We describe the first observation of extreme-ultraviolet photons produced during collisions between two ground-state neutral argon atoms. The energy dependence of the relative cross section for photon production is found to exhibit structure at about 70 eV c.m. energy, similar to that observed in the cross section for ionization in argon collisions.

An experimental analysis is made of the scattering of microwaves by the density fluctuations due to electron plasma-wave instability in a beam-plasma system. Reasonably good (i.e., within an order of magnitude) agreement is obtained with the Shapiro-Drummond-Pines theoretical estimate of the energy associated with the "linearly unstable" electron plasma waves at "quasilinear" steady state.

The upper limit of the conduction band was found to be 0.4±0.05 eV below the Fermi level in the $〈111〉$ direction of a copper crystal, in good agreement with theoretical predictions. The crystal was grown on the end of a tungsten field-emission tip and exhibited a central dark (111) region about 1000 Å in diameter. With the maximum permissible total emission, a current of 300 electrons/sec was observed from a region about 30 Å in diameter positioned on the $〈111〉$ pole.

The influence of an electric field (∼${10}^4$ ${\mathrm{V}}_{\mathrm{rms}}$/cm) on the luminescence of KBr: Tl for excitation in the $A$ band has been investigated. The measured spectrum points out beyond any doubt that there are two different centers responsible for the emission.

The specific heat $C_p$ of $\beta$ brass above and below its critical temperature $T_c=739\mathrm{}°$K has been measured over the temperature range ${10}^{-6\mathrm{}}<\epsilon <{10}^{-1\mathrm{}}$, where $\epsilon =\left|\frac{(T-T_c)}{T}\right|$. $C_V$ was then evaluated using the Pippard relations. Above $T_c$, $C_V$ is in good agreement both in magnitude and power-law dependence with Ising model calculations while below $T_c$, $C_V$ depends roughly logarithmically on $\epsilon$ for ${10}^{-5\mathrm{}}<\epsilon <{10}^{-2\mathrm{}}$.

The experimental observation and an atomic mechanism of the linear magnetoelectric effect in DyP${\mathrm{O}}_4$ are reported and shown to provide evidence for the feasibility of isothermal forced switching between time-reversed (i.e., moment-reversed) antiferromagnetic configurations by means of metamagnetic transitions.

The distributions of nuclear $M1\mathrm{}$ and $E2\mathrm{}$ moments in the nuclei ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}$, ${}_{}{}^{133}{}_{}{}^{}\mathrm{Cs}$, and ${}_{}{}^{141}{}_{}{}^{}\mathrm{Pr}$ have been investigated by observing the hfs of their muonic x-ray spectra. The $M1\mathrm{}$ hfs interaction constants are in good agreement with the values calculated from the configuration-mixing model. The measured $E2\mathrm{}$ hfs constant in the $2p_{\frac{3}{2}}$ state of muonic ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}$ is in agreement with theory only if the free-atom value for the spectroscopic quadrupole moment is corrected for atomic polarization effects.

Our on-line mass-spectrometer technique has enabled us to measure the half-lives of very neutron-rich Li and Na isotopes produced in the reaction of 24-GeV protons on heavy nuclei. A $\beta$ energy spectrum of ${}_{}{}^{27}{}_{}{}^{}\mathrm{Na}$ has also been obtained.

A new method for measuring the gravitational constant $G$ is described. Preliminary measurements give $G=(6.674\mathrm{}\pm 0.012)\times {10}^{-11\mathrm{}}$ N ${\mathrm{m}}^2$/${\mathrm{kg}}^2$ where the 0.012 represents 3 standard deviations. Furthermore there is reason to believe that with certain modifications of the apparatus and use of improved metrology techniques an increase in precision of at least one and probably two orders of magnitude will be obtained.

In a study of air-shower cores using a delayed-expansion cloud chamber, we have observed a track for which the only explanation we can see is that it is produced by a fractionally charged particle.

We have measured the ${K_S}^0$ charged-to-neutral branching ratio by examining ∼25 000 $K^{+}$ charge-exchange reactions in a Freon bubble chamber. Our result, 2.10 ± 0.06, is in poor agreement with a recent measurement by Gobbi et al. who obtained a value of 2.285 ± 0.055, while it is in fairly good agreement with the average of earlier experiments.

Angular distributions are presented for $\overline{p}-p$ elastic scattering at 8 and 16 GeV/c for $\mathrm{}\left|t\right|<1.3\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$. At both energies there is structure in the differential cross sections in the region $0.5<~\mathrm{}\left|t\right|\mathrm{}<~1.0$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$, similar to that observed at lower energies. The diffraction peak continues to expand with increasing incident momentum.

Using chiral SU(2) current algebra and partially conserved axial-vector current to generate a set of Ward identities we have derived a relation which can be interpreted as a dynamical equation for the off-shell pion form factor. We solve the equation on shell in an effective-range approximation for the pion form factor, and from unitarity we deduce the $p$-wave $\pi \pi$ phase shift. Our results are in excellent agreement with all relevant data.

Recent theoretical results on high-energy scattering are extended. We give explicit rules to obtain the high-energy behavior of the sums of large classes of Feynman diagrams. This consideration suggests, for high-energy diffraction scattering, a physical picture which is simple and natural. We emphasize that this physical picture has the virtue of yielding correctly all the high-energy results of quantum electrodynamics.

We report on ∼340 events of the reaction ${\pi }^{+}n\to {\omega }^{0}p$ at a beam momentum of 4.19 GeV/c. The differential cross section shows neither a broad dip for $t<-0.2\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ nor a dip in the region $t\approx -0.6\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$. There is a 2-standard-deviation dip in ${\rho }_{00}$ between $t=-0.2\mathrm{}$ and $t=-0.3\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ and a small negative value of $\mathrm{Re}{\rho }_{10}$ for $t<-1.0\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$. The dip in ${\rho }_{00}$ is consistent with the vanishing, in that region of $t$, of an exchanged trajectory with unnatural parity. A simple Regge-model calculation with $\rho +B$ exchange does not reproduce the data.

By Stark tuning the ${\mathrm{N}}^{14}$${\mathrm{H}}_2$D molecule into optical resonance with a standing-wave laser field, which is intense and monochromatic, it has been possible to obtain a unique vibration-rotation line assignment and its transition matrix element, and to probe ground- and excited-state Stark splittings with precision. Stark splittings as narrow as 1.5 MHz (within a Doppler width of 82 MHz) are observed for the first time in an optically excited state using the Lamb dip.

An ion-impact spectrometer has been constructed to measure the energy loss of ions inelastically scattered without charge exchange from molecular targets. Pure vibrational transitions excited by ${\mathrm{H}}^{+}$ and ${\mathrm{H}}_2^{+}$ projectiles of energies from 100 to 600 eV have been observed in ${\mathrm{H}}_2$, ${\mathrm{D}}_2$, and ${\mathrm{N}}_2$. The angular distribution of scattered ions and the energy dependence for these processes have been investigated. The excitation cross sections for pure vibrational transitions are unusually large.

By modulating a parallel-electron-current sink, the collisional drift wave is stabilized with negative feedback in the unstable regime and destabilized with positive feedback in the stable regime. Upon stabilization, improved plasma confinement is measured.

We report precise NMR frequency measurements on fluid xenon which show a temperature-dependent local magnetic field and small but significant deviations from a linear density dependence of the local field. These data can be used to obtain values for the shift of the local field from its zero-density limit as well as the temperature dependence of the shift per unit density in the low-density limit.

The anomalously large resistivity observed in collisionless shock-wave experiments is explained in terms of a drift instability of ion acoustic waves.