An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

Possessing, or pertaining to, → radioactivity.

→ radio + → active.

Determining the age of an object from the → radioactive decay of its constituting material. The technique consists of comparing the → abundance ratio of a → radioactive isotope to its → decay product. This will yield the number of half-lives that have occurred since the sample was formed. More specifically, if an object is made up of 50 % decay product then it has gone through 1 → half-life. 75% decay product equals 2 half-lives, 87.5% decay product equals 3 half-lives, 93.76% decay product equals 4 half-lives, and so on. For example, the decay product of → uranium-238 (²³⁸U) is → lead-206 (²⁰⁶Pb). The half-life of ²³⁸U is 4.5 billion years. Hence, if the sample has gone through two half-lives, it is 9 billion years old. See also: → radiocarbon dating.

→ radioactive; → dating.

Spontaneous emission by a nucleus of photons or particles.

→ radioactive; → decay.

A → nuclide that is radioactive.

→ radioactive; → isotope.

A → nuclide that disintegrates by emitting radiation and transforms into another nuclide. Same as → radionuclide.

→ radioactive; → nuclide.

The radioactive by-products from the operation of a nuclear reactor or from the reprocessing of depleted nuclear fuel. Also known as nuclear waste.

→ radioactive; → waste.

The spontaneous disintegration of certain atomic nuclei, which is accompanied by the emission of either α- or β- particles and/or a γ rays.

→ radio; → activity.

A → radioactive → isotope of → carbon, especially → carbon-14.

→ radio; → carbon

A radioactive dating technique, applied to organic materials, which measures the content of the radioactive isotope of carbon ¹⁴C. The radioactive carbon isotopes created by the impact of cosmic rays with the nitrogen atoms of the atmosphere find their way, via carbon dioxide and photosynthesis, into living material. When an organic material dies it ceases to acquire further ¹⁴C atoms, and its ¹⁴C fraction declines at a fixed exponential rate due to the radioactive decay of ¹⁴C. Comparing the remaining ¹⁴C fraction of a sample to that expected from atmospheric ¹⁴C allows the age of the sample to be estimated.

→ radiocarbon; → dating.

An element, such as uranium, whose isotopes are all radioactive.

→ radio; → element.

The process of producing an image on a sensitive surface by radiation such as X-rays or gamma rays passing through an object.

→ radio + → -graphy.

A synonym for radionuclide.

→ radio; → isotope.

The study and use of radiation and radioactive substances for the treatment of diseases.

→ radio; + → -logy.

The dissociation of molecules by radiation, for example in a reactor core, when the water used for cooling breaks down into hydrogen and oxygen.

From → radio + -lysis a combining form denoting "breaking down, loosening, decomposition," → analysis.

An instrument that measures the intensity of radiant energy.

→ radio; → -meter.

A dating method that uses measurements of certain radioactive isotopes to calculate the ages in years (absolute age) of rocks and minerals.

→ radiometer; → dating.

The detection and measurement of radiant energy, either as separate wavelengths or integrated over a broad wavelength band, and the interaction of radiation with matter in such ways as absorption, reflection, and emission.

→ radio + → -metry.

Tâbeš-sanji, from tâbeš, →radiation, + -sanj→ -metry.

A radioactive → nuclide.

→ radio + → nuclide.

A meteorological instrument that is carried aloft by a balloon to measure and send back information on atmospheric temperature, pressure, and humidity via radio to a ground receiving system.

→ radio + sonde, from Fr. sonde "sounding line."

→ radio; gomâné "a probe, a shaft sunk in order to ascertain the depth of the water when making a subterraneous canal," from Proto-Iranian *vi-mā-, from vi- "apart, away from, out" (cf. Av. vi-; O.Pers. viy- "apart, away;" Skt. vi- "apart, asunder, away, out;" L. vitare "to avoid, turn aside") + mā- "to measure" (cf. O.Pers./Av. mā(y)- "to measure;" Mod.Pers. mâ/mun/mân "measure," as in Pers. terms âzmâ- "to test;" pirâmun "perimeter," âzmun "test, trial," peymân "measuring, agreement," peymâné "a measure; a cup, bowl;" PIE base *me- "to measure;" cf. Skt. mati "measures," matra- "measure;" Gk. metron "measure;" L. metrum).