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5R is the max. legal annual dose for
a radiation worker
Beware of surplus geiger counters unless you know what you're doing. Manyof
them have radioactive "check-sources" attached, which may not be desirablesurplus
in a high school environment. I've seen some pretty "hot" sources on
geiger counters (although not the yellow civil defense models), and onceyou
buy them, it's nearly impossible to get rid of them legally. With any oldfor
geiger counters, the calibrations will be questionable. The other thing
about the yellow CD geiger counters is that some models (actually
ionization chamber counters)are so insensitive that you could get a lethal
dose before anything would register on 'em. The dosimeters in the CD kits
usually go from 0 to 200 Roentgens, when those issued to radiation workers
usually read 0 to 200 MILLI-Roentgens! (5R is the max. legal annual dose
a radiation worker, and enough to cause serious radiation sickness ifaround
absorbed all at once.) The CD dosimeter chargers are usually pretty good,
though.
For high school student use, you can get new geiger counters for
$200 from Vernier. http://www.vernier.com They can be used either with thecounters.
Vernier computer interfaces & Logger Pro software, or as stand-alone
counters. Vernier also has a book of experiments to go with their
Vickie