Ionizing radiation dose leading to the death of the irradiated individual due to acute radiation injuries. The average lethal dose (LD50) is the dose where half of the individuals with similar irradiation quantities die. LD1 is the dose leading to a mortality of 1% of the irradiated persons; consequently, LD99 is lethal for all (99%) persons irradiated. Taking account of an increased radiation sensitivity of certain population groups on the one hand and the progress of medical care on the other hand, mainly homogeneous irradiation of the whole human body – the bone marrow dose is particularly important in this case – an LD1 of 2.5 Gy, LD50 of 5 Gy and LD99 of 8 Gy results.