1. A type of emission from radioactive substances, consisting of electromagnetic radiation of great penetrating power and of wavelengths lying beyond the region of the shortest X-rays.
2. A high-energy photon, especially as emitted by a nucleus in a transition between two energy levels.

An altimeter, used at altitudes under several hundred feet, that measures the photon back-scatter from the earth resulting from the transmission of photons to earth from a cobalt-60 gamma source.

The study of gamma rays from extraterrestrial sources, especially gamma-ray bursts.

Gamma-ray astronomy is the study of astronomical objects by analysis of the most energetic electromagnetic radiation they emit.

Gamma rays are shorter in wavelength and hence more energetic than X-rays, but much harder to detect and to pinpoint.

X-rays and some gamma rays are produced throughout the universe by the same catastrophic astrophysical events; such as, supernovas and black holes, and gamma-ray astronomy can be considered an extension of X-ray astronomy to the extreme shortwave end of the spectrum.

Intense blasts of soft gamma rays of unknown origin, which range in duration from a tenth of a second to tens of seconds and occur several times a year from sources widely distributed over the sky.

An instrument used on ships to identify and measure abnormal concentrations of gamma rays in the oceans.

A level indicator in which the rising level of the liquid or other material reduces the amount of radiation passing from a gamma-ray source through the container to a Geiger counter or other radiation detector.

A gamma-ray counter built into a watertight case small enough to be lowered into a borehole.

A quantity of radioactive material that emits gamma radiation and is in a form that is convenient for radiology.

Measurement of gamma-ray intensity versus depth down a well bore.

Used to identify rock strata, their positions, and their thicknesses.