Primer on Radiation Measurement
Primer on Radiation Measurement
In the aftermath of a radiological emergency the public will see radiation and its potential hazards described in many different and sometimes confusing ways. This primer is intended to help journalists and community leaders understand these terms.
Activity or radioactivity is measured by the number of atoms disintegrating per unit time. A becquerel is 1 disintegration per second. A curie is 37 billion disintegrations per second, which is the number of disintegrations per second in 1 gram of pure radium. A disintegrating atom can emit a beta particle, an alpha particle, a gamma ray, or some combination of all these, so becquerels or curies alone do not provide enough information to assess the risk to a person from a radioactive source.
Disintegrating atoms emit different forms of radiation–—alpha particles, beta particles, gamma rays, or x-rays. As radiation moves through the body, it dislodges electrons from atoms, disrupting molecules. Each time this happens, the radiation loses some energy until it escapes from the body or disappears. The energy deposited indicates the number of molecules disrupted. The energy the radiation deposits in tissue is called the dose, or more correctly, the absorbed dose. The units of measure for absorbed dose are the gray (1 joule per kilogram of tissue) or the rad (1/100 of a gray). The cumulative dose is the total absorbed dose or energy deposited by the body or a region of the body from repeated or prolonged exposures.
Alpha particles, beta particles, gamma rays, and x-rays affect tissue in different ways. Alpha particles disrupt more molecules in a shorter distance than gamma rays. A measure of the biologic risk of the energy deposited is the dose equivalent. The units of dose equivalent are sieverts or rem. Dose equivalent is calculated by multiplying the absorbed dose by a quality factor.
Sometimes a large number of people have been exposed to a source of ionizing radiation. To assess the potential health effects, scientists often multiply the exposure per person by the number of persons and call this the collective dose. Collective dose is expressed as “person-rem” or “person-sieverts.”
Abbreviations for Radiation Measurements
When the amounts of radiation being measured are less than 1, prefixes are attached to the unit of measure as a type of shorthand. This is called scientific notation and is used in many scientific fields. The table below shows the prefixes for radiation measurement and their associated numeric notations. Prefix Equal to How Much Is That? Abbreviation Example atto- 1 X 10-18 .000000000000000001 A aCi femto- 1 X 10-15 .000000000000001 F fCi pico- 1 X 10-12 .000000000001 p pCi nano- 1 X 10-9 .000000001 n nCi micro- 1 X 10-6 .000001 µ µCi milli- 1 X 10-3 .001 m mCi centi- 1 X 10-2 .01 c cSv
When the amount to be measured is 1,000 (i.e., 1 X 103) or higher, prefixes are attached to the unit of measure to shorten very large numbers (also scientific notation). The table below shows the prefixes used in radiation measurement and their associated numeric notations.
Prefix Equal to How Much Is That? Abbreviation Example kilo- 1 X 103 1000 k kCi mega- 1 X 106 1,000,000 M MCi giga- 1 X 109 100,000,000 G GBq tera- 1 X 1012 100,000,000,000 T TBq peta- 1 X 1015 100,000,000,000,000 P PBq exa- 1 X 1018 100,000,000,000,000,000 E EBq
Health Effects of Radiation Exposure
Exposure to radiation can cause two kinds of health effects. Deterministic effectsare observable health effects that occur soon after receipt of large doses. These may include hair loss, skin burns, nausea, or death. Stochastic effects are long-term effects, such as cancer. The radiation dose determines the severity of a deterministic effect and the probability of a stochastic effect.
The object of any radiation control program is to prevent any deterministic effects and minimize the risk for stochastic effects. When a person inhales or ingests a radionuclide, the body will absorb different amounts of that radionuclide in different organs, so each organ will receive a different organ dose. Federal Guidance Report 11 (FGR-11) from the Environmental Protection Agency (EPA) lists dose conversion factors for all radionuclides. This report can be downloaded from http://www.epa.gov/radiation/pubs.htm. The dose conversion factor for each organ is the number of rem delivered to that organ by each curie or becquerel of intake of a specific radioisotope.
External, Internal, and Absorbed Doses
A person can receive an external dose by standing near a gamma or high-energy beta-emitting source. A person can receive an internal dose by ingesting or inhaling radioactive material. The external exposure stops when the person leaves the area of the source. The internal exposure continues until the radioactive material is flushed from the body by natural processes or decays.
A person who has ingested a radioactive material receives an internal dose to several different organs. The absorbed dose to each organ is different, and the sensitivity of each organ to radiation is different. FGR-11 assigns a different weighting factor to each organ. To determine a person’s risk for cancer, multiply each organ’s dose by its weighting factor, and add the results; the sum is the effective dose equivalent (“effective” because it is not really the dose to the whole body, but a sum of the relative risks to each organ; and “equivalent” because it is presented in rem or sieverts instead of rads or gray).
Committed and Total Effective Dose Equivalents
When a person inhales or ingests a radionuclide, that radionuclide is distributed to different organs and stays there for days, months, or years until it decays or is excreted. The radionuclide will deliver a radiation dose over a period of time. The dose that a person receives from the time the nuclide enters the body until it is gone is the committed dose. FGR-11 calculates doses over a 50-year period and presents the committed dose equivalent for each organ plus the committed effective dose equivalent (CEDE).
A person can receive both an internal dose and an external dose. The sum of the committed effective dose equivalent (CEDE) and the external dose is called the total effective dose equivalent (TEDE).
Bibliography
Agency for Toxic Substances and Disease Registry Glossary [online]. [cited 2002 Aug 5] Available from URL: http://www.atsdr.cdc.gov/glossary.html.
Birky BK, Slaback LA, Schleien b. Handbook of Health Physics and Radiological Health 3rd Ed. Maryland: Williamson and Wilkins, 1998. Centers for Disease Control and Prevention. Public Health Emergency Preparedness and Response [online]. [cited 2002 Sep 3] Available from URL: emergency.cdc.gov.
Centers for Disease Control and Prevention. The Savannah River Site Dose Reconstruction Project Phase II: Source Term Calculation and Ingestion Pathway Data Retrieval April 30 2001, Glossary [online]. [cited Sep 12 2002]. Available from URL: http://www.cdc.gov/nceh/radiation/savannah/glossary.pdf .
Centers for Disease Control and Prevention and the National Cancer Institute. A Feasibility Study of the Health Consequences to the American Population from Nuclear Weapons Tests Conducted by the United States and Other Nations. Vol. 1, August 2001, Glossary: pp. 234–246.
Council for Foreign Relations. Terrorism: [online]. [cited 2002 Aug 28]. Available from URL: http://www.cfr.org/issue/135/terrorism.html .
Environmental Protection Agency. Radiation Information [online]. [cited 2002 Oct 1] Available from URL: http://www.epa.gov/rpdweb00/topics.html.
Federal Emergency Management Agency. Guide for All-Hazard Emergency Operations Planning: State and Local Guide (101) FEMA [online]. [cited 2002 Aug 7]. Available from URL: http://www.fema.gov/rrr/allhzpln6g.shtm .
Feiner F, Miller DG, Walker FW. Chart of the Nuclides 13th Ed. California: General Electric Corporation, 1983.
Friis R, Sellers T. Epidemiology for Public Health Practice 2nd Ed. Gaithersburg, Maryland: Aspen Publishers, Inc. 1999.
Institute of Medicine. Appendix K Glossary and Acronyms, Biological Threats and Terrorism: Assessing the Science and Response Capabilities: Workshop Summary. Washington, DC: National Academy Press: 2002: pp.275–286.
New Mexico Department of Public Safety. New Mexico Weapons of Mass Destruction Preparedness Glossary [online]. [cited 2002 Aug 5].
U.S. Department of Transportation. 2000 Emergency Response Guidebook [online]. [cited 2002 Aug 7]. Available from URL: http://transit-safety.volpe.dot.gov/training/Archived/EPSSeminarReg/CD/documents/EmerPrep/erg2000.pdf .
In the aftermath of a radiological emergency the public will see radiation and its potential hazards described in many different and sometimes confusing ways. This primer is intended to help journalists and community leaders understand these terms.
Activity or radioactivity is measured by the number of atoms disintegrating per unit time. A becquerel is 1 disintegration per second. A curie is 37 billion disintegrations per second, which is the number of disintegrations per second in 1 gram of pure radium. A disintegrating atom can emit a beta particle, an alpha particle, a gamma ray, or some combination of all these, so becquerels or curies alone do not provide enough information to assess the risk to a person from a radioactive source.
Disintegrating atoms emit different forms of radiation–—alpha particles, beta particles, gamma rays, or x-rays. As radiation moves through the body, it dislodges electrons from atoms, disrupting molecules. Each time this happens, the radiation loses some energy until it escapes from the body or disappears. The energy deposited indicates the number of molecules disrupted. The energy the radiation deposits in tissue is called the dose, or more correctly, the absorbed dose. The units of measure for absorbed dose are the gray (1 joule per kilogram of tissue) or the rad (1/100 of a gray). The cumulative dose is the total absorbed dose or energy deposited by the body or a region of the body from repeated or prolonged exposures.
Alpha particles, beta particles, gamma rays, and x-rays affect tissue in different ways. Alpha particles disrupt more molecules in a shorter distance than gamma rays. A measure of the biologic risk of the energy deposited is the dose equivalent. The units of dose equivalent are sieverts or rem. Dose equivalent is calculated by multiplying the absorbed dose by a quality factor.
Sometimes a large number of people have been exposed to a source of ionizing radiation. To assess the potential health effects, scientists often multiply the exposure per person by the number of persons and call this the collective dose. Collective dose is expressed as “person-rem” or “person-sieverts.”
Abbreviations for Radiation Measurements
When the amounts of radiation being measured are less than 1, prefixes are attached to the unit of measure as a type of shorthand. This is called scientific notation and is used in many scientific fields. The table below shows the prefixes for radiation measurement and their associated numeric notations. Prefix Equal to How Much Is That? Abbreviation Example atto- 1 X 10-18 .000000000000000001 A aCi femto- 1 X 10-15 .000000000000001 F fCi pico- 1 X 10-12 .000000000001 p pCi nano- 1 X 10-9 .000000001 n nCi micro- 1 X 10-6 .000001 µ µCi milli- 1 X 10-3 .001 m mCi centi- 1 X 10-2 .01 c cSv
When the amount to be measured is 1,000 (i.e., 1 X 103) or higher, prefixes are attached to the unit of measure to shorten very large numbers (also scientific notation). The table below shows the prefixes used in radiation measurement and their associated numeric notations.
Prefix Equal to How Much Is That? Abbreviation Example kilo- 1 X 103 1000 k kCi mega- 1 X 106 1,000,000 M MCi giga- 1 X 109 100,000,000 G GBq tera- 1 X 1012 100,000,000,000 T TBq peta- 1 X 1015 100,000,000,000,000 P PBq exa- 1 X 1018 100,000,000,000,000,000 E EBq
Health Effects of Radiation Exposure
Exposure to radiation can cause two kinds of health effects. Deterministic effectsare observable health effects that occur soon after receipt of large doses. These may include hair loss, skin burns, nausea, or death. Stochastic effects are long-term effects, such as cancer. The radiation dose determines the severity of a deterministic effect and the probability of a stochastic effect.
The object of any radiation control program is to prevent any deterministic effects and minimize the risk for stochastic effects. When a person inhales or ingests a radionuclide, the body will absorb different amounts of that radionuclide in different organs, so each organ will receive a different organ dose. Federal Guidance Report 11 (FGR-11) from the Environmental Protection Agency (EPA) lists dose conversion factors for all radionuclides. This report can be downloaded from http://www.epa.gov/radiation/pubs.htm. The dose conversion factor for each organ is the number of rem delivered to that organ by each curie or becquerel of intake of a specific radioisotope.
External, Internal, and Absorbed Doses
A person can receive an external dose by standing near a gamma or high-energy beta-emitting source. A person can receive an internal dose by ingesting or inhaling radioactive material. The external exposure stops when the person leaves the area of the source. The internal exposure continues until the radioactive material is flushed from the body by natural processes or decays.
A person who has ingested a radioactive material receives an internal dose to several different organs. The absorbed dose to each organ is different, and the sensitivity of each organ to radiation is different. FGR-11 assigns a different weighting factor to each organ. To determine a person’s risk for cancer, multiply each organ’s dose by its weighting factor, and add the results; the sum is the effective dose equivalent (“effective” because it is not really the dose to the whole body, but a sum of the relative risks to each organ; and “equivalent” because it is presented in rem or sieverts instead of rads or gray).
Committed and Total Effective Dose Equivalents
When a person inhales or ingests a radionuclide, that radionuclide is distributed to different organs and stays there for days, months, or years until it decays or is excreted. The radionuclide will deliver a radiation dose over a period of time. The dose that a person receives from the time the nuclide enters the body until it is gone is the committed dose. FGR-11 calculates doses over a 50-year period and presents the committed dose equivalent for each organ plus the committed effective dose equivalent (CEDE).
A person can receive both an internal dose and an external dose. The sum of the committed effective dose equivalent (CEDE) and the external dose is called the total effective dose equivalent (TEDE).
Bibliography
Agency for Toxic Substances and Disease Registry Glossary [online]. [cited 2002 Aug 5] Available from URL: http://www.atsdr.cdc.gov/glossary.html.
Birky BK, Slaback LA, Schleien b. Handbook of Health Physics and Radiological Health 3rd Ed. Maryland: Williamson and Wilkins, 1998. Centers for Disease Control and Prevention. Public Health Emergency Preparedness and Response [online]. [cited 2002 Sep 3] Available from URL: emergency.cdc.gov.
Centers for Disease Control and Prevention. The Savannah River Site Dose Reconstruction Project Phase II: Source Term Calculation and Ingestion Pathway Data Retrieval April 30 2001, Glossary [online]. [cited Sep 12 2002]. Available from URL: http://www.cdc.gov/nceh/radiation/savannah/glossary.pdf .
Centers for Disease Control and Prevention and the National Cancer Institute. A Feasibility Study of the Health Consequences to the American Population from Nuclear Weapons Tests Conducted by the United States and Other Nations. Vol. 1, August 2001, Glossary: pp. 234–246.
Council for Foreign Relations. Terrorism: [online]. [cited 2002 Aug 28]. Available from URL: http://www.cfr.org/issue/135/terrorism.html .
Environmental Protection Agency. Radiation Information [online]. [cited 2002 Oct 1] Available from URL: http://www.epa.gov/rpdweb00/topics.html.
Federal Emergency Management Agency. Guide for All-Hazard Emergency Operations Planning: State and Local Guide (101) FEMA [online]. [cited 2002 Aug 7]. Available from URL: http://www.fema.gov/rrr/allhzpln6g.shtm .
Feiner F, Miller DG, Walker FW. Chart of the Nuclides 13th Ed. California: General Electric Corporation, 1983.
Friis R, Sellers T. Epidemiology for Public Health Practice 2nd Ed. Gaithersburg, Maryland: Aspen Publishers, Inc. 1999.
Institute of Medicine. Appendix K Glossary and Acronyms, Biological Threats and Terrorism: Assessing the Science and Response Capabilities: Workshop Summary. Washington, DC: National Academy Press: 2002: pp.275–286.
New Mexico Department of Public Safety. New Mexico Weapons of Mass Destruction Preparedness Glossary [online]. [cited 2002 Aug 5].
U.S. Department of Transportation. 2000 Emergency Response Guidebook [online]. [cited 2002 Aug 7]. Available from URL: http://transit-safety.volpe.dot.gov/training/Archived/EPSSeminarReg/CD/documents/EmerPrep/erg2000.pdf .
