Studies of interactions between ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and emulsion nuclei in the energy range 75-200 MeV/nucleon have not given evidence for any large pion production. This observation is in disagreement with the results recently presented by McNulty et al. who observe a very large pion production in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ reactions at energies < 280 MeV/nucleon.

Negative-pion production in relativistic heavy-ion collisions has been studied in a triggered streamer-chamber experiment with projectile nuclei ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ in the energy range 0.4-2.1 GeV/nucleon incident on targets LiH, NaF, Ba${\mathrm{I}}_2$, and ${\mathrm{Pb}}_3$${\mathrm{O}}_4$. Negative-pion yields, multiplicity distributions, and angular and momentum distributions are reported.

A simple model for pion production in relativistic heavy-ion collisions is developed based on nucleon-nucleon data, nuclear density distribution, and the assumption of straight-line trajectories. Multiplicity distributions for total pion production and for negative-pion production are predicted for ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ incident on a ${\mathrm{Pb}}_3$${\mathrm{O}}_4$ target at 1.8 GeV/nucleon. Production through intermediate baryon resonances reduces the high-multiplicity region but insufficiently to yield agreement with data. This implies the need for a coherent production mechanism.

We calculate the ${\pi }^{-}$ multiplicity distribution for Ar + ${\mathrm{Pb}}_3$${\mathrm{O}}_4$ at 1.8 GeV/nucleon. Good agreement with data is found. Effects of multipion correlations are investigated.

The alignment correlation term $A{\alpha }_{-}E{P}_2\left(cos\theta \right)$ has been measured in the ${\beta }^{-}$ decay ${}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ → ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(g.s.) by a novel technique. The result, ${\alpha }_{-}\left(E_0\right)=-\frac{(0.1\mathrm{}\pm 0.2)}{\mathrm{GeV}}$, indicates that the conserved vector current weak-magnetism form factor, $F_M$, is essentially compensated here by the weak electricity (induced tensor) form factor $F_E$. Using the decomposition of $F_E={F_E}^{\mathrm{}\left(1\right)\mathrm{}}+{F_E}^{\mathrm{}\left(2\right)\mathrm{}}$ into first- and second-class parts, as well as a reliable estimate of ${F_E}^{\mathrm{}\left(1\right)\mathrm{}}$, we conclude that ${F_E}^{\mathrm{}\left(2\right)\mathrm{}}$ is small compared to $F_M$, and compatible with zero.

Gradient couplings (weak magnetism, induced-second-class tensor) and recoil terms manifest themselves specifically through a parameter ${\alpha }_{-}$ in the angular distribution of $1^{+}$ → $0^{+}$ ${\beta }^{-}$ decays of oriented nuclei, i.e., of ${}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ to ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(g.s.). To decide between two contradictory results, we have redetermined ${\alpha }_{-}$ by a direct measurement of the alignment correlation term, $A{\alpha }_{-}E{P}_2\left(\theta \right)$, with a novel technique. We find ${\alpha }_{-}=+0.24\mathrm{}\pm 0.44$ Ge${\mathrm{V}}^{-1\mathrm{}}$, thereby confirming the Louvain result, and ruling out a "large" second-class current.

Selective excitation of the $E$, $F{}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{g}}_{}^{+}{}_{}{}^{}$ state of ${\mathrm{H}}_2$ by two-photon absorption at 193 nm is reported. The excited population is detected by observing fluorescence arising from $E$, ${}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{g}}_{}^{+}{}_{}{}^{}\to B{}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{u}}_{}^{+}{}_{}{}^{}$ transitions. Experimental determinations of the radiative lifetime of the $E$, $F$ level as 100 ± 20 ns and collisional quenching rates for ${\mathrm{H}}_2$ and He as (2.1 ± 0.4) × ${10}^{-9\mathrm{}}$ and (0.8 ± 0.4) × ${10}^{-9\mathrm{}}$ ${\mathrm{cm}}^3$/sec, respectively, have been made. These experiments involve the first selective population of an electronically excited gerade state of ${\mathrm{H}}_2$.

Using the coordinate rotation method with Pekeris trial functions, we find evidence that a resonance occurs in $e^{+}$-H $S$-wave scattering at a complex energy ($-0.257\mathrm{}374-i0.000067$) Ry. No lower resonance is found in the calculation.

Collisional excitation of neon atoms in light sources such as electric discharges, beam-foil interactions, etc., leads to a statistical population of the excited multiplets. This communication shows an anomalously high singlet-to-triplet ratio when the $2s2p^5{}_{}{}^1{}_{}{}^{}P$, ${}_{}{}^3{}_{}{}^{}P$ levels in Ne III are populated by impact of 100-keV projectiles (helium to potassium). Further, an oscillatory sturcture has been observed as a function of the element number of the projectile.

Resistivity and electron heating are measured for a hydrogen plasma in a toroidal magnetic field subjected to a parallel electric field at least 100 times the runaway value and lasting up to $400{{\omega }_{\mathrm{pi}}}^{-1\mathrm{}}$: Nearly constant in time, and scaling as $E^{\frac{1}{2}}$, the resistivity reaches values near $2{\left(\frac{m}{M}\right)}^{\frac{1}{3}}{{\omega }_{\mathrm{pe}}}^{-1\mathrm{}}$. Particle analyzer data reveal heating rates up to 100 keV/μs and indicate the presence of multiple electron beams at higher applied fields.

The customary free expansion to the walls of ions in a pulsed, laser-produced plasma in vacuum has been shown to be inhibited significantly by the rapid injection of an intense electron current from the laser target. In this manner liter-volume, $n\sim {10}^{14}$ ${\mathrm{cm}}^{-3\mathrm{}}$, high-$Z$, highly ionized plasmas with mean ion lifetimes >100 μsec have been produced.

It is shown that the eigenmodes of the collisionless drift wave in slab geometry are stable. Previous studies yielding instability (the "universal" instability) were based upon an incomplete treatment of the electron dynamics; i.e., the principal part of the plasma dispersion function was ignored.

The roots of an improved analytic eigenvalue equation for the absolute universal or collisionless drift instability in a sheared magnetic field are found numerically and compared with the eigenvalues obtained from a numerical solution of the exact differential equation. The startling result is that both techniques predict stability, no matter how weak the shear or how large the transverse wave number, in contradiction to all previous work. Stability is due primarily to the stabilizing influence of the nonresonant electrons.

We have measured the specific heat of helium near the superfluid transition for films up to 56 Å thick and for samples confined to a cylindrical geometry of up to 2000 Å in diameter. The dependence of the shift in the transition temperature on size and the growth of the specific-heat maximum do not yield exponents as expected from simple scaling arguments. The data up to $t\equiv |1-\frac{T}{T_{\lambda }}|={10}^{-2\mathrm{}}$ scale according to a form suggested by Fisher, but with an exponent $\frac{1}{\theta }=0.54\mathrm{}\pm 0.02$.

Initial measurements are reported on the extended x-ray-absorption fine structure (EXAFS) of the Fe $K$ edge in Fe${\mathrm{S}}_2$ to 64 kbar and Fe${\mathrm{F}}_2$ to 21 kbar. With this new technique the Fe-Fe spacings are directly observed to vary in accordance with high-pressure x-ray diffraction measurements of the corresponding lattice parameters. In contrast, the Fe-S spacing in pyrite is found to be much less compressible. Pressure reduction of the mean-square deviations in the iron-ligand bond lengths are also given.

The existence of a pressure-induced tricritical point in potassium dihydrogen phosphate was investigated by direct measurements of the spontaneous shear angle as a function of temperature using $\gamma$-ray diffractometry at pressures up to 2.15 kbar. High-resolution neutron diffractometry was applied to the measurement of the critical behavior of the lattice constant $c$ at various pressures up to 3.5 kbar. The results of the two methods agree and indicate tricritical behavior at a pressure of about 2 kbar.

We reconcile energy-loss spectroscopy and chemical-shift studies of the oxidation of the GaAs(110) surface, which previously have led to contradictory conclusions about the oxygen bonding site. We have calculated densities of states and 100-eV ultraviolet-photo-electron-spectroscopy (UPS) valence-band spectra to examine the site and molecular species of the chemisorbed oxygen. We conclude that for low coverages oxygen prefers to chemisorb to the surface arsenic atoms and chemisorbs as an ${\mathrm{O}}_2$ molecule.

The anomalous behavior of the magnetic crystalline anisotropy in Ni metal at 4 K can be interpreted by the passage of the top of the $X_{2\downarrow }$ sub-band through the Fermi energy, when the magnetization direction is changed. The number of holes in the corresponding hole pocket varies between 0 and 1.4×${10}^{-5\mathrm{}}$ holes/atom. Fair agreement between theory and measurements is obtained.

Self-consistent Hartree-Fock and generalized valence-bond calculations for H chemisorption on a cluster model of a NiO(001) surface have been performed. In the cases where the H approaches over a surface Ni or O site, bond strengths of less than 0.65 eV are found. This is in contrast to those found at a surface Ni vacancy site where the bond strengths are 4.5-7.7 eV. The strong bonds are due to the formation of a singly occupied orbital in the surface complex.

An example is given of a space-time which satisfies the conditions for asymptotic region is not "as large" as that of Minkowski space-time.