The SI Unit for radiation Absorption is:

Ans. B. Gray. (Ref. Harrison Medicine 18th/pg. 691).The International System (SI) unit for radiation absorbed dose (rad) is the Gray (Gy); 1 Gy = 100 rad.Units of radiation dose.# Gray (Gy) is the SI unit of absorbed dose. One gray is equal to an absorbed dose of 1 Joule/kilogram (100 rads).# Rad is the special unit of absorbed dose. One rad is equal to an absorbed dose of 100 ergs/gram or 0.01 joule/kilogram (0.01 gray).# Rem is the special unit of any of the quantities expressed as dose equivalent. The dose equivalent in rems is equal to the absorbed dose in rads multiplied by the quality factor (1 rem=0.01 sievert).# Sievert is the SI unit of any of the quantities expressed as dose equivalent. The dose equivalent in sieverts is equal to the absorbed dose in grays multiplied by the quality factor (1 Sv=100 rems).Dosimetric quantitiesQuantityDefinitionNew UnitsOld UnitsExposureCharge per unit mass of air1 R =2.58 X 10-4 C/kg---Roetngen (R)Absorbed dose to tissueT from radiation of type RDT.REnergy of radiation R absorbed per unit mass of tissue T1 rad--100 ergs/g1 Gy= 1 joule/kg1 Gy= 100 radsgray (Gy)Radiation absorbed dose (rad)Equivalent dose to tissue T HTSum of contributions of dose to T from different radiation types, each multiplied by the radilation weightilng faftor (WR)HT-[?]R WR DT,RSievert (SV)Roentgen equivalent man (rem)Effective Dose ESum of equivalent doses to organs and tissues exposed, each multiplied by the appropriate tissue weighting factor (wr)Sievert (Sv)rem Quality Factors and Absorbed Dose EquivalenciesType of radiationQuality factorAbsorbed dose equal to a unit dose equivalenta (Q) X-, gamma, or beta radiation11Alpha particles, multiple-charged particles, fission fragments and heavy particles of unknown charge200.05Neutrons of unknown energy100.1High-energy protons100.1aAbsorbed dose in rad equal to 1 rem or the absorbed dose in gray equal to 1 sievert.Educational points:Radiobiological effectiveness (RBE):RBE is the ratio of the absorbed dose of low-LET radiation (X-Rays, g rays) to cause the same level of the same biological effect as that of high-LET radiation (neutrons, a particles). LET stands for Linear Energy Transfer, and describes the average energy released per unit length of track. The RBE is used to determine the Q factor used in calculating equivalent dose from absorbed dose.