I bought a Geiger counter as a birthday present for myself. It is an Aware Electronics RM-70. It is cheaper than traditional Geiger counters because it is designed to work with a computer. By itself, it does nothing. I built a 'clicker' unit that can power and provide the standard click response to radiation events. I need to:
1. photograph clicker unit.
2. publish schematic.
3. enjoy the fun of graphs!
Southwest Airlines flight to LAX. I turned on the detector at roughly 12,000ft, and turned it off at the official 10,000ft announcement. According to the pilot cruising altitude was at 39,000ft. The big drop at 3/4 of the way across the graph was a temporary disconnection.
This is the decay of radioactive daughter products of radon-222 being captured on a coffee filter that filtered 15 minutes of air through a vacuum cleaner in someone's basement in Ohio.
If you graph this curve on a logarithmic scale, you get this:
It's not quite straight, but the slope of the line gives you the exponent of the equation far below. The unreadable timescale is the same as the graph above it.
Radon-222-> Po-218 + alpha
Polonium-218-> Pb-214 + alpha
Lead-214-> Bi-214 + e-
Bismuth-214-> Po-214 + e-
Polonium-214-> Pb-210 + alpha
Questions I have that I haven't answered: What exactly is the software recording? What are those numbers? If I listen to the pulses, it seems the software multiplies the number of pulses by 4 to get the observed numbers, which it claims are microRads/hr. If this were a singular nuclear decay, I could deal with it, but it's 5 different decays. So how do I convert into pCi/L of radon? Why does it appear the half-life of the graph is nearly 50 minutes, which just happens to be the half-lifes of the first five decay products added together? Am I recording both the alpha particles and electrons/positrons, AND the gamma rays?
Simple EPA primer on radon: http://www.epa.gov/radiation/radionuclides/radon.htm
Uranium-238 decay chain: http://www.atral.com/U2381.html
Radioactive decay follows A=A(o)e^-kt, where A(0) is the inital amount of material, A is the amount at time t, and k is the decay constant. k is related to the half-life (t 1/2) by the following: (ln 2)/k=t. To get this equation, set A=1/2 of A(0) in the first equation, remove the A(0), take the natural log of both sides, and you're done.
There are lots of fun projects associated with a Geiger counter. Cosmic radiation is one (remind me to graph my week-long Ryerson graph). Live web server graph of current levels is another.
I have another graph of a more recent trip to LAX here.