Particles light attenuation

If a light beam falls on an assembly of macroscopic particles the attenuation is given by ... 

Particle light-absorption coefficient Absorption photometer Measurement of light attenuation through a filter -h... 

For the past 4 years, in connection with multidisciplinary studies of remote sensing, we have measured the spectra of light attenuation and fluorescence of particulate matter collected from the world s oceans (5). The number of fluorescent cells for many of the open ocean areas is so low that technical problems quickly occurred in the attempt to obtain monochromatic spectra of light emission and absorption. Furthermore, when the cells are placed in cuvettes they tend to settle out therefore, spurious results are obtained. To overcome these problems we elected to concentrate the cellular particles on membrane filters, which in turn were mounted in the light path of a conventional spectrofluorometer. (For details of this method see Reference 1.)... 

The entire EM spectrum range, from microwaves to y-rays can be used as the optical probe to measure solids concentration and particle velocity. Light attenuation/scattering methods have long been used to determine solids concentration. The theoretical basis of the methods is described by the Lambert-Beer law... 

Some instruments monitor the concentration of particles in the beam by means of an obscuration detector located at the focal point of the lens. If no particles are present in the beam, all the light falls on the obscuration detector. As soon as particles enter the beam, they hIcKk some of the light and scatter light onto the elements of the detector array. The fraction of the light attenuated by scattering, absorption, or both is related to the concentration of particles in the beam (see Section 34D). 

Figure 12.1 Laser light attenuation during precipitation of titanium oxyhydroxide particles in the absence (a) and presence (b) of gravity. The Ti(iPro)< concentration was 2 mmol, and the stirring rate 500 r.p.m (Heimann, 1990).

The effect of particle shape on particle size distribution was investigated by Naito et al. (1998) with commercial particle size analyzers based on five different measuring principles electrical sensing zone, laser diffraction and scattering, x-ray sedimentation, photosedimentation, and light attenuation. The particles used are blocky aluminum oxide and barium titanate particles, flaky boron nitride particles, and rodlike silicon whisker ceramic powders. Altogether, four commer-... 

Once the size distribution is obtained, from light attenuation the sample concentration, expressed as a volume percentage of particles can be estimated at least in the Fraunhofer diffraction regime ... 

Qg is defined (Eq. 16.8) in the same way as the combined single-filter efficiency, given in Eq. 9.14. Also, Eqs. 16.7 and 16.9 are analogous to Eq. 9.19 for filters. Both relate macroscopic phenomena—light attenuation and filter penetration—to microscopic-scale particle properties, Qg and respectively. 

Like e, t is the product of two contributions the concentration N/V of the centers responsible for the effect and the contribution per particle to the attenuation. It may help us to become oriented with the latter to think of the scattering centers as opaque spheres of radius R. These project opaque cross sections of area ttR in the light path. The actual cross section is then multiplied by the scattering efficiency factor optical cross... 

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