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Encyclopedia > Radioisotopic labelling

Radioisotopic labeling is a technique for tracking the passage of a sample of substance through a system. The substance is "labelled" by including radionuclides in its chemical composition. When these decay, their presence can be determined by detecting the radiation they emit. Radioisotopic labelling is a special case of isotopic labeling. Atoms of chemical elements may have many isotopes (different forms) with different atomic numbers and different atomic weights. ... Radioactive decay is the set of various processes by which unstable atomic nuclei (nuclides) emit subatomic particles (radiation). ... Particle radiation is the radiation of energy by means of small fast-moving particles that have energy and mass. ... Isotopic labeling is a technique for tracking the passage of a sample of substance through a system. ...

For these purposes, a particularly useful type of radioactive decay is positron emission. When a positron collides with an electron, it releases two high-energy photons traveling in opposite directions. If the positron is produced within a solid object, it is likely to do this before travelling more than a millimetre. If both of these photons can be detected, the location of the decay event can be determined very precisely. Positron emission is a type of beta decay, sometimes referred to as beta plus (β+). In beta plus decay, a proton is converted to a neutron via the weak nuclear force and a beta plus particle (a positron) and a neutrino are emitted. ... In physics, the photon (from Greek φως phos, meaning light) is the quantum of the electromagnetic field, for instance light. ... A millimetre (American spelling: millimeter, symbol mm) is an SI unit of length that is equal to one thousandth of a metre. ...

Strictly speaking, radiosotopic labelling includes only cases where radioactivity is artificially introduced by experimenters, but some natural phenomena allow similar analysis to be performed. In particular, radiometric dating uses a closely related principle. Radiometric dating is a technique used to date materials based on a knowledge of the decay rates of naturally occurring isotopes, and the current abundances. ...



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