Using the ISOLDE on-line isotope separator at CERN to produce sources of ${}_{}{}^{221}{}_{}{}^{}\mathrm{Fr}$, ${}_{}{}^{221}{}_{}{}^{}\mathrm{Ra}$, ${}_{}{}^{222}{}_{}{}^{}\mathrm{Ra}$, ${}_{}{}^{223}{}_{}{}^{}\mathrm{Ra}$, and ${}_{}{}^{224}{}_{}{}^{}\mathrm{Ra}$, and using polycarbonate track-recording films sensitive to energetic carbon nuclei but not to alpha particles, we have discovered two new cases of the rare ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ decay mode—in ${}_{}{}^{222}{}_{}{}^{}\mathrm{Ra}$ and ${}_{}{}^{224}{}_{}{}^{}\mathrm{Ra}$. Our results for branching ratios, $B$, relative to alpha decay are for ${}_{}{}^{221}{}_{}{}^{}\mathrm{Fr}$ and ${}_{}{}^{221}{}_{}{}^{}\mathrm{Ra}$, $B<\mathrm{}4.4\mathrm{}\times {10}^{-12\mathrm{}}$; for ${}_{}{}^{222}{}_{}{}^{}\mathrm{Ra}$, $B=(3.7\mathrm{}\pm 0.6)\times {10}^{-10\mathrm{}}$; for ${}_{}{}^{223}{}_{}{}^{}\mathrm{Ra}$, $B=(6.1\mathrm{}\pm 1.0)\times {10}^{-10\mathrm{}}$; for ${}_{}{}^{224}{}_{}{}^{}\mathrm{Ra}$, $B=(4.3\mathrm{}\pm 1.2)\times {10}^{-11\mathrm{}}$.

The measured branching ratios for the decays of ${}_{}{}^{222,223,224}{}_{}{}^{}\mathrm{Ra}$ by alpha or ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ emissions can be accounted for within a factor of 10 in terms of the ratios of Gamow penetrabilities through potential-energy barriers consisting of a Coulomb repulsion, the nuclear proximity attraction, and an interpolation between the configuration of tangent fragments and the configuration of the parent nucleus.

Correlations between protons, deuterons, and tritons at small relative momenta were measured for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$-induced reactions on ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$. Final-state interactions are observed for all measured correlations. Analysis of the measured two-deuteron correlations favors the $d-d$ phase shifts extracted by $R$-matrix techniques over those found from the resonating-group approach. The two-deuteron correlations, which cannot be explained by the decay of unbound resonances, yield source radii which are considerably larger than those extracted from two-proton correlations.

A $K$-isomeric state in ${}_{}{}^{182}{}_{}{}^{}\mathrm{Os}$ with spin $I=(20\mathrm{}\pm 2)\hslash$ and half-life equal to 100 ns is found to decay in flagrant violation of the usual $K$-selection rules. The observations—still preliminary—are on the other hand readily understood if it is assumed that the yrast configuration of ${}_{}{}^{182}{}_{}{}^{}\mathrm{Os}$ becomes triaxial above the backbend, and that the decay proceeds via the numerous collective levels of the triaxial rotor.

An optimum laser intensity that maximizes the photoionization yield is found in a two-photon resonant, three-photon ionization experiment. At laser intensities higher than this optimum, a negative value is obtained for the exponential index describing this multiphoton process, both at zero detuning and at the detuning for which the signal is maximized. Despite the presence of large (> 1 ÅA) optical Stark shifts, Gaussian beam-focusing effects produce an excitation spectrum peaked near zero detuning and reverse the sense of its skewness.

We have observed microwave transitions of overall order up to 16 in hydrogen atoms initially in $n=60\mathrm{}$ lowest-energy Stark states. Increases in $n$ as large as 4 occur with little change in the electric quantum number $n_e$. Thus hydrogen atoms electrically polarized along the direction of a strong linearly polarized microwave electric field respond one-dimensionally to this field by maintaining their polarization. At some microwave frequencies the final-state $n$ distribution is smooth above threshold field values estimated for stochastic transitions.

Spectroscopy of emitted radiation following single-electron capture for 3-keV/u ${\mathrm{Al}}^{8+}$ ions on ${\mathrm{H}}_2$ shows state-selective capture into the $n=4, 5, \mathrm{and} 6$ energy levels on the ${\mathrm{Al}}^{7+}$ ion. We report a relative measurement of transitions in Al VIII for $207<\mathrm{}\lambda <800\mathrm{}$ Å, and a multiconfiguration Dirac-Fock calculation of energy in levels in Al VIII is used to interpret the observed transitions.

It is shown that the combination of crossed electric and magnetic fields and the Coulomb field of the atomic nucleus can lead to the localization of the Rydberg electron in the vicinity of the Stark saddle point. The localization principle is shown to be similar to the one which serves as the basis for a Penning trap. The localized electron is expected to give rise to quasibound states near and above the saddle-point ionization limit. These states are expected to cause modulations in the threshold photoionization cross sections.

The concept of $2n\mathrm{th}$-order squeezing of a quantum field is introduced as a natural generalization of the usual second-order squeezing. It is shown that the processes of degenerate parametric down conversion, harmonic generation, and resonance fluorescence all exhibit higher-order squeezing.

We show theoretically that a Rydberg atom maser produces during its evolution a squeezed field with sub-Poissonian statistics. We give a semiclassical interpretation of this effect.

Dispersion of forced sound in Xe-He mixtures is found here to show mode coupling: interference between the sound mode and another excitation mode of the gas. Qualitatively different dispersion is found, depending upon whether the He mole fraction is greater or less than a critical value, if the frequency is higher than a critical frequency. Results also show that "two-temperature hydrodynamics" must be used to describe a disparate-mass gas in this frequency range.

This work is a detailed study of ultrasonic damping and velocity in the smectic-$A$ phase of TBBA. Measurements were taken at various frequencies and angles, defined by the direction of propagation of the sound and the symmetry axis of the system. Our results are consistent with the theoretical predictions of Mazenko, Ramaswamy, and Toner but in contradiction with the experimental results obtained by Bhattacharya and Ketterson.

Brownian simulations of semidilute rods confirm that rotation of rods is ordinarily confined to cages which break up through diffusion along rod axes. However, the angular width of the cages is proportional to $\frac{1}{{\left(c{L}^3\right)}^p}$ is the rods are thin, with $p=\frac{1}{2}$ rather than the previously supposed $p=1\mathrm{}$. The latter result is found only for rods at true equilibrium, which cannot occur unless cage topology equilibrates as fast as cage size.

The oscillatory instability of Rayleigh-Bénard convection is studied in a solution of 1.46% ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ for the Prandtl-number range $0.045<~\sigma <~0.15$. The observed behaviors of the oscillatory frequency and the onset condition support the theory of oscillatory convection for a classical, low-Prandtl-number, one-component fluid.

We have measured the shear viscosity of ternary mixtures of 3-methylpyridine, water (${\mathrm{H}}_2$O), and heavy water (${\mathrm{D}}_2$O) as a function of temperature for ten different concentrations, some of which were very near the double-critical-point concentration of this mixture. The exponent to describe the power-law divergence in temperature of the viscosity nearly doubles as the concentration approaches the double-critical-point concentration.

We show that lattice-dynamical slab calculations and surface vibrational spectroscopy can be used to obtain adsorbate structural parameters directly.

The $p(2\mathrm{}\times 2)$ and $c(2\mathrm{}\times 2)$ coverages of S on Ni(100) are studied with a cluster model. Consistent with a recent lattice-dynamics study, the chemical contribution (rigid Ni lattice) to the coverage-dependent shift of the S vibrational energy is of opposite sign to that for O. Analysis of the cluster wave functions suggests that S becomes less negatively charged with coverage, while O becomes more ionic; however, this effect is small.

Fluctuations of the number of protons (${\mathrm{H}}^{+}$) that scatter conduction electrons dominate lowfrequency resistance fluctuations in Nb films. The excess-noise spectra $S_V(f, T)$ obey a scaling law: $\frac{f{S}_V(f, T)}{〈\delta V^2\mathrm{}\left(T\right)\mathrm{}〉}=g\left(\frac{f}{D\left(T\right)\mathrm{}}\right)$; for our geometry at $260<T<\mathrm{}370\mathrm{}$ K, $S_V(f, T)\propto \frac{c_0\mathrm{}\left(T\right)\mathrm{}}{f^{\alpha }}$, $\alpha =0\mathrm{}$ for $f\ll \frac{D}{\left(\pi L^2\right)}$ and $\alpha =\frac{3}{2}$ for $f\gg \frac{D}{\left(\pi L^2\right)}$, $c_0$ is the ${\mathrm{H}}^{+}$ concentration, $L$ is the film length, and the ${\mathrm{H}}^{+}$ diffusion coefficient is $D\left(T\right)=D_0{e}^{-\frac{E}{\mathrm{kT}}}$ with $D\left(300\mathrm{} \mathrm{K}\right)\simeq {10}^{-6\mathrm{}}$ ${\mathrm{cm}}^2$/s and $E\simeq 0.23$ eV. Studies of $\frac{1}{f}$ noise evoke comparable mechanisms.

A formalism is given whereby high-temperature series for the random-field Ising model on a $d$-dimensional hypercubic lattice is obtained by a partitioning of the vertices of the pure-Ising-series diagrams. For a bimodal distribution of quenched random fields we determine the series for the susceptibility to seventh order. Order by order the disorder is treated exactly. $Dlog$ Padé analyses give a susceptibility exponent $\gamma$ in $d=3\mathrm{}$ which crosses over from 1.24 in the pure limit to 1.40 as disorder increases.

We present the first microscopic calculations of the energetics of impurity-defect reactions and provide a detailed picture of the diffusion mechanisms of dopant impurities in Si. We find that vacancies mediate impurity diffusion via impurity-vacancy pairs. Self-interstitials mediate diffusion by ejecting substitutional impurities into interstitial channels and/or via impurity-self-interstitial pairs. The predicted activation energies for P and Al agree well with measured values in both intrinsic and extrinsic Si.