A competing process to direct $K$-shell ionization by heavy-ion impact is suggested to account for some recent data by Macdonald et al. It is found that the high-$Z$ dependence of the x-ray yields can be accounted for by inclusion of $K$ charge exchange into bound states of the fully stripped projectiles.

Strong first-order Raman scattering of the normally forbidden odd-parity phonons is observed in ${\mathrm{Cu}}_2$O excited by a tunable dye laser in resonance with the intrinsic dipoleforbidden $1S$ yellow exciton. The resonance enhancement and the polarization behavior of these Raman lines are explained by including the electric quadrupole term of the exciton-photon interaction in the calculation of the Raman cross section.

We present evidence that in granular metals the observed temperature dependence of the low-field conductivity, $\exp (-\frac{b}{T^{\alpha }})$ with $\alpha =\frac{1}{2}$, can be ascribed to a relationship $s{E}_c=\mathrm{const}$ between $s$, the separation of neighboring metal grains, and $E_c$, the electrostatic energy required to create a positive-negative charged pair of grains. This relationship results from simple considerations of the structure of granular metals. The predictions of the theory, for both the high- and the low-field electrical conductivity, are in excellent accord with experimental results in granular Ni-Si${\mathrm{O}}_2$ films.

The response of the magnetization to a sudden reversal of the magnetic field is studied in the kinetic Ising model by means of computer experiments on square $N\times N$ lattices. It is found that the nonequilibrium relaxation function fulfills a dynamic scaling hypothesis. The magnetization of the metastable state agrees with predictions of the cluster model and also with an analytic continuation of the linear-model equation of state.

Hyperfine fields at normal impurities in ferromagnetic metals and alloys vary systematically in sign and magnitude. These results are explained by an extension of Ruderman-Kittel-Kasuya-Yosida spin polarization to the case of an electron gas with a strong local perturbation.

Angular distributions and an excitation function have been measured for the reactions ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$(${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^6{}_{}{}^{}\mathrm{L}\mathrm{i}*$(3.56)) ${}_{}{}^6{}_{}{}^{}\mathrm{L}\mathrm{i}*$(3.56) and ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$(${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^6{}_{}{}^{}\mathrm{He}$)${}_{}{}^6{}_{}{}^{}\mathrm{Be}$ at laboratory bombarding energies between 28 and 36 MeV. A microscopic distorted-wave Born-approximation analysis which includes the tensor interaction and exchange gives good agreement with the data, except at forward angles, and predicts the correct magnitude of the cross sections. Estimates of the strengths of the effective Majorana and spin-tensor isospin interactions are given.

The polarization of breakup neutrons from the reaction $\mathrm{D}(p, n)2p$ has been measured at $E_p=21.5\mathrm{}$ MeV as a function of neutron energy with accuracy of approximately ± 0.01. The high-energy neutrons ($E_n>14\mathrm{}$ MeV) show a small but significant positive polarization ($P_n\sim 0.015$), in disagreement with the prediction ($P_n=0\mathrm{}$) of the Amado model and also in disagreement with expectations if the dominant process were simple quasifree $p-n$ scattering.

An average trapped surface is defined as a closed two-surface with the property that the area of the wave fronts formed by light rays emitted in the orthogonal inward and outward directions are both decreasing. A sufficient criterion is given for the formation of average trapped surfaces in a general gravitational collapse. The criterion has the qualitative form that if a given amount of matter is compacted into a sufficiently small region, then an average trapped surface must be formed. In the case of nearly spherically symmetric gravitational collapse, it is shown that average trapped surfaces always form to second order in the perturbations of spherical symmetry.

If particle or antiparticle total cross sections ${\sigma }_P$, ${\sigma }_A$ are unbounded as $E\to \infty$, using unitarity it is shown that on the average the ratio $\frac{〈{\sigma }_P-{\sigma }_A〉}{〈{\sigma }_P+{\sigma }_A〉}\to 0$.

We report here the results of a measurement of the integral energy distribution of the neutrino-induced muon flux deep underground using the Utah neutrino detector. Five neutrino-induced muon candidates have been obtained from the approximately ${10}^6$ muons which have passed through the detector during 603 days of live operation out of 830 days total elapsed time. By comparing the observed and expected energy distributions we are able to set lower limits on the saturation energy $E_0$ of the total neutrino-nucleon cross section or, equivalently, on the mass $M_W$ of the intermediate vector boson if scale invariance of the inelastic structure function $\nu W_2$ is assumed. We find at the $1\sigma$, $2\sigma$, and $3\sigma$ levels of confidence $E_0>320, 80, \mathrm{and} 29$ GeV or $M_W>10, 5, \mathrm{and} 3$ GeV, respectively.

EPR investigations of ${\mathrm{Ag}}^{2+}$ in the series of isomorphous hosts SrO, CaO, and MgO show that the low-temperature Jahn-Teller effect is static for SrO: ${\mathrm{Ag}}^{2+}$, predominantly static but intermediate to the dynamic effect for CaO: ${\mathrm{Ag}}^{2+}$, and predominantly dynamic but slightly intermediate to a static effect for MgO: ${\mathrm{Ag}}^{2+}$. This represents the first observation of the systematic transition from static to dynamic Jahn-Teller effects at low temperature.

A $K$-x-ray band up to the united-atom limit for $Z=70\mathrm{}$ has been observed in 30- and 60- MeV Br + Br collisions. This band can be assigned unambiguously to transitions between molecular orbitals. With a KBr target, yields at the two energies are (for $E_x>~22$ keV) 2 × ${10}^{-8\mathrm{}}$ and ${10}^{-7\mathrm{}}$ photons/projectile, respectively, or ${10}^{-4\mathrm{}}$ photons/beam $K$ vacancy, nearly independent of beam energy. Much reduced yields are found for Ti, Fe, and Zr targets.

The quantum-mechanical method developed earlier is applied to the four-photon resonant ionization of Cs. Comparisons of the present calculations with the experiments by Held et al. are given, and good agreement with the experiments is obtained. The application of the present theoretical method to the six-photon ionization of hydrogen is indicated.

The alignment of some singlet and triplet $D$ states of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ resulting from the beam-foil interaction process at 40 kV has been measured for principal quantum numbers $n=3,4,5, \mathrm{and} 6$. The measurements were based on zero-field level crossing.

Yields of projectile and target $K$ x rays from collisions between ∼ 80-MeV argon ions and thin neon targets increase dramatically as the projectile charge is increased from +6 to +17. Although incrementing the projectile charge state amounts to "tuning" projectile $L$-shell energy through target $K$-shell energy, the 60-fold (∼exponential) increase in target yield and the more than 1000-fold (>exponential) increase in projectile yield can be partially understood as the effect of a rapidly changing fluorescence yield, but not as an energy-level-matching effect.

A systematic increase in ${\mathrm{Te}}^{125}$ quadrupole splitting of up to 54% has been observed in the isoelectronic crystalline hosts of Te, Se, and S. This is attributed to nonlocal and overlap electronic contributions to the electric field gradient $q_{\mathrm{e}1}$, which increase as a result of a systematic shortening of the covalent bonds.

The electrostatic instability in a magnetoplasma, $\omega >{\omega }_{\mathrm{ce}}$, excited by a weak electron beam is found to be either convectively unstable (amplifying) or absolutely unstable (oscillating) depending upon effective plasma electron temperature and beam density. Measurements of the transition between the two types agree with calculations.

The growth of an ion acoustic instability caused by a slow electron drift is studied experimentally. A small-amplitude test wave in this unstable system develops into a large-amplitude steady state which is found to be a Bernstein-Greene-Kruskal—like ion mode with trapped electrons.

It is found that a 400-keV, 10-40-kA, 50-nsec duration hollow relativistic electron beam suffers from a severe instability when injected into neutral gas along a magnetic field. The dependence of beam distortion on beam thickness, magnetic field strength, beam current, and proximity of the surrounding conducting walls is experimentally studied. The experimental observations are consistent with the diocotron instability occurring during the first several nanoseconds of the beam pulse.

Two intense electromagnetic waves interact strongly where the local plasma frequency equals their difference frequency, resulting in an irreversible transfer of action from the higher-frequency wave to the lower-frequency wave. The amount of transfer depends only on the intensities and the density scale length. Successive transfers among a set of waves may produce efficient plasma heating.