Rad (unit) - Health Effects

Health Effects

A dose of under 100 rad will typically produce no immediate symptoms other than blood changes. 100 to 200 rad delivered in less than a day will cause acute radiation syndrome, (ARS) but is usually not fatal. Doses of 200 to 1,000 rad delivered in a few hours will cause serious illness with poor outlook at the upper end of the range. Doses of more than 1,000 rad are almost invariably fatal. The same dose given over a longer period of time is less likely to cause ARS. Dose thresholds are about 50% higher for dose rates of 20 rad/h, and even higher for lower dose rates.

Radiation increases the risk of cancer and other stochastic effects at any dose. The International Commission on Radiological Protection maintains a model of these risks as a function of absorbed dose and other factors. That model calculates an effective radiation dose, measured units of rem, which is more representative of the stochastic risk than the absorbed dose in rad. In most power plant scenarios, where the radiation environment is dominated by gamma or x rays applied uniformly to the whole body, 1 rad of absorbed dose gives 1 rem of effective dose. In other situations, the effective dose in rem might be thirty times higher or thousands of time lower than the absorbed dose in rad.