In x-ray studies of the dynamic structure factor $S(k, \omega )$ in Be, graphite, and Al a new type of excitation spectrum is observed for momentum transfers $k$ between $k_{\mathrm{F}}$ and $2k_{\mathrm{F}}$. The similarity of the observed spectra in these systems, when scaled according to electron-gas parameters, strongly indicates that the new excitation is a property of a solid-state electron gas and not a one-electron band-structure effect.

Damping and modulus measurements were made on high-purity copper subjected to both quenching and 1.0-MeV electron irradiation. During isothermal annealing at room temperature, following quenching from 700°C, we observe a monotonic decrease in the logarithmic decrement with a concurrent increase in the modulus. However, both slow cooling and quenching of the sample followed by 1.0-MeV electron irradiation give rise to a substantial increase in the decrement; i.e., the Simpson-Sosin "peaking effect" is clearly evident.

I discuss the effect of sharp structure in the electronic density of states on the temperature dependence of the interband-$s-d$-phonon-scattering resistivity. The a priori density of states of Pd is used to calculate the resistivity, which is found to be in excellent agreement with experimental high-temperature results.

Photoemission spectra for semiconducting SmS and metallic ${\mathrm{Sm}}_{0.5}$${\mathrm{Y}}_{0.5}$S give evidence of strong configuration interaction of localized states near the Fermi level involved in semiconductor-to-metal phase transitions and in unusual transport and magnetic properties. An analysis of the observed multiplet structure in photoemission spectra for semiconducting SmS shows a localized state of a mixed $f^6+f^{5}d$ character.

Sm ions in "chemically collapsed" phases of SmS, e.g., ${\mathrm{Sm}}_{0.85}$${\mathrm{Th}}_{0.15}$S and ${\mathrm{Sm}}_{0.82}$${\mathrm{Gd}}_{0.18}$S, are found to be in the state of interconfiguration fluctuations. In contrast, valence fluctuations in pure SmS are shown to be not larger than 3%. Conduction-electron screening does not drastically affect either the location or the effective intra-atomic Coulomb interaction $U_{\mathrm{eff}}$ of $4f$ levels in photoemission spectra.

Large, reversible changes in the superconducting transition temperature $T_c$ of the Nb-based $A-15\mathrm{}$ compounds ${\mathrm{Nb}}_3$Al, ${\mathrm{Nb}}_3$Sn, ${\mathrm{Nb}}_3$Ga, ${\mathrm{Nb}}_3$(Al, Ge), and ${\mathrm{Nb}}_3$Ge are observed when irradiated with high-energy ($E>\mathrm{}1\mathrm{}$ MeV) neutrons at 60°C. The transition widths of the irradiated samples are of the same order as the unirradiated samples and the original $T_c\text{'}\mathrm{s}$ are recovered by annealing. The results are discussed in terms of atomic ordering in the $A-15\mathrm{}$ structure.

A magnetic interference function has been observed for an amorphous ferromagnetic cobalt-phosphorus alloy by unpolarized-neutron diffraction. The distribution of the magnetic moments of cobalt is analyzed in terms of a partial pair-correlation function. Comparison with x-ray results gives good agreement.

The decay ${\Sigma }^{-}\to n{e}^{-}\overline{\nu }$ was studied using a hyperon beam at the Brookhaven alternating-gradient synchrotron. The ${\Sigma }^{-}$ and $e^{-}$ momenta were measured by magnetic spectrometers with magnetostrictive wire spark chambers. A threshold Cherenkov counter and a total-absorption calorimeter identified the electron and neutron, respectively. From a sample of 3507 reconstructed events we have found $\left|\frac{g_A}{g_V}\right|=0.435\mathrm{}\pm 0.035$.

Data are presented which yield a new upper limit for the weak neutral- current reaction ${\overline{\nu }}_e+d\to n+p+{\overline{\nu }}_e$ in the MeV range of 6 times theoretical expectation at a 3-standard-deviation level. These data also demonstrate the feasibility of a test which is an order of magnitude more sensitive.

The magnitude and the sign of spin-dependent scattering lengths of slow neutrons by nuclei of ${\mathrm{Li}}^7$, ${\mathrm{Al}}^{27}$, ${\mathrm{Sc}}^{45}$, ${\mathrm{Zr}}^{91}$, ${\mathrm{Nb}}^{93}$, ${\mathrm{La}}^{139}$, and ${\mathrm{Ta}}^{181}$ have been determined by measuring the dependence of the precession angle of the neutron spins on the nuclear polarization of the scattering target.

The electromagnetic decays of levels in ${}_{}{}^{48}{}_{}{}^{}\mathrm{V}$ have been studied via the reaction ${}_{}{}^{34}{}_{}{}^{}\mathrm{S}({}_{}{}^{16}{}_{}{}^{}\mathrm{O}, pn){}_{}{}^{48}{}_{}{}^{}\mathrm{V}$ at incident ion energies of 30-36 MeV. Spins, parities, and branching and mixing ratios were obtained from angular distribution, excitation function, $\gamma -\gamma$, and $n-\gamma$ coincidence measurements. Six, and possibly seven, members of a very pure rotational negative-parity band were identified. This band is based on a $1^{-}$ low-lying core excited state with probable configuration ${\left(\pi d_{\frac{3}{2}}\right)}^{-1\mathrm{}}{\left(\pi f_{\frac{7}{2}}\right)}^4{\left(\nu f_{\frac{7}{2}}\right)}^5$.

The effective nonleptonic weak interaction is examined assuming the Weinberg-Salam theory of weak interactions and an exactly-conserved-color gauge symmetry for strong interactions. It is shown that the octet part of the nonleptonic weak interaction is more singular at short distances than the 27 part. The resulting enhancement of the octet term in the effective local weak Lagrangian, together with suggested mechanisms for the suppression of matrix elements of the 27 operator, may be sufficient to account for the observed $\left|\Delta I\right|=\frac{1}{2}$ rule.

We have observed muons produced directly in Cu and W targets by 300-GeV incident protons. We find a yield of muons which is approximately a constant fraction (0.8·${10}^{-4\mathrm{}}$) of the pion yield for both positive and negative charges and for transverse momenta between 1.5 and 5.4 GeV/c.

Secondary cosmic-ray muon and hadron fluxes are calculated for particle energies above 200 GeV using accelerator data on inclusive hadron cross sections and the known primary flux. The gross differences between the calculated and measured muon and hadron charge ratios require radical reexamination of conventional views on hadron interactions or the neutron-proton ratio in the primary flux.

In an experiment at the Argonne National Laboratory zero-gradient synchrotron we have determined the forward differential cross sections for the double-charge-exchange reactions ${\pi }^{-}p\to K^{+}{\Sigma }^{-}$, $K^{-}p\to {\pi }^{+}{\Sigma }^{-}$, and $K^{-}p\to K^{+}{\Xi }^{-}$ for incident beam momenta up to 5 GeV/c. The production angle and momentum of the forward-going positive particle (${\pi }^{+}$ or $K^{+}$) were measured with a high-resolution focusing wire-spark-chamber spectrometer and the two-body final states were selected by the missing-mass technique.

We show that the singlet-triplet separation of ${\mathrm{H}}_2$ must be lowered by 157.7 ± 0.2 ${\mathrm{cm}}^{-1\mathrm{}}$ compared to the hitherto accepted value of Dieke. We have used a new kind of "level anticrossing" method in which the anticrossing is due to the coupling of a singlet and a triplet state by spin-orbit or hyperfine Fermi contact interaction.

We propose a two-center model for the description of ion-atom collisions proceeding via a quasimolecular (adiabatic) mechanism. The electronic potential of the model is given by a superposition of modified atomic Thomas-Fermi potentials, each centered about one of the colliding nuclei. Molecular correlation diagrams calculated for the NeNe system show good agreement with results from molecular-orbital Hartree-Fock calculations.

Absolute cross sections for electron emission in the complete energy and angular ranges were measured for 30-MeV ${\mathrm{O}}^{n+}$+${\mathrm{O}}_2$ collisions at incident charge states of $n=4\mathrm{} \mathrm{to} 8$. Rises in inner- and outer-shell ionization of the target are studied for increasing $n$. Electrons ejected from the outer shell of the projectile are found to be very intense at forward emission angles $\theta$. Auger electrons from the projectile are observed at $\theta <42\mathrm{}°$ for $n$ as large as 6.

The double-resonance concept is extended to the situation of two coherently driven optical transitions that do not share a common level but are coupled by molecular collisions that tip the angular momentum vector while preserving the molecular velocity and the rotational energy. This collision-induced double resonance is observed as sharp resonances, free of Doppler broadening, and can be explained in the same order of perturbation theory as the ordinary double-resonance experiment. They appear as satellite lines accompanying the usual double resonance or Lamb-dip spectra.

Examination of the Rayleigh line of a lyotropic cholesteric polypeptide liquid crystal by the techniques of quasielastic—light-scattering spectroscopy reveals the presence of two new purely dissipative, low-frequency light-scattering modes of comparable intensity. Angular and electric field dependences of the deconvoluted spectra are consistent with the identification of the mechanism as due to twist and viscous-splay normal modes recently predicted theoretically. Analysis of the twist mode on this basis yields a value of ${\gamma }_1$, the twist viscosity coefficient of the medium.