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    Radium illumination
    From: Gary LaPook
    Date: 2010 Sep 05, 15:45 -0700

      I have an A-7 bubble sextant made in 1942. Some A-7s came with
    electric illumination of the bubble and some were made with radium paint
    to illuminate the bubble. My bubble has lost its illumination so I only
    use it for daylight sights. We discussed this issue in the past but I
    have not been able to find those posts. My recollection of that
    discussion is that the radium in the original paint should still be
    putting out radiation but that the paint had lost its ability to
    fluoresce when excited by the radiation. I asked if I could just put
    another layer of a florescent paint over the original and whether the
    new layer would put out light from being exited by the radiation. I
    believe the response was that the radium put out alpha particles that
    were not energetic enough to escape the original paint so that this
    would not work.
    I got some new information about this on Wednesday. We were coming
    through customs when horns started blowing and red lights started
    flashing (I'm being overly dramatic) and two agents said "you'll have to
    come with us." In the next room I was asked "have you had a stress test
    recently?" as he held a little black box with colored LEDs next to my
    hand. "No."  "What's in the box?" "A sextant." Then another guy came
    with a real Geiger counter and held it next to the A-7. We were stuck
    for about fifteen minutes while a supervisor went to consult a reference
    book. Then we were told we could leave.
    So this pretty much established that the radium was still putting out
    radiation that was energetic enough to escape the original layer of
    florescent paint, since it escaped from inside the sextant and the
    wooden box. It turns out that radium emits alpha and beta particles and
    also gamma rays. Since the half life is 1601 years the radium has lost
    less than 3% of its radioactivity since the sextant was manufactured in
    So back to my original question, can I use some florescent paint to
    restore the bubble illumination?

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