RADIATION DOSIMETRY O THEORY RADIATION DOSES non-SI units Dose Formula SI (relationship between units) units Absorbed Dose, ΔΕ J/kg = Gray (Gy) 1 Gy = 100 rad rad AE is the energy lost from the radiation beam, and Am is the mass of the material into which the energy is absorbed. AQ Хв Дт Exposure dose, Roentgen (R) 1R = 2,58 104 C/kg C/kg х Am where AQ is the electric charge freed by such radiation in a specified volume of air divided by the mass Am of that air. Relationship between absorbed dose and exposure dose D = f:X D is adsorbed dose, f is a coefficient depending on the kind of tissue being irradiated. Equivalent Dose, H = Q•D where H is dose equivalent, Q is relative biological effectiveness of a particular kind of radiation, D is adsorbed dose. Sievert rem Н (Sv) 1 Sv =100 rem Effective Η ΣΗΤ Sievert rem Equivalent Dose where Hy = Wr H, is the tissue-weighted , Het (Sv) I Sv =100 rem dose equivalent to an organ or tissue, Hi is the dose equivalent to the organ or tissue and the Wr applicable to that organ or tissue. Table 1- Quality factors for different kinds of radiation Table 2 - Dimensionless weighting factors (Wr) Tissue W. Type of Radiation Q Gonads Breast 0.25 0.15 Hays Red bone marrow 0.12 0.12 Lungs Thyroid Bone surfaces Remainder Total body 0.03 20 0,03 0.30 Neutrons (fasl) 10 10 1.00 DOSE RATES 1. Adsorbed dose rate: Np = Table 3- Exposure constants Radionuclides ky (Gy-m/GBq-h at I m 2. Dose equivalent rate: Ny =" 88.11 15.95 WarTe 3. Exposure rate: Ny = Exposure rate at a distancer from the source of radiation can be found as 12.16 39.46 "Mo "Ga 20.54 ky'A 41.89 Nx = where is ky is exposure constant for a given radioisotope, A is activity of the radioactive S"Co 55.41 37.03 15.16 source, r is distance from the source of the radiation. 58.65 154.05 3. When the whole body is evenly exposed to 10 mGy of gamma-ray radiation, find tissue- weighted dose equivalents HT for gonads, breast, red bone marrow, lungs, thyroid and bone surfaces. Express the answer in Sievert and rem.