Ratemeter mod soundard MCA?

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Ike Stewart
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Real name: Ike Stewart

Ratemeter mod soundard MCA?

Post by Ike Stewart »

After about a 5 year break I am getting back into doing home experiments, just before an unexpected life change about 5 years I had started on gathering the parts to build a gamma spectrometer, well now I am getting the dust off those parts and am trying to get it done. Doing research the last days I have found where some people have posted youtube videos regarding modifying common rate meters to provide input for a soundcard rather than using a purpose built device like the Gamma Spectacular, etc. Does anyone here have any thoughts on this method?

If you have not seen them here are a couple of videos on the subject posted in the last year
https://www.youtube.com/watch?v=JlyGCq08250 and https://www.youtube.com/watch?v=ay2CDxY0IWc I ask as I have a few various handheld and counter top rate meters laying around though not these specific models, one the counter top models even has a front panel high voltage adjustment control, though it is an analog not a digital model.
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Richard Hull
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Re: Ratemeter mod soundard MCA?

Post by Richard Hull »

The ratemeter does absolutely nothing except act as a common HV supply for the PMT using the capacitor and resistor to send the signal to the sound card.

Sound card systems have been getting better and better at fast A to D conversion over the last ten years and are quite suitable for gamma spectroscopy when using the right PMT, controlled and stabilized high voltage and a program suited to the system. A good gamma spec demands a hyper stable DC high voltage on the PMT with a suitable socketed divider resistor and capacitor chain. A drift or a less than suitable component anywhere in the sequence of counting and conversion makes for a less than acceptable result.

There is always a tradeoff at the PMT end. A 2" PMT is OK, but a bit small. You will lose the high end of the gamma spectrum unless you take unusually long counts or have very strong sources.
A 5" PMT is overkill and will, on long counts demand background subtraction and or complex and heavy lead shielding. A 3" PMT is really ideal in amateur gamma spec work. Gets the low end fast with reasonable results on the high end in slightly longer counts, without needing long background subtraction runs as with a 5" PMT. You do not want a gamma spec of the world around you, but one of the sample placed at the tube. Really weak samples with a whisper of radiation is the purview of 5" PMTs in 1 ton lead castles.

The ideal is an HPGe gamma spec system Provided you can afford one and the constant use of liquid nitrogen at every use. Only the very serious need apply here.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Ike Stewart
Posts: 3
Joined: Tue Jan 26, 2021 3:25 pm
Real name: Ike Stewart

Re: Ratemeter mod soundard MCA?

Post by Ike Stewart »

Thanks for the reply, I have a 3 inch diameter x 2 inch thick x 3 inch PMT Rexon branded NAI scintillator I plan to use if it works (I bought it about 8-10 years ago off ebay), I just don't have the a connector cable that will connect it to my Nucleus Model L rate meter, which I think will support it. The rate meter has front panel adjustable voltage and analog meter, but does have a front panel HV adjustment that may go up to 2KV (that is the upper end of the meter dial). The guts of it look semi modern, built in 1982 it has a crystal and about half a dozen trimmer pots on the single layer hand drawn board. So last night I ordered an SHV to MHV cable off ebay, hopefully when it gets here I will be able to try it out.
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