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Radium - Geiger Counter Measurements

  1. jshaw083

    jshaw083 Sep 12, 2018

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    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.
    IMG_8404.jpg
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    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.
    122.jpg
    Photo 2018-09-12, 2 35 34 PM.jpg
    Photo 2018-09-12, 2 37 08 PM (1).jpg

    But then, I tested what would happen whether you pull the detector back even by a few inches...
    Photo 2018-09-12, 2 35 42 PM.jpg

    The value dropped drastically to 0.31 uSv/hour. Then even a bit further (maybe 5 inches)...

    Photo 2018-09-12, 2 37 24 PM.jpg
    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).
    Watch box.jpg
    Photo 2018-09-12, 2 39 27 PM.jpg
    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.
     
    Watch box.jpg
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  2. cholack

    cholack Jan 30, 2019

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    Thanks for this great post
     
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  3. Cipolla

    Cipolla Feb 2, 2019

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    Thankyou, hmm should I measure my dirty dozen 30T2
     
  4. Cipolla

    Cipolla Feb 2, 2019

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  5. Tony C.

    Tony C. Ωf Jury member Feb 2, 2019

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    This topic has been well discussed over the past year or so, catalyzed by an article from the UK about a high count coming from a collection of old radium pocket watches that were stored in a small, poorly ventilated space.

    Fears about radiation exposure from vintage watches are largely overblown. For some perspective, I wrote this on the watchuseek forum several months ago:

    ***

    As this is an interesting "Topic du Jour", I'd like to dig a little deeper.

    As luck would have it, I coincidentally bought my first radiation detector very recently, and have been testing various watches from my collection. One of the things that has quickly become clear is that there are radical differences between readings taken right on top of the crystal, and those taken in other locations. So, to use one example, I have an Eterna that is quite "hot". Below are the various results, taken with a high-quality Soeks detector, and using readings in μSv/h (i.e. microsieverts/hour). Note that microsieverts are 1000 smaller than millesieverts, so be careful not to confuse the two while pondering any related results. To be clear, the reading of 15.0 μSv/h (noted below) is equivalent to 0.015 mSv/h.

    – directly above crystal = 15.0 μSv/h

    – 4" above crystal = 2.90

    – directly on the case back = 3.45

    – adjacent to the watch = 0.60

    So, while 15 μSv/h is a high reading, it is quite clear that even if one were to wear such a watch regularly, the actual accumulated dose would need to be calculated using a far lower level. That is not to say that it would necessarily be "safe", but I believe that it is important not to overreact to the readings taken directly from a dial, or just above the crystal, as no one would be that close to the crystal, or if they somehow were, it wouldn't be for any meaningful length of time.

    What interests me the most is how one might calculate, with reasonable accuracy, what sort of dose prolonged exposure to such a watch would produce. For a bit of context, I am going to quote an apparent expert named Mark Foreman, who was responding to a Fukushima thread on another forum a few years ago. Although an event like that and wearing a vintage watch are obviously not closely analogous, I do think that he sheds some light on the topic with his response.

    "I would say that 6.7 microSv is not a super nasty radiation field. But it is higher than the occupational limit for an area which the general public has free and easy access to.

    If you were to spend 40 hours a week, 52 weeks a year in such a place you would get a 14 mSv dose which is legal for a radiation worker but is on the limit of what you can get in the UK without triggering an investigation of your exposure by the state. That occurs at 15 mSv per year.

    In Sweden I think that if you go over 7 mSv in two months or some similar dose then you have to write a letter to SSM explaining what you have done, if you were to stay in this hot spot for two months your exposure would be well below this trigger dose.

    At 14 mSv per year you would have to be a classified worker by UK law as you would get more than one third of the occupational limit (20 mSv) per year. This would require you to be placed under medical supervision and you would have to have regular blood tests.

    On the other hand this dose is very unlikely to cause any illness unless you remained there a very long time, if you were to spend 20 years in such a hot spot you would clock up 280 mSv which would give you a one on 71 chance of inducing a cancer."


    On the same thread, and still using 6.7 uVs/hr as a baseline, Frank Duncan (Chemist, retired, Radiation Safety Officer, retired, Class III Licensed Radiographer in Louisiana, retired) states:

    "6.7 μSv/hr=0.77mR/hr so this is above background but well below anything dangerous. You will experience no ill effects from being in a radiation field this low. In the US, you are allowed up to 2mR/hr exposure."

    Note that mR/hr is another type of measurement (milliroentgens per hour), but the point should be clear. So, using my Eterna example above, even the close proximity of the wrist to the case back would produce an exposure of roughly half the 6.7 μSv/h discussed by the experts. I therefore infer that even if worn regularly, a relatively "hot" vintage watch would produce only a minuscule cancer risk.

    ***

    Those interested can read the full thread here, as it addresses the related issue of radon gas, as well:

    https://forums.watchuseek.com/f11/radium-study-well-dang-4735359.html
     
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  6. jshaw083

    jshaw083 Feb 2, 2019

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    I think it's important to keep in mind as well the issue of alpha/gamma radiation. Radium emits 96% alpha radiation. So even those readings you are recording is mostly alpha radiation, which shouldn't (theoretically) be able to penetrate your skin. Most commercial radiation detectors don't discriminate between alpha and gamma, and just put out a total reading. If it were gamma radiation you were measuring, it shouldn't fall off within a few inches of the watch. It also wouldn't be different from front to back of the case (gamma would penetrate the watch and be equal on both sides).
     
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  7. Dan S

    Dan S Feb 2, 2019

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    Now we need a similar total dose analysis of radon gas exposure. As @Tony C. mentioned, this whole topic was recently given new life by measurements of radon gas concentration in a small enclosed poorly ventilated space. I'd like to have some radon readings in a "typical" bedroom of a house with an HVAC system, with and without a watch collection. I can do it myself, but my collection isn't particularly radium-rich. I'm guessing that only 5-10 of my watches have radium, and I don't know if any are especially hot.
     
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  8. jshaw083

    jshaw083 Feb 2, 2019

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    If someone had a collection of radium watches pre-1940s, that would be ideal. A lot of the watches tested in that UK study were pre-1940s watches, a lot of which were military, probably with very high radium concentrations in the lume. The amount of radium used in watches declined 100-fold between 1920s to 1950s.
     
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  9. Dan S

    Dan S Feb 2, 2019

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    I realize that you might get more exciting readings from those earlier watches, and that would certainly be relevant for collectors of early military watches, but I'm personally more interested in the effects associated with watches from the 1940s and 50s. And I would say that the vast majority of radium-lumed watches I see on OF fall into this category.
     
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  10. Tony C.

    Tony C. Ωf Jury member Feb 2, 2019

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    re: radon

    Follow the link above to the original WUS thread. Dean (aka "Tick-Talk") measured radon gas over an extended period on his collection, and the results were negligible.

    re: gamma

    I also believe the gamma to be negligible risk, as it makes up such a low percentage of radium.

    And it is of course true that the real risk from radium comes from inhalation, etc., not from wearing old watches. So those who service them are at vastly greater risk than collectors.
     
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  11. M'Bob

    M'Bob Feb 2, 2019

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    I actually measured the radon gas from just one radium-dialed watch, in a small enclosed container, and the results were frighteningly high. But this is not the end of the story: apparently, when the container is opened, the gas will dissipate in a few minutes. So, an expert in the field recommended this: if you have a number of radium watches that are stored in a relatively air-tight container, and plan to open it, open the windows, and leave the room for a while, or place them near an exhaust fan. This will reduce your chance of a significant exposure.
     
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  12. jshaw083

    jshaw083 Feb 2, 2019

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    Right, but radon concentrations are a function of units per volume....If you're measuring the concentration in a very small container it will obviously be high. I think it would go without saying you shouldn't breathe in the air directly open opening the container. What's more relevant to people is the radon concentration within a room or within their home. Given the much larger volume, the concentration presumably would be much lower.
     
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  13. M'Bob

    M'Bob Feb 2, 2019

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    Sorry to disagree, but prior to the UK study detailing the caution about radon emissions from watches, there were few if any discussions about this risk, while there were plenty of discussions over many years regarding the radium exposure risks from watches. I will go so far as to say that many collectors opened their mostly sealed watch cases containing radium-dialed watches, and probably got a good blast of radon gas to the lungs, without ever knowing there was even a potential hazard. The risks of this over the years from doing this can be debated, but nonetheless, it very much needs to go with saying.
     
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  14. Dan S

    Dan S Feb 2, 2019

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    To a reasonable approximation, the health risk is associated with the total (integrated) dose. Safe levels of radon are determined on the basis of continuous exposure for a certain number of hours per day, 15 breaths per minute, hour after hour. It is meaningless to use those levels to make a comparison with a tiny amount of radon that has been artificially contained within a small volume to make the concentration sound high, since that small amount of radon represents an extremely limited total dose.
     
  15. Rasputin

    Rasputin Feb 3, 2019

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    It's my understanding that a watch crystal blocks alpha particles. Thus wouldn't most of the radiation detected while the dial is behind the crystal be composed of beta and gamma particles?
     
    Edited Mar 10, 2019
  16. oddboy

    oddboy Zero to Grail+2998 In Six Months Feb 3, 2019

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    A classic,
     
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  17. M'Bob

    M'Bob Feb 3, 2019

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    The concentration doesn't just sound high, it is high, I have measured it. And, as I have said previously, the health risks are debatable.

    I doubt there are controlled studies on this, so I think you'll agree, we hypothesize about the health risk relative to the exposure. Still, using cost/benefit analysis, as we do in medicine all the time, the avoidance of the problem is so easy, at no cost, with no down side (unless you trip on your kid's skates on the way out of the room), why not just do it?
     
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  18. TimtimeIntl

    TimtimeIntl Feb 3, 2019

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    I've always wanted to measure the radiation from old watches, dials and hands but never had a meter (nor much knowledge to determine what the readings mean). Cool posts. Back in mid 90s when small research company I was working with on a NASA SBIR, we employed a consultant physicist. I told him I messed about with watches and he said in grad school he always slept with a wristwatch under his pillow until he measured it with a geiger counter. I don't remember the readings, nor what his true risk assessment was but he discontinued sleeping with his watch. Probably left him all alone in bed :)
     
  19. Dan S

    Dan S Feb 3, 2019

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    Again ... the concentration of a small volume is not the relevant measure. Stochastic health risks associated with radiation exposure are very well-studied, and they are primarily related to total dose. That's only debatable in the same sense that climate change or vaccine safety is debatable.

    Since this article was published, I have read probably a dozen posts on enthusiast forums from people indicating that they have decided to dispose of all their watches with radium lume. Several others have indicated that they decided to have the lume removed and replaced with modern lume. They just see a concentration number that is above the nominal safe dose, and not understanding how the values were manipulated in the study (by confining the radon in a small volume), and the concept of integrated dose, their knee-jerk reaction is to panic. So I think that those of us with technical expertise have a responsibility to be as accurate as possible, and not to exaggerate the risks.
     
    Edited Feb 3, 2019
  20. M'Bob

    M'Bob Feb 3, 2019

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    If you think the concentration of a small volume is not relevant, and you have a collection of radium-dialed watches, then open your case, don't leave the room, and breathe normally. Others may choose not to do that, and I think that's okay. No more needs to be said on that. I'm not telling people to sell their radium watches, re-lume them, or not wear them.

    I spoke to an expert, who does these analyses for a living, and paid him $400, and he said to leave the room under the circumstances noted above. It's binary - breathe it, or don't. Your choice. The rest of collectors' behavior regarding their radium watches I have no particular comment on.