Answer to Question #1959 Submitted to "Ask the Experts"

Q

Regarding military aircraft clocks from the WWII era, should there be any concern over radium radiation exposure if such a clock would be placed in an office where one could have 40 to 50 hours of exposure per week?

A

One concern is the potential for the ingestion of radioactive material in the event that the device were opened up and the radium somehow removed from the dial face. Assuming that the device is not opened up, the exposure to gamma rays emitted from the radium might be a concern. A good rule of thumb is that one microcurie (1 µCi) of ²²⁶Ra increases the exposure rate by one microroentgen per hour (1 µR/hr) at a distance of one meter. If we assume that the device in question contains 10 uCi of ²²⁶Ra (it probably has less), the increase in the exposure rate one meter away would be approximately 10 µR/hr. Over the course of a year (40 to 50 hours per week and 50 weeks per year), this would translate into 20 to 25 millirem. The latter approximates a 10% increase in the typical annual exposure to background radiation. If the device is two meters away instead of one meter, the exposure rate is reduced by a factor of four (that is, from 20 to 25 mrem/year to 5 to 6 mrem/year). Such a small radiation exposure has never been shown to result in an increased risk of cancer (or anything else). That does not exclude such a possibility, it simply means that there are far more important things to worry about. Paul Frame, CHP, PhD