ABSTRACT
Radiation originally meant α-rays, β-rays, and γ-rays emitted from natural radioactive isotopes. At present, elementary particles, nuclei, electrons, and photons, moving with speeds comparable to or higher than the rays from radioactive isotopes, are called radiation. The reason for using the term rays is that the path of particles has direction. When radiation passes through matter, it has the capability of direct or indirect ionization of atoms and molecules. Hence we use the term ionizing radiation.
