Basic Radiation Physics
Beam Quantity

The amperage and the exposure time determine the amount of electrons passing through the cathode filament. An increase in the amperage or in the exposure time will result in an increase in the number of photons generated in the x-ray tube. Since the amperage and the exposure time have a direct influence on the number of photons emitted, they form a common factor called the milliampere-seconds (mAs). When one of these two factors is increased, the other must be decreased to maintain the same beam quantity (Figure 6).^1,2,3,4,9