Loud popping neutron counter

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Loud popping neutron counter

Postby Steven Sesselmann » Sun Mar 25, 2012 5:30 am

Hi Doug,

I have seen on some of your videos, that you have amplified your neutron counter to a loud popping sound.

Today I have been messing around trying to get my he3 counter and Bf3 counter to do the same thing, but the signal is so weak, and the signal to noise ratio rather low, so I have not had much success.

Would you mind sharing how you did it?

Apologies in advance if this has already been discussed...

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Re: Loud popping neutron counter

Postby Doug Coulter » Mon Mar 26, 2012 12:20 pm

I've managed a couple of different ways, they all work. I built a custom rack panel with a cheap radio shack amplifier in it - basically it's a car-stereo amp with a built in wall wart. I put cutouts for two speakers at the edges of the panel, so I'd have stereo. Yes, that's actually helpful. The human ear/brain is a fantastic correlation detector, and you can even tell real hits from emi by ear. In the case of a particularly big and sensitive 3He tube I've got, you can definitely hear when it gets double-hits inside a dead-time due to the longer/taller pulse for that - those are "bassier". I have to say for audio monitoring, a number tube is better, it's easier to hear hit rate changes when there aren't so many it's just going SSHSHSHSSSHSHSSSHSHS. An old B10 tube (1.5" by about 18") 3 feet from the fusor is "just right" - and is what you probably heard in the movies, along with the 3He channel.

As you say, the signal out of a proportional tube (any type) is both tiny, and narrow. Well, it turns out that a RIAA curve preamp for mag cartridges helps both quite nicely - that 6dB/octave curve that goes forever is a great pulse stretcher. In one case I used a coupling transformer to eliminate a ground loop, and that helped even more (it was about 50k impedance on both sides). The transformer ringing made the clicks sound better.

Later, I wanted to be able to count these on our standard counter along with the geiger tube (or gather counts some other way), which is why I designed that preamp to generate "standard level" signals for everything. It gets about 8v pulses off these tubes, and tends to stretch them out too (regardless of what some non-EE types thought over at fusor.net for whom the words "Miller effect" are dark magic). At that point, the signal can just be tee'd on bnc cables and drive both a TTL (or CMOS as is the case here) counter and an amplifier line level input. That's how I do it now, it works great. While this might not work for all amplifiers (this one is stunningly cheapo), in my case, whatever is coming in the selected input also goes out the tape out (even if it's a signal that would make the amp clip - it's just a switched wire connection) so I don't even need a Tee - I can just hook my digital counters to line out and switch them to various groups of detectors that way.

I think I wrote this up somewhere, but obviously this is one I should harp on some more - maybe I'll get another movie and post it up here with more details. This is just super nice, a wonder for when you're tuning things to get instant feedback, and an ongoing safety device - I know not to walk out from behind the shield if the thing is singing without having to look at meters or check some other way (or remember to). Very natural. So now, I get both that - for safety and tuning - and timestamped data logging of several counter and a/d channels out of the standard counter/data aq box. I'll be making some real fantastic plots before long, plotting this versus that during runs to show things like - is max Q the same as max neutrons? Where is either max hit?

DJ's is considering doing an LM386 class little amp with "the right gain and frequency response" just for this. I really like the concept and how it's worked out here, and there's really no need for the whole 5 watts or so the RS amp has. I could design it with a built in "tick to tock" converter - a 1khz or so ringing filter on the input, to make the sound more natural and distinct - and sound more like the classic old geiger counters. I've built one for myself for the upstairs fusor (well, it's a fusion device, but not a fusor) and I'll be doing the usual bragging about that when I finally fix the last big leak and get beams going in there.

Edit: Here's what my new one looks like. The panel had the meter in it when I got it, but I added a lab analog supply (+5, +/-12v) and the little lm386 kludge and speakers from something out of a dumpster.


I have some large ferrite beads here. I use them with several turns of both power wires through them to isolate HF ground loops. This way I only need the one power supply to run a bunch of things on the rig.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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