Coincidence errors

Coincidence error, in Geiger counter measurement, 52, 53 Collimation, 110—1 3 Collimator, energy band transmitted by, 116, 118... 

More ambitious attempts at measuring the heterogeneity of the atmospheric aerosol have been undertaken as well. Single-particle analysis by mass spectrometry was demonstrated by Sinha and co-workers (31, 32). In this technique, an aerosol sample is introduced into a vacuum chamber in the form of a particle beam. The particles are injected into a Knudsen cell oven, where they undergo many collisions with the cell wall and are ultimately vaporized and ionized. The ions are then mass-analyzed with a quad-rupole or sector mass spectrometer. So that individual particles can be analyzed, the flux of particles into the Knudsen cell is limited so that coincidence errors are minimized. Ion pulses from individual particles allow the determination of the amount of the species being analyzed in the particular particle. The sensitivity of the technique is limited. For sodium, the detection... 

A coincidence correction can be applied for primary coincidence but it is preferable to use a concentration so low that this effect is negligible. Under this condition, secondary coincidence errors are also reduced. 

Laser diffraction (103) Population measure 0.1-800 Coincidence errors, sampling... 

Eckhardt, D.E., Lee L.D. 1985. A theoretical basis for the analysis of multiversion software subject to coincident errors. In IEEE Transactions on Software Engineering, SE-11 (72), pp.1511-1517. 

Sachweh B, Umhauer H, Ebert F, Biittner H, Friehmelt R (1998) In situ optical particle counter with improved coincidence error correction fin number concentrations up to 10E7 particles cm-3. J Aerosol Sci 29 1075... 

B. H. Kaye and G. G. Clark, Monte Carlo Studies of the Effect of Spatial Coincidence Errors on the Accuracy of the Size Characterization of Respirable Dust. Part. Part. Syst. Charact.. 9 (1992) 83-93. 

With the new equipment it is claimed that both types of errors are eliminated by using overlapping laser beams, producing one double crested beam profile. Each particle then creates a single, continuous signal that has two crests. Particles with only one crest are phantom particles, or with more than two crests are coincident errors and are logged for concentration calculations, but are not used in building the size distribution. The commercial development of aerosol spectrometers is a very active area of research, and one should check for the latest information with the manufacturers of such instruments. 

Place a small covered magnetic stirring har in the flask of precipitate and whilst stirring vigorously pipette duplicate portions of 10, 5, 2, 1, and 0.5 ml of slurry directly onto membrane filters in the Millipore filtration equipment A little water should be put in the filter funnel first and the aliquot of slurry added (rinse the pipette into the funnel) before applying suction. This ensures a more uniform dispersion of precipitate on the membrane filter. Dry the ten separate planchettes and precipitates thus obtained. Count each precipitate, normalize each count to the radioactive standard, and correct for coincidence error, natural background, etc. The counts found for the 10-, 5-, 2-, 1-, and 0.5-ml aliquots are multiplied by... 

Optical particle counters are restricted by coincidence errors to the measurement of aerosols with relatively low number concentrations, usually less than lO /m [lfr /cm ]. Aerosols with higher concentrations must be diluted to this level for unbiased measurement. Coincidence errors arise when two or more particles are in the sensitive volume simultaneously, causing a spurious signal that leads to an underestimation of the particle number concentration and an overestimation of the particle size. The sensitive volume is the region from which signals are generated, defined by the incident and scattered beams and the diameter of the aerosol stream. The ratio of the observed count to the true count N, is given by... 

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