One roentgen deposits 0.877 rad in dry air, 0.96 rad in soft tissue, or anywhere from 1 to more than 4 rad in bone depending on the beam energy. This unit is obsolete and no longer clearly defined. In the 1930s the roentgen was the most commonly used unit of radiation exposure. Typical tolerance of radiation-hardened microchips Typical radiotherapy dose, locally appliedДЇatal whole-body dose in 1964 Wood River Junction criticality accident Typical radiation tolerance of ordinary microchips Whole body LD 100 for acute radiation syndrome in humans Whole body LD 50 for acute radiation syndrome in humans Local dose for onset of erythema in humans Lowest dose to cause clinically observable blood changes Metals creep, harden, and become brittle under the effect of radiation.ДЇoods and medical equipment can be sterilized with radiation. Radiation-hardened components designed for military or nuclear applications can survive up to 100 Mrad (1 MGy). Silicon-based microelectronics break down under exposure to radiation. In other situations, the effective dose in rem might be thirty times higher or thousands of times lower than the absorbed dose in rad. In most power plant scenarios, where the radiation environment is dominated by X- or gamma rays applied uniformly to the whole body, 1 rad of absorbed dose gives 1 rem of effective dose. That model calculates an effective radiation dose, measured in units of rem, which is more representative of the stochastic risk than the absorbed dose in rad. The International Commission on Radiological Protection maintains a model of health risks as a function of absorbed dose and other factors. Dose thresholds are about 50% higher for dose rates of 20 rad/h, and even higher for lower dose rates. The same dose given over a longer period of time is less likely to cause ARS. Therapeutic doses of radiation therapy are often given and tolerated well even at higher doses to treat discrete, well-defined anatomical structures. Whole body doses of more than 1,000 rad are almost invariably fatal. Doses of 200 to 1,000 rad delivered in a few hours will cause serious illness, with poor prognosis at the upper end of the range. A dose of 100 to 200 rad delivered to the entire body in less than a day may cause acute radiation syndrome (ARS), but is usually not fatal. The roentgen, used to quantify the radiation exposure, may be related to the corresponding absorbed dose by use of the F-factor.ДЄ dose of under 100 rad will typically produce no immediate symptoms other than blood changes. However, the numerically equivalent SI unit, the centigray, is widely used to report absorbed doses within radiotherapy.

National Institute of Standards and Technology authors. It has been replaced by the gray (Gy) in SI derived units but is still used in the United States, though 'strongly discouraged' in chapter 5.2 of style guide for U.S. The material absorbing the radiation can be human tissue or silicon microchips or any other medium (for example, air, water, lead shielding, etc.).

It was originally defined in CGS units in 1953 as the dose causing 100 ergs of energy to be absorbed by one gram of matter. The rad is a unit of absorbed radiation dose, defined as 1 rad = 0.01 Gy = 0.01 J/kg. This article is about the radiation unit.

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