Calculations of Light Scattering Measurements Predicting Sensitivity of Depolarization to Shape Changes of Spores and Bacteria
Final rept. Mar 2005-Nov 2007
MASSACHUSETTS UNIV LOWELL
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This report presents calculations to explore the use of depolarization of scattered light as a discriminator of biological particles in an aerosol. The discrete dipole approximation was used to model appropriate shapes of several different types of particles. To model an ensemble of spores, we used experimental parameters appropriate to Bacillus cereus. For this case, two different but related assumptions for particle shapes are shown to give different and distinguishable graphs for the depolarization, D, as a function of wavelength and scattering angle. The use of two different length distributions to simulate scattering from two different strains of Escherichia coli gave rise to distinguishable graphs for D for the two strains. Here, the same shape hemispherically-capped cylinder as well as the same value for other parameters i.e., width and refractive index was assumed for the two strains. In the preceding calculations, we averaged over random orientations and size distributions based on experimental measurements for a real aerosol. The calculated results predict that D would provide some identification of aerosols made up largely of single biological particles. Calculations were also performed for small clusters made up of several spherical spores.