 Axion detector
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Conundrum
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Tue Jun 03 2014, 03:11PM
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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
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Sounds DIYable, although I fear that the signal if non superconducting magnets are used will be vanishingly small.
I did look into making a neutrino detector using the B+ channel on 40K but the signal here is pretty small.
To sense enough to determine anything useful I'd need a kilo or more of near pure 40K and very sensitive tubes.
Interestingly the work done so far seems to suggest 40K can indeed be concentrated IF clever tricks are used.
One of these is using crossed electric and magnetic fields to cause a concentration gradient, and keeping the solution at 53.2C causes 40K to crystallize first.
EDIT: Looks good so far, SBM20 (not the U variant!) works if overvoltaged a bit with a 2.2M series resistor.
I found that running them at 620V rather than 475 makes them sensitive to lower energy betas from 40K decay as long as precautions are taken against avalanching ie briefly turn off HV if this occurs.
Adding thermal feedback also helps much like with laser diodes.
Contrary to usual practice a higher value resistor doesen't help at all and actually makes things worse.
If you can't get a GM counter working reliably at tube's rated voltage then it is possible reducing R1 on some tubes helps, or simply do what I did and install a series Zener in epoxy to drop HV down 100V or so (mini tubes)
thought it was worth sharing, maybe useful to some people on here 
Also see
-A
"Bother!" said Pooh, as he wasn't expecting a visit from Homeland Security...
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