Variation in γ-ray count rates as a monitor of precipitation rates, radon concentrations, and tectonic activity

Precise and reproducible correlations between environmental γ-ray count rates (GRR) with rain precipitation rates (RPR) and snow precipitation rates (SPR) have been measured to be 0.18±0.02 and 4.3±0.04 (counts/s)/(mm/h), respectively. The GRR, observed with two 12.3 cm3 NaI detectors, also exhibit a diurnal cycle (period of 1.01±0.03 day, maximum around sunrise and location dependent amplitude) and a seasonal cycle (smaller amplitude and maximum in mid-February). Increased GRR during precipitation have been observed at ground level, but the effects of the diurnal cycle and other noise are reduced by more than 20 at 15 m above ground. An improved signal-to-noise ratio, response time of less than one hour and precise correlations between the peaks in GRR and precipitation rates enable real-time determinations of RPR and SPR to better than 1 mm/h. The relative insensitivity of these correlations to other meteorological conditions enables GRR to serve as remote and environmentally stable sensors of RPR and SPR. The time-dependence of GRR is consistent with that expected from variations in the presence of radon and radon progeny in the atmosphere. Change in the amplitude of the diurnal cycle may serve as a monitor of radon concentration. A γ-ray detector integrates over a large volume with good time resolution and thus may be responsive to real-time changes in radon concentrations due to increased exhalation from tectonic activity.