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radioactive dating any of several methods of determining the age of an artifact, rock, or bone based on the known rate of decay of radioactive isotopes.
radioactivity the emission or amount of emission of energy or subatomic particles by the nuclei of certain unstable isotopes of elements as they decay.
radio astronomy the study of the universe by observation and analysis of extraterrestrial radio waves.
radio beacon a stationary source of radio waves that emits a distinctive signal as a navigational aid for ships and aircraft.
radiobiology the branch of biology concerned with the effects of radiation on living tissue and the use of radioactive tracers in the study of biological processes.
radiocarbon a radioactive isotope of carbon, esp. the isotope that has a nuclear mass of fourteen daltons and is often used in determining the age of various organic materials; carbon 14.
radiochemistry the branch of chemistry dealing with the study of radioactive elements.
radio compass a navigational aid consisting of a radio receiver that determines the transmission direction of incoming radio waves.
radiofrequency any frequency of electromagnetic waves between approximately ten kilohertz and 300 gigahertz, that can be used for radio transmission.
radio galaxy a galaxy that emits a large amount of radio energy.
radiogram a message transmitted using radio signals or wireless telegraph. [2 definitions]
radiograph an image produced by the action of x-rays or other forms of radiation on a photographic film; autoradiogram; radiogram. [2 definitions]
radioisotope an unstable isotope that emits subatomic particles or energy in decaying to a more stable state.
radiolarian any small marine protozoan having an amoebalike body encased in a silica skeleton.
radiology the branch of medicine dealing with the examination of bones and internal organs using imaging techniques such as x-rays, ultrasound, and magnetic resonance. [2 definitions]
radiolucent showing little or no resistance to x-rays or other forms of radiant energy.
radioman one who operates or repairs radio equipment.
radiometer an instrument for measuring radiant energy or transforming radiant energy into mechanical energy, consisting of vertical vanes that absorb more heat on one side than the other, so that they rotate around an axis when irradiated.
radiopaque of a substance, resistant to penetration by radiation such as x-rays or gamma rays.
radiophone a telephone whose sound is transmitted by radio waves; radiotelephone.
radiophoto radiophotograph.