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Old 2nd June 2013, 06:25 PM   #1
nlieb is offline nlieb  United States
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Default Tubes and radioisotope decay

Raytheon OA2 voltage regulator tubes use Krypton-85 gas to start electron discharge. Krypton-85 has a λ of about 10 years, and the daughter isotope is stable rubidium-85. Assuming these things are pushing 50, that would be 5 λs - only 2^-5 or 1/32 of the original Kr-85 is still there, which means on average 1/32 the decays, thus 1/32 the radioactivity. Every ten years divide by two. Is this going to ever have an effect on their functioning? Audio quality (possibly even positive from the slight reduction in background γs reaching the signal path or larger reduction in βs that might otherwise produce slight variations in the output)?

Also, does anyone know whether voltage regulators are the only tubes affected by radioisotope decay?

Last edited by nlieb; 2nd June 2013 at 06:33 PM.
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Old 2nd June 2013, 07:04 PM   #2
TheGimp is offline TheGimp  United States
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Neon lamps are. Or at least they used to be.
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Old 2nd June 2013, 07:13 PM   #3
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Radioactive material was put into gas discharge regulators to allow the tubes to "strike" easily, in the dark. If your "ancient" specimens are mounted out in the open and exposed to light, they will surely "strike".

BTW, the rubidium produced by decaying krypton 85 will "get" any O2 it encounters. IIRC, cesium and rubidium have been used as alternatives to barium in "getter" mirrors.
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Old 2nd June 2013, 08:15 PM   #4
nlieb is offline nlieb  United States
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Quote:
Originally Posted by Eli Duttman View Post
Radioactive material was put into gas discharge regulators to allow the tubes to "strike" easily, in the dark. If your "ancient" specimens are mounted out in the open and exposed to light, they will surely "strike".

BTW, the rubidium produced by decaying krypton 85 will "get" any O2 it encounters. IIRC, cesium and rubidium have been used as alternatives to barium in "getter" mirrors.
Silly me - it's glow discharge, not x-ray discharge (thankfully), so visible spectrum photons work. Conservation of energy and all that. If it ever stops working, I should try putting an led next to it before tossing?

FYI these aren't even pre-purchase, they're pre-design questions: I want to know what I have to work with before I start crunching numbers.
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Old 2nd June 2013, 09:18 PM   #5
DF96 is offline DF96  England
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0A2 from other manufacturers may be Kr-85 free. It was usually the military versions which included a bit of radioactivity, for the reason Eli said. It brings the striking voltage nearer the normal running voltage, and less variable. An ordinary 0A2 in the dark may take a bit longer to strike or need a higher voltage but it will get there - eventually natural background radiation will do it anyway.
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