We report the measurement of the energy and angular distributions of Earth albedo neutrons from 10 to 100 MeV at 40° N geomagnetic latitude from a balloon at 120 000 ft, below 4.65 g/${\mathrm{cm}}^2$. The albedo-neutron omnidirectional energy distribution is flat to 50 MeV, then decreases with energy. The absolute neutron energy distribution is of the correct strength and shape for the albedo neutrons to be the source of the protons trapped in Earth's inner radiation belt.

Differential energy spectra of cosmic-ray protons and He nuclei have been measured for the first time by an ionization spectrometer flown at balloon altitudes. The energy range extended from 50 to > 1000 GeV. The observed differential intensities can be represented with power-law spectra with a slope of -2.75 ± 0.03 for protons and of -2.77 ± 0.05 for He nuclei. The proton-to-He ratio is 26 ± 3 at 40 GeV/nucleon and is constant within errors up to 400 GeV/nucleon.

We have found that differential equations can be form invariant under a larger class of infinitesimal transformations than those considered by Lie and Ovsjannikov. We give a generalization of the concept of point transformation. It is necessary for the systematic determination of the generators of continuous invariance groups of, e.g., the partial differential equations of physics. Applying it to Schrödinger's equation, time-dependent constants of the motion are found systematically, as illustrated here for the hydrogen atom.

The response of a gravitational wave antenna to linear, mixed, and randomly polarized sources is studied as a function of sidereal time, source coordinates, and antenna location and orientation. We find that the gravitational signals reported by Weber cannot be highly polarized tensor radiation coming from a single source at the Galactic nucleus.

If Weber's gravitational-wave observations are interpreted in terms of a source at the Galactic center, both the intensity and the frequency of the waves are more reasonable if the source is assumed to emit in a synchrotron mode (narrow angles, high harmonics). Although presently studied sources for such modes are astrophysically unsatisfactory—high-energy, nearly circular, scattering orbits—other possible sources are under study.

The existence of a mechanism for gravitational synchrotron radiation is demonstrated in solutions of the wave equation in the Schwarzschild background, with the source a particle in a highly relativistic circular geodesic. The main features (high-frequency harmonics, narrow angular distribution in latitude) are shown to hold for vector (electromagnetic) and tensor (gravitational) radiations, which are expected to be strongly polarized in the orbit plane. Detailed formulas for the spectrum are given in the scalar case.

Measurements of proton spin-lattice relaxation times $T_1$ in $\gamma$-irradiated C${\mathrm{H}}_4$ at 1.1°K have been used to observe spin conversion. A strong magnetic field dependence of the conversion rate is found, with a sharp peak at 12.5 kOe and with some indication of a second peak at 15.2 kOe. The existence of the two peaks is tentatively interpreted as corresponding to transitions from a slightly split $T$ level ($J=0\mathrm{}$) to the ground $A$ level ($J=0\mathrm{}$).

We present an experimental study of the nuclear spin-lattice relaxation in a one-dimensional metal near the metal-insulator transition. The data obtained from the charge transfer salt $N$-methyl-phenazinium-tetracyanoquinodimethan directly confirm the enhanced susceptibility predicted for a one-dimensional metal at $q\simeq 2k_{\mathrm{F}}$ and provide insight into the nature of the metal-insulator transition.

We have directly observed a time-dependent recoilless fraction. This effect is seen using delayed-coincidence Mössbauer spectroscopy. The time-dependent recoilless fraction is observed at the ${\mathrm{Fe}}^{3+}$ site and not at the ${\mathrm{Fe}}^{2+}$ site in a CoS${\mathrm{O}}_4$·7${\mathrm{H}}_2$O source. The relaxation time of the recoilless fraction is estimated to be between 10 and 100 nsec. Delayed-coincidence Mössbauer spectroscopy measurements on sources of Co${\mathrm{Cl}}_2$·6${\mathrm{H}}_2$O and Co${\left(\mathrm{N}{\mathrm{H}}_4\right)}_2$${\left(\mathrm{S}{\mathrm{O}}_4\right)}_2$·6${\mathrm{H}}_2$O did not show such an effect.

We have directly observed a time-dependent recoilless fraction. This effect is seen using delayed-coincidence Mössbauer spectroscopy. The time-dependent recoilless fraction is observed at the ${\mathrm{Fe}}^{3+}$ site and not at the ${\mathrm{Fe}}^{2+}$ site in a CoS${\mathrm{O}}_4$·7${\mathrm{H}}_2$O source. The relaxation time of the recoilless fraction is estimated to be between 10 and 100 nsec. Delayed-coincidence Mössbauer spectroscopy measurements on sources of Co${\mathrm{Cl}}_2$·6${\mathrm{H}}_2$O and Co${\left(\mathrm{N}{\mathrm{H}}_4\right)}_2$${\left(\mathrm{S}{\mathrm{O}}_4\right)}_2$·6${\mathrm{H}}_2$O did not show such an effect.

The detrapping effects of fluctuating electrostatic potentials on trapped particles in a Tokamak geometry are investigated. It is shown that nonlinear detrapping saturates the collisional trapped-particle instability at a fluctuating potential $\varphi$ such that $e\varphi \ll \epsilon T$, where $\epsilon$ is the inverse aspect ratio.

We have made a microscopic calculation of the transport coefficients $X$ of a Van der Waals fluid with an interaction potential $V\left(\mathcal{r}\right)=V^S\left(\mathcal{r}\right)+{\gamma }^3{V}^L\left(\gamma \mathcal{r}\right)$. After performing a "hydrodynamical renormalization" of the propagators of the theory, we can show that the first correction to $X$ due to $V^L$ is of order $\gamma$ when $\gamma$ is small. Explicit, model-independent expressions for this first correction are given.

Measurements of the melting pressure of a sample of ${\mathrm{He}}^3$ containing less than 40-ppm ${\mathrm{He}}^4$ impurities, self-cooled to below 2 mK in a Pomeranchuk compression cell, indicate the existence of a new phase in solid ${\mathrm{He}}^3$ below 2.7 mK of a fundamentally different nature than the anticipated antiferromagnetically ordered state. At lower temperatures, evidence of possibly a further transition is observed. We discuss these pressure measurements and supporting temperature measurements.

The propagation of electron plasma waves was studied experimentally in the regime where electron-neutral collisions dominate. It was found that the effects of collision not only enhance the damping of the wave, but also increase the wave number for a given frequency. These results are compared with some theoretical models.

A method is described of directly coupling an optical beam to surface excitations. Using this technique the frequency and linewidth of surface plasmons in doped germanium and in gold and surface phonons in calcium molybdate are determined. The method also allows the dispersion curve to be measured.

It is shown that when the self-consistent phonon approximation is applied to displacive phase transitions, it leads to inconsistent results near the transition point, and that this may give rise to spurious first-order transitions.

When illuminated by an optical source, absorbing impurities in polar crystals produce a macroscopic polarization due to both the change in electric dipole moment from ground to optically excited states and a pyroelectric effect in the host lattice following thermalization of the excitation. The relevance of these mechanisms to relaxation processes is demonstrated by a measurement of the dispersion of optical rectification in LiTa${\mathrm{O}}_3$: ${\mathrm{Cu}}^{++}$ over the range of rectified frequencies from 0 to ${10}^{12}$ Hz.

We present measurements of the low-temperature specific heat of small lead particles and bulk lead. The results on 22- and 37-Å particles show definite enhancements of the specific heat, indicating the presence of additional low-frequency modes. A decrease in the enhancement at low temperatures is interpreted as the first observation of the effect of size on lattice specific heat.

The quadrupole interaction of the 247-keV level of ${}_{}{}^{111}{}_{}{}^{}\mathrm{Cd}$ in Cd metal under pressures up to 75 kbar has been measured with the aid of time-differential perturbed angular correlations. The quadrupole interaction decreases by about 30% in this pressure range, the variation being nearly linear. We discuss the significance of these data to the understanding of the electric field gradient in Cd metal.

We report the first direct evidence of rotational levels of vibronic states in solids. These levels are associated with the ground states of shallow acceptors and provide the basis of a detailed understanding of the fine structure or "undulations" in emission spectra derived from bound excitons in GaP. This explanation is contrasted with one proposed recently by Hopfield, Kukimoto, and Dean.