Answer to Question #1697 Submitted to "Ask the Experts"

Q

I have a 1960s-era watch that I like very much, but it has radium on the hands and dial. I measure (with a Victoreen model 450 survey meter) 37µR six inches away from the front of the watch, and 37µR one inch away from the back. With an ordinary Geiger counter, I get ~3,000 cps on the front and ~50 cps on the back. I am fond of this watch and like to wear it, but I do not know whether this is a safe "dose" if I wear it for 8-10 hours a day. I know not to open it up to avoid alpha exposure. I also do not wear it to bed. Can someone give me an answer please?

A

First, a few comments about the measurement and the activity of the radium. From my experience, the pressurized version of the Victoreen 450, the version that reads out in µR/hr, does not seem to be particularly accurate at this low exposure rate—even when the instrument has been recently calibrated. Furthermore, for the measurement to be accurate, the radiation field needs to be uniform throughout the detector volume. This condition does not exist given the large detector volume of the chamber and the closeness of the latter to the source. Having said that, the measurement at 6 inches (assuming that background, ca. 10 µR/h, was subtracted out) is consistent with the typical activity expected in such a watch: a fraction of a microcurie.

The doses that have been reported for wearers of such watches are difficult to interpret for a number of reasons; for example, the exposure is very nonuniform and the assumptions about the depth and area over which the dose is calculated are not usually specified. The average "genetically significant dose" (that to the gonads) has been estimated by various authors to be 1.2, 3.3 , 2.6, 1.5, and 0.5 to 1.0 mrem per year (Robinson 1968). For a watch containing 1 µCi of ²²⁶Ra, the gonadal dose has been estimated to be 65 to 130 mrem per year if the watch were worn 24 hours per day. Doses to the forearms will be many times higher. Estimates reported by Robinson ranged from 122 mrem per year (for 0.002 µCi) up to 270,000 mrem per year (for 4.5 µCi).

Have any effects been observed due to the wearing of radium-containing watches? Not to my knowledge. Would I wear one? Probably not. But then again, I haven't worn a wristwatch in over 40 years. There are many health physicists who would love to wear one if for no other reason than the fun of seeing it set off a counter. Had one of them answered this question, you would have received a very different answer. The bottom line is that it is your decision. Even if it were possible to calculate a meaningful dose due to the wearing of your watch, and even if we knew how to convert that into a risk, we could still disagree over what is meant by safe.


Reference:
Robinson, EW. The use of radium in consumer products. MORP 68-5, Public Health Service; 1968.

Paul Frame, CHP, PhD