Geiger Müller tubes on flights

[ColoRad-o]

Tom, thank you very much for the references and the links (especially to your eBay store, which I seem to have overlooked). Before I took a GM on a flight I remember looking up the issue of altitude, but hadn't seen anything that disturbed me. Now I *am* disturbed, and will be more cautious.

But I'm still taking the bGeigie Nano on a multi-hour flight next week, because it will log altitude as well as count rates. In an informal `commemoration' this fall of a well-known trip [J Stone et al. “Spatial variations in natural background radiation: absorbed dose rates in air in Colorado”, Health Physics 76.5 (1999), pp. 516–523, before it became so easy to log geo-tagged ambient radiation rates], I took the bGN on a car trip and it has been through the Eisenhower Tunnel (about 11000 feet, almost 3,500 meters) on the trips to and from Grand Junction from Denver. There was no hysteresis in the count rate to and fro that I couldn’t attribute to slightly different GPS coverage in tunnels and covered sections of the highway. You can see the data on once you find the trip on the Safecast tile map along US Interstate 70. On a later hike, up to almost 12,000 feet.

The poor seals. (First it was the walruses!)
I’ll do a longish background count and compare with pre-abuse data.

Thanks again for setting me straight.

DMW

[Lewis]

I have never seen anything on the LND web site or in their specifications or literature describing an altitude or atmospheric pressure limit for the 7311 pancake detector or any other they manufacture. However, in 1987, Ludlum (maker of popular pancake detectors based on the LND 7311 detector) issued a newsletter (NwsLtr-4re.pdf) warning of possible failure of their detectors when being shipped on unpressurized aircraft. They sometime thereafter added to the Model 44-9 User manual the warning (which continues to this day):

Caution!
The GM tube face can rupture above 8000 feet in
altitude. When transporting this detector by air, use an
airtight container in order to avoid sudden atmospheric
changes resulting in tube failure.

According to George Dowell, Bill Lehnert of LND verified the following:

LND 7311-Routine operation at 5000-6000 feet no problem, i.e. Denver, Los Alamos. Above that they work fine until the reverse bow becomes a problem in the housing. Once the bow has reversed, the tube will continue to work fine. It is not a good idea to cycle between high altitude and low altitude, as eventually the seals will suffer.

I have shipped hundreds of these type detectors with no issue that I have ever been made aware of. However I have heard and read of numerous reports of users experiencing issues or rupture of their pancake detectors operating at high altitude, so I'm sure it is an issue to be aware of. I can verify that even here at sea level (Florida east coast), they can "pop" very easily if mishandled. Actually quite startling the first few times it happens. :)

Re: "ear barometer"--Could I feel a reduction in air pressure in an airplane cabin? Not to any significant extent, if I remember rightly. According to the WHO, "Although aircraft cabins are pressurized, cabin air pressure at cruising altitude is lower than air pressure at sea level. At typical cruising altitudes in the range 11,000–12, 200 m (36,000–40,000 feet), air pressure in the cabin is equivalent to the outside air pressure at 1800–2400 m (6000–8000 feet) above sea level."

I live at 6000 feet, so wouldn't have noticed air pressure differences even at 8000 feet equivalent altitude.

Another point I failed to note before: naturally the pressure inside the GM tube will be LOWER than atmospheric to permit the discharges required. Wikipedia claims it's about 0.1 atmosphere. Thus the roughly 25% reduction in air pressure at cabin pressures, say .76 bars vs. 1 bar at sea level, is small in comparison to the pressure gradient on the mica window of a pancake GM tube. Rooting around on the LND site, I found no mention of maximum operating altitudes.

Thanks for the replies. I now feel more comfidant traveling with my soon to be delivered ”Radiation Alert Ranger” and it seems as though as long as you dont misshandle the tube or subject it to rapidly chaging air preasures, all should be fine.

Thanks again.