radiolysis

Radiolysis is the chemical decomposition or alteration of substances caused by exposure to ionizing radiation. The energy deposited by gamma rays, X-rays, or energetic particles can ionize or excite molecules, producing short-lived reactive fragments such as solvated electrons, hydrogen atoms, hydroxyl radicals, and molecular ions. These primary species rapidly participate in a web of secondary reactions, creating a cascade of reactive intermediates and, in many systems, stable products.

In aqueous solutions, water radiolysis is the best-studied case. The initial events yield hydroxyl radicals (•OH), hydrated electrons (e_aq^-), and hydrogen atoms (H•). These species diffuse and react with solutes and solvent to form hydrogen peroxide, hydrogen, molecular oxygen, and additional radical species. The observed products and their yields depend on the radiation quality (LET), the presence of oxygen, pH, temperature, and the concentrations of scavengers or solutes. The chemistry unfolds over time from femtoseconds to microseconds for primary intermediates, then over microseconds to seconds for secondary reactions and stable products.

Radiolysis has broad applications in radiation chemistry, biology, medicine, and materials science. It underpins indirect radiation damage in living tissue through reactive oxygen species, and it is exploited for sterilization, food irradiation, and polymer degradation. Experimental study employs methods such as pulse radiolysis, spectroscopy, electron paramagnetic resonance, and chemical dosimetry, and researchers use yields known as G-values to quantify products per unit energy deposited.

Non-aqueous radiolysis follows the same general principles but with solvent-specific radical and ionic products.