A beta particle is an electron or a positron and is much lighter than an alpha particle. Thus, it takes beta particles a longer distance than alpha particles to lose energy. A medium-energy beta particle travels about one meter in air and one millimeter in body tissue. Gamma rays are electromagnetic radiation. When gamma rays interact with tissue, they ionize atoms.
Neutrons are neutral particles that have no electric charge.
Unlike alpha and beta particles, they do not interact with electrons or cause ionization directly. These processes variously result in the emission of gamma rays, beta radiation, and, in the case of spallation, more neutrons. Measuring Radioactivity Ionizing radiation can be measured using units of electron volts, ergs, and joules. It takes energy to move this electron away from the proton. It takes 13.6 electron-volts of energy to move this electron completely away from the proton.