d
The risk posed to a human being by any radiation exposure depends partly upon the absorbed dose, the amount of energy absorbed per gram of tissue. Absorbed dose is expressed in rad. A rad is equal to \(100\) ergs of energy absorbed by \(1\) gram of tissue. The more modern, internationally adopted unit is the gray (named after the English medical physicist \(L. H.\) Gray); one gray equals \(100\) rad.