Gamma Spectrometry Forum

Dear all,
I wanted to share some information about a rather exotic (at least I think so) detector.
When I recently reorganized stuff and equipment in my basement, I came across this handy little unit. It is an IM-179/U gamma dose rate meter, manufactured by Heat Pipe Corp. of America, Whippany, NJ, and I bought it about 30 years ago from a military surplus dealer. These units were supposedly made for aircrew survival kits. According to my research, it is based on an ion chamber in Neher-White configuration, i.e. the amplifier electron tube is mounted inside the chamber.
The chamber is covered with lead foil to reduce sensitivity for lower energies. The meter uses obsolete mercury batteries, 1.3 Volts for the filament and 5.2 Volts for the rest of the circuit. It appears to be still working when hooked up to an external power supply. However, I do not have a sufficient check source available to make the needle move noticeably. Full scale 200 R/h is roughly 2 Sv/h if I remember correctly. Makes me wonder how often one can "check the reading every 6 hours" if exposed to such a high dose rate...
One could probably remove the lead foil around the ion chamber to make the instrument more sensitive (and less linear).

Robert,

Thanks for sharing, it's fascinating to see how miniaturising things used to be done by intricate tiny mechanical parts, these days we just swap out the 1206 SMD surface mount components with 0201.

Nice piece...

Steven

Very interesting piece of tech you have there! Definitely a high exposure scale, different standards of exposure in cases of emergency I guess, but I'm not sure what situation I would feel comfortable traveling around in just under 2 R/hr haha! I calibrate a lot of these sorts of things (though usually GM type meters used in hospitals though I've seen some pretty weird meters come through) and its design looks kind of similar to one that I actually snagged that was being discarded by a hospital. Mine wasn't intended for wartime/post-nuclear type situations so the scale is much lower and I believe it functions in the GM regime. Do you have any sources capable of making the needle move at all? Maybe a beta emitting source would do the trick if you can get the lead foil off and find an adequately thin section of the chamber wall. Otherwise it might be hard to confirm if it is functioning as intended.

I wish I had more information specifically about that meter, but I can say that other similar open air ionization type chambers seem to have some difficulties in maintaining an accurate reading. Does it have a calibration potentiometer anywhere on it? If I had to guess, I doubt it was intended to be all that accurate given how broad of a scale it has. I don't think you can make a single scale analogue detector that is calibrated correctly in low and high exposure rates.

The unit actually has two calibration potentiometers, I'll post a picture tomorrow. Edit: here it is I do not have a sufficiently active check source at home and I did not want to remove the lead around the chamber so it's correct function is not verified. I may take it to a known hot spot someday...