LD50/30: The Dose Required to Kill a Human with 50% Risk Within 30 Days

This comprehensive review examines the LD50/30-the dose of ionizing radiation required to kill a human with a 50% risk within 30 days, if the dose is received over a very short duration. For humans, this value is 4-5 Sv (400-500 rem). The review covers the definition, historical context, radiobiological basis, clinical phases of acute radiation syndrome (ARS), factors affecting survival, historical cases (Chernobyl, Goiania, Fukushima), the relationship to other radiation doses, implications for radiation protection, and future directions. Written for professionals and students in radiation protection, nuclear safety, and CBRN defense.