In KCl the $F$ center versus dose curves obtained by making absorption measurements during gamma-ray irradiation differ considerably from those made by irradiating a crystal and then transferring it to a spectrophotometer. When the source is "turned off" the absorption drops abruptly for approximately 30 min and more slowly thereafter. The growth is accurately described by a sum of three saturating exponential terms and one linear term; the decay by the sum of four decreasing exponentials.

Spin-wave dispersion relations have been measured in high-symmetry directions for metallic Gd. Analysis shows that at least five interplanar constants are required for a satisfactory fit to the data. The energy gap at $q=0\mathrm{}$ is unmeasurably small. In the $c$ direction the measured dispersion curve gives directly the Fourier-transformed exchange interaction $J\left(0\right)-J\left(q\right)\mathrm{}$. This exhibits no other extreme value except that at the origin.

A technique of data analysis familiar in nucleon-nucleon scattering is proposed for use in the extraction of spectroscopic information from direct nuclear reactions. The method is shown to be successful in analyzing some artificial data generated by a soluble three-body model of deuteron stripping.

The differential cross section for neutron-proton elastic scattering was measured in the diffraction region with incident-neutron momenta between 8 and 30 GeV/c. The experiment was a spark-chamber-counter experiment, conducted at the alternating-gradient synchrotron. Results are presented and compared with currently available lower energy $\mathrm{np}$ data and comparable energy $\mathrm{pp}$ data.

Currently available electropion-production data near threshold have been analyzed according to the soft-pion theorem which expresses the threshold cross section in terms of the vector and axial-vector form factors of the nucleon. We determine the axial-vector form factor for $q^2$ up to ∼7 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$.

We derive a unitarity upper bound on the absorptive part $A(s, t)$ of the elastic-scattering amplitude in the physical region. In the diffraction peak region the bound on $\frac{A(s, t)}{A(s, 0)}$ is a function only of the parameter $\frac{{{\sigma }_{\mathrm{tot}}}^2\mathrm{}(-t)\mathrm{}}{4\pi {\sigma }_{\mathrm{el}}}$. Assuming the diffraction scattering to be purely absorptive and spin independent we find the $\mathrm{pp}$, $\overline{p}p$, and ${\pi }^{\pm }p$ data to lie a little below the theoretical upper bound. Further the experimental curve of $\frac{X\left(t\right)\mathrm{}}{X\left(0\right)\mathrm{}}$ vs $-\frac{4tX\left(0\right)\mathrm{}}{{\sigma }_{\mathrm{el}}}$, where $X\left(t\right)\mathrm{}\equiv \frac{d\sigma }{\mathrm{dt}}$, seems "universal."

The He II 304-Å line emitted from a $N_e\approx 3\times {10}^{17}$-${\mathrm{cm}}^{-3\mathrm{}}$,, $T_e\approx 4$-eV plasma in a $T$-type electric shock tube shows a blue shift of ∼0.05 Å. This shift is interpreted as due to the negative space charge from the polarization of plasma regions occupied by positive ions.

The "quark tracks" observed by McCusker and co-workers in cloud chambers can be explained by making reasonable assumptions about two processes: fluctuations in the number of droplets in a cloud-chamber track, and the relativistic rise of the ionization. However, before a firm conclusion can be drawn, more experimental data on the drop-count distribution of a large sample of tracks in the experiment are needed.

The partition function for a system of bosons or fermions interacting via pairwise harmonic forces is evaluated exactly. It is found that the partition function has a structure similar to that of a system of independent bosons or fermions in an external harmonic well with, however, an important modification which implies a greatly reduced density of states.

The long-slit geometry has been used to measure the angular correlation of annihilation radiation from copper alloys. The alloys 0.975 Cu-0.025 Al, 0.95 Cu-0.05 Al, and 0.77 Cu-0.23 Ni display "necks" in momentum space. In units of the copper Fermi-surface neck, the measured neck radii of 1.3, 1.5, and 0.8, respectively, are consistent with the assumption that the energy-momentum relation is unchanged upon alloying.

An attempt to confirm the chemical binding of neutrons reported by Grant and Cobble, using neutron fluxes 10 to 1000 times larger than theirs, has led to a negative result.

I have observed 30 transitions between hyperfine levels of ${\mathrm{H}}_2^{+}$, the simplest molecule. This is the first observation of the complete hyperfine structure for this system. The measured transition frequencies range from 3.989 to 1276.271 MHz, and fully define the hyperfine energy level schemes for the rotational states $K=1\mathrm{}$ and $K=2\mathrm{}$ and the vibrational states $v=4-8\mathrm{}$.

We have measured the relative Stark shift between the $m_J=\pm 1$ and the $m_J=0\mathrm{}$ Zeeman sublevels of the $2{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ metastable state in helium. This shift should be zero in the $L-S$ coupling limit. The shifts is (1.27 ±.04) × ${10}^{-6\mathrm{}}$ Hz/${\mathrm{}(\mathrm{V}/\mathrm{c}\mathrm{m})\mathrm{}}^2$, and decreases the normal magnetic field splitting between the $m_J=+1\mathrm{}$ and the $m_J=0\mathrm{}$ sublevels.

In the collision ${\mathrm{He}}^{+}$ + He → ${\mathrm{He}}^{+}$ + He*, excitation at low incident ion energies (≲1 keV) proceeds via a pseudocrossing of the elastic ${}_{}{}^2{}_{}{}^{}\Sigma _g^{}{}_{}{}^{}$ diabatic potential with excited-state ${}_{}{}^2{}_{}{}^{}\Sigma _g^{}{}_{}{}^{}$ potentials. In addition, pseudocrossings of inelastic potentials at large internuclear separations mix the amplitudes of the excited-state channels coherently. This many-state mechanism provides qualitative understanding of diverse experimental observations.

New data on the excitation of helium by low-energy helium ions have been obtained that provide strong support for the post-collision-interaction model proposed by Rosenthal and Foley in a companion paper. Certain details of the results that are not presently predicted by the theory are pointed out.

The properties of liquid ${\mathrm{He}}^3$-${\mathrm{He}}^4$ mixtures at 0°K are studied by a variational method using a Jastrow-Slater trial wave function and the Wu-Feenberg expansion of the energy expectation value: The system of mass-3 boson + mass-4 boson shows complete phase separation; the system of mass-3 fermion + mass-4 boson and the system of mass-3 boson + mass-4 fermion mixtures separate incompletely; and the system of mass-3 fermion + mass-4 fermion mixes completely. The limiting solubility of the mass-3 fermion in the mass-4 boson solvent is found to increase with pressure.

We suggest that a quantized vortex ring is formed when a roton, localized near a moving ion, is expanded by stochastic processes to become a small ring, attached to the ion. Calculations based on this notion are compared with experiment.

The effect of an applied electric field on the polarization and lifetime of $F$-center emission has been measured in KCl and KF. The results are explained using a model in which emission occurs from a $2s$-like state which has some $2p$ component due to internal-field mixing.

Magnetic-field-induced circular polarization of $F$-center emission has been observed in KF. The effect is small and temperature independent in the range 1.3 to 4.2°K, and is interpreted as orbital Zeeman mixing with $g_{\mathrm{orb}}\sim 0.04$.

We report on the preparation and optical properties of single-crystal films of Cd${\mathrm{Cr}}_2$${\mathrm{S}}_4$. The present data show no large blue shift associated with magnetic ordering near the Curie temperature contrary to that previously observed in bulk Cd${\mathrm{Cr}}_2$${\mathrm{S}}_4$ data. A large red shift correlated to the magnetic ordering is observed for a peak in the highly absorbing region. The weakness and narrowness of this absorption is inconsistent with that expected for band-to-band transitions resulting in unbound electrons and holes. We suggest an exciton model to explain this absorption.