Radiation imparts energy to the electrons of living tissues. This allows harmful chemical reactions to take place, particularly in DNA. Extreme radiation damage kills cells, particularly those in rapidly multiplying tissues, like the mucosa of the gut and the marrow. Lesser damage causes: (1) mutations, which can only express themselves when cells divide, and are responsible for cancer in the survivors, and (2) genetic deformities in their children.
The absorbed energy is measured in rads. In tissue at or near the surface of the body, an exposure of one roentgen of radiation energy results in the absorption of one rail (100 ergs/gram). Clinically, this absorbed energy expresses itself in the short term as the ’radiation sickness’ described below. If irradiation is spread over weeks or months the body can tolerate more.