The $\gamma$ rays from a nuclear explosion in space Compton-scatter electrons near the surface of the device or in a surrounding material shield. The scattered electrons leave the surface and are accelerated back toward it by the positively charged matter. Provided they are asymmetrically distributed, the accelerating electrons radiate an electromagnetic signal. The electron motions are analyzed, the electromagnetic signal is estimated, and its detectability is discussed. For a typical nuclear explosion, the electromagnetic signal is independent of the yield and contains frequencies up to 10 to 100 Mc/sec and thus will penetrate the ionosphere. Taking into account dispersion by the ambient interplanetary plasma (≈${10}^2$ electrons/cc), the peak electric field strength at a distance $R$ kilometers from the explosion is $\approx {10}^4{R}^{-\frac{3}{2}}$ v/m. The pulse length is $\approx {10}^{-10\mathrm{}}R$ sec. If only background cosmic noise limits detectability of the signal, the maximum detectable range is about ${10}^6$ km.

• Received 5 February 1962

DOI:https://doi.org/10.1103/PhysRev.126.1919