Detecting excess ionizing radiation by electromagnetic breakdown of air

Abstract

A scheme is proposed for detecting a concealed source of ionizing radiation by observing the occurrence of breakdown in atmospheric air by an electromagnetic wave whose electric field surpasses the breakdown field in a limited volume. The volume is chosen to be smaller than the reciprocal of the naturally occurring concentration of free electrons. The pulse duration of the electromagnetic wave must exceed the avalanche breakdown time (10–200 ns) and could profitably be as long as the statistical lag time in ambient air (typically, microseconds). Candidate pulsed electromagnetic sources over a wavelength range, 3 mm>λ>10.6 μm, are evaluated. Suitable candidate sources are found to be a 670 GHz gyrotron oscillator with 200 kW, 10 μs output pulses and a Transversely Excited Atmospheric-Pressure (TEA) CO2 laser with 30 MW, 100 ns output pulses. A system based on 670 GHz gyrotron would have superior sensitivity. A system based on the TEA CO2 laser could have a longer range >100 m.

Development of THz-range Gyrotrons for Detection of Concealed Radioactive Materials

“…Note that this volume being determined as a prolate spheroid with minor semi-axis r th (0) and major semi-axis L diff /2 is equal to [4] V ¼ 2p 2 3…”

“…[4]. The idea [4] is to focus powerful THz wave beam in a small spot for getting the RF electric field strong enough to break down the air if the background ionization level is sufficiently elevated. The peculiar feature of this method is the fact that the radiation can be focused in a small volume in which no free electrons may exist in the absence of additional sources of ionizing radiation that could initiate the breakdown.…”

“…The concept of using the THz radiation for this purpose was proposed in Ref. [4]. The idea [4] is to focus powerful THz wave beam in a small spot for getting the RF electric field strong enough to break down the air if the background ionization level is sufficiently elevated.…”

“…Among slow-wave devices the most remarkable are backward-wave oscillators developed by Russian corporation "Istok" which cover all range of submillimeter waves (up to 1. 4 THz frequency) at the milliwatt level of continuous-wave (CW) power [12] and are widely used in spectroscopic applications around the globe. The power level of these tubes is, obviously, not sufficient for breakdown studies.…”

Numerical estimation on free electrons generated by shielded radioactive materials under various gaseous environments

“…2 Estimates for the number of free electrons generated by a radioactive material which is under shielded environment are critical for implementing the scheme. The recent study by Dimant et al analyzed of the free electron production rate at distance from a radiation source and showed an excellent agreement between the analytic solution from the Klein-Nishina scattering theory and the numerical solution from MCNPX.…”