What are good exercises for:a bra bulge (under the arm pit), your thighs, arms,and abs?
Alpha particles (helium ions) are big and bulkyJust about anything will stop themBeta particles (electrons) are much smaller and somewhat harder to stopHigh energy gamma rays (EM radiation) are even harder still to stop.
It's a combination of factors-their mass, energy, and cross section (likelihood) to interact with those materials.
