tensors of the anion vacancy and the interstitial anion can be derived. From the symmetry of the displacement field a model for the interstitial anion is proposed.

Excitation functions of the ($p,n\tilde{p}$) reaction on ${}_{}{}^{91}{}_{}{}^{}\mathrm{Zr}$, ${}_{}{}^{119}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$, and ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ are compared with the predictions of exact solutions of the coupled Lane equations, and it is found that the distorted-wave Born-approximation and coupled-channel predictions have essentially the same overall shape if the same optical and symmetry potentials are used. A linear energy dependence of the complex symmetry potential, suggested earlier from distorted-wave Born-approximation analyses, as well as modification of the neutron optical potential are required to describe the available data from threshold to ∼45 MeV if global optical parameters are used.

We have identified a large number of nuclear $\gamma$ rays associated with negative kaons stopped in Ni, Cu, Si, and Al. Prominent among these for both the Cu and the Ni targets are transitions that take place in even-even nuclei lighter than the target by up to about twelve nucleons. In both cases, the total intensity of all of the identified nuclear $\gamma$ rays amounts to about twice that of the strongest x ray.

The electromagnetic structure of a nucleon in a nucleus is different from that of a free nucleon. This difference is examined for the two-pion part of the form factor by considering interactions with other nucleons in the course of pion emission and absorption, but without exchanging charge. For ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{H}$, the isovector part of the magnetic moment increases by an amount which is comparable to the outstanding discrepancy between the experimental and theoretical values.

In an optical spark-chamber experiment, we measured the branching ratio $\frac{(K_S\to \gamma \gamma )}{(K_S\to \mathrm{all})}$ to be (-1.9 ± 2.4) × ${10}^{-4\mathrm{}}$. The result assumes no interference between $K_S\to \gamma \gamma$ and $K_L\to \gamma \gamma$. We also measured the branching ratio $\frac{(K_L\to \gamma \gamma )}{(K_L\to \mathrm{all})}$ to be $(4.32\mathrm{}\pm 0.55)\times {10}^{-4\mathrm{}}\times {\left|\frac{{\eta }_{00}}{{\eta }_{+-}}\right|}^2$.

We extract $K^{-}$-nucleus scattering lengths from all $K^{-}$-mesonic atom data currently available. The scattering lengths obtained are shown to be model independent as long as the $K^{-}$-nucleus optical potential is local.

The infrared emission of CO molecules isolated in solid neon and argon matrices has been observed at very low temperature. The optical excitation of carbon monoxide was provided by a $Q$-switched frequency-doubled C${\mathrm{O}}_2$ laser. The fluorescence lifetime ${\tau }_F$ was found to lie in the range 4-8 msec, with no appreciable change of ${\tau }_F$ as the matrix/reactant ratio increased from 100 to 1000. On the other hand, a strong dependence of ${\tau }_F$ with temperature has been observed.

Transient responses for stimulated thermal scattering have been frequency analyzed. Under commonly encountered laboratory conditions, the spectral characteristics for the backscattered light are those predicted through the steady-state theory.

A frequency-dependent thermal conductivity, associated with the thermal relaxation of the vibrational degrees of freedom in a polyatomic gas, has been observed in a study of the density fluctuation spectrum of dilute S${\mathrm{F}}_6$. Spectra calculated from the two-temperature hydrodynamic theory of Morse, Sugawara, and Yip, which explicitly accounts for a frequency dependent thermal conductivity, are shown to agree well with the measured spectra.

A special probe has been used to detect ions reflected from a collisionless shock wave propagating perpendicular to the field in a magnetized, low-$\beta$ plasma. Reflected ions are observed only above a critical Alfvén number $M_A\approx 2.7$, and their orbits coincide with the familiar "foot" on the magnetic structure of supercritical shocks. We discuss the origin of the reflected ions.

By using a spinor representation, it is shown that the four-component statistical model of Ashkin and Teller is equivalent to a special case of a staggered eight-vertex model, while the eight-vertex model is equivalent to an asymmetrical Ashkin-Teller model.

The local mode due to an isotopic impurity is used to study indirectly the lattice dynamics of the perfect crystal. Raman scattering gives twice the local mode frequency due to ${\mathrm{H}}^{-}$ in LiD as 1879 ${\mathrm{cm}}^{-1\mathrm{}}$ which is in very good agreement with the calculated value of 1834 ${\mathrm{cm}}^{-1\mathrm{}}$. The good agreement can be considered as a measure of the realistic nature of the model used for the lattice dynamics of the perfect crystal.

We have found that the substitutional replacement of Ti for Ta in Ta${\mathrm{S}}_2$ stabilizes the octahedral $1T$ phase for $x$ between 0.1 and 0.9. A comparison of the resistivity, magnetic susceptibility, and thermoelectric power shows that at room temperature the properties vary systematically from diamagnetic, semiconducting behavior for $1T-\mathrm{T}\mathrm{a}{\mathrm{S}}_2$ to paramagnetic, metallic behavior for Ti${\mathrm{S}}_2$. This interpretation of the data contradicts all previous models which treat Ti${\mathrm{S}}_2$ as a degenerate semiconductor.

Four lifetimes have been resolved for positrons annihilating in polyethylene. The three longer lifetimes are identified with three kinds of morphologies in which the positrons annihilate. These lifetimes are observed to decrease with increase of applied static electric field across the polyethylene. This evidence and evidence from the intensities associated with these three lifetimes support the conclusion that polyethylene is polarized under the influence of a static electric field.

Because of the similarity between photoelectric yield and photoabsorption spectra in the soft x-ray region, "yield spectroscopy" can be used as a successful method for investigating fine structure in the electronic excitation spectra of solids. The continuous spectrum of synchrotron radiation is especially appropriate for such measurements. We reinvestigated the structure of the $4d$ excitations in Pr and the $2p$ excitations of Si using a single crystal.