Revision 1
March 19, 1998
by Radiation, Science, and Health, Inc.,
Edited by J. Muckerheide

1.2.6
Natural Radiation and Radioactivity

1.2.6.1
External Radioactivity and Radiation Sources

"UNSCEAR reports are considered scientifically authoritative, and are often used by nations in developing their own radiation protection standards. A recent article by two United States representatives to UNSCEAR and other U.S. scientists provides a concise summary of the conclusions of the 1986 and 1988 UNSCEAR reports (Mettler et al. 1990; UNSCEAR 1986, 1988).

"UNSCEAR estimates the annual average effective dose equivalent per person in the world population to be 3 mSv (300 millirem). Most of this (2.4 mSv) comes from natural radiation that has always been in the environment, and 0.4 to 1 mSv is attributable to medical exposures. Other sources contribute less than 0.02 mSv (2 millirem) annually. The worldwide collective effective dose equivalent annually is between 13 and 16 million person-Sv (1.3 to 1.6 billion person rem). Table 2-43 shows the estimated annual effective dose equivalents from natural sources, as given in the 1988 report (UNSCEAR 1988).

Table 2-43. UNSCEAR 1988 annual effective dose equivalents from natural radiation, averaged from the world population (from Mettler et al. 1990, Table 1)

"While many of the natural sources and doses vary among individuals and populations, independent of human activity (such as cosmic rays), some depend strongly on human activities. The most obvious source of natural radiation exposure that depends on human activity is the exposure to radon and thoron and their decay products. The locations of home and building construction, the amounts of ventilation provided, and the types of construction, all affect greatly the amounts of radon and thoron exposure to individuals. The estimated average annual natural radiation effective dose — the world population is seen from Table 2-43, the current (240 mrem) average of 2.4 mSv.

"In the 1988 report, the external estimate from cosmic radiation has been increased by about 0.05 mSv (5 mrem), as a result of taking geographical distribution, as well as altitude distribution, into account. This cosmic ray component of natural exposure, as is well known, can be raised by a factor of two or more above the average of 35.5 millrem shown in Table 2-43 simply as a result of moving to a high altitude such as that in Denver, Colorado."

"In Table 2-44, the total natural background exposure rate is compared with other sources of manmade exposures."

"The Chernobyl accident has been estimated in an appendix of the 1988 UNSCEAR report to produce a collective dose equivalent of 0.6 million personSv (60 million person-rem), mostly in the former Soviet States and Europe. Thirty percent of this collective dose has been delivered in the first year following this 1986 accident, and the remainder will be delivered in tens of years after the accident. This collective dose (in the first year) is about 2 percent of the annual natural background collective dose to the world population.

"The UNSCEAR 1988 report also presents (Table 2, Mettler et al 1990) collective effective doses from nuclear energy generation industries as integrated over 100 years, and over all time, the 24 person-Sv per GW over the next 100 years capacity of 500 GW estimated for the year 2000, would amount to a collective dose of 12,000 person-Sv (1.2 million person-rem), compared to the natural background integrated over 100 years, which would be about 16 million person-Sv (1.6 billion person-rem) per year times 100 years, or 1.6 billion person-Sv (160 billion person-rem) over 100 years.

"Thus, the average annual exposure per person from nuclear power production is shown in Table 2-44 to be only 0.0002 mSv per year (0.02 millirem per year). For comparison, the BEIR V report estimates that, averaged over the United States population, the natural background exposure is 3.0 mSv per year, 2.0 mSv of which is from radon. The annual medical diagnostic exposure is 0.39 mSv, the nuclear medicine exposure is 0. 14 mSv, consumer product exposure is 0. 10 mSv, the nuclear fuel cycle exposure is <0.01 mSv, and occupational exposure is (averaged over the total population) <0.01 Sv. The total of natural and artificial (manmade) exposure in the United States is estimated to be 3.6 mSv (360 millirem) per person (NAS 1990, pp. 18-19)."

Table 2-44. UNSCEAR 1988 estimates of annual average effective dose equivalents from manmade compared to natural sources (from Mettler et al. 1990, Table 3).