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Surplus Civil Defense Stuff
Appearing on eBay and Elsewhere
Searching through eBay, as well as web sites dealing with survival gear, one comes across many radiation detectors and geiger counters offered for sale. Perhaps the most commonly found are the CDV series. These are all government surplus detectors, originally made, under contract, for the US Civil Defense program by a variety of vendors.These were meant for use after a full scale nuclear war between the US and USSR. As a result, most of these meters are designed only to measure the incredibly huge levels of radiation that would be present in the vicinity of the actual detonation of one or more thermonuclear weapons (hydrogen bombs), or in the fallout from such devices. Many of these meters are completely useless for today's threats - a "dirty bomb", or other spreading of radioactive material, or low to moderate levels of contamination.
After sitting in warehouses for years, sometimes decades, huge numbers of these units are finding their way onto eBay, and for re-sale by individuals. Many were bought for pennies on the dollar, some are refurbished before sale, others are sold strictly as-is.
CDV-715
This is probably the most common "geiger counter" appearing on eBay. The problem is - it isn't a geiger counter!This is a survey meter. It uses an ionization chamber, typically filled with normal air, to detect radiation. As expected, it is not very sensitive. It is designed to measure only extremely high levels of radiation, found at the site of a nuclear explosion or vicinity. It's essentially useless for detecting lower levels of radiation, such as those from a nearby nuclear power plant leak, or downwind from a "dirty bomb".
It is very difficult to "test" one of these units, as they only respond to extremely high radiation levels. It is very difficult to verify that such a unit is working, as the meter will not move at all in normal use. Or worse, it will wildly swing back and forth because of ionization chamber current drift.
CDV-717
The CDV-717 is a cousin of the CDV-715, the difference being that the ion chamber detector can be removed and used remotely. Which of course doesn't matter much, since unless you're at ground zero you're not going to see the meter needle move, anyway.
CDV-700
Now, the CDV-700 actually is a geiger counter. It only detects some beta and gamma rays, and is not able to detect alpha radiation. There were numerous versions of the CDV-700 made by various contractors for the US government, some cut more corners than others. Units should be checked out before purchase, common problems include damaged geiger tubes (about $100 to replace), corroded battery connections, and faulty meters.
To summarize, before buying one of these surplus units, it is best to understand their
limitations, and also verify that they are actually functional.