We are constantly exposed to radiation from the natural environment as well as radiation from man-made sources. (In this discussion, "radiation" refers to ionizing radiation, or radiation which is energetic enough to produce ions, as opposed to less energetic forms of electromagnetic and other radiation.) If measured in millirems (mrem), the average annual radiation dose for Americans is estimated at 620 mrem per person. Many people receive more than this, although rarely are these higher amounts enough to cause injury. The normal permissible limit is 5,000 mrem for those who work around radiation, and even this is far below what will cause signs of illness.

An earlier version of this page gave the estimated annual radiation dose for Americans as 360 mrem per person, based on estimates from the 1980s. Nearly all of the change is from increased use of medical radiation--mostly x-rays, but also other radiation diagnostic and treatment procedures. The medical profession aims to minimize medical radiation exposure. For example, dental x-rays use less radiation than in the past now that more sensitive film is available. So why has the average medical radiation exposure increased? Reasons include:

• more procedures are available today for use in more treatment situations than before, and are increasingly used because of the significant medical benefits they provide--computed tomography (CAT) scans are a particular example;
• lower costs and greater household wealth generally have given more people access to treatment options (radiation and otherwise) than they used to have;
• insurance and litigation risks drive the use of more precautionary diagnostic uses of radiation.

The small radiation doses most of us are exposed to are not a noteworthy health concern (especially if compared to other everyday health risks). This is illustrated by the fact that the scientific and medical communities can't even reach a conclusion as to whether annual radiation doses of a few hundred mrem are harmful. Most regulatory agencies assume that any additional amount of radiation is harmful. However, much research indicates that small amounts of radiation (a few hundred mrem per year) actually decrease the risk of developing cancer relative to zero radiation exposure, an effect known as hormesis.

This worksheet is revised from one by the American Nuclear Society printed in 1980, updated based on a 2009 NCRP report and other sources (see end of page for listing). Note that the dose estimates on this page are approximate: many figures here are averages for occupations, broad locations, medical procedures, etc., where in reality there is much variation from case to case.

Common sources of radiation		Your annual dose (mrem)	U.S. average (mrem)
YOU	Radioactive elements in your body	28	28
WHERE YOU LIVE	Cosmic radiation (depends on your elevation above sea-level -- use table 1)	____	30
	Ground (use table 2)	____	21
	Radon and thoron (use table 2)	____	220
	House construction -- for stone or concrete add 7 mrem	____
WHAT YOU EAT, DRINK, AND BREATHE	Cosmogenic radiation (Carbon-14)	1	1
	Food	10	10
	Excessive shellfish or Brazil nut consumption	10	0
	Drinking water	5	5
HOW YOU LIVE	Natural gas use in home -- 5 mrem	____
	Eyeglasses with glass lenses -- 1 mrem	____
	Pacemaker containing plutonium -- 100 mrem	____
	Jet plane travel: total hours traveled per year ____ x 0.4 mrem	____
	TV viewing or computer use (except flat screens): average hours per day _____ x 0.15 mrem	____
	Smoke detectors (U.S. average)	0.01	0.01
	cigarette smoking (average cigarettes per day x 1.8)	____	4.5
WHERE YOU WORK	Exposure at work (for jobs around radiation see table 3)	____	1.1
MEDICAL	Number of chest x-rays ____ x 10 mrem	____	153
	Number of x-rays of extremities ____ x 1 mrem	____
	Number of dental x-rays ____ x 0.5 mrem	____
	Total for other x-rays or radiopharmaceutical examinations (see table 4)	____
	Total for computed tomography scans (CAT scans) (see table 5)	____	146
HOW CLOSE YOU ARE TO A POWER PLANT	At nuclear power plant site boundary: average hours per day ____ x 0.2 mrem	____	0
	1.5 km away from nuclear power plant: average hours per day ____ x 0.02 mrem	____
	8 km away from nuclear power plant: average hours per day ____ x 0.002 mrem	____
	over 8 km away from nuclear power plant	0
	Coal-burning power plants	0.2	0.2
	YOUR TOTAL ANNUAL DOSE	____	620

Compare your dose to the U.S. annual average of 620 mrem.

Your chances of dying of cancer are increased by 10% if you accumulate 250,000 mrem--or if you smoke 4 packs of cigarettes per day for fifty years.

• American Nuclear Society, 1980, "Your annual radiation dose" (factsheet).
• American Nuclear Society, 2015, "Radiation dose chart," American Nuclear Society, on line [http://www.ans.org/pi/resources/dosechart/].
• N. Bolus, 2013, "NCRP Report 160 and what it means for medical imaging and nuclear medicine," Journal of Nuclear Medicine Technology, 41(4):255-260.
• Institute of Physics, "Background radiation: Measuring your annual dose," IOP, on line [https://www.iop.org/education/teacher/resources/radioactivity/file_41559.pdf].
• T. D. Luckey, 2006, "Radiation hormesis: The good, the bad, and the ugly," Dose-Response, 4(3):169-180.
• J. Mauro et al., 2005, "Assessment of variations in radiation exposure in the United States," NRC, on line [http://pbadupws.nrc.gov/docs/ML1224/ML12240A227.pdf].
• R. Munroe, 2011, "Radiation chart," xkcd, on line [https://xkcd.com/radiation/].
• NASA, "Understanding space radiation," 2002, NASA, on line [http://spaceflight.nasa.gov/spacenews/factsheets/pdfs/radiation.pdf].
• National Council on Radiation Protection and Measurements, 2009, "NCRP Report No. 160, Ionizing radiation exposure of the population of the United States," NCRP [http://www.ncrppublications.org/Reports/160].
• Nuclear Regulatory Commission, 2014, "Personal annual radiation dose calculator," U.S. NRC, on line [http://www.nrc.gov/about-nrc/radiation/around-us/calculator.html].
• Oak Ridge Associated Universities, 2012, "Natural background and man-made radioactivity," NRC, on line [http://pbadupws.nrc.gov/docs/ML1122/ML11229A695.pdf].
• J. L. Prekeges, 2003, "Radiation hormesis, or, could all that radiation be good for us?," Journal of Nuclear Medicine Technology, 31(1):11-17.

© 2002, 2015 by Wm. Robert Johnston.
Last modified 12 October 2015.
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