Worlds of David Darling
Encyclopedia of Science
Home > Encyclopedia of Science


The rad is an old unit used for expressing absorbed dose of ionizing radiation. One rad (rd) represents the dosage absorbed when 1 gram of matter absorbs 100 ergs of energy. Although the rad has been superseded by the gray (1 Gy = 100 rads) for many applications internationally, it is still extensively used, especially in the US.

Related entry

   • radiation units

Related category

   • UNITS