Adjusting Ludlum 2000 for Neutrons

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David Kunkle
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Adjusting Ludlum 2000 for Neutrons

Post by David Kunkle »

My Ludlum is properly connected to the He3 tube, and I've watched Carl Willis' neutron setup video several times and looked thru the archives. But still a little confused.

Ludlum has an online manual for the 2000, but it's a newer model with a THR knob- my Ludlum has only a DISCR knob.

Part of the ebay listing where I bought the 12" He3 tube:
"My small neutron source -- (5 mCi Po210/Be) had a very good response (tested at +1750 v) --See Last two images--And once tuned with the single channel window, no significant response was seen to gamma when the neutron source was out of moderator --See images 4-6 Tested with a NIM BIN setup with Ortec 4890 Preamp/Amp and Ortec 9349-2 Ratemeter. Connector: BNC He3 tube: Russian made СИ19Н Max. Operating Voltage rating 2000V (positive voltage)"

1) Based on the previous owners work, is it OK to just go with 1750V? -or should I do what the manual says about setting the instrument plateau:

"With the detector shielded from the source, adjust the high-voltage control by 50 V increments, and take a plot of HV-versus-background count rate until the detector voltage rating is reached. Return the HV control to zero. Expose detector to source and make another count-versus-voltage plot. Plot both sets of data and select the operating point to correspond with the maximum source count and minimum background count. Avoid areas of very fast count rate changes with small changes in detector voltage. The optimum operating point for low background detectors is just above the inflection point (or break-over point) of the plateau curve. If the background count is irrelevant, shift the operating point to the plateau center for greater stability."

2) Once V is set, do I use the DISCR to tune out all counts from my U gamma source? And then I should be left with something like 1 to 2 cpm from background neutrons with the U source removed?
3) Obviously it would be nice to have a neutron test source, but do I have to have a neutron test source to insure the detector is working before I start looking for neutrons that I made?
If your experiment needs statistics, you ought to have done a better experiment.

Ernest Rutherford
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Richard Hull
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Re: Adjusting Ludlum 2000 for Neutrons

Post by Richard Hull »

The Discr and THR contols are the same just renamed Dicriminator and Threshold.

The instructions are correct.

I would take a rich gamma source like U ore,( You can't use U metal) lay it right next to the naked tube. Take the voltage up to about 1300 volts and take the discriminator all through its range. Is there a dramatic increase in counts at some point in the discr span?
NO?
Take the voltage up a bit more. Re-adjust the discr pot through its entire range.

What you are looking for is gamma ray detection. Until you get the tube at an increased count at some voltage and some discriminator level, you are not really at the right voltage.

I know nothing of the Russian tube.

If you get to some voltage where the thing is clicking along, do not increase the voltage any more....Instead find a point on the discrinator pot's span where the clicking goes away with the hot U ore source next to the tube. You should be able to count neutrons now.

This is not ideal, but is a quick way to find the tube's operating voltage and null out gamma detection.

This works with good 3-5 atmosphere 3He tubes of U.S. manufacture and most tend to huddle around 1300-1800 volt operational ranges with the mean between 1400 and 1600 volts.

Note: The best source of gammas is a boiling hot radium clock or old WWII aircraft instrument face. there is a gang of gamma seething off these from 60kev to over 2mev with most of it in the 100kev to 600kev range. U ore is fine, but not as hot in gammas. U metal has virtually no significant gammas. DO NOT TAKE THEM APART! Leave them sealed! Use as is! The gammas will zip right through the glass clock and meter faces.

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
David Kunkle
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Re: Adjusting Ludlum 2000 for Neutrons

Post by David Kunkle »

Did what you said (also made a graph like the manual says), and there is quite the obvious jump in counts at 1600V in the presence of the U ore. This is with the DISCR set to about 2/10's of its full range. The manual says to set the THR to .2 for proportional detectors. Seeing how this older model has no markings on the DISCR, I guessed at where .2 is. Then, if I carefully adjust down the DISCR further, I can get it to where there is no count difference between source and no source present- at 1 to 2 counts with 6 sec duration. Very touchy at that point on the DISCR.

The tube is labeled "Operating Voltage- 1750 V". And the manual states, "The optimum operating point for low background detectors is just above the inflection point (or break-over point) of the plateau curve. If the background count is irrelevant, shift the operating point to the plateau center for greater stability." The plateau center looks to be around 1750V. Sounds like I should be operating it somewhat above 1600V (above the inflection point), and if I understand that correctly, 1750V will give me more background noise? Where would you run it?

For a Ludlum 2000, is it necessary to turn the V to 0 before shutting it off each time? The manual doesn't mention anything at all, so I would like to assume that I can always leave the V in the same place so I don't have to reset everything each time.

Also read thru the neutron FAQs again. Without a BTI, is there no way to convert the Ludlum's cps to neutron flux?

I really would like to confirm that I can measure neutrons with this thing, but I'm hesitant to spend another $180 to "lease" a neutron source. Anyone on the forum ever sub-lease their neutron source to another member just long enough to confirm?
If your experiment needs statistics, you ought to have done a better experiment.

Ernest Rutherford
David Kunkle
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Re: Adjusting Ludlum 2000 for Neutrons

Post by David Kunkle »

Decided I really should test my Ludlum and tube. Called Amstat yesterday per Carl Willis' video to get a Nuclespot. $216 and 3 to 4 weeks out on shipping. But also something about Iowa being a nuke agreement state with the NRC, and I'll have to get an Iowa license for radioactive materials for $250/yr. Then I pulled my hair out for a while looking at the IA website. So now we're up to about $500 and whatever ridiculous grief it'd be to get my application accepted just to get some neutrons. Considered some other far fetched options, then...

Today, I decided to call the only other company that came up on a google search: NRD. $216 and 1 to 2 weeks out, but said he will try to get it out in about a week. He didn't mention anything about the NRC!... and I didn't ask! He did however mention about my credit card, and I gave him that.

Also, ordered a 5.5g piece of Be on ebay today.
If your experiment needs statistics, you ought to have done a better experiment.

Ernest Rutherford
David Kunkle
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Re: Adjusting Ludlum 2000 for Neutrons

Post by David Kunkle »

Nuclespot arrived last Fri. My setup certainly seems to be detecting neutrons. One hurdle gone. Want to run a few results by the forum. Tested using the Nuclespot sitting atop a 5.5g piece of Be, which in turn, sits on top of 6" dia X 12" long PE moderator w/ the 12" long, 1.5" dia He3 tube inside. I seemed to get the best response vs. noise at 1.6kV. Discr is touchy. Just barely turn it down and nothing- just turn it up the slightest physically possible, and it reads about 35 cpm- which I thought was about the background neutron radiation level. With the Nuclespot and Be, I get a little over 100 cpm. There's no change in count from my U ore at this voltage and discr setting. Does this sound reasonable or too low for a neutron count from this setup?

Without the PE moderator, the neutron count is about 1/2 as much. I thought it would be quite a bit lower than that?

If I go to 1750V and discr set to where it just begins to register, the count is more like 400 cpm w/ the Nuclespot, but the cpm w/ no radiation source of any type is 100 cpm, and it's sensitive to gamma from the U ore.
If your experiment needs statistics, you ought to have done a better experiment.

Ernest Rutherford
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Richard Hull
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Re: Adjusting Ludlum 2000 for Neutrons

Post by Richard Hull »

I have the long 20 inch reuters 4 atm 3He tube and it is accurate and calibrated from many yearly runs.

Typical background in a moderator is about 6-8 cpm. During the giant 2005 Solar CME, it doubled to 20 cpm of a day or two!

With a small neutron source it is about 100 cpm

With a strong U source and the tube in moderator there should be little difference from background in moderator.

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
David Kunkle
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Re: Adjusting Ludlum 2000 for Neutrons

Post by David Kunkle »

Thanks, Richard, that helps.

If I get it adjusted to 8 to 10 background cpm, it doesn't even see the Po/Be and still registers about 10 cpm. I now have it set where background gets me about 25 cpm, and 110 cpm with the Po/Be. Doesn't seem to be anything in between 10 and 25 cpm background as far as adjustability- too touchy. But, however I set the discr, it seems to register about 4 times higher cpm with the neutron source compared to background.

Unless someone tells me otherwise, I intend to leave it where it is now.
If your experiment needs statistics, you ought to have done a better experiment.

Ernest Rutherford
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Steven Haid
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Re: Adjusting Ludlum 2000 for Neutrons

Post by Steven Haid »

I purchased the same HE3 tube which has a BNC connector. The BNC connector has a maximum voltage rating of 500 volts. But the tube needs 1750 volts. The Ludlum 2000 has a Series C connector.

Did your tube have a BNC connector. Could you explain how you connected it to the Ludlum 2000?
David Kunkle
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Re: Adjusting Ludlum 2000 for Neutrons

Post by David Kunkle »

BNC connector on my tube just like yours. Problem solved easily with a cable from Ludlums. Part # 40-1010, description CBL-C-BNC 39". C connector on one cable end and BNC on the other. They also have them longer than 39" if you want. $59. plus shipping- seemed fairly reasonable. I had hashed it out on paper with a bunch of used ebay parts to accomplish the same thing, but it would've ended up costing more. You could still search ebay first- you never know what might turn up at any given time. Ludlums.com 325-235-5494. You may as well just call them since I don't believe this part # is on the website.

Welcome to the forum.
If your experiment needs statistics, you ought to have done a better experiment.

Ernest Rutherford
Jerry Biehler
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Re: Adjusting Ludlum 2000 for Neutrons

Post by Jerry Biehler »

It might be MHV connectors on it, the female side looks darn near identical to a BNC.

https://en.wikipedia.org/wiki/MHV_connector
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Steven Haid
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Re: Adjusting Ludlum 2000 for Neutrons

Post by Steven Haid »

Thanks for the advice on getting the C-BNC cable from Ludlum. It arrived yesterday and I connected my Ludlum 2929 to the HE3 tube and it gets counts.

The Ludlum 2929 is a dual channel scaler that is generally used with an Alpha/Beta sample counter. The manual says it also works with Proportional detectors, which is what the He3 tube is.

The Ludlum 2929 has an Amplifier Output connector. I was able to connect an oscilloscope and see the pulses. My plan is to connect the Amp Out to an ADC and write software to analyze the pulses. Unfortunately the pulse widths from Amp Out are about 2 us wide, and the ADC I purchased has a sample interval of 2 us. I may need to try and make the pulses wider with a capacitor.

To test it I plan to first measure the CPM with a Uranium ore sample, and then introduce Beryllium and see what affect that has on the rate. I should first do more research on this to see if it has a chance of producing neutrons.
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Richard Hull
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Re: Adjusting Ludlum 2000 for Neutrons

Post by Richard Hull »

I think you will be very disappointed in the proposed U-Be source. As a matter of fact even a super hot radium source like an old meter dial and Be would not be all that good. The hottest piece of U ore imaginable would never equal one WII aircraft meter. In general, for every 10,000 alphas actually entering Be you will get 1 neutron. I used a borrowed Po-Be source of 1 millicurie and got about 30 neutrons per minute over my normal 6-8 counts per minute background. A millicurie alpha source is a real blast of alphas into the Be.

Still, give your idea a shot and report back. You will be way down in the statisitcs fighting background, even with a hot radium source (which I do not recommend).
You will need an alpha source of 100,000 per second or 6,000,000 per minute to climb well out of the background. In U ore you will only get alphas from the surface U mineral as all the others within the ore are absobed in the rock.

Neutrons are tough love, no joy items. Atoms hold on to them jealously. They will spit out almost anything except one of their neutrons.

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
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