Units of exposure, dose, and activity

1. As used in these rules, the unit of exposure is the coulomb per kilogram (C/kg) of air. One roentgen is equal to two hundred fifty-eight millionths coulomb per kilogram of air. 2. As used in these rules, the units of dose are: a. Rad is the special unit of absorbed dose. One rad is equal to an absorbed dose of one hundred erg per gram or one one-hundredths (1/100) joule per kilogram (0.01 Gy). b. Gray (Gy) is the SI unit of absorbed dose. One gray is equal to an absorbed dose of one joule per kilogram (100 rad). 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 Sv). 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 Sv = 100 rem). 3. As used in these rules, the quality factors for converting absorbed dose to dose equivalent are shown in table I. Table I QUALITY FACTORS AND ABSORBED DOSE EQUIVALENTS TYPE OF RADIATION Quality Factor (Q) Absorbed Dose Equal to a Unit Dose Equivalent* X, gamma, or beta radiation and high-speed electrons 1 1 Alpha particles, multiple-charged particles, fission fragments, and heavy particles of unknown charge 20 0.05 Neutrons of unknown energy 10 0.1 High-energy protons 10 0.1 * Absorbed dose in rad equal to one rem or the absorbed dose in gray equal to one 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 subsection 3, one one hundredth sievert [1 rem] of neutron radiation of unknown energies may, for purposes of these rules, be assumed to result from a total fluence of twenty-five 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 gray or rad to dose equivalent in rem or sievert. Table II MEAN QUALITY FACTORS, Q, AND FLUENCE PER UNIT DOSE EQUIVALENT FOR MONOENERGETIC NEUTRONS Neutron Fluence per Unit Energy (MeV) Quality Factora (Q) Fluence per Unit Dose Equivalentb (neutrons cm-2 rem-1) Dose Equivalentb (neutrons cm-2 Sv-1) (thermal) 2.5E-8 2 980E+6 980E+8 1E-7 2 980E+6 980E+8 1E-6 2 810E+6 810E+8 1E-5 2 810E+6 810E+8 1E-4 2 840E+6 840E+8 1E-3 2 980E+6 980E+8 1E-2 2.5 1010E+6 1010E+8 1E-1 7.5 170E+6 170E+8 5E-1 11 39E+6 39E+8 1 11 27E+6 27E+8 2.5 9 29E+6 29E+8 5 8 23E+6 23E+8 7 7 24E+6 24E+8 10 6.5 24E+6 24E+8 14 7.5 17E+6 17E+8 20 8 16E+6 16E+8 40 7 14E+6 14E+8 60 5.5 16E+6 16E+8 1E+2 4 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 a Value of quality factor (Q) at the point where the dose equivalent is maximum in a 30-centimeter diameter cylinder tissue-equivalent phantom. b Monoenergetic neutrons incident normally on a 30-centimeter diameter cylinder tissue-equivalent phantom. 5. For purposes of these rules, activity is expressed in the special unit of curie (Ci) or in the international system (SI) unit of becquerel (Bq), or their multiples, or disintegrations or transformations per unit of time. a. One curie (Ci) = 3.7E+10 disintegrations or transformations per second (dps or tps) = 3.7E+10 becquerel (Bq) = 2.22E+12 disintegrations or transformations per minute (dpm or tpm). b. One becquerel (Bq) = one disintegration or transformation per second (dps or tps). 6. SI numerical prefix conversions. See table III for a listing of numerical prefixes to convert SI units or special units by appropriate multiples: Table III SI Numerical Prefix Conversion Table Multiplication Factors Prefix Symbol 1 000 000 000 000 000 000 = 1018 exa E 1 000 000 000 000 000 = 1015 peta P 1 000 000 000 000 = 1012 tera T 1 000 000 000 = 109 giga G 1 000 000 = 106 mega M 1 000 = 103 kilo k 100 = 102 hecto h 10 = 101 deka da 0.1 = 10-1 deci d 0.01 = 10-2 centi c 0.001 = 10-3 milli m 0.000 001 = 10-6 micro u 0.000 000 001 = 10-9 nana n 0.000 000 000 001 = 10-12 pico p 0.000 000 000 000 001 = 10-15 femto f 0.000 000 000 000 000 001 = 10-18 atto a