Depending on its effects on matter and its ability to ionize the matter, radiation is classified in two main categories: ionizing and nonionizing radiations.
Ionizing radiation
Radiation passing through the matter which breaks the bonds of atoms or molecules by removing the electron is called ionization radiation. It passes through the matter or living organisms, and it produces various effects.
Ionizing radiation is produced by radioactive decay, nuclear fission, and fusion, by extremely hot objects, and by particle accelerators. The emission of ionizing radiation is explained in Section 2.1. The ionizing radiation is again divided into two types: direct and indirect ionizing radiation.
Direct ionizing radiation
Directly ionizing radiation deposits energy in the medium through direct Coulomb interaction between the ionizing charged particles and orbital electrons of atoms in the medium, for example, α, β, protons, and heavy ions.
Indirect ionizing radiation
Indirectly ionizing radiation deposits energy in the medium through a two-step process; in the first step, charged particles are released in the medium. In the second step, the released charged particles deposit energy to the medium through direct coulomb interaction with orbital electron of the atoms in the medium, for example, X-rays, photons, γ rays, and neutrons.
Nonionizing radiation
Nonionizing radiation is part of the electromagnetic radiation where there is insufficient energy to cause ionization. But it has sufficient energy only for excitation and not to produce ions when passing through matter . Radiowaves, microwaves, infrared, ultraviolet, and visible radiation are the examples of nonionizing radiations. Nonionizing radiation is essential to life, but excessive exposures will cause biological effects.