The Eberline PNC-1 neutron counter and its history and capability

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Richard Hull
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The Eberline PNC-1 neutron counter and its history and capability

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The PNC-1 was one of the first post war neutron detectors that was produced in some significant volume and available to the public, private industry, academic institutions and the government. The amazing thing about the PNC-1 was that it was transistorized, light in weight and used common "D" cells batteries. There would soon be many competitors but being the first, Eberline quickly gained respect for this counter to be a robust and sensitive, for the period, to detect and announce moderate to heavy neutron flux concentrations. Another factor is that it could be used in a lab where lower flux rates could be detected and data taken due to its handy removable moderator and detector assembly which would allow the instrument to be placed to a more remote distance for data taking, while the detector/moderator block could be placed very close to the weak source of neutrons in the lab. It was a hit for both reactor monitoring and lab work with lesser source of neutrons.

The PNC-1 used a small Nancy Wood BF3 tube for detection on a nice aluminum base attached to the PNC-1 electronics block using paraffin as the moderator. A big plus is the actual tube held in the moderator by a ball and spring detent ring could be removed to detect environmental slow or thermal neutrons outside its moderator! Another big plus. In many ways, for the early nuclear biz it was perfect and sold accordingly. In the very late 50's and early 60's. It was the instrument of choice for about $1500 in 1960 money. ( A small fortune.)

Nancy Wood assembled BF3 tubes during world war II for the Manhattan project. After WWII, she started a business manufacturing the tubes for neutron counter systems. Her tubes were an instant hit and used in many future manufacturer's neutron counters. She stopped manufacture in the 1970's. However, so many instruments were out there that used her tubes, she had to find someone to make them for her in retirement. Today, to my knowledge, they are now unavailable outside of lucky NOS finds or pulls from old working gear. LND does make some suitable and adaptable replacement BF3 tubes for most of the older Nancy Wood tubes.

In my early daze, (literally), of fusor work with fusor III, my first neutron and fusion producing fusor, circa 1999, the output was pitiable, I latched onto the terribly inefficient Bicron BC 720 fast neutron scintillator. With data from it just outside of background, I nursed a figure of 10e3 neutrons TIER out of fusor III at 22kv. I saw that I needed a formal calibrated counter. I found my first PNC-1 on e-bay and had to pay $650 for it!! I sent it off for calibration and full check out for an additional $55.00. When It was returned, I felt I was in real business now. To my amazement, fusor III barely moved the needle up to 50 cpm. Still, 2-3 cpm was background so I was, statistically, well out of any noise or doubt about my fusing in fusor III.

I learned quickly that the small BF3 tube in the PNC -1 was just too small to intercept and count the low neutron levels of a fledgling fusor in a bold and vivid manner. However, it was sufficient! The great thing with an analog meter is that you can easily see an improvement in output immediately during future runs following improvements or modifications to the fusor.

By any modern standard this is a dinosaur, but is still a viable instrument for the advancing fusioneer. I have repaired two subsequent PNC-1 units I obtained and then sold to other fusioneer at my HEAS gathering in October in past years.

I retain my original and picture it below. I still use it on fusor V for instant visual output recognition. I also include a most valuable chart for converting the PNC-1 events per minute to dose rate in mrem/hr., with example to figuring the flux at the moderator.
Also, a Nancy wood tube as found in the PNC-1

Richard Hull
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Face-on view of the electronics box of the PNC-1
Face-on view of the electronics box of the PNC-1
separated electronics from moderator detector at work on fusor V
separated electronics from moderator detector at work on fusor V
Valuable chart for converting PNC-1 events/min to mrem/hr dose rates which in turn might yield flux rates using the standard 7-8 n/sqcm/sec rate for 2.45 mev neutrons.
Valuable chart for converting PNC-1 events/min to mrem/hr dose rates which in turn might yield flux rates using the standard 7-8 n/sqcm/sec rate for 2.45 mev neutrons.
Nancy Wood BF3 tube out of an Eberline neutron detector
Nancy Wood BF3 tube out of an Eberline neutron detector
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
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Jim Kovalchick
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Re: The Eberline PNC-1 neutron counter and its history and capability

Post by Jim Kovalchick »

Richard,
Great write up on a classic counter. You know I treasure mine, and I benchmark all my fusor runs with it. It was a highlight of my fusor work when I first had enough neutrons to range up my PNC. I've since ranged up again.

Jim K
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