We report critical-neutron-scattering measurements as a function of concentration and temperature in a crystal of ${\mathrm{Mn}}_c{\mathrm{Zn}}_{1-c}{\mathrm{F}}_2$ which has a concentration gradient such that $c$ spans the percolation threshold $c_p$. The results are consistent with a multicritical-point description of percolation in magnets and illustrate explicitly the importance of spinspace crossover effects on percolation. We observe no critical scattering associated with the three-dimensional phase transition for $c>~c_p$.

We have detected anisotropy in the cosmic blackbody radiation with a 33-GHz (0.9 cm) twin-antenna Dicke radiometer flown to an altitude of 20 km aboard a U-2 aircraft. In data distributed over two-thirds of the northern hemisphere, we observe an anisotropy which is well fitted by a first-order spherical harmonic with an amplitude of (3.5 ± 0.6) × ${10}^{-3\mathrm{}}$ °K, and direction [11.0 ± 0.6 h right ascension (R.A.) and 6° ± 10° declination (dec)]. This observation is readily interpreted as due to motion of the earth relative to the radiation with a velocity of 390 ± 60 km/sec.

A proper treatment of the continuous-time random-walk problem leads to a frequency-dependent conductivity in agreement with our earlier work.

Astronomical observations at the x-ray, optical, and radio frequencies are used to show that the lifetime of neutrinos for radiative decay divided by the rest mass, $\frac{{\tau }_0}{m_{\nu }}$, exceeds ${10}^{17}$ sec/eV. If one makes the further assumption that $m_{\nu }>{10}^{-3\mathrm{}}$ eV, then ${\tau }_0>~{10}^{19}$ sec. If there are other competing decays of neutrinos, it is then shown that $\frac{{\Gamma }_{{\nu }_e}({\nu }_e\to x+\gamma )}{{\Gamma }_{{\nu }_e}\left(\mathrm{total}\right)}<~{10}^{-15\mathrm{}}$ and $\frac{{\Gamma }_{{\nu }_{\mu }}({\nu }_{\mu }\to x+\gamma )}{{\Gamma }_{{\nu }_{\mu }}\left(\mathrm{total}\right)}<~3\times {10}^{-6\mathrm{}}$.

A generalized unitary pole approximation concerning the three-body amplitudes in the kernel of four-body integral equations is introduced. We furthermore study the dependence of the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ binding energy and of four-body cross sections upon a position-space cut-off parameter in the effective interactions.

$\beta$-delayed protons have been observed from ${}_{}{}^{32}{}_{}{}^{}\mathrm{Ar}$ ($t_{\frac{1}{2}}\sim 75$ msec), the most neutron-deficient nucleus whose radioactive decay has ever been recorded. From the proton spectrum, the $T=2\mathrm{}$ state in ${}_{}{}^{32}{}_{}{}^{}\mathrm{Cl}$ has been identified to have a mass excess of -8295.6±5.2 keV. As the fourth accurately known member of an isobaric quintet, it provides an accurate test for a cubic term in the isobaric-multiplet mass equation as applied to narrow $T=2\mathrm{}$ states: The coefficient of such a possible term is determined to be 0.5±2.5 keV.

We have searched for optical rotation near the 8757-Å magnetic-dipole absorption line in atomic bismuth vapor. The experiment is sensitive to parity nonconservation in the weak neutral-current interaction between electrons and nucleons in atoms. We find $R\equiv \mathrm{Im}\left(\frac{E_1}{M_1}\right)=(-0.7\mathrm{}\pm 3.2)\times {10}^{-8\mathrm{}}$, which is considerably smaller than the value $R=-2.5\mathrm{}\times {10}^{-7\mathrm{}}$ obtained by central-field calculations for this bismuth line using the Weinberg-Salam theory of neutral currents.

We report the results of a laser experiment to search for the parity-nonconserving optical rotation in atomic bismuth. We work at wavelengths close to the 648-nm $J=\frac{3}{2}$ — $J=\frac{5}{2}$ $M_1$ transition from the ground state. We find $R=\mathrm{Im}\left(\frac{E_1}{M_1}\right)=(+2.7\mathrm{}\pm 4.7)\times {10}^{-8\mathrm{}}$, in disagreement with the theoretical value $R=-30\mathrm{}\times {10}^{-8\mathrm{}}$ predicted for this transition on the basis of the Weinberg-Salam model of the weak interactions combined with relativistic central-field atomic theory.

Metastable, autoionizing high-spin states are studied using the ion-beam time-of-flight method in connection with single-collision excitation. High-resolution, time-delayed spectra are obtained from Li, Be, and B excited in 200-keV impact on C${\mathrm{H}}_4$ Evidence is found for the $\left(1s2s2\mathrm{}{p}^2\right){}_{}{}^5{}_{}{}^{}P$ state in B ii. Excitation energies for the observed quartet and quintet states are given, and the branching ratio associated with the B ii $\left(1s2s2\mathrm{}{p}^2\right){}_{}{}^5{}_{}{}^{}P$ decay is estimated.

Measurements of strongly density-dependent Rayleigh linewidth of depolarized doubly scattered light are presented. A new theory based on the coupling between spatial and temporal parts of coherence is proposed to explain our data. In addition, it is shown experimentally that successive application of Van Hove space-time correlation formulation to double scattering is not valid in general.

The anomalous slowing of an ion beam injected perpendicularly to the confining magnetic field of a low-$\beta$ plasma is experimentally verified in the nonlinear stages of the excited lower-hybrid instability. Furthermore, a transition of the main nonlinear mechanism from the quasilinear to the particle-trapping regime is demonstrated by varying beam parameters.

Plasma heating experiment is performed using a low-frequency shear Alfvén wave in the Heliotron-$D$ device. The excitation of the wave is confirmed, and an efficient plasma heating is observed; electrons are heated up to about 2 times and ions more than 1.5 times of the initial temperatures by applying an rf pulse of 400-kW power level.

A method has been developed for producing free-standing crystals of hcp ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. Stress-strain relations have been measured for such crystals plastically deformed under conditions of unconstrained shear. An upper bound for the flow stress of 5×${10}^4$ dyn/${\mathrm{cm}}^2$ is determined. Comparison is made with experiments on constrained crystals.

Recent work has shown that the resonant mixing of defect internal modes with lattice phonons can lead to striking modifications of the one-phonon coherent neutron-scattering cross section. Here, line shapes for phonons in KCl: C${\mathrm{N}}^{-}$ are calculated from a two-level model and shown to agree reasonably well with experiment. Our results demonstrate that neutron scattering can be used to study the coupling of complex defects with the lattice even at very low defect concentrations.

We have studied the surface resonances on Mo(100) and W(100) with angle-resolved, $\hslash \omega$-dependent photoemission using synchrotron radiation. For normal emission, two resonances are seen. They are located 0.3 and 3.3 (0.4 and 4.2) eV below $E_{\mathrm{F}}$ for Mo (W). The high-lying resonance remains symmetric and narrow for all photon energies used. Its intensity peaks at $\hslash \omega =15\mathrm{} \mathrm{and} 30 \left(14\mathrm{} \mathrm{and} 29\right)$ eV for Mo (W). For $\theta >~2°$, a second highlying resonance appears a few tenths of an eV below the first one. Many-body phenomena are not required to explain the data.

The critical rf magnetic field ${H_c}^{\mathrm{rf}}$ of several type-I and type-II superconductors has been measured between 90 and 300 MHz and near $T_c$ has been found to approach the ideal superheating field in nearly all cases. However, in the same samples the dc critical field shows little evidence of superheating. The temperature dependence of ${H_c}^{\mathrm{rf}}$ suggests that rf-stimulated vortex nucleation occurs in the type-I materials.

Dielectric and Brillouin scattering experiments on a lithium ammonium tartrate crystal have shown that the transition in this crystal is described by the free energy of a piezoelectric crystal, $F=\frac{1}{2}{\left({\chi }^x\right)}^{-1\mathrm{}}{P}^2+aPx+\frac{1}{2}\beta (T-T_0)x^2,$ where the primary order parameter is the homogeneous strain, which gives rise to ferroelectricity through the piezoelectric coupling with the polarization.

The dipolar broadening of the magnetic field sensed by an interstitial impurity in a rigid lattice is calculated with the electric-field gradient set up by the impurity taken into account. This is shown to give a strong dependence of the dipolar width on the applied magnetic field. The theory is especially applicable to the linewidth of precessing muons in metals.

The depolarization of positive muons implanted in single crystals of Cu has been studied as a function of applied magnetic field and of crystal orientation at 20 and 80 K. The depolarization due to static dipolar magnetic interactions with the Cu nuclei shows an unusual dependence on magnetic-field strength which can be explained by quadrupole interactions of the neighbor Cu nuclei in an electric-field gradient. The muon is self-trapped at the octahedral interstitial site. The nearest neighbors are displaced away from the muon by ∼ 5%.

We introduce a three-dimensional $\overrightarrow{\mathrm{k}}·\overrightarrow{\mathrm{p}}$ model for the electronic structure of $A-15\mathrm{}$ compounds based upon a six-dimensional irreducible representation $R\left(4\right)\mathrm{}$ of the space group ${O_h}^3-Pn3m$. By locating the Fermi level near the maximum in the density of states, the temperature-dependent free energy accounts quantitatively for anomalous normal-state physical properties of ${\mathrm{Nb}}_3$Sn and other $A-15\mathrm{}$ compounds. No use is made of tight-binding approximations nor assumptions of one dimensionality or quasi one dimensionality.