The deterministic effect of ionizing radiation on human health can lead to acute radiation syndrome which occurs upon high doses and high dose rates.
This contrasts with the deterministic effects of acute radiation syndrome which increase in severity with dose above a threshold. Acute radiation syndrome (ARS), also known as radiation sickness or radiation poisoning, is a collection of health effects that are caused by being exposed to high amounts of ionizing radiation, in a short period of time. At high doses, this causes DNA damage that may be irreparable. ARS is caused by exposure to a large dose of ionizing radiation (> ~0.1 Gy) over a short period of time (> ~0.1 Gy/h). Exposure to high doses of radiation cause DNA damage, later creating serious and even lethal chromosomal aberrations if left unrepaired. Ingestion of radioactive materials caused many radiation-induced cancers in the 1930s, but no one was exposed to high enough doses at high enough rates to bring on ARS. 
