A Monte Carlo simulation study of L-band emission upon gamma radiolysis of water

Abstract

Several studies have confirmed visible light and ultraviolet emission during water molecule radiolysis; however, radiofrequency emission has been scarcely investigated. This simulation study has revealed that the gamma radiolysis of water creates excited hydrogen atoms which emit radio recombination L-band (1 GHz–2 GHz) radio waves of sufficient strength that a radio-imaging device can detect. The physical and physicochemical stages of radiolysis of water have been modeled via application of Monte Carlo simulation techniques (utilizing Geant4) up to 1 ps from the onset of gamma photon interaction with water molecules. Subsequently an L-band emission analysis up to a few ms duration was accomplished to obtain and understand RF power emission characteristics as a function of gamma radiation dose rate. The generated L-band 1.4 GHz RF power is 19 dBm per one Gy/h of absorbed dose rate. The generated RF power varies linearly with absorbed dose rate up to 3.38 Gy/h, beyond which non-linearity manifests due to line broadening. Unlike conventional gamma radiation detectors, the proposed RF-based gamma radiation detection model indicates that the detection sensitivity of the RF detector does not deteriorate rapidly with an increase in altitude above radiation source at ground. Consequently, source-detector standoff distances are increased significantly at least up to two orders of magnitude higher than the current gamma radiation detection scenario. Preliminary experiments were conducted using an experimentally simulated signal, an RF transmitter and an RF receiver along with suitable data acquisition unit. This was performed to determine the sensitivity of the RF receiver, which would enable laboratory scale testing with safe gamma sources of dose rate less than 0.1 mGy/h.