We have observed atoms consisting of a pion and a muon produced in the decay ${K_L}^0\to {\left(\pi \mu \right)}_{\mathrm{atom}}\nu$. This represents the first observations of an atom composed of two unstable particles and of an atomic decay of an elementary particle.

We have observed thirty events of the process $\nu p\to \nu p$ with a background expectation of seven events. The neutral-current to charged-current ratio $\frac{\sigma (\nu p\to \nu p)}{\sigma (\nu n\to {\mu }^{-}p)}$ is measured to be 0.17±0.05 for $0.3<\mathrm{}{q}^2<0.9\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ where $-q^2$ is the square of the four-momentum transfer to the proton.

We present evidence, from a study of multihadronic final states produced in $e^{+}{e}^{-}$ annihilation at center-of-mass energies between 3.90 and 4.60 GeV, for the production of a new neutral state with mass 1865±15 MeV/${\mathit{c}}^2$ and decay width less than 40 MeV/${\mathit{c}}^2$ that decays to $K^{\pm }{\pi }^{\mp }$ and $K^{\pm }{\pi }^{\mp }{\pi }^{\pm }{\pi }^{\mp }$. The recoil-mass spectrum for this state suggests that it is produced only in association with systems of comparable or larger mass.

The basis for a low-threshold, high-efficiency, direct-counting detector for solar neutrinos from the $p-p$ fusion reaction is proposed. The inverse $\beta$ decay of ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}$ to the 614-keV excited state of ${}_{}{}^{115}{}_{}{}^{}\mathrm{Sn}$ ($T_{\frac{1}{2}}=3.26\mathrm{}$ μsec) provides a unique delayed-coincidence signature and is estimated to yield a solar-neutrino capture rate of ∼750 solar neutrino units, ∼85 of which is due to $pp+pep$ neutrinos.

Inelastic scattering of 45-MeV protons and 70-MeV ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ particles has been used to study the giant-resonance region of ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. The giant resonance is found to be highly structured with states of different multipolarities, such as dipole, quadrupole, and octupole. A monopole state is found at 9.11 MeV which exhausts about 2% of the monopole-sum-rule strength.

Isoscalar giant quadrupole resonances are theoretically studied for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$. A remarkable difference in the widths of these resonances observed in ($\alpha , {\alpha }^{\prime }$) experiments is explained. Both one-particle, one-hole and two-particle, two-hole correlations are found to be responsible for producing the difference.

The large-$q^2$ falloff of the elastic deuteron form factor is used to relate meson exchange to underlying quark currents, to relate the deuteron form factor to large-angle $n-p$ scattering, to demonstrate scale-invariant behavior of the nucleon-nucleon potential, and to determine the deuteron wave function at small $n-p$ separation.

Direct-semidirect radiative-capture calculations are compared to new detailed ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}(p_{\mathrm{pol}}, {\gamma }_0){}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ measurements in the giant-dipole-resonance region. The calculations provide a good description of the data by including only direct $E2\mathrm{}$ and direct plus collective $E1\mathrm{}$. The experimentally determined $E2\mathrm{}$ cross section exhausts (6.8±1.4)% of the isoscalar sum rule and shows no sign of a resonance.

The transverse polarization transfer coefficient, ${K_v}^{y^{\prime }}\left(0\mathrm{}°\right)$ has been measured for the reaction ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}(p, n){}_{}{}^{11}{}_{}{}^{}\mathrm{C}\mathrm{}\left(0\right)\mathrm{}$ at $E_P=16.3, 21.3, \mathrm{and} 26.5$ MeV. The results are not in agreement with direct-reaction-theory calculations using an empirical charge-exchange effective interaction which includes both central and tensor forces.

Angular distributions at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=7.44\mathrm{}$ MeV, along with excitation functions at 0° and 180°, were measured for several neutron groups from the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^{13}{}_{}{}^{}\mathrm{C}, n){}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$. A pronounced backward-angle resonance was observed at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}\simeq 7.2$ MeV for groups corresponding to several of the low-lying states in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$. The results suggest a direct contribution to the reaction mechanism.

We report here the first experimental demonstration of Doppler-free three-photon spectroscopy. The Doppler broadening is eliminated by insuring that the sum of the momenta of the three photons simultaneously exchanged between the atom and the laser beams is equal to 0. This is accomplished by making a proper choice of the angles between the three exciting beams. The observation has been made on the sodium $3S_{\frac{1}{2}}-3\mathrm{}{P}_{\frac{1}{2}}$ transition with absorption of two photons and induced emission of one.

Electron temperature profiles, turbulence levels, and anomalous transport are calculated for tokamak discharges using the hypothesis that the dissipative trapped-electron instability drives the plasma to marginal stability.

The equilibrium stability criterion for diffuse interfaces in a two-component solution with a miscibility gap requires that the interdiffusion flux vanish. If the system is continuously deformed, convective fluxes disrupt the equilibrium in the interface regions and induce a counter diffusive flux, which is dissipative and contributes to the apparent viscosity of the mixture. Chemical free energy is recoverably stored, causing viscoelastic phenomena. Both effects are significant.

A self-consistent calculation for hydrogen chemisorption is reported, where the surface is described both by the jellium model and by a model that includes ion pseudopotentials to lowest order. It predicts that for H on Al(100) a bridge configuration is the most favorable (binding energy 1.9 eV), and that the activation energy for surface diffusion is 0.1-0.2 eV.

The recent Anderson model of the electronic structure of the amorphous chalcogenides predicts formation of paired localized singlet states through large electron-phonon interaction. We show that the interpretation of the absorption in the Urbach-tail region is completely consistent with modulation of band edges due to random internal electrical field associated with these bipolarons. They arise from electron transfer between Te dangling bonds, $x\le 0.33$, or Ge dangling bonds, $x>\mathrm{}0.33\mathrm{}$.

We find a strong dependence of the strength of the peak in the absorption coeficient at the Ta $L_3$-absorption edge of $1T$-Ta${\mathrm{S}}_2$ as a function of the orientation of the x-ray polarization with respect to the crystal layers. This variation can be related to the character of the unfilled $d$ states just above the Fermi energy.

The hyperfine interaction of xenon atoms (${}_{}{}^{129m}{}_{}{}^{}\mathrm{Xe}$) implanted in iron has been studied with nuclear magnetic resonance on oriented nuclei. A sharp resonance line was found at ${\nu }_1=188.12\mathrm{}\pm 0.02$ MHz for substitutionally implanted atoms. In addition a broad resonance line corresponding to vacancy-associated xenon atoms was detected at ${\nu }_2=152.0\mathrm{}\pm 0.6$ MHz. By measuring ${\nu }_1$ for different external fields, the nuclear $g$ factor of the $I^{\pi }={\frac{11}{2}}^{-}$ state ($g=0.154\mathrm{}\pm 0.005$), as well as the values and the sign of the internal fields, was determined.

Evidence is obtained for the excitation of surface excitons in solid Ar, Kr, and Xe in optical transmission and reflection experiments using synchrotron radiation. They are located at photon energies ranging from 0.6 eV for Ar to 0.1 eV for Xe below the corresponding bulk excitons excited from the valence bands. Their halfwidths (20-50 MeV) are less than half the values found for the bulk excitons. Some are split by an amount considerably smaller than the spin-orbit splitting of the valence bands.

The detection of Mg ii fine structure and hydrogen hyperfine absorption lines toward the radio source AO 0235 + 164 allows us to place upper limits on the variability of three products of the fine-structure constant, the nuclear $g$ factor of the proton, and the ratio of electron to proton mass, viz. $\frac{{\alpha }^2{g}_{p}m}{M}$ $\frac{g_{p}m}{M}$, and $\alpha$. Since the spectral lines are observed at a high red shift, $z=0.5\mathrm{}$, the limits obtained on the variation with time of these quantities (adopting $z$ as a measure of the Hubble expansion) apply over at least 35% of the age of the universe.

The nonlinear coupling of three wave packets is solved for interactions either evolving in time and one-dimensional space or occurring in steady state in two dimensions. Solutions are given using the inverse-scattering technique and numerical integration of the differential equations.