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Light Scattering Method And Apparatus For The Chemical Characterization Of Particulate Matter
3,901,602 issued 8/26/75
Inventors: Gravatt, Claude C.

Full Patent Text Including Drawings

Abstract

A light scattering method and apparatus for chemically identifying individual particles of matter or multiple particles of matter, such as are found in aerosols, without collecting and chemically analyzing the material. In the case of single particle analysis, plane-polarized light is impinged on the particle and the intensity of the light scattered into the plane of polarization over a specified angular range is measured. The intensity is related to the particle's coefficient of absorption and its size. In multiple particle analysis, the intensity of the light scattered into a plane perpendicular to the plane of polarization is also measured to determine the total number of particles of matter. This information may be used to normalize the intensity measurement of the first scattered light beam. A smoke detector is presented as an apparatus embodying the multiple particle analysis technique whereby fire-produced aerosols may be detected without interference from non-fire-produced aerosols of similar density.

Claims

What is claimed is:
1. A method of determining the absorption coefficients of individual particles suspended in a fluid medium, comprising:
impinging substantially plane-polarized light on an individual particle; and
measuring the intensity of the light scattered by the particle into a divergent beam lying substantially in the plane of polarization of the impinging light and within an angular range from about 30.degree. to about 90.degree. with respect to the forward direction of the impinging light.
2. The method set forth in claim 1 and further including measuring the size of the individual particle.
3. The method set forth in claim 1, wherein said angular range extends from about 40.degree. to about 70.degree. with respect to the forward direction of said impinging light.
4. A method of determining the absorption coefficients of multiple particles suspended in a fluid medium, comprising:
impinging substantially plane-polarized light on a stream of said particles;
measuring the intensity of the light scattered by said particles into a first divergent beam lying substantially in the plane of polarization of the impinging light and within an angular range from about 30.degree. to about 90.degree. with respect to the forward direction of said impinging light; and
measuring the intensity of the light scattered by said particles into a second divergent beam the intensity of which is related to the total number of particles.
5. The method set forth in claim 4 and further including determining the ratio of the intensity of said first divergent beam to the intensity of said second divergent beam.
6. Apparatus responsive to the absorption coefficients of particles suspended in a fluid medium, comprising:
a light scattering cell;
means for projecting a beam of substantially collimated plane-polarized light through said cell;
means for flowing a stream of substantially widely spaced individual particles in said medium through said cell;
first means for collecting the rays scattered from said particles substantially into the plane of polarization of the projected beam and within an angular range from about 30.degree. to about 90.degree. with respect to the forward direction of said projected beam; and
first means for measuring the intensity of said rays collected by said first collecting means.
7. Apparatus as set forth in claim 6 and further including means for measuring the sizes of said individual particles.
8. Apparatus as set forth in claim 6, wherein said angular range extends from about 40.degree. to about 70.degree. with respect to the forward direction of said projected beam.
9. Apparatus as set forth in claim 6, wherein said flowing means is adapted to flow a stream of substantially closely spaced multiple particles through said cell; and
second means for collecting the rays scattered from said particles into a beam the intensity of which is related to the total number of particles; and
second means for measuring the intensity of said rays collected by said second collecting means.
10. Apparatus as set forth in claim 9 and further including means for determining the ratio of said first measured intensity to said second measured intensity.