Table 7: Background Radiation in Denver:
Average Annual Dose Equivalent of Ionizing Radiation and Risk

Source
Annual Effective Dose Equivalent (mSv/yr)(1)
Annual Risk per million people (2) (cancer deaths attributable to these sources)
Lifetime Risk per million people (3) (cancer deaths attributable to these sources)
Natural
Radon
10.4
310
22,000
Cosmic
0.50
40
2800
Terrestrial
0.46
37
2600
Internal
0.39
31
2200
sub-total
11.8
420
deaths per million
30,000
deaths per million
Artificial
Medical
a) x-ray diagnosis
0.39
31
2200
b) Nuclear medicine
0.14
11
770
Consumer products
0.1
8
560
sub-total
0.6
50
deaths per million
3500
deaths per million
TOTAL
12.4
470
deaths per million
33,000
deaths per million
  1. Effective dose equivalent from Health Effects of Exposure to Low Levels of Ionizing Radiation, BEIR V, National Research Council, Washington DC, 1990. p.18. Based on data from the National Council on Radiation Protection and Measurements, Ionizing Radiation Exposures of the Population of the United States, Report No. 93, Washington DC, 1987, except for radon, cosmic and terrestrial radiation. Radon effective dose in that report was calculated based on an average of 1.1 pCi/L; it is scaled above to an indoor average of 5.7 pCi/L for Denver County. Cosmic and terrestrial radiation doses which are from "What's your annual radiation dose?" . Cosmic radiation consists of both the energetic protons, alpha particles and electrons that strike the atmosphere and the secondary particles they generate as they pass through the air. Terrestrial radiation is predominantly gamma radiation received from the radioactive elements in rocks and soil. This exposure is related to the local geology and composition of the soil, but on average consists of gamma radiation from airborne radon (and its daughters) and potassium 40 and thorium 232(and its daughters) in soil. Medical radiation includes exposure from diagnostic x-rays and nuclear medicine. Internal radiation is from natural radionuclides deposited within the body which are breathed, or ingested with food and water. Radiation from consumer products includes radioactive elements in building materials and airport inspection systems. Everyone in the population is exposed to natural radiation, while exposure to artificial radiation varies from person to person.
  2. Annual risk is lifetime risk divided by a 70 year lifespan.
  3. Except for radon, lifetime risk is calculated from an average of 560 deaths per 100,000 people with a continuous lifetime (70 year) exposure to 1 mSv/year. Table 4-2 in Health Effects of Exposure to Low Levels of Ionizing Radiation, BEIR V, National Research Council, Washington DC, 1990. p.172. Lifetime risk from indoor radon exposure was calculated as in Table 3.

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