A Simulation of the Nuclear High‐Altitude Electromagnetic Pulse (HEMP) Produced by the X‐Ray in the Ionosphere

Abstract

Price, 1974), because X-rays have been absorbed within several tens of meters from the burst, thus only energetic γ-rays with several kilometers free path can proceed at low altitudes. In general, the absorption region of γ-rays is between 20-km and 40-km E altitudes (Karzas & Latter, 1965;Maraschi & Cavaliere, 1977), where γ-rays produce a significant amount of free electrons that screen electrical effects caused by the X-ray (Higgins et al., 1973). As a result, when studying the EMP below 30 km E , only γ-rays need to be considered.However, when we research the impact of HEMP on the ionosphere at altitudes greater than 60 km E , X-rays will play the dominant role. Since X-rays have a higher density than γ-rays by a factor of  4 510 10 E at altitudes of 50-100 km E (Higgins et al., 1973), and X-rays are strongly absorbed within this layer. Therefore, the number density of photoelectrons produced by X-rays is much greater than that of Compton electrons produced by γ-rays. As a result, when studying the HEMP generated in the ionosphere's D-region (at the altitude of 60-90 km E), we only consider photoelectrons produced by X-rays. The basic physical mechanism of nuclear HEMP generated by X-rays is similar to that of the EMP produced by γ-rays (Karzas & Latter, 1965;Longmire, 1978): X-rays generate photoelectrons by photoionizing air molecules, and photoelectrons deflected by the geomagnetic field constitute the primary current, which causes the EMP. As photoelectrons ionize air molecules, they can also generate a significant amount of secondary electrons. Secondary electrons