Background Radiation

background radiation [′bak‚grau̇nd ‚rād·ē′ā·shən]

(nucleonics)

The radiation in humans' natural environment, including cosmic rays and radiation from the naturally radioactive elements. Also known as natural radiation.

(physics)

Radiation which is due to sources other than the source of interest in a measurement of radiation and which is detected by the measuring apparatus.

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Background Radiation 

(also natural radiation, natural background radiation), the ionizing radiation from cosmic rays and naturally occurring radionuclides. Cosmic rays are streams of high-energy particles that enter the earth’s atmosphere from outer space. Naturally occurring radionuclides, which belong to the group of highly dispersed elements, are always present in the environment (seeRADIOACTIVITY OF ROCKS, RADIOACTIVITY OF WATER, and RADIOACTIVITY IN THE ATMOSPHERE) and in plants and animals. All organisms are subjected to background radiation; the average annual doses to which humans are subjected are given in Table 1.

Depending on the height above sea level and the quantity of radionuclides in the environment, the background radiation varies within wide limits. In areas with a high concentration of radionuclides, the level can exceed 1,000 millirads per year (mrad/yr). Life appeared and developed on earth under conditions that included ionizing radiation. The biological effect of background radiation, however, has not yet been definitively established. It is believed that the radiation plays a part in some mutations, that is, changes in heredity, in animals and plants.

Table 1. Annual dose of background radiation absorbed by humans (in mrad)
Source	Sex cells	Lungs	Bony tissue	Bone marrow
External radiation
Cosmic rays ...............	28.35	31.35	28.35	28.35
Radionuclides in the environment ...............	44	32	44	44
Internal radiation
3H ...............	0.001	0.001	0.001	0.001
14C ...............	0.7	0.6	0.8	0.7
40Ka ...............	19	17	15	15
87Rb ...............	0.3	0.4	0.6	0.6
210Po ...............	0.6	0.3	1.6	0.3
220Rn ...............	0.003	5	0.05	0.05
222Rn ...............	0.07	40	0.08	0.08
226Ra ...............	0.02	0.03	0.6	0.1
228Ra ...............	0.03	0.06	0.8	0.1
238U ...............	0.03	0.04	0.3	0.06
Overall average ...............	93	130	92	89
Contribution of alpha particles and neutrons (percent) ...............	1.2	36	4.1	1.2

Nuclear explosions and the discharge into the environment of wastes from nuclear power plants and certain other enterprises using radioactive materials have raised the level of background radiation. Annual doses from global radioactive fallout have ranged up to tens of millirads. For the most part, these doses are determined by measuring the quantity of the artificial radionuclides ⁹⁰Sr and ¹³⁷Cs entering the body. In regions receiving local fallout, the doses of external and internal radiation are higher. Here, an important part is played by short-lived isotopes of fission products (¹³¹J, ⁸⁹Sr, ¹⁴⁰Ba). An increase in background radiation can lead to a buildup of harmful mutations in humans and other organisms.

REFERENCES

Sivintsev, Iu. V. Fonovoe obluchenie chelovecheskogo organismo. Moscow, 1960.
Belousova, I. M., and Iu. M. Shtukkenberg. Estestvennaia radioaktivnost’. Moscow, 1961.
Moiseev, A. A., and V. I. Ivanov. Spravochnik po dozimetrii i radiatsionnoi gigiene, 2nd ed. Moscow, 1974.
Ionizing Radiation: Levels and Effects. A Report of the United Nations Scientific Committee on the Effects of Atomic Radiation to the General Assembly (with annexes), vol. 1. New York, 1972.

I. IA. VASILENKO