We have measured the differential cross section for ${\pi }^{-}p\to {\eta }^{0}n$ at 6.0 GeV/c from 6730 very clean events in which the decay $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$ was detected. The high statistics reveals a sizable forward turnover, implying a dominance of the helicity-flip amplitude. A precisely determined $A_2$ trajectory, linear for $\mathrm{}\left|t\right|<1.0\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$, is found from combining our data with those at energies up to 101 GeV.

The first-order nature of the antiferromagnetic transitions in Cr, Eu, U${\mathrm{O}}_2$, and MnO can be explained by noting that the corresponding Landau-Ginzburg-Wilson Hamiltonians possess no stable fixed points in $4-\epsilon$ dimensions. We predict that all fcc type-I ($\overrightarrow{\mathrm{m}}\perp \overrightarrow{\mathrm{k}}$), type-II, and type-III ($\overrightarrow{\mathrm{m}}\perp \mathrm{}\left[100\right]\mathrm{}$, $\overrightarrow{\mathrm{k}}=\left[\frac{1}{2}01\right]$) antiferromagnetic transitions are first order.

The Schottky barrier for holes on common III-V and II-VI semiconductors contacted by Au is shown to depend only on the anion electronegativity.

We report results from a study of ${\pi }^{-}p\to {\omega }^{0}n$ at 6.0 GeV/c based on 28 000 events from a charged and neutral spectrometer. Background under the ${\omega }^0$ is only 7%, a large improvement over deuterium-bubble-chamber work. Density matrix elements, projected cross sections, and effective trajectories for natural and unnatural exchanges are presented.

The ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}(n, f)$ cross section and the angular anisotropy of fission fragments have been measured up to 5 MeV. The broad vibrational levels located above 1 MeV are resolved into sharp structures which are interpreted as rotational states. The rotational constants $\frac{h^2}{2\mathcal{I}}$ of highly deformed ${}_{}{}^{233}{}_{}{}^{}\mathrm{Th}$ are found to be 2.46 and 2.73 keV at 1.5 and 1.6 MeV, respectively. Our results are interpreted in terms of a hypothetical third minimum in the fission barrier.

A technique is described for high-resolution spectroscopy using resonance absorption from a laser to monitor the time evolution of a coherently excited superposition of atomic states. As a demonstration a measurement was made of the $3{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ hyperfine splitting in sodium.

Quantum beats are analyzed by means of a boson-type second-quantization method which exhibits the collective behavior of $n$-level systems and displays both quantum mechanical and classical (or semiclassical) results. Theoretical criteria for predicting the existence of beats are found which differ from those in the recent literature and indicate a reevaluation of suggested experiments.

Experimental studies indicate that electron rings can be trapped and confined in Astron geometry without a stabilizing conducting wall if a quadrupole-Ioffe or toroidal magnetic field is applied. The ring characteristics are similar to those previously observed in the presence of a conducting wall. All rings trapped with a toroidal field appear to be stably confined. In a Ioffe field, rings with axial self-fields $\delta B\lesssim 0.6B_0$ exhibit a faster-than-usual initial ring decay.

Experimental results are reported for the first time on orifice flows in which deposited electron-beam energy exceeds flow stagnation enthalpy. The experiment simulates the ion-beam-gas-flow interaction of the gas-target neutron generators planned for fusion engineering research. While gas-dynamic stability is observed, plasma-dynamic-gas-dynamic interactions are found to be important at high power and ionization densities.

We show that the motion of charged particles, radially confined by slowly converging surface magnetic fields to the interior, $\mathcal{r}<R\left(z\right)\mathrm{}$, of a cylindrical region, has an adiabatic invariant for $\left(\frac{\mathrm{dR}}{\mathrm{dz}}\right)\ll 1$. This provides axial confinement of particles outside of a loss cone, with critical velocity pitch angle given by ${{sin}^2\theta }_c={\left(\frac{R_{min}}{R_{max}}\right)}^2$. Computational results verifying the theory are presented and the single-particle lifetime, $\tau$, is found to scale as ${\left|\frac{\mathrm{dR}}{\mathrm{dz}}\right|}^{-5\mathrm{}}$ for suitably smooth $R\left(z\right)\mathrm{}$.

On the basis of an analysis of data on a large number of compounds exhibiting displacive phase transitions, it is observed (with no known exceptions) that the transition temperature decreases with hydrostatic pressure for those transitions associated with soft zone-center optic phonons and increases for those transitions associated with soft zone-boundary optic phonons. This difference in behavior is tentatively interpreted in terms of a reversal in the roles of the short-range and long-range forces in the lattice dynamics of the two cases.

We have deduced from measurements of the neutron elastic cross section that below the Néel temperature ($T_{\mathrm{N}}$) the oxygen atoms in U${\mathrm{O}}_2$ are shifted from their ideal fluorite positions. We find quantitative agreement with experiment by assuming a rearrangement (internal shear deformation with amplitude 0.014 Å) of the oxygen sublattice. The dominance of this deformation mode in the spin-lattice interactions suggests the presence of a non-collinear magnetic structure in U${\mathrm{O}}_2$.

Resistivity annealing following irradiation with 3-MeV electrons at 4.5 K has been investigated on tungsten single crystals. High-purity samples showed a recovery stage between 24 and 30 K, which apparently shifts with increasing dose to lower temperatures. We conclude that it is associated with long-range migration of self-interstitial atoms with a migration energy of 54 ± 5 meV. The relationship to recent conclusions of other authors is discussed.

We calculate the frequency-dependent mobility of a classical Brownian particle moving in a periodic potential. The problem is solved by applying a generalized version of Mori's continued-fraction method. The results are then used to interpret the observed frequency-dependent conductivity for the superionic conductor AgI.

Specific-heat and electrical-resistivity measurements in Ce${\mathrm{Al}}_3$ below 0.2 K reveal enormous magnitudes of the linear specific-heat term $C=\gamma T$ ($\gamma =1620\mathrm{}$ mJ mole/${\mathrm{K}}^2$) and the $T^2$ term in $\rho =A{T}^2$ ($A=35\mathrm{}$ μΩ cm/${\mathrm{K}}^2$). We conclude that the $4f$ electrons obey Fermi statistics at low temperatures because of the formation of virtual bound $4f$ states.

It is shown that the probability for the magnitude of the internal field $\left|\overrightarrow{\mathrm{H}}\right|$ of a spin-glass is proportional to $H^{2}d\left|\overrightarrow{\mathrm{H}}\right|$ for very small internal fields. If one assumes that the spins are quantized in the magnitude of the field the low-temperature specific heat is proportional to $T^3$ in disagreement with the experimentally measured linear dependence.

The $a$-axis, temperature-dependent electrical resistivity of high-purity, stoichiometric Ti${\mathrm{S}}_2$ is proportional to $T^2$ from at least 10 to 400 K. This unique behavior is apparently caused by electron-electron scattering.

Resistivity measurements of frozen mixtures of Xe and Fe versus concentration and temperature exhibit various conduction regions including a nonconducting-to-conducting transition at ∼30 at.% Fe. Mössbauer-effect measurements reveal no changes in isomer shift or hyperfine magnetic field with concentration above ∼14 at.% Fe. However, the change in shape of the Mössbauer spectra suggests that a transition from a paramagnetic relaxing phase to a magnetically ordered phase occurs at ∼30 at.% Fe.

We consider an Ising model in which the spins are coupled by infinite-ranged random interactions independently distributed with a Gaussian probability density. Both "spinglass" and ferromagnetic phases occur. The competition between the phases and the type of order present in each are studied.

An overview of the valence-band region of ${\left(\mathrm{SN}\right)}_x$ by means of photoelectron spectroscopy is presented. The spectrum gives, in general, an excellent account of the density of occupied states compared with band-structure calculations. Deviations between theory and experiment in the region of the conduction band are taken as strong evidence for interchain coupling. The interchain matrix element is estimated to be 0.6 times the value of the intrachain matrix element. The consequences of this result are discussed.