Answer to Question #173 Submitted to "Ask the Experts"

Q

Does freezing rain and snow enhance the collection of radon/thoron in precipitation? We routinely collect water samples from the storm water effluents outside our production areas. Yesterday, during a period of freezing rain and snow, we saw elevated gross alpha and beta-gamma activity in the runoff. When the samples were recounted six hours later, no radioactivity was detectable on the samples. Has anyone seen similar occurrences during periods of freezing rain and snow?

A

To my knowledge no one has published anything on such an occurrence. However, what you observed would not surprise me. Radon/thoron (a gas) would have some solubility in ice, so some absorption of soil gas would occur. In addition, daughters (from the soil gas) in contact with ice would plate-out on the surface of the ice. Once the ice melted, the daughters would be taken along for a ride with the runoff. Also, as a rule of thumb, gas solubility increases as temperature decreases. So, cold water puddled in a storm sewer would pick up an increased amount of radon and thoron. Last but not least is the published fact that rain and ice coverage on the ground increases the radon flux in areas not covered by ice (i.e., a basement in a house). Therefore, I would predict that the radon concentration in the storm sewer will probably increase significantly during the episodic weather event. This, in combination with increased solubility in water because of the lower temperature and potential daughter plate-out in the runoff, might explain what you observed. David Wilson