{"data":{"id":"us-va/12vac5-481-240","jurisdiction":"us-va","citation":"12VAC5-481-240","heading":"Units of exposure and dose","body":"A. As used in this chapter, the unit of exposure is the coulomb per kilogram (C/kg) of air and the units of radiation dose are gray (Gy), rad, rem, and sievert. (See 12VAC5-481-10 for definitions.) One roentgen is equal to 2.58E-4 coulomb per kilogram of air.\n\n1. Gray (Gy) is the SI unit of absorbed dose. One gray is equal to an absorbed dose of 1 joule per kilogram (100 rad).\n\n2. 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 Gy).\n\n3. 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).\n\n4. Sievert is the SI unit of any of the quantities as dose equivalent. The dose equivalent is equal to the absorbed dose in gray multiplied by the quality factor (1 Sv = 100 rem).\n\nB. As used in this chapter, the quality factors for converting absorbed dose to dose equivalent are shown in Quality Factors and Absorbed Dose Equivalencies table in this subsection.\n\nQuality Factors and Absorbed Dose Equivalencies\n\nType of Radiation\n\nQuality factor (Q)\n\nAbsorbed dose equal to a unit dose equivalenta\n\nX, gamma, or beta\n\n1\n\n1\n\nAlpha particles, multiple-charged particles, fission  fragments and heavy particles of unknown charge\n\n20\n\n0.05\n\nNeutrons of unknown energy\n\n10\n\n0.1\n\nHigh energy protons\n\n10\n\n0.1\n\naAbsorbed dose in rad equal to 1 rem or the  absorbed dose in gray equal to 1 sievert.\n\nC. If it is more convenient to measure the neutron fluence rate than to determine the neutron dose equivalent rate in rems per hour or sieverts per hour, as provided in subsection B of this section, 1 rem (0.01 Sv) of neutron radiation of unknown energies may, for purposes of this chapter, 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 of the neutrons, the licensee may use the fluence rate per unit dose equivalent of the approximate Q value from the Mean Quality Factors, Q, and Fluence per Unit Dose Equivalent for Monoenergetic Neutrons table in this subsection to convert a measured tissue dose in rads to dose equivalent in rems.\n\nMean Quality Factors, Q, and Fluence per Unit Dose  Equivalent for Monoenergetic Neutrons\n\nNeutron energy (MeV)\n\nQuality factor (Q)a\n\nFluence per unit dose equivalent\n\n(neutrons cm-2 rem-1)b\n\n(thermal)\n\n2.5 x 10-8\n\n2\n\n980 x 106\n\n1 x 10-7\n\n2\n\n980 x 106\n\n1 x 10-6\n\n2\n\n810 x 106\n\n1 x 10-5\n\n2\n\n810 x 106\n\n1 x 10-4\n\n2\n\n840 x 106\n\n1 x 10-3\n\n2\n\n980 x 106\n\n1 x 10-2\n\n2.5\n\n1010 x 106\n\n1 x 10-1\n\n7.5\n\n170 x 106\n\n5 x 10-1\n\n11\n\n39 x 106\n\n1\n\n11\n\n27 x 106\n\n2.5\n\n9\n\n29 x 106\n\n5\n\n8\n\n23 x 106\n\n7\n\n7\n\n24 x 106\n\n10\n\n6.5\n\n24 x 106\n\n14\n\n7.5\n\n17 x 106\n\n20\n\n8\n\n16 x 106\n\n40\n\n7\n\n14 x 106\n\n60\n\n5.5\n\n16 x 106\n\n1 x 102\n\n4\n\n20 x 106\n\n2x102\n\n3.5\n\n19x106\n\n3x102\n\n3.5\n\n16x106\n\n4x102\n\n3.5\n\n14x106\n\naValue of quality factor (Q) at the point  where the dose equivalent is maximum in a 30-cm diameter cylinder tissue-equivalent  phantom.\n\nbMonoenergetic neutrons incident normally on a  30-cm diameter cylinder tissue-equivalent phantom.","path":["Title 12. Health","Agency 5. Department of Health","Chapter 481. Virginia Radiation Protection Regulations","Part I. General Provisions"],"source_url":"https://law.lis.virginia.gov/admincode/title12/agency5/chapter481/section240/","current_through":"2026 Regular Session (effective July 1, 2026)","vintage":"","retrieved_at":"2026-09-14T04:50:25Z","sha256":"14bca6492af298f3d2c778269d60ed95188322c57686f0e96079a4be7531f82b","source_id":"us-va-vac","stale":false,"prev":"us-va/12vac5-481-230","next":"us-va/12vac5-481-250"},"notice":"GroundRules: Original legal text. Not legal advice."}