The magnetic moment of a particle of nonzero spin $S$ is computed by the introduction of minimal coupling into the appropriate Galilean-invariant wave equation. It is shown that the requirement that the differential equations be of first order, together with a minimality assumption on the number of components, uniquely implies a $g$ factor of $\frac{1}{S}$. The role played by this minimality condition is made explicit by means of a counterexample.

A method is presented for constructing current-algebra amplitudes which satisfy (1) threshold theorems, (2) crossing symmetry, (3) approximate unitarity, and (4) cutplane analyticity, and which reduce to the usual tree approximation in the narrow-resonance limit. Pion-pion scattering is considered in detail to illustrate the method. A derivation of the Kawarabyashi-Suzuki-Riazuddin-Fayyazuddin relation is provided which makes no reference to vector-meson dominance.

The lifetime against autoionization of the ${}_{}{}^4{}_{}{}^{}P_{\frac{5}{2}}^{}{}_{}{}^{}°$ state of ${\mathrm{He}}^{-}$ is calculated using an accurate description of the initial- and final-state wave functions. In these calculations the initial ${}_{}{}^4{}_{}{}^{}P_{\frac{5}{2}}^{}{}_{}{}^{}°$ state is represented by a variational wave function consisting of several angular configurations. The final ${}_{}{}^4{}_{}{}^{}F_{\frac{5}{2}}^{}{}_{}{}^{}°$ continuum state is obtained by polarized-orbital theory. A lifetime of 4.55×${10}^{-4\mathrm{}}$ sec is predicted which is in good agreement with the most recent experimental measurement.

The decay of the differentially metastable autoionizing $\mathrm{}\left(1s2s2p\right)\mathrm{}{}_{}{}^4{}_{}{}^{}P_J^{}{}_{}{}^{}$ states of the ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{-}{}_{}{}^{}$ ion has been studied by time-of-flight techniques in an axial magnetic field, and Zeeman quenching has been observed. Two distinct lifetime components (11 μsec, 210 μsec) have been identified in a 100-eV beam with an axial field of 400 G. The zero-field lifetimes obtained from these and other measurements are 11 ± 5 μsec for $J=\frac{1}{2}$, $\frac{3}{2}$, and 345 ± 90 μsec for $J=\frac{5}{2}$. The $\frac{5}{2}-\frac{3}{2}$ fine-structure interval is estimated to be 0.050 ± 0.015 ${\mathrm{cm}}^{-1\mathrm{}}$.

Cross sections for $K$-shell vacancy production in carbon atoms are measured for incident ${\mathrm{N}}^{+}$, ${\mathrm{O}}^{+}$, ${\mathrm{Ne}}^{+}$, and ${\mathrm{Ar}}^{+}$ in various energy ranges. The measured cross sections agree with a theoretical model based on the Landau-Zener theory of level crossing.

The value of the frequency shift in the spectrum of the stimulated thermal scattering, $\Delta \nu$, is shown to be proportional to the amplitude and the inverse duration of the incident light pulse and to depend in a minor way on its spectral width $\Delta {\nu }_0$. Under ordinary experimental conditions in liquids, the calculation yields $\Delta \nu \simeq 0.002 {\mathrm{cm}}^{-1\mathrm{}}\ll \frac{\Delta {\nu }_0}{2}\simeq 0.01$ ${\mathrm{cm}}^{-1\mathrm{}}$. The relation $\Delta \nu \ll \Delta {\nu }_0$ is experimentally confirmed.

A new type of ${\mathrm{Gd}}^{3+}$ ESR center has been observed in the Ca${\mathrm{F}}_2$ Lattice. This new ${\mathrm{Gd}}^{3+}$ center is produced as a result of x-ray irradiation of Ca${\mathrm{F}}_2$ crystals originally containing the tetragonal ${\mathrm{Gd}}^{3+}$ center charge compensated by an ${\mathrm{F}}^{-}$ ion. The crystal-field splitting associated with this new center is trigonally symmetric along the [111] axis of the Ca${\mathrm{F}}_2$ lattice and is characterized principally by ${b_2}^0\approx 2899\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$.

The electron-nuclear double-resonance method is used to obtain greatly enhanced NMR signals from the distant nuclei in molecular crystals which have been x irradiated to produce paramagnetic centers. Reduction of the ESR by over 98% is observed for protons in malonic acid, and the deuteron and carbon-13 NMR have also been studied in the perdeuterated crystals. Deuteron $\Delta m=2\mathrm{}$ transitions have been readily detected, as well as the $\Delta m=1\mathrm{}$ signals in crystals with only 1% D/H isotopic ratio.

The longitudinal and transverse sound velocities have been measured in x-ray-oriented single crystals of bcc ${\mathrm{He}}^3$ at a molar volume of 22.6 ${\mathrm{cm}}^3$. General agreement with the predicted anisotropy is found; however, the transverse velocities fall significantly below the expected values. A ${\theta }_{\mathrm{D}}$ of 23.7°K calculated using the elastic moduli is in excellent agreement with the value extrapolated from specific-heat measurements.

For a fluid in which the interaction potential has a hard core plus a negative part, softening of the hard core can produce a second transition if a first already exists. We give a general argument for the occurrence of the second transition in the lattice gas, plus explicit results for one-dimensional fluid models with two first-order transitions. One such model also provides an example of the breakdown of the law of rectilinear diameters.

The thermoluminescence of KCl: Tl following gamma-ray irradiation was studied using a new technique. Most of the emission occurs at 3050 Å, but three weak bands also appear. The 3050-Å glow curves, after different doses, consist of one or more peaks from a set of seven peaks occuring between 312 and 537°K. The total 3050-Å emission increases and then decreases, and the most intense glow peak shifts from low to high temperature with increasing dose.

We have measured transverse electroreflectance at the fundamental direct edge of germanium. Both the magnitude and spectral shape of the response are polarization dependent; the latter is shown to arise from (a) incipient removal of the light-heavy hole degeneracy and (b) deviations of the transition matrix elements from their zero-field values.

The dependence of the $M$-center reorientation efficiency on $M^{+}$ concentration indicates that at low temperatures, $M$ centers reorient indirectly by absorbing light, forming $M^{+}$ centers which then absorb and rotate. Reoriented $M$ centers are produced only after reoriented $M^{+}$ centers capture electrons. We further show that $M^{+}$ centers reorient with high efficiency during the radiationless transition, $2p{\pi }_u\to 2p{\sigma }_u$.

Radiation near 5.3 μm arising from the collinear phase-matched mixing of a 10.6-μm $Q$-switched laser beam and a pulsed ultrasonic shear wave has been observed in GaAs. Phase matching occurs when the crystal momentum of the acoustic phonon is adjusted to equal the familiar momentum mismatch observed in conventional second-harmonic generation in cubic GaAs. Three components of the susceptibility governing the four-wave interaction process were measured.

The polarization selection rules governing the band-edge electroreflectance and photoreflectance spectra of CdSn${\mathrm{P}}_2$ are opposite to those observed in wurtzite II-VI semiconductors and to theoretical predictions for similar chalcopyrite semiconductors. This result is explained by a new valence-band model with the essential feature that the sign of the crystal-field splitting is opposite to that observed in wurtzite II-VI semiconductors.

The metamorphism of critical points due to Coulomb interaction, predicted by the theory of Toyozawa, has been determined experimentally through a careful examination of the temperature dependence of the line shapes of the $E_1$ and $E_1+{\Delta }_1$ structure of InAs. Besides, it has been possible to determine the shift coefficient $\frac{\partial {\omega }_g}{\partial T}=-5.5\mathrm{}\times {10}^{-4\mathrm{}}$ eV/°K and the broadening parameter $\frac{\partial \Gamma }{\partial T}=+0.9\mathrm{}\times {10}^{-4\mathrm{}}$ eV/°K of the $E_1$ structure.

We present experimental evidence of the directional dependence of the photoconductivity in homopolar cubic semiconductors. The change of the photoconductivity with light wave vector and polarization is about $\frac{1}{20}$ of the change of the conductivity brought about by illuminating a semiconductor. All our measurements were made on germanium at room temperature. We also present a theoretical argument based on symmetry considerations for the existence of a directional bulk effect of the photoconductivity.

An unambiguous and model-independent test for the presence of isotensor terms in photopion production is suggested. On analyzing the available data, striking evidence for the presence of such a term is found.

A reaction with no expected secondary Regge poles ($\gamma p\to \varphi p$) is suggested as a means for direct experimental study of the Pomeranchuk exchange amplitude. From existing data on this reaction, we find a Pomeranchuk trajectory slope of ${{\alpha }_P}^{\prime }\mathrm{}\left(0\right)\mathrm{}\simeq \frac{1}{2}$.

A general representation for scattering amplitudes is proposed which is crossing symmetric, satisfies Regge behavior and duality, and possesses double spectral functions. As the width parameter goes to zero, the resonance poles on the second sheet move onto the real axis and the amplitude reduces to the Veneziano model. Partial waves generated from this amplitude exhibit correct threshold behavior in both the real and imaginary parts. A generalization to more-point functions is also proposed.