Ludlum Model 3 with He-3 Tube

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Liam David
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Ludlum Model 3 with He-3 Tube

Post by Liam David »

I recently acquired a Ludlum Model 3 and a large He-3 tube. The seller said the tube responded well at 1500V, which is the upper end of the Model 3's voltage range, so would the Model 3 work with such a tube? Technically it's not made for proportional tubes and the discrimination can't be adjusted, but all other specs check out OK.
-Liam David
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Richard Hull
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Re: Ludlum Model 3 with He-3 Tube

Post by Richard Hull »

Large 3He tube? What size is large? Inquiring minds want to know.... large is a relative term with not a hint of how large.

Is it in a moderator? Can it be removed if it is?

Any writing or engravings on the tube? manufacturer? part number?

No discriminator?!!! Not good.

How does the guy know that it works? Is he a neutron metrologist? What was his test source?

How much coin did you have to part with for this wonderment?

The great thing about selling a neutron counter is no one can test it! Certainly not the casual guy looking for same. The best kind of pig in a poke.

To start, test the Ludlum. Reduce the voltage and plug in a GM tube. Make sure the instrument can at least be a viable GM counter and is not, itself, defective.

We can't help you without a ton of details on the tube.

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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Liam David
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Location: PPPL

Re: Ludlum Model 3 with He-3 Tube

Post by Liam David »

Sorry, I'll give a few more details. I contacted Ludlum a month ago and they were nice enough to donate a Model 3 with 44-9 probe and Model 26 handheld frisker. Everything is functional and calibrated. The neutron tube seller had a NIM bin setup and provided a video showing the tube's response using a small Po-210/Be neutron source. He did all the usual gamma rejection and moderator demonstrations to prove its functionality. He said it worked well at 1500V, the maximum voltage the Ludlum can provide.
The tube is 17.5" long and 1.5" diameter with the outer SS shield. It has a 12" active area. It's a Russian built tube with a CH19H (in Russian) part number. On the tube, it says 1750V, but the seller said it worked with 1500V... Any other details needed?
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Richard Hull
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Re: Ludlum Model 3 with He-3 Tube

Post by Richard Hull »

If Ludlum, the corporation, is donating it, as a functional neutron counter, then that is good enough for me. You are lucky, assuming you get enough neutrons to tickle it into reading on the lowest scale. The assumtion is that the thing has a metered, visual output. You might try and tap into the meter input circuitry to obtain the pre-integrated pulses and run those to a digital counter. This would make for a much more useful indicator, (statistically), for ultra low neutron production rates in first pass data collection runs at lower voltages.

Metered counters are great around nuclear reactors and "stiff", stable neutron sources, but they are not too useful around novice fusors. Once a fusor is really a "going concern" at 30kv+ with an experienced user, meters are just great.

Keep us informed.

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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