USGS-GD-Scientific Capabilities - GRAIN SIZE ANALYZER Technique




The laser particle size analyzer employs low-angle light scattering based on Mie theory; light is produced from a neon-helium laser source. The laser PSA is a unified optical system that uses a single technique for the full range of particle sizes to be analyzed. The analyzer can determine a full range of particle sizes in as little as quarter-phi increments from as small as 0.5 microns to nearly 4000 microns, or from very fine clay to small pebbles. The small container accessory of the laser permits analysis of samples as small as 0.1 g in weight if they are relatively fine grained. Any type of sediment can be analyzed, but samples need to be pre-treated to remove flocculating agents such as cements, organic matter, etc., to obtain an accurate reading of the grain size distribution.

Prior to the advent of laser-diffraction technology, the analysis of particle-size distribution was a labor intensive, time-consuming process that required the services of an experienced, skilled laboratory technician over several days. The laser PSA will do a complete analysis in seconds (typically less than 30 seconds per sample). Time is required to remove cementing and flocculating agents prior to laser analysis. Traditional particle-size analysis combined two or more techniques (sieving and pipetting, for example) to obtain a full range of grain size, and typically the most detailed analyses were at one-phi intervals.


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