Ludlum 42-31

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Joe Gayo
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Ludlum 42-31

Post by Joe Gayo » Sun May 12, 2019 7:27 pm

I'm trying to figure out the correct operating voltage for this tube (Ludlum 42-31).

The website for Model 42-31H Neutron Detector says 1200V but the LND referenced by the same page says 750V (https://www.lndinc.com/products/neutron ... ors/25185/).

It's also very possible that the "H" means He3 and the non-H variant is a BF3 tube. The BF3 tube referenced 01-5018 (https://ludlums.com/images/pdf_files/Mo ... f_tube.pdf) is said to be a Nancy Wood G-5-1 (https://www.qsl.net/k/k0ff/0%2018Manual ... 0jun98.pdf) that operates at 1600-1900V.

Through a window on the tube it says 201 (could be partial) and this lines up to a couple of LND BF3 tubes but nothing exactly.

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Richard Hull
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Re: Ludlum 42-31

Post by Richard Hull » Mon May 13, 2019 4:55 am

I would work my way up in voltage starting at 750v. You have a great working fusor and you will see neutrons aplenty as you raise the voltage, slowly.
This assumes you never get a firm piece of data on the tube. BF3 tubes tend to take a lot more bias than 3He tubes, Boron lined detectors are more in the 600-800 volt range and are very critical of voltage adjustment.

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Bob Reite
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Re: Ludlum 42-31

Post by Bob Reite » Tue May 14, 2019 7:51 pm

BF3 tubes are usually operated between 1800 and 2000 volts. The "sweet spot" for mine is at 1900 volts.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.

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Re: Ludlum 42-31

Post by Joe Gayo » Wed May 15, 2019 12:06 am

I see some reasonable response at 1100 - 1200 V but I have the secondary amplifier gain set significantly higher (128x versus 4x) than my other detection system. I suspect that I need to raise the voltage but I'm reluctant since I don't want to damage my tube.

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Re: Ludlum 42-31

Post by Bob Reite » Thu May 16, 2019 2:54 am

If indeed, you have the 42-31 3He tube, that should be operated no higher than 1100 volts. But if your model number is just "42-31" that would be the BF3 tube which is rated at 2000 volts max.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.

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Re: Ludlum 42-31

Post by Joe Gayo » Fri May 17, 2019 5:05 am

Bob,

Just so I'm clear you have a 42-31 and bias it at 1900V, or you are talking about BF3 tubes in general.

Thanks, Joe

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Bob Reite
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Re: Ludlum 42-31

Post by Bob Reite » Sat May 18, 2019 4:25 am

BF3 tubes in general operate between 1800 and 2000
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.

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Re: Ludlum 42-31

Post by Bruce Meagher » Sat May 18, 2019 5:06 pm

One way to determine if you have a BF3 or He3 tube is to look at the output pulse height spectrum. The two spectrums are significantly different. Knoll’s book covers this in detail, but there are many practical examples in past fusor posts. One He3 pulse height spectrum I captured is described in this thread:

viewtopic.php?t=10569

Here are some other useful ones:

viewtopic.php?t=5613
viewtopic.php?t=6308

With your fusor's outstanding neutron production the features of these different spectrums should be easily identifiable.

Bruce
Last edited by Bruce Meagher on Sun May 19, 2019 2:59 am, edited 1 time in total.

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Re: Ludlum 42-31

Post by Joe Gayo » Sun May 19, 2019 12:49 am

I definitely have a BF3 tube and the sweet spot is 1850V. Thank you, everyone, for your help.

P.S. I now have 2 NIM electronic detection systems, 1 portable electronic system, and a bubble dosimeter.

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Re: Ludlum 42-31

Post by Bob Reite » Mon May 20, 2019 3:28 am

Hopefully you are ready to make neutrons soon, as the bubble detectors have a limited shelf life, used or not. Use the bubble detector to calibrate your electronic detectors.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.

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