A technique for adapting the quantum defect method to symmetrical diatomic molecules is derived and applied to ${\mathrm{Li}}_2$ with reasonable success.

The temperature dependence of the spin-lattice relaxation time of the oriented ${\mathrm{H}}_3$C-$\dot{\mathrm{C}}{R}_1{R}_2$ radical in x-irradiated single crystals of acetyl-($d, l$)-alanine has been observed to be dominated by "spin-flip" transitions between the rotational states of the methyl group. The energy separation of these levels has been confirmed by an analysis of the ESR spectra of the radical. The low-temperature ESR spectra show quantum effects also not previously observed.

We present a spin-temperature model, valid at low temperature, of nuclear dynamic polarization using electronic spin systems with $g$-factor anisotropy and hyperfine structure. Predictions for the maximum polarization corresponding to some free radicals are compared with experiment.

It is shown that the collisional damping on the free streaming motion of plasma can be very important in certain circumstances even though the collisional frequency is small compared with the plasma frequency. Both spatial and temporal echoes are treated in this note. In the latter case, for example, we found that the collisional damping goes as $\exp [-\beta {{\omega }_p}^2{t}^3]$ (where $\beta$ is the collisional frequency).

A reanalysis of the data used to determine the critical exponent $\delta$ given by Roach and Douglass in a recent Letter shows that the value of this exponent is significantly larger than the value they obtained and satisfies Griffiths' inequality.

We report experimental observation of a new plasma echo at upper hybrid resonance and present a simple theoretical model which exhibits some major features of the results.

A high-pressure polymorph of ${\mathrm{Cd}}_3$${\mathrm{As}}_2$ has been retained at atmospheric pressure and temperatures below 150°K. It is metallic, but no superconducting transition was found down to 1.1°K. The crystal structure is $D{5}_2$ with $a=4.30\mathrm{}$ Å, $c=6.87\mathrm{}$ Å, and $\frac{c}{a}=1.60\mathrm{}$.

Positron annihilation studies with a collinear point detector geometry have been carried out on a copper single crystal and reveal an angular dependence consistent with the shape of the Fermi surface superimposed upon an anisotropic contribution from the filled Brillouin zones.

It is shown that the recent Letter by Lykken which claims to confirm Kittel's model of standing-spin-wave resonance in Permalloy films does not in fact confirm that model.

Results obtained in the temperature range 0.3-1.2°K give direct evidence that electron-electron scattering in the transition metal Pt is at least an order of magnitude greater than in Ag. Our results do not confirm the anomalous behavior in thermal conductivity which has been reported for numerous metals below 1°K.