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Radiocarbon dating
Radiocarbon dating, also called carbon-14 dating, is a method that determines the age of carbon-bearing materials by measuring their carbon-14 content, usable back about 50,000 years.
Radiochemical analysis
Radiochemical analysis is a family of analytical chemistry methods that detect, quantify, and characterize elements and compounds by measuring radioactivity, spanning neutron activation analysis, isotope dilution, and radioimmunoassay.
Radiochemical separation
Radiochemical separation is a chemical procedure that isolates a radionuclide from its sample matrix and from interfering radionuclides before counting, when radiation detectors alone cannot identify or quantify it reliably.
Radiofluorination
Radiofluorination is the chemical introduction of radioactive fluorine-18 into a molecule, most often to make PET radiotracers; fluorine-18's 109.7-minute half-life makes it well suited to molecular imaging.
Radiolabeled metal–organic frameworks
Radiolabeled metal–organic frameworks are highly porous crystalline materials built from metal ions and organic linkers, carrying a radionuclide for PET or SPECT imaging and cancer therapy.
Radiolarite
Radiolarite is a hard siliceous sedimentary rock made of radiolarian skeletons, the lithified equivalent of radiolarian ooze, and a raw material for prehistoric stone tools.
Radioluminescence
Radioluminescence, also known as radiofluorescence or scintillation, is the light emitted when ionizing radiation excites a material; it underlies radiation detection, tritium exit signs, and radiotherapy dosimetry.
Radiolysis
Radiolysis is the use of ionizing radiation, such as gamma rays, X-rays, or electron beams, to break chemical bonds and decompose or synthesize molecules in gases, liquids, or solids.
Radiometric calibration
Radiometric calibration is the process of relating a radiation sensor's output, such as image pixel values, to physical light quantities like radiance or irradiance, traceable to the SI.
Radiometric dating
Radiometric dating, also called radioactive dating, is a family of techniques that determine the age of rocks and materials by measuring radioactive isotopes and their decay products at known rates.
Radion
The radion is a hypothetical scalar particle appearing in theories with compactified extra dimensions, whose value measures the size of, or separation between branes in, the extra dimension.
Radionuclide
A radionuclide, also known as a radioisotope or radioactive isotope, is an unstable atom that spontaneously decays, emitting radiation such as alpha and beta particles until it becomes stable.
Radionuclide therapy
Radionuclide therapy, also called molecular radiotherapy or radioligand therapy, treats cancer by injecting radioactive substances that accumulate in or bind to tumor cells, a method used since the 1940s.
Radiosonde
A radiosonde, also called a rawinsonde or balloon sonde, is a balloon-borne instrument measuring pressure, temperature, and humidity up to 35 km, invented in 1929 and launched twice daily worldwide.
Radiosurgery
Radiosurgery, also known as stereotactic radiosurgery (SRS), is a non-surgical radiation therapy that delivers precisely targeted, high radiation doses, most often to brain targets, with about 1 mm accuracy.
Radiosynthesis
Radiosynthesis is the chemical synthesis of radiolabeled compounds, incorporating positron-emitting isotopes such as carbon-11 and fluorine-18 into biologically active molecules, most often radiotracers for PET imaging.
Radithor
Radithor was a patent medicine of radium dissolved in distilled water, sold as a cure-all tonic from about 1925 to 1930 by Bailey Radium Laboratories of East Orange, New Jersey.
Radium
Radium (element 88, Ra) is an intensely radioactive alkaline earth metal discovered by the Curies in 1898 and once used in luminous paint and quack health tonics.
Radium Girls
The Radium Girls, also known as radium dial painters, were young women who painted glowing watch dials with radium paint in the 1910s and 1920s and were fatally poisoned.
Radium monofluoride
Radium monofluoride (RaF) is a radioactive diatomic molecule of radium and fluorine, first laser-studied at CERN's ISOLDE facility in 2020 and valued for its sensitivity to physics beyond the Standard Model.
Radium-226
Radium-226 is the longest-lived isotope of radium, with a half-life of 1600 years, once used in luminous watch dials and cancer therapy and still used as a calibration standard.
Radius
A radius is the straight line from the center of a circle to any point on its circumference, equal to half the diameter and denoted r.
Radius of convergence
The radius of convergence, or interval of convergence, of a power series is the number R within which the series converges, equal to the distance to the nearest singularity.
Radius of curvature
The radius of curvature of a curve at a point is the radius of the circle that best approximates the curve there, equal to one over the curvature.
Radius of gyration
The radius of gyration is the distance from an axis at which a body's whole mass, concentrated as a point, would give the same moment of inertia.
Radius of influence
The radius of influence of a pumping well is the maximum distance up to which pumping significantly affects the aquifer, a concept used in wellhead protection and permitting.
Radius of maximum wind
The radius of maximum wind (RMW) is the distance from a tropical cyclone's center to its maximum winds, generally at the inner edge of the eyewall in strong hurricanes.
Radius valley
The radius valley, also known as the radius gap or Fulton gap, is a scarcity of close-in exoplanets between 1.5 and 2.0 Earth radii, first resolved by the California-Kepler Survey in 2017.
Radix
The radix, also called the number base or numeral base, is the count of distinct digits a positional numeral system uses, such as 10 for decimal or 2 for binary.
Radon
Radon, a radioactive noble gas, atomic number 86, forms from decaying radium in soil, accumulates in homes, and causes about 21,000 lung cancer deaths yearly in the US.