An expression is developed for the optical dielectric constant of a medium containing submicroscopic voids. For an absorbing host medium, voids introduce additional optical structure resembling that due to surface roughness. Void resonance absorption may account for unexplained structure recently reported in the optical constants of amorphous germanium.

The doublet structure observed for the first exciton transition in T1C1 is investigated with the aid of uniaxial stress. It is shown experimentally that the direct energy gap belongs to point $X=\left(\frac{\pi }{a}\right)\left(001\right)\mathrm{}$ of the Brillouin zone. The exciton structure following from this identification is discussed, and a new interpretation of the doublet splitting based on $X$-point degeneracy is suggested. First conclusive evidence is given for intervalley scattering of direct excitons created by transitions outside the center of the Brillouin zone.

We find an $\exp [-{\left(\frac{t}{{\tau }_1}\right)}^{\frac{1}{2}}]$ time dependence for the recovery of the ${\mathrm{Al}}^{27}$ nuclear magnetization in the system ${\mathrm{La}}_{1-c}{\mathrm{Gd}}_c{\mathrm{Al}}_2$. This is characteristic of diffusionless relaxation and an especially direct interpretation of the data is possible in this limit. Variation of ${\tau }_1$ with temperature and magnetic field indicates that longitudinal dipolar fluctuations of the Gd moments relax the ${\mathrm{Al}}^{27}$ nuclei while its concentration dependence indicates Ruderman-Kittel-Kasuya-Yosida coupling between the Gd spins.

A way to deal with cluster effects in disordered alloys is given through an extension of the coherent-potential-approximation theory. An explicit expression is derived for pair effects and is shown to give the exact $c^2$ term in the lower concentration limit.

Weak-current effects can explain the experimentally observed mirror asymmetry in nuclear $\beta$ decays despite the absence of energy dependence predicted by a naive model for second-class currents. Meson exchange with $\omega \to \pi$ decay in the nucleus can result either from second-class currents or electromagnetic $\omega \rho$ mixing and can be enhanced by a factor $A$ due to nuclear coherence.

Forward-angle spectra of $\alpha$ particles inelastically scattered from heavy nuclei at incident energies up to 90 MeV are found to exhibit a broad but conspicous plateau. The integrated cross section of this plateau constitutes about 25% of the total ($\alpha ,{\alpha }^{\prime }$) cross section at an incident energy of 65 MeV. The total ($\alpha ,{\alpha }^{\prime }$) cross section is, in turn, about $\frac{1}{6}$ of the total reaction cross section. It is suggested that nucleon pickup (to form the unstable nuclei${}_{}{}^5{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^5{}_{}{}^{}\mathrm{Li}$) may be responsible for a portion of the plateaulike structure in the observed spectra.

There have been recent suggestions, based on backward-angle anomalies of elastic $\alpha$-particle scattering, that ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ have strikingly different $\alpha$-clustering probabilities. Since a convincing body of evidence exists for the $\alpha$-pickup character of the (${}_{}{}^3{}_{}{}^{}\mathrm{He}$, ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$) reaction, we investigated the reactions ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(${}_{}{}^3{}_{}{}^{}\mathrm{He}$, ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$)${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$(${}_{}{}^3{}_{}{}^{}\mathrm{He}$, ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$)${}_{}{}^{36}{}_{}{}^{}\mathrm{S}$ at an incident energy of 41 MeV. No substantial difference was found between the groundstate transitions.

A new method is proposed to carry out the angular-momentum projection from a given intrinsic wave function. The method is based on the construction of a generating function for the various powers of the step-up and step-down operators and a property of Lie algebra. It has the advantage that no integrations over the Euler angles have to be performed.

A new high-resolution (±5 MeV) missing-mass spectrometer was used to search for minor peaks and structure in the $N^{*}$ spectrum with ∼${10}^5$ events per 2-MeV mass bin. All the widths were found to be narrower than widths obtained from $\pi p$ phase-shift analyses. For example, our result for $N^{*}\mathrm{}\left(1512\right)\mathrm{}$ is $\Gamma =88\mathrm{}\pm 2$ MeV as compared with the "table value" of 105-155 MeV. No narrow structure greater than 5% of the cross section for the known peaks was observed.

We have measured wide-angle electron-positron pairs from the reaction $\gamma +\mathrm{C}\to \mathrm{C}+e^{+}+e^{-}$ in the invariant-mass region $920<m<\mathrm{}1080\mathrm{}$ MeV/${\mathit{c}}^2$ for incident photon energy $6<k<\mathrm{}7.4\mathrm{}$ GeV. The photoproduction amplitude of the $\phi$ meson was found to deviate from pure imaginary by 25° ± 15° corresponding to a ratio of the real to imaginary part of the $\phi$-nucleon amplitude of $\beta ={-0.48\mathrm{}}_{-0.45\mathrm{}}^{+0.33\mathrm{}}$. The forward photoproduction cross section ${\left[d\sigma \right(\gamma +C\to C+\phi (\phi \to e^{+}{e}^{-})\left)dt\right]}_{t=0\mathrm{}}$ was found to be 96 ± 14 nb/${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$.

The pion-exchange multiperipheral model is used to predict the amount and spectrum of pion production at small c.m. momenta in high-energy collisions. The transverse momentum distribution, which agrees with the present experimental data, is predicted to remain unchanged at all higher energies, but the number of pions produced per unit volume of phase space, which is related to the average multiplicity, is predicted to decrease.

It is shown that if the chiral SU(3) ⊗ SU(3) and scale-invariant limits coincide, chiral-symmetry breaking by (3, 3*) ⊕ (3*, 3) terms provide a consistent description incorporating the results of Cheng and Dashen and of Gell-Mann, Oakes, and Renner.

It is suggested that perturbation-theory corrections to the limit of spontaneously broken SU(3) ⊗ SU(3) symmetry fail because of the existence of a radius of convergence which is much smaller than the experimental values of the symmetry-breaking parameters. The results are compatible with SU(3) being a good symmetry for states even though the Lagrangian has approximate SU(2) ⊗ SU(2) symmetry.

We present the results on the two-particle production cross section for the process $a+b\to x_1+x_2+\mathrm{anything}$ at high energy predicted by the dual-resonance model. The distribution functions for all the kinematic regions are shown to have the desired variable dependence and properties. In particular, we find that the two-particle "correlation length" is of the order of 1 ${\mathrm{GeV}}^{-1\mathrm{}}$.

We examine the large-order behavior of perturbation theory for the anharmonic oscillator, a simple quantum-field-theory model. New analytical techniques are exhibited and used to derive formulas giving the precise rate of divergence of perturbation theory for all energy levels of the $x^{2N}$ oscillator. We compute higher-order corrections to these formulas for the $x^4$ oscillator with and without Wick ordering.

Pulse propagation in S${\mathrm{F}}_6$ has been investigated using 200-nsec pulses of a C${\mathrm{O}}_2$ laser. Operating at $\lambda =10.53\mathrm{}$ μm ($P14\mathrm{}$ transition) we have observed a breakup of the pulse envelope, an oscillatory energy transmission, and an energy-dependent pulse delay. We interpret our data in terms of the existing theory of self-induced transparency; the corresponding Bloch-type equations were derived assuming thermal equilibrium between rotational $M$ sublevels.

We report first differential cross-section measurements for inner-shell ionization of surface atoms by electron impact. Comparison is made with calculations derived from a simple extension of the Burhop theory for ionization of isolated atoms. The trends of the predicted values are in qualitative agreement with experiment.

Atomic electron binding energies for ${}_{100}{}^{}{}_{}{}^{}\mathrm{Fm}$ have been measured (± ∼10 eV) for shells $K$, $L_{1-3}$, $N_{1-5}$, $N_{6,7}$, $O_{1-3}$, $O_{4,5}$, and $P_{2,3}$ from conversion electron spectroscopy in the $\beta$ decay ${}_{}{}^{254m}{}_{}{}^{}\mathrm{Es}\to {}_{}{}^{254}{}_{}{}^{}\mathrm{Fm}$. The $P_{2,3}$ value of 24 ± 9 eV is unexpectedly low compared to empirical and to self-consistent field-based extrapolations. Preferential judgements among published actinide binding-energy tabulations are presented.

The initial magnitude and direction of the residual asymmetry in the decays of polarized positive muons stopped in solutions in transverse magnetic fields are observed to depend strongly upon the concentration of dissolved compounds. Such effects were seen in methanol solutions of ${\mathrm{I}}_2$ and in aqueous solutions of Fe${\mathrm{Cl}}_3$ and Fe(${\mathrm{CI}}_4$)${\mathrm{O}}_3$. The underlying fast depolarization mechanism can be qualitatively and quantitatively understood by assuming muonium formation with subsequent chemical reaction of the atomic muonium with dissolved compounds.

A rigorous microscopic analysis of a weakly interacting Bose gas at zero temperature shows that the elementary excitation spectrum $\omega \mathrm{}\left(k\right)\mathrm{}$ is not an analytic function of the wave vector $k$ in the long-wavelength limit but has the form $k[c_0+c_2{k}^2+c_{L4\mathrm{}}{k}^4\ln (\frac{1}{k})+\cdots ]$. It is pointed out that the structure factor $S\left(k\right)\mathrm{}$ is not an analytic function of $k$ and that the specific heat $C_v\mathrm{}\left(T\right)\mathrm{}$ at low temperatures $T$ has the form $C_v=T^3[C_0+C_2{T}^2+C_{L4\mathrm{}}{T}^4\ln (\frac{1}{T})+\cdots ]$. The extension of these results to liquid ${\mathrm{He}}^4$ is discussed.