R313-12-20. Units of Exposure and Dose

(1) As used in Title R313, the unit of EXPOSURE is the coulomb per kilogram (C per kg). One roentgen is equal to 2.58 x 10-4 coulomb per kilogram of air. (2) As used in Title R313, the units of dose are: (a) Gray (Gy) is the SI unit of absorbed dose. One gray is equal to an absorbed dose of one joule per kilogram. One gray equals 100 rad. (b) Rad is the special unit of absorbed dose. One rad is equal to an absorbed dose of 100 erg per gram or 0.01 joule per kilogram. One rad equals 0.01 Gy. (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. One rem equals 0.01 Sv. (d) Sievert (Sv) 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. One Sv equals 100 rem. (3) As used in Title R313, the quality factors for converting absorbed dose to dose equivalent are shown in Table 1. Table 1 Quality Factors and Absorbed Dose Equivalences 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 For the column in Table 1 labeled "Absorbed Dose Equal to a Unit Dose Equivalent", the absorbed dose in rad is equal to one rem or the absorbed dose in gray is equal to one Sv. (4) If it is more convenient to measure the neutron fluence rate than to determine the neutron dose equivalent rate in sievert per hour or rem per hour, as provided in Subsection R313-12-20(3), 0.01 Sv of neutron radiation of unknown energies may, for purposes of Title R313, 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 2 to convert a measured tissue dose in gray or rad to dose equivalent in sievert or rem. Table 2 Mean Quality Factors, Q, and Fluence Per Unit Dose Equivalent for Monoenergetic Neutrons Neutron Energy Mev Quality Factor Q Fluence per Unit Dose Equivalent neutrons cm-2 rem-1 Fluence per Unit Dose Equivalent neutrons cm-2 Sv-1 thermal 2.5 x 10-8 2 980 x 106 980 x 108 1 x 10-7 2 980 x 106 980 x 108 1 x 10-6 2 810 x 106 810 x 108 1 x 10-5 2 810 x 106 810 x 108 1 x 10-4 2 840 x 106 840 x 108 1 x 10-3 2 980 x 106 980 x 108 1 x 10-2 2.5 1010 x 106 1010 x 108 1 x 10-1 7.5 170 x 106 170 x 108 5 x 10-1 11 39 x 106 39 x 108 1 11 27 x 106 27 x 108 2.5 9 29 x 106 29 x 108 5 8 23 x 106 23 x 108 7 7 24 x 106 24 x 108 10 6.5 24 x 106 24 x 108 14 7.5 17 x 106 17 x 108 20 8 16 x 106 16 x 108 40 7 14 x 106 14 x 108 60 5.5 16 x 106 16 x 108 1 x 102 4 20 x 106 20 x 108 2 x 102 3.5 19 x 106 19 x 108 3 x 102 3.5 16 x 106 16 x 108 4 x 102 3.5 14 x 106 14 x 108 For the column in Table 2 labeled "Quality Factor", the values of Q are at the point when the dose equivalent is maximum in a 30 cm diameter cylinder tissue-equivalent phantom. For the columns in Table 2 labeled "Fluence per Unit Dose Equivalent", the values are for monoenergetic neutrons incident normally on a 30 cm diameter cylinder tissue equivalent phantom.