Transition radiation in the optical region of the spectrum from individual charged pions and protons in the momentum region of 0.8 to 3.5 BeV/c was obtained from a stack of thin metal foils spaced uniformly in vacuum. The radiation was observed simultaneously in the forward and in the backward directions, with a forward-to-backward intensity ratio of the order of 8 to 1. A logarithmic increase in the intensity of the transition radiation with the total energy of the particle is found in the momentum region of the present investigation.

Two new results for Compton scattering are noted: (a) a relation for $S>~1$ which tests whether the total cross sections for unpolarized photons on a polarized stable target are asymptotically independent of the target polarization, (b) the existence of low-energy theorems for all intrinsic multipole moments. The electric-quadrupole theorem is given explicitly.

Two superconvergent sum rules are used to calculate the forward Regge rho-exchange parameters using only experimental data below the asymptotic region. The residue and intercept found in this manner are consistent with those determined by the asymptotic data.

The self-consistent charge distribution in covalently bonded crystals and molecules is divided into two components, an atomic and a bonding part. Both can be calculated in elemental crystals from macroscopic dielectric properties. The theory is easily generalized to treat heteropolar and anisotropic effects, lattice vibrations, dipole and quadrupole moments, and bond lengths in large molecules.

The phase-separation and superfluid-transition temperatures of ${\mathrm{He}}^3$-${\mathrm{He}}^4$ liquid mixtures have been investigated as functions of ${\mathrm{He}}^3$ concentration under conditions of saturated vapor pressure by means of dielectric-constant and thermal-equilibrium time-constant measurements. The $\lambda$ line, which divides the normal and superfluid phases in the temperature-concentration plane, is found to intersect the phase-separation curve at its peak.

Phonons have been excited in crystalline solids at the fractional harmonic frequencies $\frac{p{\omega }_0}{q}$, where $p$ and $q$ are integers, of the acoustic input frequency ${\omega }_0$. These phonons have been detected by their quadrupole saturation of nmr levels and with pick-up transducers.

The first observations of the ${\mathrm{Pr}}^{141}$ and ${\mathrm{Tm}}^{169}$ nmr in rare-earth intermetallic compounds are described. The calculated and observed values for the nmr frequency shifts are in good agreement.

We report the observation of a peak in the ${\mathrm{Na}}^{23}$ nuclear relaxation rates in NaN${\mathrm{O}}_2$ at the ferroelectric transition. This effect is explained on the basis of the theory of the transition in terms of lattice dynamics. It is argued that nuclear spin-phonon relaxation can be a powerful tool of investigation of the ferroelectric transition.

A study of the cross sections of proton decay of isobaric analog states formed in the ($d, n$) reaction has been made with a variety of medium mass targets. Particular attention is paid to the large variation in cross sections for reactions which proceed through the analogs of $d_{\frac{5}{2}}$, $s_{\frac{1}{2}}$, and $d_{\frac{3}{2}}$ states in the Zr, Mo, and Sn isotopes. At energies ($E_{\mathrm{inc}}\sim 16$ MeV) far above threshold this variation is shown to be consistent with a sequential process in which the ($d, n$) formation mechanism is direct. The cross sections to the target ground states are large only when the neutron decay channels are closed.

The energy dependence, charge dependence, and angular distributions of pion-proton elastic scattering near 180° have been measured at beam momenta from 5.9 to 17.1 GeV/c. The 180° cross sections decrease with energy as ${P_{\mathrm{lab}}}^{-1.1\mathrm{}}$ for ${\pi }^{-}-p$ and ${P_{\mathrm{lab}}}^{-1.4\mathrm{}}$ for ${\pi }^{+}-p$. At all energies the ${\pi }^{+}-p$ backward peak is quite sharp and has a width about ½ that of the forward diffraction peak. The ${\pi }^{-}-p$ backward peaks are about twice as wide as the forward diffraction peak and appear to go through a maximum before reaching 180°.