RADIATION DOSIMETRY O THEORY RADIATION DOSES non-SI units (relationship between units) Dose Formula SI units ΔΕ J/kg = Gray (Gy) Absorbed Dose, rad 1 Gy = 100 rad Δm AE is the energy lost from the radiation beam, and Am is the mass of the material into which the energy is absorbed. Exposure dose, ΔΟ C/kg Roentgen (R) 1R = 2,58 ·104 C/kg Δm 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. H = Q · D where H is dose equivalent, Q is relative biological effectiveness of a particular kind of radiation, D is adsorbed dose. Equivalent Dose, Н Sievert rem (Sv) 1 Sy =100 rem Effective HEΣΗ Sievert rem 1 Sy =100 rem Equivalent Dose where HT = WT·H, is the tissue-weighted , Hef (Sv) dose equivalent to an organ or tissue, H, is the dose equivalent to the organ or tissue and the WT applicable to that organ or tissue. Table 1 – Quality factors for different kinds of radiation Table 2 – Dimensionless weighting factors (Wt) Tissue WT Type of Radiation Gonads 0.25 Breast Red bone marrow 0.15 Х-гаys 0.12 0.12 Lungs Thyroid Bone surfaces Remainder Total body 0.03 20 0.03 Neutrons (fast) 10 0,30 Protons 10 1.00 DOSE RATES 1. Adsorbed dose rate: Np =" Table 3 – Exposure constants %3D Radionuclides ky (µGy-m³/GBq-h at 1 m)* 137CS 99mTc 2. Dose equivalent rate: Nµ = - н %3D 88.11 15.95 3. Exposure rate: Nỵ = 201TI 99MO 12.16 Exposure rate at a distance r from the source of radiation can be found as ky'A 39.46 67GA 20.54 1231 "In 41.89 Nx = , where is ky is exposure constant for a given radioisotope, A is activity of the radioactive 121 source, r is distance from the source of the radiation. r2 55.41 37.03 57CO 1311 15.16 58.65 154.05 9. A person is exposed to ionizing radiation which deposits 10 J of energy in their tissue. (a) What dose (in Gy) would an 80 kg adult and a 15 kg child receive under these circumstances? (b) What dose (in rem) would the adult and child each receive if the radiation were low energy (< 0.03MeV) ß radiation? (c) What dose (in Sv) would the adult and child each receive if the radiation were low energy a radiation? (RBE)=10.)