physics notes

"Radioactive detectors" work in different ways depending on what is being 
detected.  As a material decays (breaks up) it can emit alpha particles, 
beta particles, gamma rays, neutrons, etc.  The most common means of 
detecting radioactivity is to measure these emissions using an ionization 
chamber. When held in the vicinity of the material, the particles emitted 
from radioactive material pass through a membrane and into the gas-filled 
box (chamber).  Because the particles are energetic, they ionize the gas, 
i.e., separate the gas molecules into positively and negatively charged 
parts. The charge can be made to flow in nearby wires.  This flow creates 
an electrical current.  The strength of this current determines how much 
activity there is.  From that, and a knowledge of the the radioactive 
materials, one can estimate the amount of radioactivity.

Dr. Ali Khounsary
Advanced Photon Source
Argonne National Laboratory
Argonne, IL 60439