RADIATION UNITS

1.The roentgen:It is unit of radiation exposure. One roentgen of exposure liberate a charge of 2.58x10^-4 /kg of air.

2.The rad (SI unit gray) :It is unit of absorbed dose .one rad is equal to the  radiation necessary to deposit energy of 100ergs in one gram of irradiated material(1 gray =100rad).The absorbed is independent of the composition of the radiated material and energy of the beam

3.The rem(SI sunit Sievert): It is a unit of absorbed dose equivalent. The rem is a unit used in only radiation protection. The rem is a measure of the biological effectiveness of radiation(1Sievert =100).

The absorbed dose equivalent is equal to the absorbed dose multiplied by a quality factor:

Rem=Rads x quality factor

( approx.quality factor for x rays,gamma rays ,beta particles,electrons ===1,for alpha particles ==20).

Because quality factor for x rays is 1,the rad and rem are equal.

REF

4^th edition ,1990  reprinted 2010 , Christensen’s Physics of Diagnostic radiology]