Background radiation

—the type of ionizing radiation to which a person is exposed from natural sources such as cosmic radiation originating in space, or terrestrial radiation due to naturally occurring radionuclides in the soil or air, or radiation from natural radionuclides incorporated in the makeup of the body.

Becquerel (Bq)

—the special name for the unit of radioactivity equal to the number of disintegrations per second (s−1). The older special name for a different unit of activity was the Curie (Ci), which was equal to 3.7×1010 disintegrations per second; the becquerel introduced with the system international (SI) in 1981 is equal to 1 disintegration per second. Thus, 1 Ci is equal to 3.7×1010 Bq.


—a series of National Academy of Sciences’ studies conducted by committees on the biological effects of ionizing radiations (BEIR VII is the current study).


—a general category of tumors that does not invade surrounding tissue. Benign tumors are characterized by slow growth through expansion. Such tumors are usually not referred to as cancer.

Beta particle

—an electron (positive or negative) emitted during decay of some isotopes. Beta particles have a short range in air (less than a few meters) and even shorter range in more dense material (less than a few mm in tissue). Beta-emitting isotopes (e.g. strontium-90) deposited on the skin in large amounts can cause skin burns and other more serious effects. Many of the radioactive isotopes found in fallout are beta emitters.


—Centers for Disease Control and Prevention (


—a beta-particle and gamma-ray emitting isotope of cesium. Cesium-137 is a major long-term pollutant of fallout from nuclear testing. It has a physical half-life of 30 years.

Chain reaction

—a reaction where fissile atoms (e.g., atoms of uranium-235) absorb neutrons, then split, releasing energy and more neutrons, which in turn cause additional atom splitting and neutron releases so that the process continues. Nuclear weapons tests that were conducted around the world were based on uncontrolled chain reactions. Fission fragments arising from the atom splitting are radioactive and appear in fallout.

CI (confidence interval)

—a range about a parameter estimated in a trial that, in some predetermined proportion of trials, will include the true value of that parameter. Commonly, this proportion is selected to be 67, 90 or 95%.

Collective dose

—see collective effective dose.

Collective effective dose

—quantity obtained by multiplying the average effective dose by the number of people exposed to a given source of ionizing radiation. It is usually expressed in man sievert (man Sv).

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