Q. Define roentgen and activity and Curie?
One roentgen (1R) is described as the quantity of radiation which produces 1.6 × 1012 pairs of ions in 1 gram of air.
The activity of a radioactive substance is described as the rate at which the atoms decay. Curie is described as the quantity of a radioactive substance which gives 3.7 × 1010 disintegrations per second or 3.7 × 1010 Becquerel.