Radiation is all around us as a part of our natural environment. It may be measured in units of millirems (mrem). The average annual radiation dose for Americans is estimated at 360 mrem per person. Many people receive more than this, but this is not dangerous. 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. Recent research is leading to the conclusion that annual radiation doses of hundreds of mrem actually reduce the risk of cancer.
This worksheet is revised and updated from one by the American Nuclear Society printed in 1980.
| Common sources of radiation | Your annual dose (mrem) | |
|---|---|---|
| YOU | Radioactive elements in your body | 39 |
| WHERE YOU LIVE | Cosmic radiation at sea level (depends on your elevation above sea-level -- use table 1; U.S. average = 27 mrem) | ___ |
| Ground (use table 2; U.S. average = 26 mrem) | ___ | |
| Radon (use table 2; U.S. average = 200 mrem) | ___ | |
| House construction -- for stone or concrete add 7 mrem | ___ | |
| WHAT YOU EAT, DRINK, AND BREATHE | Cosmogenic radiation (Carbon-14) | 1 |
| Food | 10 | |
| Drinking water | 5 | |
| Fallout from nuclear weapons testing | 0.1 | |
| HOW YOU LIVE | Natural gas use in home -- 5 mrem | ___ |
| Eyeglasses with glass lenses -- 1 mrem | ___ | |
| Pacemaker -- 160 mrem | ___ | |
| Jet plane travel: total hours traveled in past year _____ x 0.4 mrem/hour | ___ | |
| TV viewing or computer use (except flat screens): average hours per day _____ x 0.15 mrem/hour | ___ | |
| Smoke detectors (U.S. average) | 0.01 | |
| WHERE YOU WORK | Exposure at work -- U.S. average = 1.1 mrem (for jobs around radiation see table 3) | ___ |
| MEDICAL | Number of chest x-rays ____ x 5 mrem | ___ |
| Number of x-rays of extremities ____ x 1 mrem | ___ | |
| Number of dental x-rays ____ x 10 mrem | ___ | |
| Total for other x-rays or radiopharmaceutical examinations (see table 4) (Total U.S. average, medical = 60 mrem) | ___ | |
| HOW CLOSE YOU ARE TO A COAL POWER PLANT OR NUCLEAR POWER PLANT | At site boundary: average hours/day ____ x 0.2 mrem/hour | ___ |
| 1.5 km away: average hours/day ____ x 0.02 mrem/hour | ___ | |
| 8 km away: average hours/day ____ x 0.002 mrem/hour | ___ | |
| over 8 km away | 0 | |
| Coal-burning plants (U.S. average) | 0.2 | |
| YOUR TOTAL ANNUAL DOSE | ___ | |
Compare your dose to the U.S. annual average of 360 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.
| elevation (meters) | annual dose (mrem) |
|---|---|
| 0 | 26 |
| 300 | 28 |
| 600 | 31 |
| 900 | 35 |
| 1200 | 41 |
| 1500 | 47 |
| 1800 | 55 |
| 2100 | 66 |
| 2400 | 79 |
| 2700 | 96 |
Table 2: Radiation from ground and radon
| location | annual dose from ground (mrem) | annual dose from radon |
|---|---|---|
| U.S. average | 28 | 200 |
| Atlantic coast | 16 | 100 |
| Rocky Mountains | 40 | |
| Central U.S. | 20 | |
| South Texas | 20 | 100 |
| areas with monazite sands | 500 |
Table 3: Average annual doses for nuclear-related occupations
| occupation | annual dose (mrem) |
|---|---|
| medical radiologist | 320 |
| nuclear power plant worker | 760 |
| nuclear industry | 380 |
| Dept. of Defense nuclear-related | 180 |
| Dept. of Energy nuclear-related | 300 |
| universities nuclear-related | 210 |
Table 4: Typical doses for some medical procedures (whole body dose)
| procedure | dose (mrem) |
|---|---|
| head or neck x-ray | 15 |
| cervical spine x-ray | 22 |
| lumber spine x-ray | 130 |
| pelvis x-ray | 44 |
| hip x-ray | 83 |
| upper GI series | 245 |
| lower GI series | 405 |
| barium enema | 54 |
| bone scan | 440 |
| thyroid treatment with radioiodine | 7000 |
| CAT scan | 800 |
Table 5: Biological effects of radiation
| Increase of 1% in chances of developing cancer | 25,000 mrem |
| Radiation sickness | 100,000 mrem within 48 hours or less |
| 50% chance of death from radiation sickness | 450,000 mrem within 24 hours or less |
Note: Dosage figures from man-made sources are approximate; some may be outdated, given that many of these figures are declining over time as technology improves. For example, the dose associated with a particular type of x-ray is decreasing as more sensitive films permit use of a smaller x-ray dosage.
© 2002 by Wm. Robert Johnston.
Last modified 25 June 2002.
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