ABSTRACT
There are two types of ionizing radiation: photon and hadron. Photon radiations include x-rays and gamma rays. X-rays are generated by abruptly stopping accelerated electrons and some of the kinetic energy is converted to x-rays, while gamma rays are due to the decay of unstable isotopes where energy is released as the isotope is changing to a more stable form. Other types of photon radiation include visible light, microwaves and radiowaves, all of which have longer wavelengths and lower energy and hence are not ionizing radiations. Hadron radiation are particles that include protons, alpha particles, neutrons and heavy charged ions such as carbon (12C) and iron (56Fe), and these particles can interact with the nucleus of atoms. Upon interaction with the nucleus, a fast neutron for example can produce three alpha particles from carbon, or four alpha particles from oxygen. Interaction with hydrogen during radiotherapy is more likely due to the high water content of tissue, and a neutron interacting with a hydrogen nucleus results in the release of a proton, which can cause ionization of the tissue (Hall 2000).
