Radium - Geiger Counter Measurements

jshaw083

Hi all,
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.

TNTwatch

Your method to distinguish alpha from gamma seems fine, but the 3 tools at the beginning of the thread below are not equipped to detect alpha, yet people were able to measure about 17-18 µSv/h with them. What do you think was detected there?

https://omegaforums.net/threads/radium-emissions-on-early-2998.78228/

PS: I was just trying to determine if an alpha particle detector could be additionally helpful to our hobby, or just a beta and gamma counter is good enough.

jshaw083

To be honest, I'm not sure I can explain this. I've read reports that the cheap handheld radiation detectors are fairly inaccurate and not congruent with commercial radiation detectors. Could be that it's just detecting gamma but not measuring it accurately. Or that the 2998 models have a lot of radium in that lume. Which would be surprising for any watch made post-1940s (since even at that point watch companies were drastically cutting back the amount of radium they used on dials). Would be interesting to see how the levels measured by these portable detectors compare to those used by professionals (e.g. Thermo-Fischer).

I think we mainly care about gamma radiation from a health perspective. As far as anyone has ever been able to tell, alpha radiation is harmless, unless emitted from inside the body (which is what happens when you inhale/ingest radium chips, like the radium girls).

TNTwatch

Haven't been able to look much further into this and just got a few quick thoughts, so correct me if I'm wrong:

1. The RadEye PRD you used is capable of gamma detection only. It's the RadEye SX that is capable of detecting Alpha and Beta additionally, and I think it's also able to tell what kind of radiation detected.

2. A tool that is able to detect both benign and dangerous radiations but unable to tell them apart is potentially more dangerous than a more limited device that focus on one or the other type. When there's just a benign one, a false alarm may be raised unnecessarily. When the more dangerous gamma exists, the situation could be dismissed as a benign one instead.

3. Radiation normally disperses omnidirectionally so it's strength relates to distance by the inverse squared law. Double the distance - a quarter of the strength. I looked back your first post and at the end where you checked the watch box, the measurements appear to be close to this inverse squared rule.

4. As many measurements shown in this and the other thread, as well as many places elsewhere, gamma only tools are useful enough for radium watches. A beta capable device could be useful if it's of high quality and sensitive enough to detect minute amount of beta particles that may still remain on tritium watches.

jshaw083

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.

L Leica

i bought a watch online and border custom had it opened as they claimed it detected radioactive signal thru their scan. I did not know anything about radium prior my purchase so I was pretty much surprised and shocked by it. I took the watch to a local Nuclear Medical Facility and they did a quick scan and said it is very active, but i didnt think it is economical to pay for a full report.

I found a local dealer which carries geiger counter and I spent $400 on their top of the line model. I quickly did a scan in my car and the reading was 150-157uSv/hr . It was a sunny day and I did it right under the sun with the watch on my wrist, I figured it might not be accurate. I tried again and run a 5mins reading several time it average at 135uSv/hr . I sent the video to manufacturer and they said everything looks correct.

The tech at the lab suggest me not to wear it , if i would have known i wouldnt buy it.

77deluxe

What kind of watch?

L Leica

after my research on the serial , I believe its a 1957 watch . Rolex Precision had dots lune and on both hands. I am not a vintage watch collector, bought it solely thought it looks good.

jshaw083

That's an extremely high reading (as far as radium watches go). What model/brand is it and from what year?

To give you some perspective, my radium watches range from 0.50 uSv/hour to 2.20 uSv/hour measured at the crystal surface.

jshaw083

...I don't think a Rolex from 1957 should have a reading that's that high, regardless of the model... Most watch manufacturers began reducing radium content in the 1930-40s and by 1957 most watches only had a small fraction of the radium contained in watches from the earlier 1900s. Are you sure your counter is accurate?

L Leica

i placed in 2cm above the crystal