Why not? Plenty of members advertise their own stuff.Finnnicus - 22-3-2013 at 18:43
Just wondering if there was some sort of question here. Very cool project though.IrC - 23-3-2013 at 07:14
It is a very well done repeat on one online over a decade. Thompson used a Ludlum in his, a model which is getting hard to find and expensive today. I
imagine Charlie prefers the higher voltage, stiffer supply and higher gain in the Ludlum model. Was cheaper and more readily available before the
reactor meltdown in Japan. You could actually watch prices on various surplus gear (and KI) go up by the hour on ebay during that disaster. Really put
a dent in amateur hacking of radiation detection gear. Around the third day sellers on ebay were charging $350 for 14 100 mg tablets of the KI, around
$8/package a day before the Tsunami. I built a copy of Charlies project in 2002 using a CDV 700 I found on ebay, with a giant PM tube and block of
scintillator plastic Mr. Thompson provided. As mentioned by Prutchi, the Dow Corning #4 was my choice also due to price.
That's what I like about this new article linked above. Money savings to use old civil defense gear. So many of those yellow meters were made.
Especially the Ion chamber versions. You needed to use the front end circuit in place of the GM tube for the CDV-700. In mine I used 22m resistors. I
notice no schematic of the preamp circuit in Prutchi's article, don't think I overlooked it but the one Charles has posted at the link below is what I
used and works great.
I have built many of these using my own design circuit in a gutted CDV-715 which is so much cheaper than the GM version. At one time on ebay I was
buying a dozen of the 715's at a time for 4 bucks each. Sadly during the Japan disaster I saw these useless Ion chamber models go to upwards of $150
each by sellers claiming they were what you needed. To people on the west coast no less. One wonders if any of the buyers ever realized that even
seeing the meter move on one meant they were cooked already. Hopefully at least some figured it out via the internet.
Not being real impressed with the plastic I prefer the NaI/Tl crystals which are even harder to find. Especially non yellow non wrinkled ones.
Charlie did mention to me one time He has a method of restoring them which IIRC involved careful baking but that I have never tried. In any case
hopefully you will find the link to the GIF a useful addition to this thread, look at the preamp circuit at the top. It works great.
HammerOfLight - 7-10-2013 at 21:48
I knocked out a sensitive ION chamber using a soup can, a plastic bead, a straightened paper clip, and a 50 volt power supply, and a rebuilt
electrometer. Read americium cores from smoke detectors, and thorium welding rods. I am really proud of the repair on the electrometer, it's an old
one built in the late 70's, I had to replace some leaky electrolyte capacitors, and resolder some wires.bfesser - 8-10-2013 at 06:16
Sounds great, <strong>HammerOfLight</strong>. Could you post some photos?Harristotle - 11-10-2013 at 02:31
HammerOfLight: oh wow! You bring back fond memories.
I made my poor students in 2009 do this!
I have attached the assignment sheet that I wrote for this. Please note that this work is based on a much more comprehensive work, which I can no
longer locate. So the idea of building a supersensitive ion chamber out of a high gain darlington is not mine.
The main issue with this circuit is drift. I also am looking at using it as a Flame Ionisation Detector - there is a huge register of current flow
when a burning candle is placed near it - that is the best way to test that it works. By the way, hardware-purchased MIG welding rods worked better
than the smoke detectors described in this sheet - we didn't really register the low keV xrays from the americium fire detectors. Brazil nuts are
apparently also detectably radioactive, and probably can be used.
