radiationdamage

Radiation damage refers to harm caused to biological tissue by exposure to ionizing radiation, such as X-rays, gamma rays, or high-energy charged particles. It can affect cells, tissues, and organs and may occur through direct ionization of biomolecules or indirect effects mediated by reactive species.

Direct damage occurs when radiation ionizes DNA or other critical molecules, causing breaks and chemical alterations. Indirect damage results from radiolysis of water, producing reactive oxygen species that subsequently attack cellular components. The extent of damage depends on dose, dose rate, and radiation quality, often summarized by linear energy transfer (LET). Oxygen presence enhances damage (the oxygen enhancement ratio).

Biological outcomes vary: deterministic effects have thresholds and increase in severity with dose (skin erythema, epilation, radiation sickness, organ failure). Stochastic effects are probabilistic, with cancer and heritable effects having no known threshold and increasing with dose.

Cellular outcomes include DNA repair via base excision repair, nucleotide excision repair, and double-strand break repair by non-homologous end joining and homologous recombination. When damage exceeds repair capacity, cells may undergo apoptosis, senescence, or mitotic catastrophe, contributing to tissue injury or carcinogenesis.

Radiation protection aims to limit exposure through shielding, organizational controls, and safety standards. In medicine, controlled doses are used in radiotherapy to destroy tumors while sparing healthy tissue. Dose is measured as absorbed dose in grays (Gy); the biological risk is represented by sieverts (Sv), which factor in radiation type and exposure duration.