A new technique is introduced which provides a unified formalism for treating diffusion-controlled reaction kinetics in a discrete lattice. Illustrative calculations are presented for vacancy-interstitial reactions in a fcc lattice.

We show that the symmetry of bound electron states in GaP depends upon the choice of origin for the group operations and hence upon the location of impurity in the crystal lattice. This provides an explanation of the discrepancy between the high radiative efficiency associated with group VI donors and group V isoelectronic centers and the low efficiency of group IV donors (Si) in GaP.

In a recent Letter Schroeer and Triftshäuser offered a reinterpretation to the extensive data on cobaltous oxide by the present authors. We show herein that a careful examination of the microcrystal model proposed by Schroeer and Triftshäuser does not, in fact, account for the main observation on cobaltous oxide.

It is shown that the collective potential energy surfaces for rapid deformations leading to nuclear scission favor asymmetric mass division. A "walk-run" fission process is proposed, in which a slow deformation to the saddle-point shape is appropriately described by the liquid-drop model, and a rapid collective deformation then carriers the nucleus from saddle point to scission. The most probable mass ratio decreases with decreasing $\frac{Z^2}{A}$, in qualitative agreement with empirical fact.

We have measured $\frac{d^2\sigma }{d\Omega \mathrm{dp}}$, the differential cross section for the production of ${\pi }^{\pm }$ mesons, at high $P_{\perp }$, in 12.5-GeV/c proton-proton collisions. We covered the range $P_{\perp }^{}{}_{}{}^2=1.0-4.0\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ and the cross section appears to break at about 1.5 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$. Thus, $\frac{d^2\sigma }{d\Omega \mathrm{dp}}$ appears to be the sum of two Gaussians in $P_{\perp }$.

An upper limit is given for the two-body annihilations $\overline{p}+p\to K+{\overline{K}}^{*}(\overline{K}+K^{*})$, where $K^{*}$ denotes a $J^P=0^{+}$, $s=+1\mathrm{}$ resonance with a mass below $K\pi$ threshold. This upper limit is compared with other two-body annihilation processes.

The presently accepted Regge parametrization of ${\pi }^0$ photoproduction claims that the $t\sim 0.5$ ${\mathrm{BeV}}^2$ cross section is completely provided by $B$ exchange. We show that this statement disagrees with vector dominance by a factor of at least 4 and probably 10 or more. Additional $I=0\mathrm{}$ poles or cuts are needed both in this process and in the $I=0\mathrm{}$ $t$-channel combination of $\pi +N\to \rho +N$ cross sections.

The problem of interaction of atoms with intense light is reformulated via a time-dependent unitary transformation. An effective electronic binding potential is obtained. The effective perturbation remains bounded as the intensity of the incident light increases.

A 2.2-m streamer chamber in a large electromagnet was used with a 16-GeV bremsstrahlung beam to study multibody photoproduction. This paper reports on the 851 three-prong, three-constraint kinematic fit events of the type $\gamma p\to {\pi }^{+}{\pi }^{-}p$; at energies above 6 GeV, these go almost completely to a $p{\rho }^0$ final state.

Partial cross sections for ${\pi }^0$ and ${\eta }^0$ production are measured at 12 energies. Pion multiplicities up to five are considered.

Angular distributions are measured at 12 energies. Coefficients of Legendre polynomial expansions of these distributions are given. Also presented are comparisons of the forward and backward cross sections with predictions.

A spark-chamber missing-mass spectrometer was used to measure the differential cross section for the reaction $p+p\to d+{\pi }^{+}$ at closely spaced intervals of incident momentum between 3.4 and 12.3 GeV/c and at small c.m. angle. The data confirm the existence of a prominent peak in the forward cross section at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}\simeq 2.9$ GeV and show a hitherto unreported shoulder at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}\simeq 3.6$ GeV. The results make evident the inadequacies of present one-pion-exchange and one-nucleon-exchange models.

On the basis of current algebra, the Nambu-Sakurai hypothesis of partial conservation of strangeness-changing vector currents, and unsubtracted dispersion relations for $f_{+}\left(q^2\right)$ and $q^2{f}_{-}\left(q^2\right)$, the $K_{l3\mathrm{}}$ parameters $\xi$, ${\lambda }_{+}$, and ${\lambda }_{-}$ are found to be consistent with the present experimental indications. The only input in the theory is $\frac{F_K}{F_{\pi }{f}_{+}\mathrm{}\left(0\right)\mathrm{}}=1.28\mathrm{}$ from the Cabibbo theory. The mass of the conjectured $\kappa$ is in agreement with the recently reported result of broken chiral symmetry.

We prove low-energy theorems for Compton scattering, which are exact when the electromagnetic interaction is included up to fourth order and the strong interactions to all orders. These theorems give the terms of order ${\omega }^2\ln \omega$, where $\omega$ is the photon c.m. momentum, besides establishing the classical low-energy theorem to the order $e^4$.

The trajectories and residues of $\rho$ and ${\rho }^{\prime }$ Regge poles are determined in the range $0>~t>~-1.0\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ from a simultaneous fit to (i) continuous-moment sum rules, using $\pi N$ phase shifts up to 2 GeV/c, and (ii) ${\pi }^{-}\rho \to {\pi }^{0}n$ scattering cross section data above 4 GeV/c. The ${\rho }^{\prime }$ trajectory is found to be roughly parallel to the $\rho$ and about a half-unit lower. The ${\pi }^{-}\rho \to {\pi }^{0}n$ polarization is correctly predicted in magnitude and sign.

Infinitely rising trajectories are shown to be consistent with the usual features of dispersion theory and Regge-pole theory only if the trajectories behave, to within logarithmic factors, as $\sqrt{s}$ as $s\to +\infty$. For such trajectories the imaginary part must increase more rapidly than the real part.

The transition probability of the $1{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}-2{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ transition has been measured in the heliumlike ions ${\mathrm{O}}^{6+}$ and ${\mathrm{N}}^{5+}$. The results are (5.2 ± 1)×${10}^8$ ${\sec }^{-1\mathrm{}}$ and (1.7 ± 0.3)×${10}^8$ ${\sec }^{-1\mathrm{}}$, respectively. They agree well with very recent calculations.

High-resolution electron-impact measurements reveal that just above the threshold for excitation of the $2p$ level of atomic hydrogen there is a complicated resonance structure, part of which had not previously been predicted or observed.

Detailed numerical reexamination of the $1s-2p$ cross section for the excitation of hydrogen by electron impact shows structure at 10.4 and 10.6 eV which has not been previously reported. The calculations tend to confirm the recent data of Williams and McGowan. It is suggested that the structure is the result of interference between background potential scattering and the resonance just above $n=2\mathrm{}$ threshold.

We show that in analyzing coincidence-Mössbauer data it is necessary to include the finite resolution time determined by the electronics. By so doing, we are able to fit spectra in which only "time filtering" effects are present. Results are also presented showing the enhanced resolution capability of this technique.