Which type of radiation has the highest biological impact per unit dose?

Alpha particles have the highest biological impact per unit dose due to their considerable mass and charge. As heavy, positively charged particles composed of two protons and two neutrons, alpha particles have a higher likelihood of interacting with biological tissues compared to other types of radiation.

Their high linear energy transfer (LET) means that as they pass through matter, they deposit a large amount of energy over a very short distance. This leads to significant ionization of nearby atoms, which can cause extensive damage to cellular structures, including DNA. Such damage can result in mutations, cell death, or cancer development, particularly when alpha-emitting materials are ingested or inhaled, allowing the radiation to wreak havoc in sensitive tissues.

In contrast, beta particles, gamma rays, and X-rays have lower mass and charge, thus resulting in less energy being deposited in the tissue for the same amount of radiation exposure. Beta particles have a medium LET and cause damage that is primarily restricted to the tissue immediately surrounding their path. Gamma rays and X-rays, being high-energy electromagnetic radiation, have low LET and can penetrate deeply with less ionization along their path, reducing their biological impact per unit dose compared to alpha particles. Therefore, the distinctive characteristics of alpha particles make them the most biolog