Minor amounts of radioactivity due not to abnormal amounts of radioactive minerals nearby, but to cosmic rays and minor residual radioactivity in the vicinity.

Celestial emission towards the direction of the source. The contributions are: Zodiacal Light, diffuse galactic emission and local diffuse emission in the vicinity of the source.

Natural radiation caused by sun exposure, cosmic rays from space, and radioactive elements found in the earth's crust. Radon, which emanates from the ground, is an example of natural radiation. Cosmic rays include energetic protons, electrons, gamma rays, and x-rays. The primary radioactive elements found in the earth's crust are uranium, thorium, and potassium, and their radioactive derivatives.

Radiation from: (i). Naturally occurring radioactive materials which have not been technologically enhanced; (ii). Cosmic sources; (iii). Global fallout as it exists in the environment (such as from the testing of nuclear explosive devices); (iv). Radon and its progeny in concentrations or levels existing in buildings or the environment which have not been elevated as a result of current or prior activities; and (v). Consumer products containing nominal amounts of radioactive material or producing nominal amounts of radiation.

The “normal” response in the geophysical data – that response observed over most of the survey area. Anomalies are usually measured relative to the background. In airborne gamma-ray spectrometric surveys the term defines the cosmic, radon, and aircraft responses in the absence of a signal from the ground.