Fundamentals of Liquid Scintillation Counting

Most research applications of radioisotopes require an eventual quantitation of the isotope, which is done by measuring the intensity of radiation emitted. Common nomenclature expresses this intensity as disintegrations per minute (DPM). The becquerel (Bq) is the SI unit for radiation, corresponding to 60 DPM (one disintegration per second). The curie, an earlier and still…

Another commonly encountered artifact is chemiluminescence. This is caused by any chemical reaction which generates an excited product molecule, which decays to emit light. These reactions generate only a single photon, which may be quenched, or may reach the counter to register as a low energy emission event. Such reactions can generate 105-106 cpm, skewing…

Living creatures contain both hydrophobic and hydrophilic compounds, any of which may be labeled during the course of a radioactive experiment. As discussed in earlier sections, the best solvents for scintillation counting are the aromatic organics, such as toluene and xylene. Hydrophobic compounds can be counted directly in such solvents, but hydrophilic materials, which include…

While the effectiveness of a scintillation cocktail may be expressed a number of ways, it is most often given as the percentage of emission events that produce a detectable pulse of photons, referred to as the counting efficiency. In other words, one way to express the counting efficiency is to take the ratio of the…

A beta particle, passing through a scintillation cocktail, leaves a trail of energized solvent molecules. These excited solvent molecules transfer their energy to scintillator molecules, which give off light. Each scintillator molecule gives off only one photon on activation, (and the wavelength of that photon is characteristic of the scintillator, not the ß-particle), but multiple…

By eliminating the combustion steps needed for gas phase analysis, the introduction of liquid scintillation counting (LSC) reduced the time required to analyze radioactive samples from hours to minutes. For low energy (“soft”) β emitters, LSC offers unmatched convenience and sensitivity. LSC detects radioactivity via the same type of light emission events which are used…