Acute Radiation Syndrome: A condition caused by a brief whole body exposure to more than one sievert dose equivalent of radiation. Acute radiation syndrome is initially characterized by ANOREXIA; NAUSEA; VOMITING; but can progress to hematological, gastrointestinal, neurological, pulmonary, and other major organ dysfunction.Radioactive Hazard Release: Uncontrolled release of radioactive material from its containment. This either threatens to, or does, cause exposure to a radioactive hazard. Such an incident may occur accidentally or deliberately.Radiation Injuries, Experimental: Experimentally produced harmful effects of ionizing or non-ionizing RADIATION in CHORDATA animals.Radiation Injuries: Harmful effects of non-experimental exposure to ionizing or non-ionizing radiation in VERTEBRATES.Whole-Body Irradiation: Irradiation of the whole body with ionizing or non-ionizing radiation. It is applicable to humans or animals but not to microorganisms.Radiation-Protective Agents: Drugs used to protect against ionizing radiation. They are usually of interest for use in radiation therapy but have been considered for other, e.g. military, purposes.Radiation Dosage: The amount of radiation energy that is deposited in a unit mass of material, such as tissues of plants or animal. In RADIOTHERAPY, radiation dosage is expressed in gray units (Gy). In RADIOLOGIC HEALTH, the dosage is expressed by the product of absorbed dose (Gy) and quality factor (a function of linear energy transfer), and is called radiation dose equivalent in sievert units (Sv).Lethal Dose 50: The dose amount of poisonous or toxic substance or dose of ionizing radiation required to kill 50% of the tested population.Dose-Response Relationship, Radiation: The relationship between the dose of administered radiation and the response of the organism or tissue to the radiation.Radiodermatitis: A cutaneous inflammatory reaction occurring as a result of exposure to ionizing radiation.Syndrome: A characteristic symptom complex.Radiation Pneumonitis: Inflammation of the lung due to harmful effects of ionizing or non-ionizing radiation.