The magnetic tricritical behavior of Fe${\mathrm{Cl}}_2$ has been measured using an optical technique in which magnetic circular dichroism is used to determine the total magnetization as a function of temperature and magnetic field. We report tricritical point exponents ${\beta }_u$, ${\beta }_{+}$, and ${\beta }_{-}$ that are consistent with Landau theory, and a magnetization versus temperature phase diagram that exhibits a discontinuity in slope between the $M^{+}$ and $M_{\lambda }$ branches at the tricritical point.

An angular distribution of the polarization transfer coefficient ${K_y}^{y^{\prime }}\left(\theta \right)$ in $d-p$ elastic scattering has been measured at $E_d=45.4\mathrm{}$ MeV. Our results are in very good agreement with the prediction of a recent three-body calculation.

We report results from an experiment designed to test Compton scattering as a means to avoid charged-particle background in the measurement of x-ray transition radiation. Low-$Z$ scatterers (LiH, Be) were used to ensure Compton-scattering domination of other interactions for initial photon energies between 10 and 150 keV. We demonstrate that the technique can be usefully applied at energies of the Fermi National Accelerator Laboratory.

The Taylor instability in a rotating fluid confined between two cylinders has been investigated by light scattering. For rotation rates $f$ asymptotically close to the critical rotation rate $f_c$, we find that the amplitude of the ordered flow varies as ${(f-f_c)}^{0.50\pm 0.03}$. The axial structure of the ordered flow is sinusoidal near $f_c$, but harmonics become substantial for $f-f_c$ large. The main features of the Landau approach to hydrodynamic instabilities are thus confirmed.

We report the first observation of objects moving through He II with equilibrium drift velocities $\overline{v}$ beyond the Landau critical velocity $v_c$ for roton creation. With $T\sim 0.4$ K, $P=25\mathrm{}$ bar, $F=2\mathrm{}$ kV ${\mathrm{cm}}^{-1\mathrm{}}$, $\overline{v}-v_c$ for negative ions is larger than a theoretical prediction by a factor of ∼${10}^5$. The vortex-ring nucleation rate is found to decrease with $F$ above 300 V ${\mathrm{cm}}^{-1\mathrm{}}$, thus resolving apparent inconsistencies between earlier experiments.

A new model of electron flow in high-voltage diodes and superpinch formation is presented. The relativistic cold-fluid-Maxwell equations are reduced, under certain assumptions, to one equation. The model is based on the solution for the electron flow in large aspect-ratio diodes and the inclusion of cathode and anode plasmas. The anode plasma is assumed to be a field-free region. Results are compared to the parapotential-flow model.

Room-temperature pressure studies (<3 kbar) on $a$-${\mathrm{As}}_2$${\mathrm{Se}}_3$ reveal that both hole transport, as determined from time-of-flight experiments, and dark dc conductivity increase with hydrostatic pressure as $\exp \left(\alpha p\right)$, where $\alpha \sim 0.45$ ${\mathrm{kbar}}^{-1\mathrm{}}$, independent of sample parameters. The pressure dependence and the shape of the phototransient strongly support the recently proposed stochastic hopping transport. The pressure dependence of the dark conductivity suggests a bulk controlled process.

The attempt frequency for ion diffusion in the superionic conductors sodium and silver $\beta$-alumina is directly observed as a resonance in the far infrared dielectric response. Correlation of the measured attempt frequency with the observed diffusion coefficient suggests that the best conductors, Na and Ag $\beta$-alumina, can be described by a single ion hopping motion despite the relatively high density of diffusing species.

We have observed a coupled mode of a phonon with a plasmon in the Landau damping region for the first time by Raman scattering from heavily doped $n$-GaAs specimens at 100 K with the use of Ar-ion laser lines. The line shape as well as the dispersion relation was calculated by taking into account the nonlocal effect caused by the motion of free carriers, giving good agreement with the observed spectra.

The new solid electrolyte pentapyridinium 18-silver iodide, ${\left({\mathrm{C}}_5{\mathrm{H}}_5\mathrm{N}\mathrm{H}\right)}_5$${\mathrm{Ag}}_{18}$${\mathrm{I}}_{23}$, effectively allows the current-carrying ${\mathrm{Ag}}^{+}$ ions to move in only two dimensions. Comparison with the other solid electrolyte in the ${\mathrm{C}}_5$${\mathrm{H}}_5$NHI-AgI system, namely (${\mathrm{C}}_5$${\mathrm{H}}_5$NH)${\mathrm{Ag}}_5$${\mathrm{I}}_6$, demonstrates that three-dimensionally interconnecting diffusion pathways are more favorable to high conductivity.

An empirical study is made of the total reaction cross sections for ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ reactions with ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$, ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$, ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$, and ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$. Systematic differences are revealed that are attributed to the effects of nuclear deformation. This behavior can be accounted for by a reduction of the average interaction barrier by 0.3 to 0.6 MeV or by an increase in the width of the spectrum of barriers by 0.4 to 0.7 MeV.

We have produced element 106 by bombarding ${}_{}{}^{249}{}_{}{}^{}\mathrm{Cf}$ with ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ ions accelerated by the SuperHILAC. The new nuclide ${}_{}{}^{263}{}_{}{}^{}106$, produced by the (${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, $4n$) reaction, is shown to decay by $\alpha$ emission with a half-life of 0.9±0.2 sec and a principal $\alpha$ energy of 9.06±0.04 MeV to the known nuclide ${}_{}{}^{259}{}_{}{}^{}\mathrm{Rf}$, which in turn is shown to decay to the known nuclide ${}_{}{}^{255}{}_{}{}^{}\mathrm{No}$.

Gamma radiation from 100-MeV protons incident on targets of ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ has been observed. Residual nuclei were identified by using the known $\gamma$ rays. Some of the strongest $\gamma$ rays observed involved residual nuclei equivalent to the target nucleus minus one to three $\alpha$ particles. These results can be understood on the basis of a pre-equilibrium stage involving an intranuclear nucleon-nucleon cascade followed by an evaporation process.

New observations show a small difference between the sun's polar and equatorial limb darkening functions. This excess equatorial brightness varies in time and can be of sufficient magnitude to account for the solar oblateness inferred by Dicke and Goldenberg from their measurements. This removes the serious consequence of their work for Einstein's general theory of relativity. The problems of a solar-edge definition and the derivation of a solar mass quadrupole moment are discussed.

Differential cross sections for the reactions $\gamma p\to {\pi }^{0}p, {\pi }^{+}n$ and $\gamma n\to {\pi }^{-}p, {\pi }^{0}n$ were measured in a single experiment using tagged photons in the energy region 240-450 MeV incident on ${}_{}{}^1{}_{}{}^{}\mathrm{H}_2^{}{}_{}{}^{}$ and ${}_{}{}^2{}_{}{}^{}\mathrm{H}_2^{}{}_{}{}^{}$ targets. Results of the measurements of the ratios $\frac{{\pi }^{0}n}{{\pi }^{0}p}$ and $\frac{{\pi }^{-}p}{{\pi }^{+}n}$ are presented. The ratio of isotensor to isovector amplitude is found to be 0.00±0.02.

Data are presented on deep inelastic scattering of 56.3- and 150-GeV ${\mu }^{+}$ from an iron target at the Fermi National Acceleratory Laboratory. Observed event rates, averaged over a wide range in $\omega$, are compared to scale-invariance predictions for $q^2$ up to 44 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$. The ratio of the 150-GeV data to the scale-invariance prediction versus $q^2$ is not constant for all accepted $\omega$ values. A fit of the form ${(1+\frac{g^2}{{\Lambda }^2})}^{-2\mathrm{}}$ yields a lower limit of $\Lambda >10\mathrm{}$ GeV with 90% confidence, averaged over a restricted $\omega$ range.

Influence of the one-pion exchange current brought about by the $N^{*}\mathrm{}\left(1236\right)\mathrm{}$ excitation is considered for the photon spectrum of radiative muon capture in calcium. It is found that the relative rate of radiative to ordinary muon capture is substantially lowered and that the discrepancy between partial conservation of axial-vector current theory and experiment is removed.

I apply current-algebra techniques to study threshold pion production induced by the weak neutral current. In addition to specific predictions for the Weinberg-Salam-model current, I find upper bounds on the magnitude of threshold pion production for an isoscalar neutral current and for a general hadronic neutral current formed from the usual vector and axial-vector nonets. Violation of these bounds would suggest the presence of new coupling types in the neutral semileptonic interaction.

I have observed a strong nondivergent beam of radiation from targets with cylindrical bores, emitted in a direction parallel to the target face, when electrons strike the target at grazing angles. The spectroscopic analysis has so far revealed six discrete bands in the range 350-20 keV, which agree well with my predicted values. The theory of bremsstrahlung apparently does not account for the high intensity in the forward direction or for the discrete frequencies of the radiation.

Semiempirical Ne $K$ fluorescence yields for the vacancy configurations $K{L}^i$ were deduced for $i=1\mathrm{} \mathrm{to} 7$ by comparing satellite intensities in 30-MeV ${\mathrm{O}}^{5+}$+Ne and 35-MeV ${\mathrm{O}}^{8+}$ +Ne x-ray and Auger spectra measured recently with high resolution. For some cases the semiempirical fluorescence yields are found to be significantly larger than theoretical values and to differ with previous semiempirical values for the higher degrees of multiple ionization.