Exposure to radiation can cause various health effects depending on the dosage. A dose of 25 rems may cause detectable changes in blood work, while doses over 100 rems risk radiation sickness with symptoms like nausea and vomiting. Exposure over 300 rems can cause temporary hair loss but more internal harm, and doses over 800 rems are always fatal. The atomic bombings of Hiroshima and Nagasaki killed many from radiation exposure rather than the explosions directly. Major nuclear accidents like Chernobyl and Three Mile Island exposed workers and communities to radiation due to cooling system failures and reactor explosions, demonstrating radiation's health risks. Currently there is no effective medical treatment for high radiation doses.