Scintillation counter An instrument that

Scintillation counter an instrument that measures radioactive decay by sensing the flashes of light produced in a substance by the radiation. (21.4)... 

Scintillation counter an instrument that measures the rate of radioactive decay by sensing flashes of light that the radiation produces in a detector. 

For general purpose tracer work, however, and particularly in polymer chemistry, the liquid scintillation counter surpasses all other instruments in its sensitivity and adaptability. There is no question on the author s mind that at the present time such an instrument would be the first choice, particularly where tritium, carbon-14 or sulphur-35 were involved. Samples for assay are dissolved in a phosphor whose major solvent usually consists of toluene, toluene-alcohol, or dioxan. Many polymers and low molecular weight compounds are readily soluble in these solvents. Prospective users should not be deterred by alleged complications due to "variable quench effects" as these effects are readily corrected for via internal or external standards or the channels ratio method (7, 46, 91). Dilution quench corrections, though valid, are tedious and unnecessary. Where samples are insoluble in phosphor they may be suspended (e.g. as gels or as paper cut from chromatograms, etc.) or they can be burnt and the combustion products absorbed in a suitable phosphor solution. A modification of the Schoniger flask combustion technique is particularly suitable for this purpose (43—45). 

The channels ratio method makes use of existing counts within the sample vial. This method is suitable when large numbers of counts are present, but it becomes very time consuming with samples containing few counts, because a long time is required to accumulate sufficient counts for statistical accuracy. Most modern scintillation counters therefore employ an automatic external standardization system of quench analysis to avoid the time required for the internal channels ratio method. This method utilizes a specially selected external y radiation source carried in a lead-shielded chamber that is buried in the instrument. Before the regular counting of the sample, the external standard is... 

Like most measuring instruments, the scintillation counter is not 100% efficient. The most sophisticated instruments presently available possess an efficiency near 60 and 90% for and " C, respectively. It will be recalled from earlier remarks that... 

Substances that are electronically excited by radiation can also be used to detect and measure radiation. For example, some substances excited by radiation give off light as electrons return to their lower-energy states. These substances are called phosphors. Different substances respond to different particles. Zinc sulfide, for example, responds to alpha particles. An instrument called a scintillation counter is used to detect and measure radiation, based on the tiny flashes of light produced when radiation strikes a suitable phosphor. The flashes of light are magnified electronically and counted to measure the amount of radiation. 

Early X-ray equipment used photographic emulsions for detection and recording of radiation. For convenience, speed, and accuracy, however, modern instruments arc generally equipped with transducers that convert radiant energy into an electrical signal. Three types of transducers are used gas-filled transducers, scintillation counters, and semiconductor transducers. Before considering the function of each of these de-... 

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