1. Field of the Invention
The present invention relates to a device for determining the histogram of a particle-size distribution for products or substances composed of particles, grains or discrete cells and, more especially, to such a device wherein a histogram is provided by analyzing a diffraction spectrum of the substance in a coherent optical system.
The device of the invention permits, in particular, a haematological analysis of blood smears or blood particles in liquid flow. It may also be employed in the granulometric study of industrial powders.
2. Description of the Prior Art
The method of analysing powders by diffraction in coherent optical systems was introduced by N. L. Anderson and R. E. Beissner in an article entitled "Counting and Classifying Small Objects by Far-Field Light Scattering", Applied Physics, July, 1971, Volume 10, No. 7, pages 1503-1508. This method provides an overall analysis of the sample, giving quick results with sound statistical validity. The principle thereof is as follows: the sample (powder, blood smear, cells in a liquid medium, etc) is illuminated by a laser. By taking measurements from the diffraction spectrum, the characteristics of the population under examination may be deduced.
Marcel Bessis and Narla Mohandas, Transactions of the Academy of Sciences of Paris, June 17, 1974, Volume 278, pages 3263-3265, and April 26, 1976, Volume 282, pages 1567-1570, were the first to employ analysis by diffraction of biological samples, with a rather particular application in mind: namely, the study of cell deformability.
Two pieces of equipment for granulometric analysis by diffraction are on the market: Compagnie Industrielle des Lasers, a French Company of 91460 Marcoussis, France, uses a laser granulometer for the study of powders, by responding to 8 measurement points on the histogram, and Leeds and Northrup Company, North Wales, PA 19454, makes a device referred to as Microtrac which responds to 13 measurement points on the histogram.
The foregoing systems and devices process a predetermined number of discrete measurements at a limited number of measurement points. Although this is suitable for industrial powders, the use of a limited number of measurement points is not usually suitable for biomedical applications where a greater resolution in the histogram is called for.
The objective of the invention is to provide a continuous histogram of the distribution of particle sizes or, at least a very high number, a thousand or more, of points of this histogram.