Answer to Question #10295 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
I have a question related to a World War II gauge containing radioluminous paint. As an aircraft enthusiast I bought an old speed indicator 10 years ago. It has an open-pressure valve linked to the inside of the case and another situated within the gauge. In addition, the seal on the front of the gauge is quite aged and surely not tight anymore. The gauge stood 3.5 years in my room, where I also slept and smoked for half a year. Having recently heard about radon emanation, I am very concerned that radon levels might have been very high in the room and affected my health. A measurement revealed 11 microsieverts per hour (µSv h-1) at a distance 1.3 centimeters (cm) from the front glass. Which radon emanation coefficient does radioluminous paint have? How much radon could have escaped from the paint? Could paint flakes have left the front side despite the fact that the paint looked okay? Furthermore, not knowing about the radioactive paint, I had blown into one of the two valves several times—which had before been linked by a probably airtight sleeve for many years—in order to see the gauge work. I'm not sure if the pressure gauge was fully tight anymore. Could I have taken in radon daughters or was there no risk?
The question of radiation dose from radium gauges has been addressed in documents prepared for the U.S. Nuclear Regulatory Commission (Boerner and Buchholz 2007, Buchholz 2008). Total effective dose equivalents (doses) are estimated for various scenarios: amateur repair, collecting a large number of gauges, a catastrophic fire involving a collection of gauges, postfire cleanup activities, handling or cleanup of nonintact gauges, and active use in commercial vehicles or aircraft.
The following pathways are considered in the article by Buchholz (2008): external exposure, inhalation of paint, ingestion of paint, inhalation of radon, and inhalation of smoke. All of the dose estimates in the article by Buchholz (2008) are based on 37 kilobecquerels (kBq) of radium.
The first step is to estimate the amount of radium in your gauge. In a study involving over 2,000 radium instruments in a U.S. military inventory (Buchholz 2008), most of the gauges contained less than 37 kBq, many fewer contained 37 to 555 kBq, and there were several outliers listed at much higher activities. Based on a formula in the article by Boerner and Buchholz (2007) and your measurement of 11 μSv h-1 at a distance of 1.3 cm from the glass surface (estimated to be 2.5 cm from the radium), an activity of 32 kBq can be estimated. This value is consistent with the findings from the U.S. military inventory.
In the article by Buchholz (2008), the largest estimated dose of 0.15 millisievert per year (mSv y-1) came from amateur repair activities and included external exposure, inhalation of paint, ingestion of paint, and inhalation of radon. Doses from other collector scenarios ranged from less than 0.01 to 0.021 mSv y-1. While not directly applicable to your situation, the estimated annual dose from active use in commercial vehicles or aircraft is 0.066 mSv y-1, attributed to external dose. These doses may be compared with the dose from natural background radiation, which is quite variable but averages about 3 mSv y-1. While I suggest that you review these studies yourself, the data in the reports indicate to me that your risk from owning and handling your gauge as described in your question was very small.
Tom Gesell, PhD (with assistance from Charles Roessler, PhD, CHP, and Joel Lubenau, CHP)
Boerner AJ, Buchholz MA. Radium timepiece dose modeling: Final report revision 1. Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee; 2007. Available at: http://pbadupws.nrc.gov/docs/ML0731/ML073120009.pdf. Accessed 11 September 2017.
Buchholz MA. Supplement to radium timepiece dose modeling: Radium gauge dose modeling. Second draft report. Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee; 2008. Available at: http://pbadupws.nrc.gov/docs/ML1008/ML100840103.pdf. Accessed 11 September 2017.