The thermal x-rays produced by a nuclear burst in outer space cause polarization currents in the medium which, if distributed anisotropically, will emit electromagnetic radiation. Roughly, a burst of thermal x rays, equivalent in energy to 1 ton of high explosive, produces a detectable 10-Mc/sec signal at a range of 1 km. Since only the ratio of x-ray energy to range enters into the strength of the radiated signal, other ranges follow by adjusting the x-ray energy proportionately. This works up to ∼3×${10}^3$ km; beyond this range, dispersive effects begin to reduce the signal received.

The power in the electromagnetic signal varies as the square of the electron density, so this effect may provide a sensitive measure of the density of electrons in outer space.

• Received 18 March 1961

DOI:https://doi.org/10.1103/PhysRev.119.827