Exposure

Date: 2015-10-07; view: 537.

One of the earliest observed properties of x-rays was their ability to ionize air, and in 1928 the International Congress of Radiology specified this property as a means of measuring the amount of x-radiation, and defined a unit which was named the roentgen , (R).

The roentgen is defined as that amount of x- or gamma radiation which will produce by ionisation one electrostatic unit of charge in 1 cubic centimeter of dry air at STP. The SI unit of exposure is the coulomb per kilogram ( ). The concept of exposure is now seldom used in radiation protection but is usually reserved for expressing the output of radioactive sources of radiation.