What type of radiation primarily causes cellular damage during direct action?

X-ray photons are the type of radiation that primarily cause cellular damage during direct action due to their ability to interact with biological tissues. In direct action, X-ray photons have enough energy to ionize atoms directly within the cells. This ionization can lead to the breaking of chemical bonds and the generation of free radicals, which can ultimately result in damage to DNA, proteins, and other critical cellular structures.

X-ray photons possess a high enough energy level to penetrate tissues effectively and interact at the cellular level, making them particularly adept at causing immediate damage. The effects of this direct action can include disruptions in cellular processes that may lead to cell death, mutations, or tumor formation.

Alpha particles, while highly ionizing, typically have very low penetration power and do not travel far outside their source, which limits their ability to cause cellular damage through direct action in comparison to X-rays. Similarly, beta particles and gamma rays have different interaction mechanisms with matter; while gamma rays can cause indirect cellular damage primarily through the formation of free radicals, they are not as direct in causing immediate ionization compared to X-ray photons. Therefore, X-ray photons are recognized as the primary contributors to direct cellular damage during exposure.