Hi all, I know there has been a lot of interest lately in radium dials following the study from the University of Northampton. I've acquired 5 radium watches over the past 12 months. I have access to an industrial grade Geiger counter through my work. I also have an interest in science in general. So I decided to take a few measurements. As many of you will know, radium emits mainly alpha particles/alpha radiation. Alpha particles are large (like helium atoms). For that reason, they often collide with air molecules and matter, and don't make it very far at all (a few inches in air, and do not penetrate skin or most materials like a safe). About 4% of radium radiation emissions is gamma radiation. Gamma rays penetrate pretty well everything, and travel until they encounter a material they cannot penetrate (like lead). I first measured the radiation from the first radium watch I acquired, a vintage Tissot automatic from 1952, pictured below. The readings I got were 2.50 uSv/hour from the front of the case, and 1.54 uSv/hour from the caseback, as pictured below. The higher reading translates to about 21.9 mSv/year. I thought these values were a bit high, since the effective limit for the public based on the Canadian Nuclear Safety Commission is 1 mSv/year, and for nuclear energy workers, is 50 mSv/year. So I wondered whether these values mainly reflected the alpha emissions, rather than gamma. The detector I used picks up alpha, beta and gamma, and does not differentiate them (i.e. gives a total value). http://nuclearsafety.gc.ca/eng/resources/radiation/introduction-to-radiation/radiation-doses.cfm So I decided to re-measure with my other radium watches. I recently acquired @ConElPueblo's 1946 LeCoultre, which features fantastic radium hour markers and lumed hands. The values from from of case on contact, and case back were 0.97 uSv/hour and 0.64 uSv/hour, as pictured below. But then, I tested what would happen whether you pull the detector back even by a few inches... The value dropped drastically to 0.31 uSv/hour. Then even a bit further (maybe 5 inches)... 0.18 uSv/hour, which is barely above background. Basically, the detector is picking up alpha radiation close to the watch, but these rays dissipate very easily due to the air surrounding the watch. Radiation is pretty much background level even a foot away from the watch. I would hypothesise that most of the radiation picked up by geiger counters we use on our watches is alpha. Alpha is generally considered harmless (I believe the limit for nuclear workers is somewhere around 500 mSv/year "at the wrist", i.e. close contact). This might be applicable when you're actually wearing the watch, but again, most of this shouldn't make it past your skin. Tried the same principle with my watch box. Measured at the surface of the box, and then about a foot away, readings were 0.53 uSv/hour and 0.04 uSv/hour respectively. Even at the case surface, most of the radiation had been dampened by the watch box itself, again suggesting this is alpha (gamma would definitely penetrate the watch box). At any rate, I hope this helps some people understand how radium works. It re-assured me. By no means am I saying for certain that radium watches are safe. These were just my observations...Also, I haven't checked radon levels, which in my opinion seem to be the greater concern with a large collection of radium watches in an enclosed space. -J.