TRACERLAB NP2 Neutron Detector - Ineffective for Fusor Use

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Mark Rowley
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TRACERLAB NP2 Neutron Detector - Ineffective for Fusor Use

Post by Mark Rowley » Mon May 03, 2021 10:37 pm

Most here will recognize this type of unit as the source for Carl Willis’s famous Neutron Oven. It’s a TRACERLAB NP2 neutron detector containing a Reuter Stokes RSM-320-M2 BF3 tube (1950 volt bias). Being a collector of vintage radiation detection gear, this is just one of the several classic neutron meters sitting here in the shop.

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Based on the pulser, 1cps or 60cpm is equivalent to 1mRem on the meter scale.


The Reuter Stokes tube is contained in the center of the black poly moderator while surrounded by a boron doped core (white).

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As of now, I’ve had two of these which I’ve experimented with during various fusor runs and such. Both have been in electrically good condition and have responded accordingly with static sources. However, when near the electrically noisy and X-ray intense environment of the fusor, these meters greatly over respond providing a significant false register. To be sure I wasn’t counting neuts, I ran the fusor with air but at roughy 30kV so I could generate a few xrays. Identical results.

It’s my opinion these were primarily designed for the detection of non-electrically generated neutrons such as fission reactors, Pu and isotopic neutron sources.

I’m interested if anyone else here has has similar experiences with this type of detector (inc the MILSPEC variant). It may be worthwhile to officially list these units as non-applicable to Fusor use as it can easily mislead a newbie into a “fools gold” eureka.

There are other similar units from the mid 60’s to early 70’s that may be subject to the same issues.

Mark Rowley
Last edited by Mark Rowley on Tue May 04, 2021 4:42 am, edited 1 time in total.

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Richard Hull
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Re: TRACERLAB NP2 Neutron Detector - Ineffective for Fusor Use

Post by Richard Hull » Tue May 04, 2021 3:57 am

I agree totally. I have had one of these for some time made by Victoreen. These were contract produced by a number of different instrument makers to the same specs. I discovered this noise angle back in 2000 with fusor III. The results were out of agreement with my BC-720 counter and my Eberline PNC-1. I guessed that noise in mine started at about 26kv. I post an image taken in January 2000.

Richard Hull
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Jan 14th 2000 I used 5 different neutron counters in those early days this Victoreen snoopy was one of them It proven vulnerable to noise and has never been used since.
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
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Mark Rowley
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Re: TRACERLAB NP2 Neutron Detector - Ineffective for Fusor Use

Post by Mark Rowley » Tue May 04, 2021 6:48 pm

I haven’t seen that pic in ages! In some ways it’s been a lightning fast 20 years, others not so much.

Of historical interest (clearly not for fusor use), one of the relics on my shelf is the Raychronix F-1 Fast Neutron Detector from 1952. Early proton recoil design with equally vintage electronics.

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Mark Rowley

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