The direction, rate and volume of sediment in transport is measured, primarily. either by radioactive or by fluorescent tracer particles. Tracers are designed to simulate grain-dimensional and mass behavioral properties of traced sediments. Aside from visual-manual methods, impractical with high concentrations, no means has so far been available for the rapid counting and sizing of fluorescent tracer particles. A recently developed Automatic Fuorescent Particle Counter (AFPC) allows automated high speed processing of sand samples, the simultaneous counting of several colors of fluorescent tracer particles in the samples, and a method of sizing individual tracer grains. The instrument is a combination of a mechanical sample handling component, an optical assembly for the simultaneous recognition of certain sets of four colors, and a pulse handling electronics section incorporating threshold decision logic for channeling and tabulating tracer counts. Sand samples are processed at a maximum rate of 52.6 grams per minute (based on a median grain size of 250 microns), or 55,000 particles per second. Four spectrally distinct fluorescent tracers can be counted at a maximum rate of 200 particles per color per second. The high resolution AFPC eliminates one of the most serious problems associated with quantitative sediment transport research using fluorescent tracers, namely the inability of sample analyses to keep in step with the experimental work.

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