Fast Neutron Counter

12 10 2010

All photos.

I just scored this sweet vintage military fast neutron counter for $370!



Serial A 21

Unit of Radiac Set AN/PDR-47C


By contractor


Denville NJ


Probe, Radiac


Where would I get this thing calibrated?







2 responses

13 10 2010

wherever someone has a neutron source and a calibrated neutron counter, presumably.

13 10 2010

Dr. Karam says:

Here are a few things I can tell from the photos….

Probably 1960s vintage, based on the meter design and the graphics on the materials that came with it.

Best not to use this to read dose rate – don’t worry about converting rep to rem – the conversion factors have changed anyhow since this was built. For your purposes I think the big thing is to get a reliable count rate (neutrons per second or per minute). If you get a decent neutron flux, let me know and I can come out with Hailu to measure the dose rate.

You should be getting a background count rate, even if your fusor is not operating. Sea-level neutron flux is about 1 neutron per square cm per second, but not all of these neutrons can be detected by your meter. My guess is that you should see a couple of neutrons per minute from background. If your reading is consistently zero then there may be a problem with the meter. The most common problems are bad batteries (or the batteries not inserted with the correct polarity) or an electrical problem between the probe and the meter (broken wires, broken soldered connection, etc.).

And a couple of interesting tidbits.

The USS Fulton was a submarine tender – a sort of floating repair facility. I don’t know much about it other than that it was World War II vintage and basically cared for boats from the War until sometime in the late 80s or early 90s. Some of my shipmates worked on it or were on nuclear subs that it worked on. The Fulton was named after Robert Fulton, who developed the steamship.

Also, the meter designation “AN-PDR” was a designation for all of the radiation detectors we used in the Navy. I was told it stood for “Army-Navy Portable Detector, Radiation”. So we had the AN-PDR 70 (a big neutron detector), AN-PDR 56 (alpha detector), AN-PDR 45 (high-level gamma dose rate), and so forth.

Finally, the term “radiac” is another military acronym that stands for Radiation Detection, Indication, And Computation. So all military meters were called radiacs, and the term spread somewhat into the civilian world.

That’s about all I can dredge up from these photos. Let me know if you want us to come out again to check your meters against ours, or if you are getting a high count rate on your neutron detector.

Oh – two other things. I’m not sure what company manufactured this meter but you might try contacting MJW Corporation about calibration and repair – they are located in Buffalo and they should have lower rates than many others. You can also try Ludlum, located in Texas. For that matter, if you want to take a short vacation in Sweetwater, Ludlum will let you sit at a workbench with one of their technicians to learn meter calibration and basic repairs. Although I’ve got to say that Sweetwater is not quite as interesting as NYC. The other thing is that you might try contacting the National Urban Security Technology Laboratory (NUSTL) in Manhattan – they are near Houston and Varick. They have helped us check our meters with their sources – including a neutron source. I’m not sure if they are allowed to work with private individuals, but if nothing else they might be willing to give you a hand. Or if they won’t let you bring your meter as a private citizen, perhaps we can take it along with ours the next time we are asking them for help checking our neutron meters.

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