Trapped particles can be accelerated or decelerated by diffusing at random in an inhomogeneous magnetic field via two or more diffusion modes which affect the particle energy differently. Acceleration through such "bimodal diffusion" can account for the high-energy particles trapped in the earth's radiation belts.

We have measured ${\eta }^0$ photoproduction at 4 GeV. We find our results to be consistent with a theoretical preduction relating this cross section to ${\omega }^0$ production by $\pi$ mesons using a vector-dominance model; there is no evidence for a dip or change of slope at $-t=0.6\mathrm{}$ as seen in ${\pi }^0$ photoproduction.

The upper limit on the solar neutrino flux set by Davis, Harmer, and Hoffman places an upper limit on the sun's initial helium abundance that is small compared with that estimated for other galactic objects. Adopting current estimates of low-energy nuclear cross-section factors, the upper limit is essentially equal to a lower bound set by demanding that the sum is at least 4½ × ${10}^9$ yr old.

In the $3\pi$ mass spectrum from the reaction ${\pi }^{-}p\to p{\pi }^{+}{\pi }^{-}{\pi }^{-}$ at 13 and 20 GeV/c, we observe an unstructured $A$ enhancement and the production of the $\pi \mathrm{}\left(1640\right)\mathrm{}$ meson. Our data for the ${\pi }^{-}{\rho }^0$ mass are compared with the predictions of the one-pion exchange, the diffraction-dissociation, and the double-Regge-pole models. Only the double-Regge-pole model is able to reproduce the shape of the $A$ enhancement.

The effect of $\mathrm{CP}$ nonconservation in hyperon nonleptonic decay is evaluated according to a recent theory of Oakes. Only the ratio $\frac{\beta }{\alpha }$ for the $\Sigma _{+}^{}{}_{}{}^{+}$ decay mode is predicted to show a sizable effect which, in fact, demands an order of magnitude greater accuracy than has been obtained to date experimentally.

Vibrational excitation of C${\mathrm{O}}_2$ is studied using a double electrostatic analyzer. The asymmetric stretch vibration (001) exhibits a peak cross section about 3 × ${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ at 0.9 eV, and the 002 mode excitation is an order of magnitude lower. Six energy loss peaks associated with the symmetric stretch mode (100, 200, etc.) are observed in the energy range 3-4.5 eV, with a peak at 3.8 eV. The data are consistent with the existence of two short-lived compound states. The first, around 0.9 eV, exhibits $p$-wave character, and the second, around 3.8 eV, exhibits $s$-wave behavior.

We have observed appreciable light modulation at the 6.835-GHz hfs transition frequency of optically pumped ${\mathrm{Rb}}^{87}$ vapor. The frequency separation between the levels involved in the transition exceeded the total spectral width of the initial lamp profile. These observations indicate that persistent doubts as to the feasibility of a transmission-light-modulation experiment under such conditions are groundless.

Paramagnetic resonance absorption between the $N=3\mathrm{}$, $J=4\mathrm{}$, $M=-4\mathrm{}$ and $N=5\mathrm{}$, $J=5\mathrm{}$, $M=-4\mathrm{}$ levels of ground state ${\mathrm{O}}_2$ was observed at the HCN laser frequency of 890 759 ± 3 MHz in a magnetic field of 16 418 ± 1 G. This is the first observation of absorption in a gaseous sample in which laser electron-paramagnetic-resonance techniques were used.

A departure from the usual assumption of a uniform magnetic field in the calculation of the Harris dispersion relation is shown to lead to new velocity-space instability. If the magnetic field variations are small and if a particle transit time through a complete cycle of the field is less than the instability growth time, an average (velocity-dependent) gyrofrequency may be assumed which leads to negative-mass-type instabilities.

The profile of hydrogen beta has been measured for a temperature of 16 700°K and an electron number density of 2 × ${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$ using an arc-generated plasma. These data are compared with theory on area normalization and half-width bases and found to agree with theory within the accuracy quoted for theory.

${\mathrm{H}}_{\beta }$ spectral-line profiles produced in atmospheric-pressure high-current arc experiments at the Fowler-Milne normal electron density are compared with theory and found to agree within the approximately 10% uncertainty of the theory under these conditions.

During the implosion phase of a low-density $\theta$ pinch in helium preheated to $T_e\approx 1$ eV at $N_e\approx 5\times {10}^{13}$ ${\mathrm{cm}}^{-3\mathrm{}}$, the He I $2{}_{}{}^1{}_{}{}^{}P-4{}_{}{}^1{}_{}{}^{}D$ and $2{}_{}{}^3{}_{}{}^{}P-4{}_{}{}^3{}_{}{}^{}D$ lines show satellites displaced away from the forbidden $2P-\mathrm{nF}$ transitions by 0.3-0.6 Å. These satellites are identified with those predicted by Baranger and Mozer as due to the effects of nonthermal longitudinal plasma oscillations on atomic spectra.

Measurements of the containment of a distribution of single particles in a stellarator are described. Containment for more than ${10}^7$ transits is observed for particles born outside the loss region of phase space.

Collisionless unstable modes, involving the entire velocity space and not due to Landau damping effects, are shown to exist in two-dimensional configurations in which the particle orbits are periodic along the magnetic field lines, where the magnetic intensity varies along the field, and the particle density gradient is in a perpendicular direction. One mode is associated with the velocity dependence of the electron excursion frequency and one with the trapping of ions in the magnetic field wells. Their relevance to laboratory and space plasmas is pointed out.

Calculations show that the large, positive, isotope effect in $\alpha -\mathrm{uranium}$ does not necessarily establish the existence of a new coupling mechanism to produce superconductivity.

The gradual decrease to zero of supercurrent due to depairing in thin tin films has been observed as a function of external magnetic field in reasonable agreement with theory.

The different effect of cerium and gadolinium impurities on the pressure dependence of the superconducting transition temperature of lanthanum is due to different electronic structures of the rare-earth impurity. The ionic model explains the properties of gadolinium alloys, while the resonant scattering theory explains those of cerium alloys.

The shape of the intrinsic-emission magnon sideband is well described assuming a wave-vector representation but with zero dispersion for the exciton. An observed difference in the decay rates of the intrinsic-emission zero-magon line and magnon side-band implies that the zone-center and zone-boundary excitons are distinct thermodynamic states. Thus, the exciton wave-vector states are, at least approximately, eigenstates.

The Zeeman effect of the intrinsic Sn${\mathrm{O}}_2$ exciton (direct forbidden) has been measured at 1.8°K, thus facilitating the identification as well as the interpretation of the anisotropic exciton spectra. The exciton symmetries and possible band symmetries are obtained on the basis of group theory and appear to be consistent with the valence band of O $2p$ functions and the conduction band of Sn $5s$ functions, both being crystal field split.