RBE (relative biological effectiveness): A factor used to compare
the biological effectiveness of absorbed radiation doses from different types of
ionizing radiation; more specifically, the experimentally determined ratio of an
absorbed dose of a radiation in question to the absorbed dose of a reference
radiation required produce an identical biological effect in a particular
experimental organism or tissue; if 10 mGy of fast neutrons equaled in lethality
to 20 mGy of 250kVp x-rays, the RBE of fast neutrons would be two.
Gray (Gy): The International System (SI) unit of absorbed dose of
radiation, 1Gy = 1 J kg-1 = 100 rad