Spin-axis relaxation in spin-exchange collisions of alkali atoms

We present calculations of spin-relaxation rates of alkali-metal atoms due to the spin-axis interaction acting in binary collisions between the atoms. We show that for the high-temperature conditions of interest here, the spin relaxation rates calculated with classical-path trajectories are nearly the same as those calculated with the distorted-wave Born approximation. We compare these calculations to recent experiments that used magnetic decoupling to isolate spin relaxation due to binary collisions from that due to the formation of triplet van-der-Waals molecules. The values of the spin-axis coupling coefficients deduced from measurements of binary collision rates are consistent with those deduced from molecular decoupling experiments. All the experimental data is consistent with a simple and physically plausible scaling law for the spin-axis coupling coefficients.Comment: text+1 figur

Spin Relaxation Resonances Due to the Spin-Axis Interaction in Dense Rubidium and Cesium Vapor

Resonances in the magnetic decoupling curves for the spin relaxation of dense alkali-metal vapors prove that much of the relaxation is due to the spin-axis interaction in triplet dimers. Initial estimates of the spin-axis coupling coefficients for the dimers are 290 MHz for Rb; 2500 MHz for Cs.Comment: submitted to Physical Review Letters, text + 3 figure

Microwave radiation by a relativistic electron beam propagation through low‐pressure air

Intense relativistic electron beams fired into air at varying pressures display a wide range of microwave signatures. These experiments held beam current, energy, and pulse length constant while varying gas pressure. Our observing window is 10 to 40 GHz. At low pressures ( less than 10m Torr) exponential spectra result, consistent with beam reflexing or virtual cathode oscillations. Above 20 m Torr the spectrum flattens and suggests collective emission at the beam-generated plasma frequencies. Power falls linearly with pressure above 20 m Torr, until electron-Neutral collisions damp the emission at a few Torr. However, weak 10 GHz emission appears at full atmospheric pressure

MICROWAVE-RADIATION BY A RELATIVISTIC ELECTRON-BEAM PROPAGATION THROUGH LOW-PRESSURE AIR

Intense relativistic electron beams fired into air at varying pressures display a wide range of microwave signatures. These experiments held beam current, energy, and pulse length constant while varying gas pressure. Our observing window is 10 to 40 GHz. At low pressures ( less than 10m Torr) exponential spectra result, consistent with beam reflexing or virtual cathode oscillations. Above 20 m Torr the spectrum flattens and suggests collective emission at the beam-generated plasma frequencies. Power falls linearly with pressure above 20 m Torr, until electron-Neutral collisions damp the emission at a few Torr. However, weak 10 GHz emission appears at full atmospheric pressure