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    Re: Radium illumination
    From: John Huth
    Date: 2010 Sep 5, 18:57 -0400
    Probably phosphorescent paint is what you want.   It makes sense, radium has a half-life of 1600 years, so it'll be putting out radiation for quite some time.



    On Sun, Sep 5, 2010 at 6:45 PM, Gary LaPook <glapook@pacbell.net> wrote:
     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 1942.

    So back to my original question, can I use some florescent paint to restore the bubble illumination?

    gl





       
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