How to use a Geiger Counter? - (Oct/15/2010 )

Hi,

I know that if you use a geiger counter and it "clicks" repeatedly, that means that something is contaminated--however, how do you read the needle? I was doing a survey today of my lab coat and my counter clicked a few times over the course of the survey--so I figured that there was no problem. But the needle did move a little once, while the other times it didn't...I had it set to 10x (because that's what someone else in the lab does, not because I really know what it means). Can anyone: a. tell me how to read the thing? and b. tell me if there's any danger in my situation? (didn't go past the "1K" mark on the CPM scale, again, whatever that means).

Thanks!

Please especially let me know if there is any fear of radioactive contamination--I'm afraid that I'm quite new to all of this and I don't know if there's something I should be concerned about (especially since I need to wash my lab coat soon!)

CPM are counts/clicks per minute. 1K = 1000; 10x should be the multiplier to change range, i.e. you have to multiply the reads by 10 when you use 10x. If the measurements are in this (low) range this is natural radiation (= background radiation) that occurs everywhere more or less strong (random decay; radon, cosmic rays, etc.). If you life in higher altitudes or near radon emitting rocks then you'll have a much higher background, and even that is not dangerous, as humans live with this since they exist and therefore adapted to it, e.g. with DNA repair mechanisms.
Ask your radiation commissary/officer what is normal in your environment and what doses you can expect, if you work with radioactive substances. There is also a maximum exposure people are allowed to receive, ask also about this, it is normally expressed in millirem (you can calculate it more or less good from the CPMs).