alpha particle:

An energetic nucleus of a helium atom, consisting of two protons and two neutrons, that is emitted spontaneously from nuclei in decay of some radionuclides; also called alpha radiation and sometimes shortened to alpha (for example, alpha-emitting radionuclide). Alpha particles are weakly penetrating and can be stopped by a sheet of paper or the outer dead layer of skin.

atmospheric testing:

Detonation of nuclear weapons or devices in the atmosphere or close to the earth’s surface as part of the nuclear-weapons testing program.


The smallest particle of a chemical element that cannot be divided or broken up by chemical means. An atom consists of a central nucleus of protons and neutrons and orbital electrons surrounding the nucleus.

atomic bomb:

A nuclear weapon that relies on fission only, in contrast to a thermonuclear (“hydrogen”) bomb that uses fission and fusion.

atomic nucleus:

The dense core of an atom, composed of protons and neutrons.

atomic veteran:

A person who, while serving as a member of the armed forces, was a participant at one or more atmospheric nuclear-weapons tests, served in occupation forces in Hiroshima or Nagasaki, Japan, or was a prisoner of war in Japan at the time of the bombings of Hiroshima and Nagasaki.


The reduction in intensities of radiation in passing through matter by a combination of scattering and other interactions with electrons and atomic nuclei.

background radiation:

Ionizing radiation that occurs naturally in the environment including: cosmic radiation; radiation emitted by naturally occurring radionuclides in air, water, soil, and rock; radiation emitted by naturally occurring radionuclides in tissues of humans and other organisms; and radiation emitted by human-made materials containing incidental amounts of naturally occurring radionuclides (such as building materials). Background radiation may also include radiation emitted by residual fallout from nuclear-weapons tests that has been dispersed throughout the world. The average annual effective dose due to natural background radiation in the United States is about 0.1 rem, excluding the dose due to indoor radon, and the average annual effective dose due to indoor radon is about 0.2 rem.

badged dose:

An estimate of a person’s external radiation dose, specifically the deep equivalent dose from external exposure to photons, as derived from readings of exposure by one or more film badges assigned to the person.

basal cells:

Cells in the epidermis that give rise to more specialized cells and act as stem cells.

basal cell carcinoma:

A malignant growth originating from basal cells that is most common in fair-skinned or sun-exposed areas; the most common form of skin cancer.


The special name for the SI unit of activity; 1 Bq = 1 s−1.

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