Low-energy ion-surface collisions have been observed to result in the emission of optical radiation arising from sputtering with simultaneous excitation. Emission functions have been obtained showing structure and energy thresholds which provide detailed information important in the understanding of this newly observed low-energy phenomenon. These data can be understood in terms of excited-state sputtering efficiencies and radiationless de-excitation processes which compete with radiative de-excitation of the excited states of the sputtered atoms.

We propose a variant of magnetic pumping heating which makes use of a torsional rather than a compressional magnetic perturbation. It is efficient in large-aspect-ratio toroidal configurations such as Tokomaks. Typically, in this case, it is twice as efficient as the compressional magnetic pumping for magnetic perturbations of the same intensity, while using a working frequency three times smaller.

A generalization of the parametric representation for thermodynamic scaling is proposed, introducing a new critical exponent $\epsilon$. Expansions about the critical point are deduced for the fluids, and to lowest order the asymptotic power-low forms are recovered. An exponent $1-{\alpha }^{\prime }$ is obtained for the diameter of the coexistence curve. Experimental data are shown to support the predicted forms.

The intensity of the long-lived component in the positron lifetime spectrum of NaCl is found to be correlated with the x-ray-induced growth and thermal annealing of the $V$-region color centers. If this lifetime component is attributed to positrons annihilating on defects, called annihilation or $A$ centers, the data indicate that $V$-center formation reduces $A$-center formation. The results suggest that positron-annihilation measurements can serve as an important complement to color-center measurements in the study of defects in ionic crystals.

Exciton effects have been included in a calculation of the indirect differential electro-absorption coefficient at the fundamental optical absorption edge of Ge. The theory is in very good agreement with experiment; this is the first successful attempt to obtain a quantitative fit to electroabsorption data. The theoretical fit yields a value of 0.6701 eV for the indirect band gap of Ge at 296°K.

It is shown that, contrary to a recent claim by Cooke, Davis, and Wood, the results of their phase-shift analysis of the Fermi surface of copper by the Korringa-Kohn-Ros-toker method are consistent with those of an earlier augmented-plane-wave calculation by Lee.

The excitons of Pb${\mathrm{I}}_2$ can be accurately described in terms of two overlapping Wannier series and, by means of magnetic circular-dichroism measurements, it is shown that the effective mass of an electron in the conduction band and of a hole in the valence band are ${m_e}^{*}=0.27\mathrm{}$ and ${m_h}^{*}=0.40\mathrm{}$, respectively.

We report measurements of the dichroism and birefringence of CdSn${\mathrm{P}}_2$, and discuss the physical origin of these phenomena in chalcopyrite crystals. Generalizing from our results to other crystals provides a unified interpretation for previously unexplained results in several II-IV-${\mathrm{V}}_2$ and I-III-${\mathrm{VI}}_2$ chalcopyrite crystals.

A new type of metallic solid solution has been prepared in which $<~12.5$ at.% of comparatively small metal atoms (Cu) fill interstitial sites in a host metal composed of larger atoms (Y). At higher solute concentrations, both interstitial and substitutional sites are occupied. These solid solutions are metastable; they were formed by ultrarapid quenching from the liquid.

Lattice resonances of $E_{\mathrm{g}}$ symmetry (16.35 ${\mathrm{cm}}^{-1\mathrm{}}$) and $A_{1\mathrm{g}}$ symmetry (25 ${\mathrm{cm}}^{-1\mathrm{}}$) have been found in KI:${\mathrm{Ag}}^{+}$ using far-infrared spectroscopic techniques. The two even-parity modes are found to be anharmonically coupled to the $T_{1\mathrm{u}}$-symmetry resonant mode at 17.3 ${\mathrm{cm}}^{-1\mathrm{}}$, giving rise to the combination bands observed at 30 and 44.4 ${\mathrm{cm}}^{-1\mathrm{}}$.

Data on the temperature and field dependence of the susceptibility of La:Ce alloys are presented for temperatures $T>~0.6$°K and fields up to 50 kG. The data show that the susceptibility $\chi =cF(T,H)$, where $F$ is nearly independent of the concentration $c$. A phenomenological model predicts a susceptibility which agrees with the experimental $F(T,H)$.

Neutron scattering experiments on ${\mathrm{Tb}}_2$ ${\left(\mathrm{M}\mathrm{o}{\mathrm{O}}_4\right)}_3$ show the ferroelectric orthorhombic phase to result from a phonon instability at the (½, ½, 0) Brillouin zone corner of the parent tetragonal phase. Anharmonic coupling to these antiferroelectric displacements produces a spontaneous strain which in turn causes a spontaneous polarization through normal piezoelectric coupling. The rare-earth molybdates thus represent a new class of displacive ferroelectric materials without a soft polar mode.

A spontaneous-fission activity decaying with a half-life of 380 ± 60 μsec, identified as ${}_{}{}^{258}{}_{}{}^{}\mathrm{Fm}$, was discovered among the recoil products from the bombardment of ${}_{}{}^{257}{}_{}{}^{}\mathrm{Fm}$ with 12.5-MeV deuterons. The sharply decreasing spontaneous-fission lifetimes of nuclei with $N>\mathrm{}152\mathrm{}$ show a determined trend contrary to theoretical predictions. The exceedingly short half-life of ${}_{}{}^{258}{}_{}{}^{}\mathrm{Fm}$ has led us to conclude that even-even nuclei in the immediate region beyond $N=158\mathrm{}$ are becoming catastrophically unstable toward fission.

We present results of an experiment to measure the differential cross section of the reaction ${\pi }^{-}p\to {\pi }^{0}n$ between the forward and backward peaks. The measurements were made at incident ${\pi }^{-}$ momenta of 3.67 and 4.83 $\frac{\mathrm{GeV}}{c}$. The $t$ range $1.7<~\mathrm{}\left|t\right|\mathrm{}<~4.9 {\left(\frac{\mathrm{GeV}}{c}\right)}^2$ was covered at the lower momentum and $1.8<~\mathrm{}\left|t\right|\mathrm{}<~7 {\left(\frac{\mathrm{GeV}}{c}\right)}^2$ at the higher momentum. At the lower momentum the cross section is essentially constant between $\mathrm{}\left|t\right|=2.4\mathrm{}$ and 4.8 ${\left(\frac{\mathrm{GeV}}{c}\right)}^2$ while at the higher momentum the angular distribution exhibits a broad minimum centered at $\mathrm{}\left|t\right|=4.4\mathrm{} {\left(\frac{\mathrm{GeV}}{c}\right)}^2$.

Rigorous bounds are established on the absorptive part of the scattering amplitude, $A(s,t)\mathrm{}$, for $t$ real and within the Lehman-Martin ellipse. This result is used to prove an upper bound on ${\left[\frac{d\ln A(s,t)\mathrm{}}{\mathrm{dt}}\right]}_{t=0\mathrm{}}$, and to show that $A(s,t)\mathrm{}$ cannot have a zero in the region $0>t>\mathrm{}\frac{-4\mathrm{}{t}_0}{{\left(\ln s\right)}^2}$ for $s\to \infty$ (${\sqrt{t}}_0=2\mathrm{}{m}_{\pi }$ for $\pi \pi$, $\pi N$, $\mathrm{KN}$, and $\mathrm{NN}$ scattering). No assumption is made about the high-energy behavior of the total cross sections.

A model is presented which describes the nonadiabatic loss of particles from magnetic mirror traps through a Schrödinger-like equation where the role of $\hslash$ is played by the "first action invariant." The process is thus found to be analogous to the "tunneling effect" in quantum mechanics. The predictions of the model for the lifetimes compare very well with the experimental results.

The assumption that the superfluid-helium bulk viscosities are connected with internal relaxation processes is shown to lead to a relation between the four bulk viscosities such that only one is left independent. In this case absorption of second sound is independent of the bulk viscosities.

It is shown that lattice-model approximations for liquid crystals agree qualitatively with experiment only if rotational invariance is maintained. Results for simple models satisfying this criterion indicate that the isotropic-nematic phase transition is weakly first order.

Careful measurements have been made of the power and frequency dependence of the ac Josephson steps in a superconducting tunnel junction exposed to microwave radiation. At values of $2\alpha =\frac{2e{V}_{\mathrm{rf}}}{\mathrm{hf}}>25\mathrm{}$, significant deviations from Bessel function behavior [$J_N\left(2\mathrm{}\alpha \right)$] begin to occur. These deviations are correctly predicted in the detailed microscopic theory of Werthamer and are a consequence of the logarithmic singularity in the ac Josephson current at $f_{\mathrm{J}}=\frac{4\Delta }{h}$, i.e., the Riedel peak.

A self-consistent treatment of the Kondo scattering of conduction electrons from magnetic impurities is presented in order to treat finite concentrations of such impurities in superconductors. The present theory leads to a concentration dependence for the transition temperature which differs markedly from the Abrikosov-Gor'kov result. The theory appears to account nicely for various experimental results. We also find that superconductivity, under certain circumstances, does not exist at all temperatures below $T_c$.