The velocity autocorrelation $\varphi \mathrm{}\left(t\right)\mathrm{}$ function is calculated for electrons moving along a high electric field in $n$-type silicon. For short times $t$, it varies as $\exp (-\frac{t}{{\tau }_0})$, but for times greater than approximately $1.5{\tau }_0$, the short-time exponential decay appears to go over to a $t^{-\frac{3}{2}}$ decay. This representation covers the initial relaxation, but a second exponential also appears as relaxation to the nonequilibrium steady state occurs.

The effect of particle coagulation on an aerosol with a truncated Junge initial size distribution was calculated for arbitrary particle size and time by obtaining an exact analytical solution to the Smoluchowski equation. The solution exhibits a crossover from the Junge form to an asymptotic exponential form. The persistence of a Jung-type size distribution for atmospheric aerosols and smoke aerosols is shown to be consistent with coagulation theory.

In one of the first applications of the new accelerator mass-spectrometry technique to nuclear physics problems, the half-life of ${}_{}{}^{32}{}_{}{}^{}\mathrm{Si}$ has been determined to be 108±18 yr. This result, which disagrees with the accepted value of 330±40 yr, has special significance because of the use of ${}_{}{}^{32}{}_{}{}^{}\mathrm{Si}$ for dating studies.

The half-life of ${}_{}{}^{32}{}_{}{}^{}\mathrm{Si}$ has been measured to be $T_{\frac{1}{2}}=101\mathrm{}\pm 18$ yr, considerably shorter than the previously accepted value of ≈ 300 yr. The new value was obtained by measuring the specific $\beta$ activity with a liquid-scintillation-counter technique and the ${}_{}{}^{32}{}_{}{}^{}\mathrm{Si}$ concentration with tandem-accelerator mass spectrometry. It is expected that the present result will have a strong impact on studies with cosmogenic ${}_{}{}^{32}{}_{}{}^{}\mathrm{Si}$.

It is pointed out that the regime of very low critical masses, of the order of 10 μg, can be reached in highly compressed ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ pellets by laser-driven implosions. The estimated temperatures range up to ${10}^{12}$ K in the overdense uranium-fission-fragment plasma, favoring thermonuclear synthesis of superheavy nuclei. This approach is expected to make possible the testing of superheavy-nuclei production cross sections down to ${10}^{-41\mathrm{}}$-${10}^{-42\mathrm{}}$ ${\mathrm{cm}}^2$.

The inelastic scattering of 20-MeV vector-polarized deuterons from ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$, and ${}_{}{}^{54}{}_{}{}^{}\mathrm{Cr}$ provides an experimental determination of sign and magnitude of the quadrupole mass transition amplitudes $〈{2_1}^{+}\mathrm{}\left|\right|\mathrm{}{Q}^m\mathrm{}\left|\right|\mathrm{}{2_1}^{+}〉$, $〈{2_2}^{+}\mathrm{}\left|\right|\mathrm{}{Q}^m\mathrm{}\left|\right|\mathrm{}{2_2}^{+}〉$, and $〈{0_1}^{+}\mathrm{}\left|\right|\mathrm{}{Q}^m\mathrm{}\left|\right|\mathrm{}{2_2}^{+}〉〈{2_2}^{+}\mathrm{}\left|\right|\mathrm{}{Q}^m\mathrm{}\left|\right|\mathrm{}{2_1}^{+}〉〈{2_1}^{+}|\times |Q^m\mathrm{}\left|\right|\mathrm{}{0_1}^{+}〉$, which correspond to the static quadrupole moments ${Q_2}_{1^{+}}$ and ${Q_2}_{2^{+}}$ and the $P_3$ interference term in the case of electromagnetic transitions.

High-multiplicity events were selected in collisions of 800-MeV/nucleon Ar on KCl and Pb. In these events, projectile fragments are highly suppressed, and the angular distributions of high-energy protons are almost isotropic in a moving frame whose rapidity is $y_0$ ($y_0\simeq 0.60$ for KCl and 0.43 for Pb targets). Comparisons with inclusive proton data are used to estimate the relative importance of single and multiple $\mathrm{NN}$ collisions. Pion spectra in high-multiplicity events are also presented.

Absolute cross sections for a number of binary processes in the ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$+${}_{}{}^{159}{}_{}{}^{}\mathrm{Tb}$ reaction have been determined by use of $\gamma$-particle coincidence techniques. The data are used to test a "sum-rule model" of complete- and incomplete-fusion reactions. The model assumes the reaction probabilities to be scaled by the available phase space and to be constrained additionally by the entrance-channel angular momentum limitations.

The $4s-4p$, $4p-4d$, and $4d-4f$ transitions of ten copperlike and zinclike ions from ${\mathrm{Ba}}^{26+}$ to ${\mathrm{W}}^{45+}$ have been observed by means of a laser-produced plasma and a 2.2-m grazing-incidence spectrograph. The spectra are accompanied by a prominent continuum lying just below the $4p{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}-4d{}_{}{}^2{}_{}{}^{}D_{\frac{3}{2}}^{}{}_{}{}^{}$ transitions in the copperlike ions. The results support the identification of the resonance lines of ${\mathrm{Xe}}^{24+}$ and ${\mathrm{Xe}}^{25+}$ in the Princeton University ST tokamak by Hinnov.

Transmission yield of fast ${\mathrm{H}}_2^{+}$ through carbon foils has been measured over a wide range of foil thicknesses for 0.4-1.2-MeV/amu ${\mathrm{H}}_2^{+}$ projectiles. A model is described which gives an excellent quantitative account of this yield as well as that of the associated ${\mathrm{H}}^0$ production.

A new type of time correlation analysis of resonance fluorescence is presented. A strontium atomic beam is excited by a 28-ÅA-off-resonance laser. The photons of the two sidebands of the fluorescence triplet are shown to be emitted in a well-defined time order. A simple interpretation of this effect is given which implies a quantum jump of the atom from the lower to the upper state through a multiphoton process.

Vibrational and rotational Raman transitions are shown to be shifted to lower frequencies in the presence of a nonresonant, high-intensity optical field. Experimental results using coherent anti-Stokes Raman spectroscopy for hydrogen and nitrogen are presented. The magnitude of the observed shift is in agreement with a calculation which considers the coupling of the optical field to the internuclear separation via the molecular electronic polarizability. The magnitude of the shift is predicted to be proportional to the optical field intensity.

For ${\mathrm{Ar}}^{*}$ + ${\mathrm{O}}_2$ collisions at ≈ 100 eV energies an intense rainbow peak has been observed in the neutral-product angular distribution. The surprisingly large inelasticities (1-2 eV) and the absence of elastic scattering in this small-angle feature are explained by a charge-transfer model involving transient formation of an ${\mathrm{Ar}}^{+}$ + ${\mathrm{O}}_2^{-}$ intermediate. Large product inelasticities are understood by examing the relative timing of the projectile motion and the ${\mathrm{O}}_2^{-}$ vibration on the intermediate surface.

Close-coupling calculations on the atomic collisions at cryogenic energies in a 100-kG magnetic field between spin-polarized hydrogen (H↑) and deuterium (D↑) have demonstrated the resonant spin-flip process postulated by Stwalley and the importance of minimizing the presence of D↑ in the experimental preparations of bulk H↑ currently in progress. Other interesting features are presented and briefly discussed including multiple Ramsauer-Townsend effects and direct electron and nuclear single- and double-spin-flip processes.

Excited neutral atoms having positive Stark energies may be trapped near magnitude minima of electrostatic fields. At moderate field strengths Rydberg atoms have trap depths comparable to ambient $\mathrm{kT}$ and as much as 100 times those of recently proposed optical-field traps. Polar molecules and metastable hydrogen and positronium atoms also can be trapped. A slow nondegenerate atom in a quadrupole field is harmonically bound. Sustained trapping and cooling should be possible, allowing Doppler-free few-atom spectroscopy and novel collision studies.

The first experimental evidence of the diffusive character of the phase variable which describes the position of the convective rolls is presented. To produce a phase modulation a small alternating flow in a slightly supercritical fluid layer is injected. With use of this method, the diffusion coefficient $D_{\parallel }$ concerning the propagation of phase disturbances parallel to the roll axis is measured.

A theory is developed, with use of Feynman's effective-potential method, for the quantum-mechanical (QM) effects on the critical properties of Lennard-Jones fluids. The theory (i) provides a good description of the QM effects on the critical temperature, pressure, and volume; (ii) predicts no QM effects on critical exponents; (iii) correctly describes the QM corrections to critical amplitudes; and (iv) introduces QM corrections to the "correction-to-scaling" confluent singular terms obtained via classical renormalization-group theory.

A study of Bragg reflections in both blue phases (BPI, BPII) of two mixtures of chiral and nonchiral biphenyls indicates both phases probably have the same translational symmetry and are either body-centered or simple cubic. The temperature dependence of several Bragg reflections indicates that the BPI-BPII transition may be either continuous or discontinuous and that, given the bcc lattice, the lattice parameter is commensurate with the pitch. These results are discussed relative to existing theories.

Properties of two-dimensional ${\mathrm{O}}_2$ adsorbed on graphite are calculated in the extremely low-coverage $\delta$ region and for monolayers, with use of pattern-recognition optimization and Monte Carlo techniques. Equilibrium configurations and orientations, orientational order-disorder, melting, and dissociation transitions are predicted at various ${\mathrm{O}}_2$ densities. Phase characteristics, including a plastic crystallite phase, are compared with experiment.

Neutron scattering measurements have been made on pure, hydrogenated, and deuterated samples of amorphous silicon ($a$-Si) in the wave-vector range 0.007-8.75 ${\mathrm{\AA }}^{-1\mathrm{}}$. Small-angle data indicate structures in the samples of average radius of gyration as large as 270 Å. Large-angle data show that for the concentrations we have measured (14%), the structure of $a$-Si is not altered by the incorporation of large amounts of H or D. The silicon-hydrogen and silicon-deuterium partial structure factors have also been obtained.