Radiation Terms and Units There are different but interrelated units for measuring radioactivity and estimating health effects. Radioactivity Absorbed Dose Effective Dose Radioactivity Radioactivity is a measure of the by a material. RADIOACTIVE MATERIAL Radioactivity is a measure of the ionizing radiation released by a radioactive material. Different types of ionizing radiation have the potential to damage human tissue. Use Measuring soil, water and air samples Units Bq | becquerels Ci j curies international unit U.S. unit 1 becquerel (Bq) = 2.703X1011 curie (Ci) 1 curie (Ci) = 3.7 x 10'° becquerel (Bq) 1 kilobecquerel (kBq) = 1,000 Bq 1 picocurie (pCi) = 0.000 000 000 001 Ci Examples Surface water natural radium-226 level; 0.0037 to 0.0185 Bq per liter (L) or 0.1 to 0,5 pCi/L Drinking water radium limit for daily consumption: 0.185 Bq/Lor 5.0 pCi/L Absorbed Dose Absorbed dose measures ionizing RADIATION PASSES THROUGH A HUMAN IN HUMAN m TISSUE mr Absorbed dose describes the amount of energy deposited per unit mass in an object or person. Use Measuring dose from medical equipment Units Gy | gray rad | rad international unit U.S. unit 1 milligray (mGy) = 0,001 Gy 1 rad = 0.01 gray (Gy) 1 milligray (mGy) = 0,001 Gy Examples Dose to the lens of eyes from a brain CT scan: about 60 mGy or 6 rad Dose to the thyroid from a chest CT scan: about 10 mGy or 1 rad Effective Dose Effective dose indicates radiation HEflTOISflSnSlfor a population. FACTOR IN &EPA United States Environmental Protection Agency Effective dose takes the absorbed dose (see above) and adjusts it for radiation type and relative organ sensitivity. The result is an indicator for the potential for long-term health effects (i.e., cancer and hereditary effects) from an exposure. It is used to set regulatory limits that protect against long-term health effects in a population. It also allows experts to compare anticipated health effects from different exposure situations. Because this value is a calculated approximation, not a physical quantity, it cannot be used to predict individual health effects. Use Used to set protective levels for groups of people Units Sv | sievert international unit rem | rem U.S. unit 1 sievert (Sv) = 100 rem 1 rem = 0.01 sievert (Sv) 1 millisievert (mSv) = 0.001 Sv 1 microsievert (|jSv) = 0.000 001 Sv 1 millirem (mrem) = 0.001 rem Examples Worker radiation limit annual dose limit: 0.05 Sv or 5 rem Evacuate/shelter in place guidance for emergencies: needed if projected dose exceeds 10-50 mSv or 1-5 rem over four days o epa.gov/radiation/radiation-terms-and-units ------- Reference Material © Q Sources for Radioactivity Unit Examples Agency for Toxic Substances and Disease Registry, 1990. "Toxicological Profile for Radium" (p. 53). Retrieved from https://www.atsdr.cdc.gov/toxprofiles/tp144.pdf Radionuclides Rule. Retrieved from https://www.epa.gov/dwreginfo/radionuclides-rule Sources for Absorbed Dose Unit Examples Gao, Yiming et al., 2020. Patient-Specific Organ and Effective Dose Estimates in Adult Oncologic CT. American Journal of Roentgenology, 214:4, 738-746. Retrieved from https://www.ajronline.org/doi/ full/10.2214/AJR.19.21197 Sources for Effective Dose Unit Examples United States Nuclear Regulatory Commission, 1991. "Regulations (10 CFR) Subpart C - Occupational Dose Limits." Retrieved from https://www.nrc.gov/reading-rm/doc-collections/cfr/part020/part020- 1201.html ©United States Environmental Protection Agency, 2017. "PAG Manual: Protective Action Guides and Planning Guidance for Radiological Incidents" (p. 50). Retrieved from https://www.epa.gov/sites/ default/files/2017-01/documents/epa pag manual final revisions 01-11-2017 cover disclaimer 8.pdf ------- |