Introduction

Radiation biology is the study of the effects of radiation on biological systems. When radiating energy and living cells interact, energy transfer leads to one of two phenomena: excitation or ionization. Low-energy nonionizing radiation, e.g., ultraviolet radiation, microwaves, and extra-low-frequency electromagnetic radiation, causes molecular excitation. Excitation results when an electron changes its energy level without being ejected from the orbit of the atom.1-3

Ionizing radiation is sufficiently energetic to eject an electron from an atom’s orbit resulting in an ion pair (the electron and the rest of the atom), i.e., causes ionization.1,4,5 Ionization may be produced by particulate and high-energy electromagnetic radiation. Particulate radiation is a stream of atomic or subatomic particles such as α-particles and neutrons produced by nuclear disintegration; high energy electromagnetic radiation includes δ-rays and x-rays (photons).1,5-8

Gamma-rays are emitted by radioactive substances. Photons are man-made, produced by x-ray units when fast moving electrons interact with tungsten atoms.9 When photons with sufficient energy liberate orbital electrons from atoms and their corresponding molecules, the creation of unpaired electrons results in the formation of highly reactive free radicals. Free radicals in a biological system can damage cellular proteins by altering their chemical structure.1,5-8,10,11

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