It is demonstrated that the interference of the low-energy-electron multiply scattered amplitudes can be in large part eliminated by averaging data taken with different diffraction geometry but at fixed momentum transfer. This essentially yields a measurement of the kinematic intensities, which are most directly useful for surface crystallography.

Gantmakher-Kaner oscillations in gallium have been observed at 1.3°K at 9.2 GHz in the transmission mode for the field-normal case in addition to angles well away from the normal. A set of Gantmakher-Kaner oscillations with striking properties and a very small period has been associated with electrons on a small "approximately ellipsoidal" Fermi surface piece oriented along $k_b$. These oscillations have harmonic content which provides direct evidence for multiple reflections in the gallium slab indicating specular surface scattering for these particular electrons. A dramatic disappearance of just the fundamental as the dc field is decreased below the cyclotron resonance field cannot be explained by current theories of Gantmakher-Kaner oscillations.

The optical properties of crystalline and amorphous ${\mathrm{As}}_2$${\mathrm{S}}_3$ and ${\mathrm{As}}_2$${\mathrm{Se}}_3$ have been investigated from 1 to 14 eV. A simple rigid-band relationship connects the band structures of the two crystals, and the lowest-energy features observed near the interband thresholds are assigned to direct transitions. The effect of disorder on the electronic spectra, aside from the disappearance of critical-point structure, is remarkably slight; the principal density-of-states thresholds are preserved, essentially unshifted, in the glasses.

Only diffusive behavior of the longitudinal hydrodynamic mode in anisotropic antiferromagnets has been observed in recent neutron-scattering experiments below $T_N$. On the basis of a microscopic hydrodynamic theory it is shown here that in an appropriate range of frequencies and wave numbers, the longitudinal mode can become a propagating collective mode, i.e., the second magnon. Numerical estimates of the energy and momentum transfer and of the strength of this mode are made for Mn${\mathrm{F}}_2$ and ${\mathrm{K}}_2$Ni${\mathrm{F}}_4$.

We have measured the spin-resonance spectra of crystals cut from beneath {110} and {112} facets of flux-grown yttrium aluminum garnet doped with ${\mathrm{Nd}}^{3+}$ and ${\mathrm{Yb}}^{3+}$. Sites which are crystallographically equivalent, but differ in their orientation relative to the facet normal, are found to be unequally populated. Such site preference can account in principle for the recently reported noncubic magnetocrystalline anisotropy of mixed rare-earth iron garnets.

We have studied the temperature dependence of characteristic energy losses of slow electrons scattered from a Ni (111) surface. The volume loss energy shows an anomalous variation in the region of Curie temperature superimposed on a linear decrease from $T=100\mathrm{} \mathrm{to} 700$°C.

The (${}_{}{}^3{}_{}{}^{}\mathrm{He}$,$d$) reaction on ${}_{}{}^{70,72,74,76}{}_{}{}^{}\mathrm{Ge}$ has been studied at 17-MeV incident energy. In all four isotopes, a ${\mathrm{½}}^{+}$ state is observed about 600 keV above the low-lying ${\frac{9}{2}}^{+}$ isomeric state. The presence of these ${\mathrm{½}}^{+}$ states provides a convincing argument in favor of the validity of the rotational model with prolate deformation and with strong Coriolis coupling in this region of the periodic table.

The angular distribution of the 501-keV $\gamma$ radiation from low-temperature polarized ${}_{}{}^{180m}{}_{}{}^{}\mathrm{Hf}$ was found to exhibit a very large parity-nonconserving forward-backward asymmetry. At a polarization of 71%, the measured asymmetry is -(1.49 ± 0.25)%. This asymmetry corresponds to an $\frac{\tilde{E}2}{M2\mathrm{}}$ mixing ratio of magnitude 0.038 ± 0.007 in fairly good agreement with circular-polarization experiments. We also deduce the $\frac{E3\mathrm{}}{M2\mathrm{}}$ mixing ratio to be +6.0 ± 0.5, agreeing with angular-correlation measurements.

The total cross section for interaction of slow neutrons by parahydrogen has been measured to 0.1%. A pressure dependence has been found whose origin is obscure. By extrapolation to $p=0\mathrm{}$, a value for the coherent scattering length of (-3.707±0.008) × ${10}^{-13\mathrm{}}$ cm is found, in agreement with the liquid-mirror result of (-3.721±0.004) × ${10}^{-13\mathrm{}}$ cm.

A comparison is made of single-particle momentum distributions of pions produced in $7.0-\frac{\mathrm{GeV}}{c} {\pi }^{+}p$, $12.7-\frac{\mathrm{GeV}}{c} K^{+}p$, $28.5-\frac{\mathrm{GeV}}{c} \mathrm{pp}$, and $24.8-\frac{\mathrm{GeV}}{c} {\pi }^{-}p$ interactions. We observe that the distributions for negative pions which have low laboratory momentum (target fragments) in ${\pi }^{+}p$, $K^{+}p$, and $\mathrm{pp}$ interactions agree with each other when normalized by their respective asymptotic total cross sections. However, the corresponding distributions from the ${\pi }^{-}p$ reaction are significantly different from the rest. This difference is particularly interesting in view of recent theoretical predictions for inclusive reactions.

New data are presented on the longitudinal- and transverse-momentum spectra of ${\pi }^{-}$ mesons produced in both ${\pi }^{-}p$ and ${\pi }^{+}p$ interactions at 18.5 $\frac{\mathrm{GeV}}{c}$. These distributions are studied as a function of the number of charged particles observed in the final states. The spectra are discussed in terms of relevant models and are compared with similar data from $\mathrm{pp}$ interactions. The data cannot be factorized into a simple product of independent functions of longitudinal and transverse momentum. The distributions suggest strongly that a simple quark-quark model is inadequate to explain multipion production.

The photoproduction of ${\varphi }^0$ mesons from hydrogen, deuterium, and complex nuclei has been measured at energies from 6.4 to 9.0 GeV. Results are presented on the $t$ dependence from hydrogen and carbon. Forward cross sections for ${\varphi }^0$ photoproduction from ${\mathrm{D}}_2$, C, Mg, Cu, Ag, and Pb are analyzed in terms of the ${\varphi }^0$-photon coupling constant, the $\varphi$-nucleon total cross section, and the real part of the $\varphi$-nucleon scattering amplitude.

Results are presented on the forward photoproduction of ${\varphi }^0$ mesons from hydrogen and carbon by linearly polarized photons from coherent bremsstrahlung produced by 10-GeV electrons on a diamond crystal. The polarization asymmetry has been measured at an average energy $〈E_{\varphi }〉=5.7\mathrm{}$ GeV. The asymmetry from carbon is consistent with a diffractive production process. The asymmetry from hydrogen seems to be inconsistent with a purely diffractive production process even after consideration of inelastic contributions to the forward ${\varphi }^0$ production.

Compton-scattering cross sections from hydrogen ($\gamma p\to \gamma p$) and from deuterium have been measured at four-momentum transfer $t$ in the range $0.014<~-t<~0.17$ Ge${\mathrm{V}}^2$ and photon energies of 8 and 16 GeV. Fits to our proton data of the form $\frac{d\sigma }{\mathrm{dt}}={\mathrm{Ae}}^{\mathrm{Bt}}$ give $B\approx 7.8$ Ge${\mathrm{V}}^{-2\mathrm{}}$ and an intercept $A$ which is in agreement with the optical point. Both coherent scattering from deuterons and incoherent scattering from neutrons and protons are seen from deuterium. A small difference between the neutron and proton cross sections is seen, indicating the presence of about a 3% isovector $t$-channel exchange amplitude in addition to the predominant isoscalar amplitude. The vector-dominance model predicts lower cross sections (by at least 20%) for both the hydrogen and deuterium cases.

A theorem is proved which shows that if $\mathrm{CP}$-invariance violation originates in a semistrong and/or electromagnetic—or in fact any—interaction belonging to a $(3^{*},3)\oplus (3,3^{*})$ representation of $\mathrm{SU}\mathrm{}\left(3\right)\mathrm{}\otimes \mathrm{SU}\mathrm{}\left(3\right)\mathrm{}$, the $\mathrm{CP}$-invariance—violating term is a pure singlet of SU(3).

We present a method of using mass dispersion relations for relating symmetry-breaking parameters in Lagrangians to breaking effects in states and deducing precise relations between physical $S$-matrix elements from operator algebras. We apply the method with the canonical equal-time and light-cone operator structures of the gluon model to deduce some $\mathrm{SU}\mathrm{}\left(3\right)\mathrm{}\otimes \mathrm{SU}\mathrm{}\left(3\right)\mathrm{}$ symmetry-breaking effects. We find $\frac{f_K}{f_{\pi }}\simeq 1.20$, $\xi \mathrm{}\left(0\right)=-0.7\mathrm{}$, a 50% correction to the Callan-Treiman relation, and ${\alpha }_8\equiv \left[\mathrm{SU}\mathrm{}\right(3\left)\mathrm{} \mathrm{breaking}\mathrm{parameter}\right]$ $\simeq 0.14$ GeV, and explain why these values are completely consistent with $\frac{Z_K}{Z_{\pi }}\gg 1$.

A model of high-energy scattering is developed which incorporates assumed analytic properties. The approximations involved in the phenomenological fits of Orear and Krisch are discussed. An improved formula is suggested which has correct analytic properties and reproduces the Orear and Krisch fits in appropriate limits.

Variations of exotic-atom energy levels and widths with the strength of the nuclear interaction are explained with the aid of a soluble model.

Rayleigh scattering has been studied along the critical isochore and the coexistence curve of carbon dioxide. Measured intensities interpreted according to the theory of Ornstein and Zernike agree with expectation based on classical $\mathrm{PVT}$ measurements. It is suggested that over many decades of temperature distance from $T_c$ the $\mathrm{PVT}$ and optical data are consistent with a reduced compressibility ${\left(\frac{\partial \rho }{\partial \mu }\right)}_T=\Gamma t^{-\gamma }$, and ${\Gamma }^{\prime }{\mathrm{}(-t)\mathrm{}}^{{-\gamma }^{\prime }}$, with $t=\frac{(T-T_c)}{T_c}$, where $\gamma =1.17\mathrm{}\pm 0.02={\gamma }^{\prime }$ and $\Gamma =0.072\mathrm{}\pm 0.006=4.1{\Gamma }_{\mathrm{gas}}^{\prime }\simeq 3.6{\Gamma }_{\mathrm{liq}}^{\prime }$.

The equilibrium thermodynamics of a one-dimensional fermion system with a repulsive $\delta$-function interaction is found to be derivable from the solution of a set of coupled integral equations. The equations for the attractive case are also given.