Radiation corresponding to transitions from excited shallow donor states and from conduction-band states to the donor ground state has been observed in impact-ionized GaAs at temperatures near 4.2°K. Spectral measurements show a main peak at a wavelength of 282 μ (4.4 meV), corresponding to a $2p\to 1s$ transition, and a broader continuum extending to higher photon energies. A total radiated power of ${10}^{-7\mathrm{}}$ W has been measured corresponding to an external quantum efficiency of about ${10}^{-6\mathrm{}}$.

The contributions of internal strain and charge redistribution to the piezoelectric constants of tetrahedrally coordinated $A^N{B}^{8-N}$ crystals are discussed. It is shown that the reversal of sign of the piezoelectric constant on going from $N=1\mathrm{} \mathrm{and} 2$ to $N=3\mathrm{}$ can be explained quantitatively in terms of the dependence of charge redistribution on bond ionicity.

We present experimental data and theoretical results for electroexcitation of $T=1\mathrm{}$ particle-hole states in ${\mathrm{O}}^{16}$.

Yale University's electron accelerator has been used to study elastic electron scattering from ${\mathrm{Nd}}^{142}$. The energy was varied between 15 and 60 MeV, while angular distributions were obtained at angles between 70° and 150°. The results indicate an anomalously small skin thickness. A comparison with the effect of dispersion corrections on the interpretation of muonic x-ray results suggests that similar corrections are needed in the present case.

Optical-model analysis of elastic-scattering data taken at 40 MeV produces the familiar potential ambiguities, but at 80 MeV a single set is obtained. The parameters $V$, $W$, ${\mathcal{r}}_0$, and $a$ are found to be highly correlated and hence cannot be uniquely determined. The functions which are determined most uniquely are the rms radius of the real and imaginary potential and the products $V{{\mathcal{r}}_{0R}}^4$ and $W{{\mathcal{r}}_{0I}}^4$.

All the current models for pulsars call for very large magnetic fields in rotating neutron stars. Since general relativistic effects are important in the latter, electromagnetism too must be framed consistently (which has been overlooked so far). It is shown that in a rotating neutron star even a uniform magnetic field, static in the corotating frame, implies in the same frame the static electric field which is crucial to the pulsar emission theories.

We report a new measurement of the positron $g$ factor. Our result is five times more accurate than the best previous value for this quantity. It shows that the positron and electron $g$ factors are identical to within one part per million.

The concept that internal quantum numbers do not change in diffractive production is extended to the quantum numbers of the quark model. The resulting approximate selection rules are discussed and compared with the predictions of other models.

A solution of the $c$-number self-consistency condition $a_i-d_{\mathrm{ijk}}{a}_j{a}_k=h_i$ is obtained, where $a_i$ represents the matrix elements of unitary octet vector charge and $h_i$ is a driving term. With a reasonable choice of a driving term, we obtain $sin\theta =0.22-0.14\mathrm{}$ for the Cabibbo angle $\theta$. The choice of $h_i$ that leads to $tan\theta =\frac{m_n}{m_{\Lambda }}$ (where $m_n$ and $m_{\Lambda }$ are the quark masses) is also pointed out.

Recently observed peripheral peaks in reactions where single-meson exchange is forbidden are explained as kinematical reflections. Experimental and theoretical implications are discussed.

The characteristic $K\beta$ x rays produced by 15.0-MeV oxygen (${\mathrm{O}}^{4+}$) ions on Ni are found to shift in the spectrum by 112±15 eV relative to the energies produced by x-ray and proton excitation in Ni. Similarly, in Cu an energy shift of 97 ± 15 eV is observed. The observed shift is possibly due to the larger $K\beta$ energies of the multiply ionized Ni or Cu produced in ${\mathrm{O}}^{4+}$ bombardments as opposed to the singly ionized Cu or Ni $K\beta$ x rays.

The trapped-electron spectrum of Ne has been measured in the energy region from 40 to 50 eV. New negative-ion resonances are observed.

The nuclear alignment following Coulomb excitation was detected by observing directly the sublevel populations with the quadrupole Mössbauer effect. The alignment was preserved in flight from the target to a single crystal of Zn by frequent collisions with gas molecules. The hyperfine magnetic field acting on the recoil nuclei in flight was determined by observing the residual alignment for different gas pressures.

Evidence for a substantial nuclear ordering in solid bcc ${\mathrm{He}}^3$ at melting pressure has been inferred from solid entropies $s_S$ deduced from measurements of the slope of the melting curve for a liquid-solid mixture cooled by adiabatic compression. At 3.4 mK we find experimentally that $\frac{s_S}{R}=0.83\mathrm{}\ln 2$. It is likely that much lower temperatures and solid entropies are obtained during parts of the experiments. The possibility for bulk nuclear polarization is also discussed.

It is found that in many cases electron trapping can have an important effect on ion waves. Trapping can render the linear stability theory invalid, and the conditions under which this may occur are discussed. Assuming the trapping process to be the mechanism whereby an unstable plasma reaches a quasistationary turbulent state, we also derive an expression for the saturation energy spectrum.

Enhanced radiation temperatures have been observed at the plasma frequency in nearly Maxwellian helium afterglow plasmas. These measurements confirm the predicted bremsstrahlung emission from plasma oscillations generated by suprathermal electrons.

A method is described for the complete calculation of electronic energies in crystalline solids without approximating overlap, electron-repulsion, or exchange contributions. The practicality of the method is confirmed by preliminary results, which also indicate reasons for the considerable success of independent-electron methods.

We have observed a new interaction mechanism between a sound wave and the nuclear spin system in a single crystal of aluminum. The coupling is via the oscillating magnetic field induced by the sound wave in the presence of a large applied magnetic field and the magnetic moment of the nucleus. The experimental results agree with the theoretical predictions based on this mechanism.

Measurements have been made of the field dependence of the cyclotron mass of conduction-band electrons in the moderately polar semiconductor CdTe. These measurements, when compared with predictions deduced from the Fröhlich Hamiltonian by the novel variational calculation to be described, give the first quantitative experimental test of large-polaron theory.

Optical properties exhibit the different behavior of valence electrons in the liquid and the solid phases of mercury. Interband transitions occurring only in the solid were identified with the help of energy-band calculations.