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Instruments and radioactivity

Article about: Good morning collectors; I guess we all are aware that old instruments, such as compasses, gauges, watches, etc., intended to be readed in low light circumstances, were paintend with radium

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    Default Instruments and radioactivity

    Good morning collectors;
    I guess we all are aware that old instruments, such as compasses, gauges, watches, etc., intended to be readed in low light circumstances, were paintend with radium based compounds. While after 70+ years they are no more glowing, the radium is still active, emitting mainly alpha rays but also beta and gamma.
    I tested a couple of items with a radiometer to show how they can be “hot” and thus to be handled and stored with respect. The device I used is a Terra P, a non professional instrument based on a Geiger Muller tube capable of reading beta and gamma rays, but not alpha. As stated alpha rays are the radium’s main emission, but are also easily stopped by the glasses of instruments, so not a great concern unless you ingest or inhale dust particles of the paint...
    The measures are in uS/h (microsievert/hour); 1 uS/h is equal to 1/1.000.000 of a Sievert; a seriously harmful dose is between 2 and 3 Sievert, while a chest radiography gives you 20 uS.
    The radioactive background of my house is 0,18 uS/h.
    Now the first instrument: this is a 1944 British air speed indicator, never issued; being the speed readed in knots instead of mph, it was intended for a fast Royal Navy aircraft (I’ve been told Mosquito or Seafire).
    Instruments and radioactivity
    It is quite hot, reading around 130 uS/h: more than 700 times the background. The Terra P starts screaming at 1 meter circa from the ASI.
    Instruments and radioactivity
    Now is the turn of a British T.G. CO. bakelite MkI march compass. Also made in 1944 to replace the more expensive brass MkIII model, she contains much more less radium paint than the ASI
    Instruments and radioactivity
    But this is an example of how (sometimes) sizes doesn’t matter: the reading is almost double (actually she reached 265 uS/h). This is due to the radium paint stripe on the mirror not shielded, thus emitting freely. So this has to be handled with care, not just because the high level of emissions (and remember that the alpha rays are not registered by the device), but also because the risk of get in touch with particles of that paint.
    Instruments and radioactivity
    The radium compounds on instruments were dropped around 60’s, and a less dangerous paint was used instead: a tritium based compound. Less dangerous, yes, but still radioactive. For comparison I introduce you an Italian compass, clone of the British MkIII, made around the 70’s and issued until recent times:
    Instruments and radioactivity
    Again, the radioactive paint is applied to the lid with no shield, so the reading just over it is consistent, reaching 35 uS/h. Much more less than the MkI, but still almost 200 times the background, and more than 1 chest x-ray.
    Instruments and radioactivity
    In conclusion, these old instruments are not lethal, because the radioactivity drops drastically with distance, but it is a good practice to handle them with caution, especially those with exposed paint. And, of course, not to sleep with one of them under your pillow.
    Last edited by ziomanno; 06-20-2020 at 07:15 PM.

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