Not Quite As Simple CSA

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Richard Hester
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Re: Not Quite As Simple CSA

Post by Richard Hester » Mon Apr 25, 2011 4:49 am

Here's a simpler version of the postamp/shaper that works the same as the previous (same response).
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Richard Hull
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Re: Not Quite As Simple CSA

Post by Richard Hull » Thu Apr 28, 2011 8:08 pm

Once again, nice amps and thanks for sharing. These with the usual input and bias circuitry added ought to do OK for a 3He counter tube.

Richard Hull
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Fusion is the energy of the future....and it always will be
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Richard Hester
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Re: Not Quite As Simple CSA

Post by Richard Hester » Fri Apr 29, 2011 3:42 am

Keep in mind that the circuits I just posted are a postamp and shaper to take the output of a charge-sensitive preamp such as the one cited at the beginning of this tread, amplify the output, and shape the response to ease amplitude discrimination.They're not too useful without the preamp ahead of them. They are particularly germane to this thread, as the preamp that started the thread was aimed at He3 proportional tubes where the output pulse is fairly tiny, even with a small value for charge storage cap (~1pF) for the charge sensitive amplifier. The output of the charge sensitive amp is about ~50mV, so the postamp and shaper can make life much easier for a discriminator or SCA.

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Re: Not Quite As Simple CSA

Post by Richard Hull » Fri Apr 29, 2011 1:54 pm

I am sorry, I was commenting on the entire thread. Sometimes I assume too much of the reader, being an electronics guy, myself. The original "CSA" linked to your last or next to the last "postamp" circuit is what I was referring to. This combo should replace most any older NIM based preamp setup and can be attached directly to the tube head, itself in a small box, utilizing batteries or the common 9 pin nim plug using the 12 volt line with a regulator.

I like attaching the preamp/postamp right to the head of the tube. It is a real noise reduction system if well executed.

I didn't look at the FET and transistor limits but I'll bet NIM 12volts could be used with only minor alterations.

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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.

Richard Hester
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Re: Not Quite As Simple CSA

Post by Richard Hester » Fri Apr 29, 2011 5:32 pm

If you really wanted to get nifty, the next step would be to gin up a low power discriminator circuit that you would adjust once to chop away all the gamma grass (assuming your HV to the tube is stable and repeatable). This would drive an LED coupled to an optical fiber, going to a remote counter. Having all the analog stuff in one box at the detector would go a long way toward making the detection system more noise immune.The optical fiber is perhaps gilding the lily, but it wouldn't be all that hard to do. Someone here (John Hendron, I think) mentioned using a 555 timer in the context of a discriminator. I'd vote for clever use of a CMOS 555 - I'll do some thinking.

I'll look at my simulations to see what 12V will do to the biasing in both circuits. It may not be much of an issue.

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Re: Not Quite As Simple CSA

Post by Richard Hull » Fri Apr 29, 2011 8:33 pm

I figured once you had a 2 volt signal in hand, standard coax and good termination would obviate most of the noise in all but the harshest environments. However, it would, indeed be cool to run the signal thru fiber, especially if you are working a high pulsed energy fusion system.

I figured that 12 volts, NIM, might need some tweeking on the biasing networks. I imagine a linear regulator (LM317T) set for 9 volts would be a good, no bother, solution. Only a super "greenie-weenie" would worry about the 3V disappation losses with the few milliamp demand of the circuit.

Good work as always Richard....and thanks.

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.

Richard Hester
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Re: Not Quite As Simple CSA

Post by Richard Hester » Fri Jun 10, 2011 8:58 pm

Attached is a picture of a board incorporating variants of the charge sensitive amplifier and postamp/shaper circuits presented here, plus a simple discriminator/cable driver circuit constructed using an LM393 dual comparator. I've done the initial power-up and tweaking for DC operating conditions, and will try to mate this up with a detector system. Since I don't have any neutron tubes and sources configured at this time, my first step will be to feed this bad boy with the output of an NaI(Tl) scintillator with the PMT run at reduced voltage to bring the gain and pulse amplitude down.

My goal is to include the board inside of a detector assembly using one of the Russian corona tubes. I haven't figured out whether I want to use the B-10 or He3 corona tube to start with. If I interperet DC's results from his testing of a B10 tube correctly, I won't need to use a postamp with the B10 tube, so I would feed the output of the charge sensitive amp right into the shaper circuit. This may be eventually what happens with the NaI scintillator system two, as I will likely get a good, strong ~1V output from the charge sensitive preamp even with the PMT crippled by a low supply voltage. The post-amp will come in useful for people using He3 and B10 proportional tubes with their lower amplitude output.

Anyway, this one is still in the development phase, and I'll post schematics when I have a better idea of what's happening. The board shown is about 4" by 1 3/4", so it can very handily be mounted on the underside of a gallon paint can lid.
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Re: Not Quite As Simple CSA

Post by Tyler Christensen » Fri Jun 10, 2011 10:13 pm

Regarding not using a post-amp, worked fine for me... my amp/shaper broke and I just fed right into my SCA directly from the CSA pre-amp box and it worked great for BF3, B10, He3, and Geiger... probably not "optimal" but I got the same count rates I'd expect on all detectors, so I didn't see any issues with it.

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Re: Not Quite As Simple CSA

Post by Richard Hester » Fri Jun 10, 2011 10:31 pm

Maybe so in your case, but on this board, the discriminator is included. Without the post-amp, the threshold pot for the discriminator would have to be cranked all the way down to the low end, with out any real latitude for adjustment.

When all the homework is done, this should be a setup that woulld allow me to feed a detector head directly into a counter.

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Re: Not Quite As Simple CSA

Post by Richard Hull » Mon Jun 13, 2011 6:48 pm

We have grown used to Richard's all-in-one solutions and the wait is worth while.

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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