Measurements of photoelectric yield and energy distributions from amorphous silicon films are presented. The results are consistent with an exponential tail in the density of states extending from the valence band to the Fermi level. Mild heat treatment decreases the amplitude of this tail. Tentative explanations of these observations are given.

We have measured the microwave conductivity of $n$-type germanium with $N_D-N_A\sim {10}^{14}$ ${\mathrm{cm}}^{-3\mathrm{}}$ during impact ionization at 4.2°K, by means of a cavity perturbation method which requires no knowledge of the electronic spatial distribution. Values of the electronic temperature derived from the microwave conductivity are compared with theoretical predictions and Hall mobility data at higher temperatures.

The magnetization of very dilute Cu:Fe alloys contains one term proportional to $c$ due to the isolated impurities and another proportional to $c^2$ which is attributed to nearly magnetic or magnetic pairs. The susceptibility of the isolated iron atoms follows a Curie-Weiss law $C{(T+T_k)}^{-1\mathrm{}}$ with $T_k=29\mathrm{}$ K well below $T_k$. The $c^2$ term which is nearly saturated in 60 kOe at 1.3 K is responsible for the important temperature dependence of the initial susceptibility below $T_k$.

We investigate the appearance of magnetism in the Hubbard model. In the limit of large value of the interaction $U$, we show that localized moments appear below a critical temperature $T_L$. We find a Ruderman-Kittel interaction between these moments, which gives an ordered magnetic phase at a critical temperature $T_c$ smaller than $T_L$.

The longitudinal and transverse form-factor spectra for electroexcitation of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ giant resonance were determined separately. Results are presented for an excitation energy range of from 15 to 30 MeV and for a momentum-transfer range of 0.84-1.56 ${\mathrm{F}}^{-1\mathrm{}}$. We have found levels with the following excitation energies (MeV), spins, and parities: 18.6 ($3^{-}$), 19.6 ($4^{-}$), 20.0 ($2^{+}$), 20.6 ($3^{+}$), 21.6 ($3^{-}$), 22.0 ($1^{-}$), 22.7 ($1^{-}$), and 23.8 ($1^{-}$). We have also found new evidence of the spin-isospin mode for the 22.7-MeV ($1^{-}$) excitation.

The reactions ${}_{}{}^9{}_{}{}^{}\mathrm{Be}({}_{}{}^3{}_{}{}^{}\mathrm{He},\gamma \gamma )$, ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}\mathrm{}(d,p)\mathrm{}$, ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}(d,\alpha )$, and ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}(d,\gamma \gamma )$ have been used to search for the lowest $T=2\mathrm{}$ state of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$. A possible candidate for the state has been observed in ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ (${}_{}{}^3{}_{}{}^{}\mathrm{He},\gamma \gamma$) at $E_x=27.585\mathrm{}\pm 0.005$ MeV. For the other three reactions, no resonances were observed and upper limits have been set on partial widths.

It is proved that if velocity-dependent and/or quadratic spin-orbit potentials are present, they must satisfy very restrictive positivity conditions; otherwise the many-body Hamiltonian has a spectrum that is not bounded below. These conditions are not fulfilled by several currently available nuclear potentials.

The electromagnetic structure of the ${\mathrm{He}}^3$ nucleus has been investigated by means of high-energy electron scattering. A separation of the charge and magnetic form factors has been accomplished. The charge form-factor data extend to $q^2=20\mathrm{}$ ${\mathrm{fm}}^{-2\mathrm{}}$ and exhibit a diffraction minimum at $q^2=11.6\mathrm{}$ ${\mathrm{fm}}^{-2\mathrm{}}$; the magnetic scattering is measured to $q^2=12.5\mathrm{}$ ${\mathrm{fm}}^{-2\mathrm{}}$. The results are discussed in terms of models for the charge and magnetic distributions of the nucleus.

Experimental data on the microgiant spreading widths of analog resonances indicate that these widths decrease slightly with increasing mass number $A$ for $A=37-50\mathrm{}$ and then increase again for $A>\mathrm{}60\mathrm{}$. A calculation is presented in which this remarkable property can be understood in terms of a model in which the distribution of Coulomb mixing strength in a nucleus has two peaks with the analog state lying between these two peaks and moving with respect to them with changes in $A$ and $T_{\zeta }$.

Ions are accelerated when a high-current relativistic electron beam is injected into a low-pressure gas-filled region. A correlation is observed between electron-beam front velocities in hydrogen and mean proton velocities that places an upper limit on the length of the acceleration region and indicates that the net beam-current rise is preceded by the protons after particle acceleration. The apparent field strengths in the acceleration region are ≥ (3 to 6) × ${10}^7$ V/m.

The early history of the universe is discussed in the context of an exponentially rising density of particle states.

The polarization in ${\pi }^{+}p$ elastic scattering in the backward hemisphere has been measured at 2.50, 2.75, 2.93, 3.25, and $3.75 \frac{\mathrm{GeV}}{c}$. The data cover a range $u$ of -0.5 to +0.1 ${\left(\frac{\mathrm{GeV}}{c}\right)}^2$ and show a positive peak at approximately the same c.m. angle as the minimum in the differential cross section. At angles farther away from 180° the polarization becomes negative. The data are not well explained by either resonance or Reggepole models.

Assuming the existence of certain limits we give an exact solution of a two-dimensional elastic Ising model with quadratic coupling. The main results are these: (I) If the lattice is slightly stretched, thermodynamic instability occurs for temperatures in a neighborhood of the critical point. (II) Outside this neighborhood, ${\kappa }_T$, $\alpha$, and $C_p$ diverge. (III) The nearest-neighbor spin-spin correlation function is nonzero for any pressure when $T$ becomes infinite. (IV) Antiferromagnetic as well as ferromagnetic behavior can occur for weak coupling at any pressure. (V) For strong coupling, at 0 pressure the model can have a Curie and Néel point or no critical point.

An electron drift driven by an applied constant electric field causes an ion acoustic instability. A steady state is proposed in which ballistic clumps of plasma behave like dressed test particles and collisionally scatter each other. The applied field is balanced by the dynamical friction force on the clumps. The resulting conductivity is $\sigma \approx \frac{10{\omega }_{\mathrm{pe}}}{k{\lambda }_D}$.

New secondary electron emission spectra have been obtained by a rapid analyzer, which presents the full spectra in the range from 0 to 100 eV in 1 msec on an oscilloscope. The spectra show distinct peaks corresponding in energy to the volume and surface plasmons: for Al at 15.2 eV; ${\mathrm{Al}}_2$${\mathrm{O}}_3$ at 31, 22.5, and 17.5 eV; and KCl at 13.6, 9, and 7 eV. It is suggested that these groups of secondary electrons originate from plasmon decay.

The current-phase relation $I_s\left(\varphi \right)$ for an Anderson-Dayem bridge is investigated making experimental use of the quantum interference between two such bridges. Near $T_c$ and for critical currents $\lesssim 10$ μA, $I_s\left(\varphi \right)$ is found to be nearly sinusoidal.

We calculate the electronic dielectric constants for amorphous semiconductors from their short-range structural data. The agreement with measured values supports the contention in Phillips' spectroscopic theory of bonding that it is the chemical bond which is of primary importance in determining the electronic dielectric constants.

The reflection spectrum of solid ${\mathrm{N}}_2$ at 4.2°K has been measured over the wavelength range 550-1550 Å for the first time. These data reveal that Rydberg states thought to perturb excited vibrational levels of the $b{}_{}{}^1{}_{}{}^{}\Pi _{\mathrm{u}}^{}{}_{}{}^{}$ state are present though not directly observable in the solid.

A small tail above the Fermi energy has been found in the energy distribution of field-emitted electrons on three crystal planes of clean tungsten, at 20°K. The current in the tail is proportional to the square of total probe hole current, and is interpreted as resulting from electron-electron scattering in the metal.

We give a semiquantitative model for the density of states and transport properties of an electron in a system of randomly located hard-core scatterers. Our main results are these: (a) The density of states has the usual square-root behavior for high energies and a tail of localized states at the low-energy end; the energy at which the transition occurs is computed from percolation theory. (b) For a fixed temperature the fraction of electrons in localized states increases drastically with the density of scatterers above a critical density. Thus, our model provides a physical explanation for the mobility transition found by Neustadter and Coopersmith.