A semi-DIY preamplifier for radiation detectors

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
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Rich Feldman
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Real name: Rich Feldman
Location: Santa Clara County, CA, USA

Re: A semi-DIY preamplifier for radiation detectors

Post by Rich Feldman » Wed Apr 24, 2019 3:00 am

My first unattended data collection was inspired by Greg Courville's low-rate counting method, but might be more primitive.
No computer or MCA was occupied during a 115-minute run, then same configuration in a 94 minute run with accidental loss of 44 minutes in the middle. Electrical changes for noise reduction have not been made yet.

An old Wingscapes Birdcam was set in front of scope, as close as it can focus without reading glasses (which come later).
Time lapse mode with minimum delay setting, 30s, takes a picture about every 40s.
Each image shows the result of most recent scope trigger event. There could have been more than one trigger, or none, since the previous image.

Then pictures were individually categorized by eye, like Greg did IIRC.
Most are first image of a "good" pulse. The automatically measured height went into a spreadsheet.
About 28% of the images are redundant (no scope trigger since last event). Sometimes 3 or 4 in a row.
Then there are pictures of "bad" waveforms, where trigger event was some disturbance other than a charge impulse into CSP.
A few are of "deformed" pulses, and two show unmeasurably narrow "glitches" with no 140-us tail.

Here are the largest "good" pulse (36 mV), a small one (11.2 mV), four deformed ones, and one bad waveform.
Now a chart of all good and deformed pulses, by height and when they happened. Run2 is appended right after Run1.
Finally a short numerical summary:
I think most of these counts are from the intended AmBe source kluge, but don't claim to have proper evidence yet.
Have shown some evidence about the instrument's repeatability.
For later: try removing the alpha source, the beryllium, and both of them.
Then with those parts in the original positions, remove the moderator.
Scientists need to play Devil's advocate.
Don't infer success too quickly from "I saw just what I expected and wanted to happen".
All models are wrong; some models are useful. -- George Box

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Richard Hull
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Re: A semi-DIY preamplifier for radiation detectors

Post by Richard Hull » Wed Apr 24, 2019 5:59 am

Decent Am-Be sources start to be highly useful at the 25uCi level in working up neutron detection schemes. Zero statistical work is needed at the 100uCi level. Much also depends on the detector tube type, active volume and pre-amp.

At best, one might expect a 10,000:1 ratio in well coupled sources. Thus, a 1uci isotropic source buried in powered Be would produce 3 neutrons/sec.... probably less and this is isotropic emission!
A 25 uCi source, well coupled, would do about 75 n/s iso. In a tight, pure water or plastic moderator a fabulous 3He detector might count 1 count every two seconds, reliably.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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