We have made low-temperature specific-heat measurements demonstrating tunneling of hydrogen trapped by interstitial nitrogen in niobium.

We propose a practical scheme to calculate structural energies in crystalline semiconductors. The method is applied to Si to calculate changes in charge densities and harmonic energies for $\mathrm{TO}\left(\Gamma \right)$, $\mathrm{TA}\mathrm{}\left(X\right)\mathrm{}$, and $C_{11}-C_{12}$ distortions. Cubic anharmonic terms are also found for $\mathrm{TO}\left(\Gamma \right)$. For the shear modes a proper description of the electron-electron interaction is found to be vital. Electronic charge densities demonstrate the importance of dynamic redistribution of valence charge in covalent semiconductors.

We describe a theory of core-level binding-energy shifts in metals (relative to the free atom). Precise definitions of the intuitive concepts of chemical, relaxation, and configuration shifts are given which permit their straightforward and unambiguous evaluation. Parameter-free calculations for the $3d$ transition series agree well with experiment. The simplicity of the theory should make it widely applicable.

Rotation of the plane of polarization of a linearly polarized x-ray beam by simple transmission through a (110) silicon crystal has been observed. Both the amount of rotation and the amount of absorption of x rays depend on the orientation of the crystal in the incident beam. Contemporary scattering-theory calculations are used to explain this effect, including the x-ray analog to optical birefringence, for a suitable crystal sample.

We report magnetic susceptibility results for the valence fluctuation system $\mathrm{Ce}{\mathrm{In}}_{3-x}{\mathrm{Sn}}_x$. In the intermediate-valence regime the characteristic energy of spin fluctuations does not vary monotonically with solute $\frac{e}{a}$ ratio, but oscillates with $x$ in the same manner as the conduction-electron density of states. This provides experimental evidence for the role played by the conduction electrons in controlling the spin fluctuation energy.

We present evidence for a fundamentally new mechanism for impact-induced desorption, viz., core-hole Auger decay. We thereby explain why observed thresholds for electron-stimulated desorption (ESD) of positive ions (${\mathrm{O}}^{+}$, O${\mathrm{H}}^{+}$, and ${\mathrm{F}}^{+}$) from certain $d$-band metal oxides (Ti${\mathrm{O}}_2$, ${\mathrm{V}}_2$${\mathrm{O}}_5$, and W${\mathrm{O}}_3$) correlate in energy with the ionization potential of the highest-lying atomic core levels. We conclude that electron-stimulated desorption is in many interesting cases an atom-specific, valence-sensitive probe of surfaces.

At low temperatures the muon jump rate is nearly linear in temperature for vanadium. This result provides evidence of one-phonon-assisted tunneling in the presence of impurity-induced lattice strains. A local maximum is observed in the depolarization rate near 80 K, which can be explained in a model of diffusion to impurity traps at higher temperatures.

Photoemission studies combined with measurements of the magnetic susceptibility show that La segregates to the surface of La${\mathrm{Ni}}_5$ in the presence of ${\mathrm{O}}_2$ or ${\mathrm{H}}_2$O, and the Ni precipitations are formed during hydrogenation. This represents a self-restoring mechanism of the active surface, since the highly reactive La removes the oxygen and keeps the Ni metallic. Dissociative adsorption of ${\mathrm{H}}_2$ may then occur at the Ni atoms.

We present results on charged multiplicity $n_{\mathrm{ch}}=2\mathrm{}$ and $n_{\mathrm{ch}}>2\mathrm{}$ muon events produced in $e^{+}{e}^{-}$ collisions with $〈s^{\frac{1}{2}}〉=7.3\mathrm{}$ GeV at 90° to the beams. The background-subtracted inclusive cross section for the $n_{\mathrm{ch}}=2\mathrm{}$ events is 10.2±5.4 pb/sr, in agreement with the expected contribution from the heavy lepton $\tau$. The cross section for the $n_{\mathrm{ch}}>2\mathrm{}$ events is 19.0±6.5 pb/sr whereas we expect only 2.9 pb/sr from the $\tau$, indicating that we may be seeing the weak decays of charmed mesons.

$\Delta J=1\mathrm{}$ bands built on deformed $\frac{9^{+}}{2}$ proton-hole states have been observed in ${}_{}{}^{119-125}{}_{}{}^{}\mathrm{Cs}$. The $\frac{9^{+}}{2}$ bandhead energies drop phenomenally to become the ground state in ${}_{}{}^{119}{}_{}{}^{}\mathrm{Cs}\mathrm{}(N=64\mathrm{})\mathrm{}$. The band systematics for $N(62-74)\mathrm{}$ and $Z(51-55)\mathrm{}$ are defined. A deformed-structure relationship is suggested between the excitations of a $1g_{\frac{9}{2}}$ proton and a pair of $1g_{\frac{9}{2}}$ protons across the $Z=50\mathrm{}$ closed shell.

The ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ binding energy and the $n$-${}_{}{}^3{}_{}{}^{}\mathrm{H}$ and $p$-${}_{}{}^3{}_{}{}^{}\mathrm{H}$ phase shifts below the $d+d$ threshold are calculated from Alt-Grassberger-Sandhas equations taking into account the full subamplitudes. As two-body interaction a separable $s$-wave spin-dependent potential is used.

A momentum-dependent real potential for ion-ion scattering is calculated, from Reid's soft-core potential, with Brueckner's theory. The densities of the two nuclei are kept fixed and the Pauli principle is obeyed by rearrangement in momentum space. The calculated potential is increasingly attractive up to 2 ${\mathrm{fm}}^{-1\mathrm{}}$ relative momentum per particle. At this relative momentum, the attraction does not decrease at small distances; for larger momenta, the potential finally becomes repulsive.

The circular polarization of the $\gamma$ rays from the 1.08→0.0 MeV transition of ${}_{}{}^{18}{}_{}{}^{}\mathrm{F}$ has been measured to be (-0.7 ± 2.0) × ${10}^{-3\mathrm{}}$, a value significantly smaller than predicted by recent calculations which include the effects of neutral weak currents.

We have observed resonant excitation of swift channeled hydrogenlike ions ($Z=5\mathrm{}$ to $Z=9\mathrm{}$) and heliumlike ${\mathrm{F}}^{7+}$ which arises from a coherent periodic perturbation by the atoms in the bounding crystal rows. The resonance excitation was seen through the reduction in the transmission of fixed-charge-state ions through channels in thin crystals of Au and Ag.

A new ion-beam magnetic resonance method using laser-induced fluorescence for both state selection and signal detection has been demonstrated for the first time. The hyperfine intervals of the $5d{}_{}{}^4{}_{}{}^{}D_{\frac{7}{2}}^{}{}_{}{}^{}$ level of ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}_{}^{+}{}_{}{}^{}$ and ${}_{}{}^{131}{}_{}{}^{}\mathrm{Xe}_{}^{+}{}_{}{}^{}$ have been measured to better than 1 ppm accuracy.

An unpolarized hydrogenlike atom in the metastable $2S_{\frac{1}{2}}$ state in an electric field decays primarily by one- or two-photon emission. The angular distribution of the single-photon radiation is expected to be asymmetric with respect to the electric field direction as a result of $E1-M1\mathrm{}$ interference. Observable consequences of this effect in high-$Z$ Lamb-shift experiments in progress are pointed out. A lowest-order estimate is given for the dependence of the asymmetry on the nuclear charge and the applied field strength.

Using new relativistic molecular calculations within the Dirac-Slater scheme it is now feasible to study theoretically molecules containing superheavy elements. This opens a new era for the prediction of the physics and chemistry of superheavy elements. As an example we present the results for $\left({}_{110}{}^{}{}_{}{}^{}X\right){\mathrm{F}}_6$, where it is shown that relativistic effects are nearly of the same order of magnitude as the crystal-field splitting.

We have found a class of stationary translating and stationary rotating solutions to the Euler equations in two dimensions—a Hamiltonian system. These "$V$ states" are non-linear dispersive waves that seem to play a role in our observation of long-time recurrence and breaking phenomena.

By extending the laser-frequency-switching technique to a 100-psec time scale, we have observed for the Na $D_1$ line the first-order free-induction decay, its inhomogeneous dephasing time ${T_2}^{*}$, its interference with the nonlinear free-induction decay, and a 1.8-GHz interference beat of the ground-state hfs. Detailed theoretical predictions of these new coherence effects are faithfully observed.