Active Remote Detection of Radioactivity Based on Electromagnetic Signatures
Interim rept. Jul 2012-Jul 2013
NAVAL RESEARCH LAB WASHINGTON DC
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This paper presents a new concept for the remote detection of radioactive materials. The concept is based on the detection of electromagnetic signatures in the vicinity of radioactive material and can enable stand-off detection at distances greater than 100 m. Radioactive materials emit gamma rays which ionize the surrounding air. The ionized electrons rapidly attach to oxygen molecules forming O-2 ions. The density of O2 around radioactive material can be several orders of magnitude greater than background levels. The elevated population of O-2 extends several meters around the radioactive material. Electrons are easily photo-detached from O-2 ions by a laser pulse. The photo-detached electrons, in the presence of laser radiation, initiate avalanche ionization which results in a rapid increase in electron density. The rise in electron density can induce a frequency modulation on a probe beam which becomes a direct spectral signature for the presence of radioactive material.