Scintillation counter An instrument

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. 

Scintillometer sin-t°l- Ia-ms-t3r n [L scintilla + ISV -0- + -meter] (1877) (scintillation counter) An instrument used to detect the presence of and measure the concentration of beta-emitting radioactive isotopes. When the emitted beta particle is intercepted by a molecule of the scintillant material in solution, a tiny flash of light is given off By counting the flashes over a period of hours one obtains an estimate of concentration of the known beta emitter. 

Scattering on the Triple-Axis-Diffractometer [1,2] at the HASYLAB high-energy beamline BW5 is performed in the horizontal plane using an Eulerian cradle as sample stage and a germanium solid-state detector. The beam is monochromatized by a singlecrystal monochromator (e.g. Si 111, FWHM 5.8 ), focused by various slit systems (Huber, Riso) and iron collimators and monitorized by a scintillation counter. The instrument is controlled by a p-VAX computer via CAMAC. 

The radioactivity in urine, bile, plasma, HPLC fractions, and extracts is determined by mixing aliquots of the samples with a scintillation cocktail (e.g., Ecolite cocktail) (5 or 15 mL) and counting with LSC (e.g., Packard 2250CA Tri-Carb Liquid Scintillation counter, Packard Instrument Company, Meriden, CT) for 5-10 min. Radioactivity in feces, blood, and tissues is usually determined by combustion of aliquots by an oxidizer followed by LSC. Another method to determine total radioactivity is to digest the aliquots of feces,... 

Oatley and a succession of brilliant students, collaborating with others at the Cavendish Laboratory, by degrees developed an effective instrument a key component was an efficient plastic scintillation counter for the image-forming... 

Radioactivity of uranium can be measured by alpha counters. The metal is digested in nitric acid. Alpha activity is measured by a counting instrument, such as an alpha scintillation counter or gas-flow proportional counter. Uranium may be separated from the other radioactive substances by radiochemical methods. The metal or its compound(s) is first dissolved. Uranium is coprecipitated with ferric hydroxide. Precipitate is dissolved in an acid and the solution passed through an anion exchange column. Uranium is eluted with dilute hydrochloric acid. The solution is evaporated to near dryness. Uranium is converted to its nitrate and alpha activity is counted. Alternatively, uranium is separated and electrodeposited onto a stainless steel disk and alpha particles counted by alpha pulse height analysis using a silicon surface barrier detector, a semiconductor particle-type 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 internal standard ratio method for quench correction is tedious and time-consuming and it destroys the sample, so it is not an ideal method. Scintillation counters are equipped with a standard radiation source inside the instrument but outside the scintillation solution. The radiation source, usually a gamma emitter, is mechanically moved into a position next to the vial containing the sample, and the combined system of standard and sample is counted. Gamma rays from the standard excite solvent molecules in the sample, and the scintillation process occurs as previously described. However, the instrument is adjusted to register only scintillations due to y particle collisions with solvent molecules. This method for quench correction, called the external standard method, is fast and precise. 

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... 

The final measurement can contribute considerably to imprecision and for optical immunoassays is instrument-related. For radioimmunoassays, considerable improvements in both time and precision may be made by employing y-labelled drugs and counting in a 16-head y-counter. Scintillation counters have an accuracy of measurement which is approximately the square root of the total number of counts, e.g. about 1% counting error when measuring 10000 counts. 

This instrument was developed as a centrifugal version of the Allen and Svarovsky s [13] x-ray gravitational sedimentoineter in order to reduce the analysis time and measure down to smaller sizes [14,1.5]. fhe x-rays are generated by an air cooled low power x-ray tube and, after passing through the suspension, they are detected by a scintillation counter. The signal 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... 

Nephelometric and turbidimetric methods (see Chapter 3) are performed on most current automated analytical systems, although most nephelometric assays are performed on dedicated instruments. RID requires no instrumentation other than pipettes, although some type of illuminated plate reader is advantageous. RIA requires radiation scintillation counters and an automated pipetting station. 

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