Introduction

Radiation biology examines how radiation affects biological systems. When radiating energy interacts with living cells, energy transfer results in either excitation or ionization. Low-energy nonionizing radiation, such as ultraviolet radiation, microwaves, and extra-low-frequency electromagnetic radiation, induces molecular excitation. This excitation happens when an electron shifts its energy level without leaving the atom's orbit.^1-3

Ionizing radiation has enough energy to remove an electron from an atom’s orbit, creating an ion pair (the ejected electron and the remaining atom), thereby causing ionization.^1,4,5 Both particulate radiation and electromagnetic radiation can lead to ionization. Particulate radiation consists of streams of atomic or subatomic particles, such as α-particles and neutrons, generated by nuclear disintegration, while high-energy electromagnetic radiation includes δ-rays and x-rays (photons).^1,5-8

Radioactive substances emit gamma-rays. X-ray photons are man-made. They are 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