Quantitative observations have for the first time been made of the surface diffusion of single self-adsorbed tungsten atoms and atom pairs. Measurements on the (211) plane indicate that motion of single atoms is normal, occuring over a barrier of 74 kJ/mole, with a pre-exponential factor $D_0={10}^{-3\mathrm{}}$ ${\mathrm{cm}}^2$/sec. Motion of pairs formed by atoms in adjacent [111] channels is highly correlated; it involves a much smaller barrier, 28 kJ/mole, and a pre-exponential factor of only ${10}^{-12\mathrm{}}$ ${\mathrm{cm}}^2$/sec.

We compute exactly the four coefficients $C_{0\pm }$ and $C_{1\pm }$ in the expansion ${\beta }^{-1\mathrm{}}\chi =C_{0\pm }{|1-\frac{T_c}{T}|}^{-\frac{7}{4}}+C_{1\pm }{|1-\frac{T_c}{T}|}^{-\frac{3}{4}}+O\left(1\right)\mathrm{}$ for the susceptibility of the rectangular two-dimensional Ising model.

A special renormalization transformation is constructed for one-component spin systems on a two-dimensional triangular lattice. Fixed point, eigenvalues, and eigenvectors are determined in various approximations, which converge well to known Ising data.

Measurements of the magnetization of Fe${\mathrm{Br}}_2$ and Fe${\mathrm{Cl}}_2$ as a function of magnetic field, temperature, and hydrostatic pressure establish lines of tricritical points $T_{3c}$ with slopes $\frac{{\left(T_{3c}\right)}^{-1\mathrm{}}d{T}_{3c}}{\mathrm{dP}}=-0.025, +0.021, \mathrm{and} +0.040\mathrm{}$ ${\mathrm{kbar}}^{-1\mathrm{}}$ for the low- and high-pressure phases of Fe${\mathrm{Cl}}_2$ and for Fe${\mathrm{Br}}_2$, respectively. The variation of the tricritical transition with pressure should provide sensitive tests of theories relating interaction constants in the Hamiltonian to tricritical behavior in magnetic systems.

Recent neutron-diffraction experiments by Mook, Lynn, and Nicklow, as well as previous photoemission experiments by Pierce and Spicer, provide evidence that the Stoner band splitting in nickel might not go to zero at $T_c$, as it does in conventional band theory of magnetism. It will be shown that the persistence of such splitting in the paramagnetic regime can be explained quite naturally within the framework of the random-phase-approximation theory of spin fluctuations.

The ground-band level sequence in ${}_{}{}^{184}{}_{}{}^{}\mathrm{Hg}$ has been identified to spin ${10}^{+}$ and possibly to ${14}^{+}$. Lifetimes for the $2^{+}$, $4^{+}$, and $6^{+}$ states have been measured. The results imply the onset of a permanent deformation above the $2^{+}$ level.

The elastic scattering of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ on ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ and the reaction ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$)${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$ have been measured at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=30\mathrm{}$ MeV. The elastic-scattering angular distribution exhibits a smooth Fresnel-type diffraction pattern, whereas for the (${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$) reaction we observe strong oscillations in the ground- state transition.

Differential cross sections as a function of transverse momentum are presented for the production at ∼90° (in the c.m. system) of ${\pi }^{\pm }$, $K^{\pm }$, $p$, and $\overline{p}$ in $p$-nucleus collisions at incident proton energies of 200 and 300 GeV.

Measurements are reported of the resonant structure, caused by autoionization, in the angular distribution of xenon photoelectrons. The measurements were made within the autoionizing structure lying between the ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ and ${}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ ionization thresholds for the wavelength range 956 to 1015 Å. The results show a periodic variation in the asymmetry parameter $\beta$ with maximum excursions of about + 0.9 to - 0.9. The overall variation and magnitude of $\beta$ is in accord with the recent theoretical predictions of Dill.

$K$-Auger transitions of neon produced by 33-MeV ${\mathrm{O}}^{5+}$ bombardment are clearly resolved above a broad peaked background. Besides the 5 normal transitions, we observe 58 satellite lines stemming from initial configurations having single $K$-shell, multiple $L$-shell vacancies. Transition energies and relative intensities are measured and compared with those obtained with 1.5-keV electron bombardment. Calculated energies for Auger satellite transitions are used to give possible identifications for observed lines.

Using foil-excited H beams (80-400 keV) we have applied a simple technique recently proposed by Eck to unambiguously separate genuine excitation coherence from that induced by fine structure and probe fields. We find compelling evidence for strong excitation coherence and have studied quantities related to the collision-averaged $s-p$ phase coherence angle. Using Eck's theory, the data exhibit coherent fore-aft oscillations of the electron cloud with respect to the proton.

The folded-diagram procedure of Brandow, suitable for many-body perturbation-theory calculations when unperturbed functions are degenerate, is applied to the four lowest excited ${\Sigma }^{+}$ states of ${\mathrm{H}}_2$ at $R=1.4\mathrm{}$ bohr. Calculating energies up to third order (inclusive) and estimating higher-order corrections, an agreement of 1 kcal/mole is obtained with the accurate results of Kolos and Wolniewicz.

Relative production cross sections for beam ($Z_1$) and target ($Z_2$) $K$ vacancies in heavyion collisions are explained for situations where $Z_1\simeq Z_2$. Electron promotion creates a vacancy in the $2p\sigma$ molecular orbital. As the collision partners retreat, the vacancy has a probability $w(v_1, Z_1, Z_2)<~\frac{1}{2}$ to be transferred to the $1s$ level of the higher-$Z$ collision partner. With a charge-transfer theory of Demkov, a universal form for $w$ is obtained, which is in excellent agreement with all available data for Ni, Br, and I beams over extended target and energy ranges.

Chlorine $K$ x-ray-production cross sections have been measured in single collisions of chlorine ions in low incident charge states with gas targets at MeV energies. The cross sections are nonmonotonic as a function of target atomic number, but they approach monotonicity with increasing projectile energy. To explain these results in terms of $2p\sigma -2p\pi$ transitions in nearly symmetric collisions effectively requires $2p$ vacancy production simultaneous with the promotion of Cl $1s$ electrons.

Electron paramagnetic resonance has been observed in the mixed-valency platinum complex ${\mathrm{K}}_2\mathrm{Pt}{\left(\mathrm{CN}\right)}_4{\mathrm{Br}}_{\frac{1}{3}}·3{\mathrm{H}}_2\mathrm{O}$. The $g$ factors observed are characteristic of $d_{z^2}$-like hole states. The variation of the observed signal intensity is not consistent with the interrupted-strand model or the disorder model but is in accord with the predictions of the Peierls-distortion model.

We demonstrate the importance of including the dynamical exchange-interaction term in the Hamiltonian of a rare-earth system. The probability distribution of the dynamic exchange field is derived in the molecular field approximation. The result is exemplified for the zero-field magnetization and crystal field spectroscopy of NdSb.

The $\gamma$-ray spectra resulting from the bombardment of ${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ with 500-MeV/c negative pions were measured. For ${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$, lines were present from the decay of first excited states of ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}({}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}-1\mathrm{}\alpha )$, ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}({}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}-2\mathrm{}\alpha )$, and ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ti}({}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}-3\mathrm{}\alpha )$. Single neutron removal was not observed. Similar results were obtained for ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$. A comparison is made with results obtained with stopped $K^{-}$ and proton beams.

We develop a straightforward, fast approach to exact finite-range distorted-wave Born-approximation calculations, and apply it to the analyses of the reactions ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$)${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ and ${}_{}{}^{88}{}_{}{}^{}\mathrm{Sr}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$)${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$.

The three-body reaction ${}_{}{}^9{}_{}{}^{}\mathrm{Be}+d\to t+\alpha +\alpha$ has been studied in a kinematically complete way at $E_d=26.3\mathrm{}$ MeV. The data are represented in terms of projections for selected parts of the Dalitz plot, emphasizing the two-body resonance structure. Excitation energies and widths for the broad resonances are deduced. Although the reaction mechanism is shown to be predominantly sequential, we have observed a significant three-body breakup contribution (about 19% over the entire three-body phase space).

We analyze the possibility of neutrino emission from matter accreting into a neutron-star member of a binary x-ray source. Estimates of the expected fluxes and neutrino energy are given for selected values of the accretion rate under the assumption that the neutrino production is mainly due to the reaction $\gamma \leftrightarrows e^{-}+e^{+}\to {\nu }_e+{\overline{\nu }}_e$.