A semi-DIY preamplifier for radiation detectors

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Rex Allers
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Re: A semi-DIY preamplifier for radiation detectors

Post by Rex Allers »

Good stuff, Rich.

What is your alpha source? Is it from one of those big old smoke detectors?
If so, I've heard bad stuff about them shedding radioactive material. I'm sure you are careful but it'd be good to monitor your work area.
Rex Allers
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Rich Feldman
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Re: A semi-DIY preamplifier for radiation detectors

Post by Rich Feldman »

Yup, and you are not the first to relay that warning. In fact the larger of two sources in F5B model is directly visible from outside, through the window screen. Topic for a different thread.

As for heeding warnings,
1. Tool-free disassembly, to the point where we can handle one large part that contains inconveniently-disposed alpha sources, is as far as I intend to go.
2. I wash my hands frequently. Have not yet started wearing disposable gloves.
3. Just received a nice old alpha-particle detector, including electronics, the better to monitor stuff. Anybody here got experience with DIAD II - 900?
4. My first name is not Carl. Middle name is, but spelled with a K, so probably safe enough. :-)
All models are wrong; some models are useful. -- George Box
Peter Schmelcher
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Re: A semi-DIY preamplifier for radiation detectors

Post by Peter Schmelcher »

Rich you might have a waveform template or limits test feature in your scope. It's a feature in my tds3054 circa 2000. Back in the day the shape of a digital one or zero was a telecom standard. My scope has 8 straight test violation lines (voltage vs time, at any angle). If the analog channel waveform crosses a test line a violation is counted and incremented to the total for that individual line. Overshoot or undershoot the waveform fails and if the duty cycle was not 50% it would also fail, however, the way I perceive the testing feature is 8 bins and you pick the width and height of the bins – sounds like an 8 bin multi-channel analyzer. Ever want to count 2 violation events over a week and know how the waveform failed so that it can be fix, I got the T-shirt.
Food for thought
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Richard Hull
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Re: A semi-DIY preamplifier for radiation detectors

Post by Richard Hull »

Background here is between 6 to 10 detections/min. 1-inch by 20-inch Reuter & Stokes 3He P4 (4 atm) tube 1700 volts bias, Princeton Gamma Tech preamp. Ortec spectro NIM amp and Ortec digital NIM counter. Tube in 6-inch diameter PVC tube water tank moderator. My system has been fixed rigidly from 2002- until 2020. (no alterations in position or settings).
High CME Solar storm time monitored in 2000-2005 and in 2012 time frame saw counts as high as time averaged 24 detections/minute. There could have been moments of higher count rates as I did not continuously monitor. I consider 8 CPM my norm here over vast periods of time. No diurnal differences noted worth mention.

I have wondered about neutron detects versus cosmic rays. As the bulk of neutrons at ground level are from cosmic starring at about 11 miles up in the atmosphere, what few counts I get might be from the rare fast or thermal neuts that make it to the ground here. (water in the lower atmosphere really impacts any fast neuts formed at the 11 mile high region.) For me, 100% of all neuts I detect are of cosmic origin with any increase being from severe CME events of solar proton storms.

Calibration done in 2002 with one month old calibration at Factory of my first PNC-1 Eberline while running fusor III. Rechecked between 2005-2007 with 3 BTI bubble detectors while running my Fusor IV.

I have checked water evaporation in the tank and winter versus summer backgrounds with about a 10% thermal variation (~ 1 cpm) and almost no detectable change of any significance with a 20% reduction in water level. Before major runs, I check and add water to a fill line in the tank to warrant no significant change in function.

Once working and calibrated, I am paranoid about keeping all things fixed in my neutron counter setup. Note: I have two 3He Reuter and Stokes tubes, one large 2-inch by 18-inch BF3 tube and three functional, portable, electronic neutron detection instruments on hand with two rem balls (All BF3 tubed). I had a big sell off of my many 3He tubes back at HEAS 2018. None left that I wish to sell.

I have noted that absolute neutron counting is virtually impossible at the amateur level and a +/- 20% level for excellent professional systems with good statisitics at the low end, the best the amateur can hope for with a perfectly adjusted neutron detection system is a +/- 5% differential accuracy at the lower end. I dare say a +/-1% differential at 200cpm count over a normal background. When running fusor IV and getting 5,000 or more CPM, background is of no consequence in the differential area. At this level, the differential for improvement recognition is up a bit. A run with 5167 cpm versus 5310cpm might not be an improvement based on the variability of the gas pressure, voltage and current in a fusor that is the norm. As always, knowing your source, your counting system and the environment it is in is a skill learned over time.

Rich is doing a great job in trying to discriminate his detection tube with the electronics he has. He will make it, but the hotter the neut source the better. If you can get that N source, then discrimination is a snap as you can see in the fabulous and without peer, Carl Willis videos on setting up you neutron tube and electronics for perfect setting of dials for warranted neutron detection.

Richard Hull
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