We have found no evidence for the existence of long-lived, massive particles in the cosmic radiation at sea leavel. The experimental limit for masses above 2 BeV/${\mathit{c}}^2$ is 2.2 × ${10}^{-8\mathrm{}}$ particles ${\left({\mathrm{cm}}^2\mathrm{s}\mathrm{r}\mathrm{s}\mathrm{e}\mathrm{c}\right)}^{-1\mathrm{}}$.

We have made a detailed calculation of the lifetime and attentuation mean free path of high-energy cosmic rays against photomeson production. The calculation utilized the results of recent laboratory studies of photomeson production which have become available since 1966. The implications of the result are discussed.

We have used a magnetic spectrometer with wide-gap spark chambers to measure the single ${\pi }^{+}$ photoproduction cross sections from hydrogen at lab angles of 110°, 127.5° and 152°, between 0.9- and 3.2-GeV photon energy (About 40 photon energies at each angle). The cross section drops fairly rapidly with increasing energy, with superimposed bumps or shoulders at energies corresponding rather closely to the known resonances $N\left(1688\right)\mathrm{}$, $\Delta \mathrm{}\left(1920\right)\mathrm{}$, and $\Delta \mathrm{}\left(2420\right)\mathrm{}$. There is a shallow minimum at an energy corresponding to the $N\left(2190\right)\mathrm{}$ resonance.

Constraints of continuous moment sum rules as applied to the symmetric $\pi N$ scattering amplitude are used to rule out all two-pole models for its asymptotic behavior. Two three-pole solutions are discussed having $\sigma \left(\infty \right)$ equal to 21 and 17 mb, respectively.

The angular conditions for the isospin-factored current algebra at infinite momentum are decomposed into a set of momentum-transfer-independent conditions. The solutions to the angular conditions are constructed and related to wave equations. The existence of spacelike solutions is established for any nontrivial solution, and the decoupling problem is discussed.

The technique which we used previously to observe quantum beats due to coherent electron-impact excitation of Zeeman magnetic sublevels is extended to the observation of the Lamb shift in the $n=4\mathrm{}$ state of ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$. The quantum beats in our new experiment are due to temporal variations of the fluorescent light. We extend Series' theory and report the first experimental observation of the effect predicted by Series.

A strong recoilless resonance absorption was observed for the 6.2-keV level ($T_{\frac{1}{2}}=6.8\mathrm{}$ μsec) of ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$. Using sources of ${}_{}{}^{181}{}_{}{}^{}\mathrm{W}$ in W-metal and Ta-metal absorbers, a line-width of 11 times the natural width was obtained, with isomer shifts in the range between 0.83 and 0.94 mm/sec, depending on the quality of the sources. From the hyperfine splitting in a longitudinal magnetic field the magnetic moment of the 6.2-keV level was determined to be ${\mu }_1=+(5.14\mathrm{}\pm 0.15){\mu }_N$.

An electric field of 4 kV/cm applied to a crystal of SrTi${\mathrm{O}}_3$:${\mathrm{Cr}}^{3+}$ at 4.2°K shifts the chromium $R$ lines by about 2 ${\mathrm{cm}}^{-1\mathrm{}}$ and increases their integrated intensity by 8%. The intensity increase is attributed to an induced electric dipole transition made possible when the ${\mathrm{Cr}}^{3+}$ ion is displaced from the center of symmetry by the applied electric field.

We present measurements of the negative ion mobility in He II for $T<~0.5$°K. We show that the usual kinetic-theory approach to ion drift in He II is inadequate, and we describe a more realistic model. It is found that inelastic phonon scattering is the dominant process determining the mobility of the electron bubble at these temperatures.

Moderate, pulsed microwave heating of the free electrons in a weakly ionized helium afterglow plasma at 9.5 Torr at a gas temperature of 77°K produces an unusual modulation of the visible afterglow light. Observations of a second (probing) microwave signal indicate an accompanying significant increase in free-electron density under the assumption that there is no significant anomalous phase shift or absorption of the probing signal.

A general procedure is outlined for the first-principles calculation of the rate of decay of a metastable phase.

The frequency dependence of phonon-photon double-quantum transitions in MgO:${\mathrm{Fe}}^{+2\mathrm{}}$ was investigated by using 8.7-GHz photons to detect 9.3-, 4.7-, and 3.1-GHz phonons. The transition probability for simultaneous absorption of both a phonon and a photon markedly decreased with decreasing phonon frequency. In the case of 4.7- and 3.1-GHz phonons, a new type of phonon-photon transition was observed.

Densities of states and core-electron energy levels of Fe, Co, Ni, Cu, and Pt were studied by means of x-ray photoelectron spectroscopy. The density-of-states results are in good agreement with similar data from other experimental techniques and with theory, but do not agree with the results of early ultraviolet photoemission work on Fe, Co, and Ni. The core levels of Fe metal and Co metal do not show exchange-induced splittings.

We have observed combined spin-cyclotron resonance in the $M_J=\pm \frac{1}{2}$ valence bands of uniaxially stressed Ge from which we obtain directly the first measurement of the free-hole $g$ factor, $g_h=2\mathrm{}\kappa =7.20\mathrm{}\pm 0.08$.

The diffusion of a "warm" band of phonons, generated by continuously saturating a spin resonance at one end of a Sr${\mathrm{F}}_2$:${\mathrm{Tm}}^{2+}$ crystal, was measured throughout the rest of the crystal by optically monitoring the spatial distribution of the spin temperature. We interpret the experimental results in terms of a phonon transmission coefficient into the helium (∼4%) and a mean free path determined by diffuse scattering (∼25%) off the crystal surfaces.

The infrared reflection spectra of ${\mathrm{Ga}}_{1-x}{\mathrm{In}}_x\mathrm{As}$ crystals reveal a new type of mixed-crystal behavior in which two bands are seen, one near the InAs Reststrahlen region and one which shifts monotonically with $x$ between the InAs and GaAs Reststrahlen regions. A discussion is given in terms of postulated criteria using local and gap modes.

Structure in $\frac{d^{2}I}{d{V}^2}$ symmetrical about zero bias is observed in $p$-type GaAs-Pb junctions at bias energies equal to the transverse optical phonon energy of bulk GaAs. This is interpreted as due to hole-TO-phonon interaction through a deformation potential coupling in bulk GaAs.

We present a new model of the intermediate state in current-carrying superconductors. The model predicts a resistance transition which is in reasonable agreement with experimental values. An introductory treatment of secondary effects is also given.

Strong Gantmakher-Kaner size-effect oscillations have been observed for a magnetic field along the [110] direction in very pure copper. Their period is in good agreement with an extremum in $\frac{\partial A}{\partial k_z}$ for this direction, where $A$ is the cross-sectional area of the Fermi surface. Their large amplitude is attributed to a damped helicon mode below the usual helicon absorption edge. Related results are given for the field along [111].

Longitudinal and transverse diffusion coefficients for mass-identified ${\mathrm{N}}^{+}$ and ${\mathrm{N}}_2^{+}$ ions in nitrogen in an applied electric field have been measured at room temperature on the $\frac{E}{N}$ range from 12 × ${10}^{-17\mathrm{}}$ up to 300 × ${10}^{-17\mathrm{}}$ V ${\mathrm{cm}}^2$. For $\frac{E}{N}$ below about 30 × ${10}^{-17\mathrm{}}$ V ${\mathrm{cm}}^2$ the longitudinal and transverse coefficients were found to be equal and to have the value predicted by the Einstein relation. At higher $\frac{E}{N}$ both increased with increasing $\frac{E}{N}$, the longitudinal coefficient always being greater than or equal to the transverse.