Summary

• The roentgen  is a unit of radiation exposure  measured in terms of air ionisation . It applies only to x- or gamma radiation.
• The gray  (Gy) is a unit of absorbed dose   which represents an energy absorption of per kilogram of absorbing material.
• The radiation weighting factors  ( ) are used to convert from absorbed dose (D) to equivalent dose (H) .
• The sievert  (Sv) is the unit of equivalent dose and is the product of the absorbed dose and the radiation weighting factor of the radiation causing it. It takes into account the biological effects  of an absorbed dose.