Units of Exposure and Dose

Units of Exposure and Dose. 1. As used in these regulations, the unit of Exposure is the coulomb per kilogram (C/kg) of air. One roentgen is equal to 2.58E-4 coulomb per kilogram of air. 2. As used in these regulations, the units of dose are: a. Gray (Gy) is the SI unit of absorbed dose. One gray is equal to an absorbed dose of 1 joule per kilogram (100 rads). b. Rad is the special unit of absorbed dose. One rad is equal to an absorbed dose of 100 ergs per gram or 0.01 joule per kilogram (0.01 gray). c. Rem is the special unit of any of the quantities expressed as dose equivalent. The dose equivalent in rem is equal to the absorbed dose in rad multiplied by the quality factor (1 rem = 0.01 sievert). d. Sievert is the SI unit of any of the quantities expressed as dose equivalent. The dose equivalent in sievert is equal to the absorbed dose in gray multiplied by the quality factor (1 sievert = 100 rems). 3. As used in these regulations, the quality factors for converting absorbed dose to dose equivalent are shown in Table I. TABLE I QUALITY FACTORS AND ABSORBED DOSE EQUIVALENCIES Quality Factor Absorbed Dose Equal to TYPE OF RADIATION (Q) a Unit Dose Equivalenta X-ray, gamma, or beta radiation and high-speed electrons Alpha particles, multiple-charged particles, fission fragments and heavy particles of unknown charge 0.05 Neutrons of unknown energy 0.1 High-energy protons 0.1 aAbsorbed dose in rad equal to 1 rem or the absorbed dose in gray equal to 1 sievert. 4 If it is more convenient to measure the neutron fluence rate than to determine the neutron dose equivalent rate in rem per hour or sievert per hour, as provided in 1.1.15(3), 1 rem (0.01 sievert) of neutron radiation of unknown energies may, for purposes of these regulations, be assumed to result from a total fluence of 25 million neutrons per square centimeter incident upon the body. If sufficient information exists to estimate the approximate energy distribution of the neutrons, the licensee or registrant may use the fluence rate per unit dose equivalent or the appropriate Q value from Table II to convert a measured tissue dose in rad or gray to dose equivalent in rem or sievert. TABLE II MEAN QUALITY FACT0RS, Q, AND FLUENCE PER UNIT DOSE EQUIVALENT FOR MONOENERGETIC NEUTRONS Neutron Quality Fluence per Unit Fluence per Unit Energy Factora Dose Equivalentb Dose Equivalentb (MeV) (Q) (neutrons cm-2rem-1) (neutrons cm-2Sv-1) (thermal) 2.5E-8 980E+6 980E+8 1E-7 980E+6 980E+8 1E-6 810E+6 810E+8 1E-5 810E+6 810E+8 1E-4 840E+6 840E+8 1E-3 980E+6 980E+8 1E-2 2.5 1010E+6 1010E+8 1E-1 7.5 170E+6 170E+8 5E-1 39E+6 39E+8 27E+6 27E+8 2.5 29E+6 29E+8 23E+6 23E+8 24E+6 24E+8 6.5 24E+6 24E+8 7.5 17E+6 17E+8 16E+6 16E+8 14E+6 14E+8 5.5 16E+6 16E+8 1E+2 20E+6 20E+8 2E+2 3.5 19E+6 19E+8 3E+2 3.5 16E+6 16E+8 4E+2 3.5 14E+6 14E+8 aValue of quality factor (Q) at the point where the dose equivalent is maximum in a 30-centimeter diameter cylinder tissue-equivalent phantom. bMonoenergetic neutrons incident normally on a 30-centimeter diameter cylinder tissue-equivalent phantom.