SORTING OUT MINERAL-CONTAINING OBJECTS OR PLASTIC OBJECTS

Abstract

A method and a sorting plant for sorting out mineral-containing objects or plastic objects from a single layer material stream is shown. Here it is provided that objects (12) of the material stream are irradiated with stimulating light and the resulting fluorescent light is detected in the form of an image of the fluorescent points, the objects of the material stream are irradiated with object detection light outside the fluorescent light, and the transmitted light after passage between the objects or the reflected light of the objects is detected in the form of an image of the individual objects, an object is then defined as containing at least one specific mineral or one specific plastic if the fluorescent light of said object lies in a predetermined intensity range for at least one predetermined wavelength range, and the so defined objects are separated from other objects of the material stream.

Claims

1. A method for sorting out mineral-containing objects or plastic objects from a single layer material stream, characterized in that objects of the material stream are irradiated with stimulating light, and the resulting fluorescent light is detected in the form of an image of the fluorescent points, the objects of the material stream are irradiated with object detection light outside the fluorescent light, and the transmitted light after passage between objects or the reflected light of the objects is detected in the form of an image of the individual objects, an object is then defined as containing at least a specific mineral or a specific plastic when the fluorescent light of said object lies in a predetermined intensity range for at least one predetermined wavelength range, and objects defined in this way are separated from other objects of the material stream.

2. The method as in claim 1, characterized in that the stimulating light is UV light.

3. The method as in claim 1, characterized in that the stimulating light is visible light.

4. The method as in claim 1, characterized in that the object detection light comprises additional UV light, and/or visible and/or IR light.

5. The method as in claim 1, characterized in that the stimulating light is also used as object detection light.

6. The method as in claim 1, characterized in that the fluorescent light on the one hand and the transmitted or reflected light of the object detection light on the other are detected in the form of a joint image with the same detector.

7. The method as in claim 1, characterized in that the image of an object is divided into a plurality of partial regions and a partial region is defined as containing a specific mineral or a specific plastic when the fluorescent light from said partial region lies in a predetermined wavelength and intensity range.

8. The method as in claim 7, characterized in that an object is defined as containing a specific mineral or a specific plastic if the sum of the partial regions that contain the specific mineral or specific plastic, in a ratio to a reference surface such as the total surface of the image of the object, exceeds a predetermined threshold of the intensity.

9. The method as in claim 1, characterized in that the fluorescent light is measured in an incident light method.

10. The method as in claim 1, characterized in that on the basis of the intensity of the fluorescent light in the predetermined intensity range for objects containing a specific mineral or a specific plastic, a further subdivision of said objects with respect to mineral content or plastic content is carried out.

11. The method as in claim 1, characterized in that the stimulating light and/or the additional light is/are pulsed.

12. A sorting plant for conducting a method as in claim 1, characterized in that it comprises at least a stimulating light source, with which a single layer material stream of objects can be illuminated, a first detector for detection of the fluorescent light generated in the object by the stimulating light source, in the form of an image, a device for creating an image of the individual objects, a device for producing a single layer material stream of objects, with which the material stream can be transported past the stimulating light source, and a device for sorting out, which then defines an object as containing a specific mineral or a specific plastic and separates it from other objects of the material stream if the fluorescent light of said object lies in a predetermined intensity range for a predetermined wavelength range.

13. The sorting plant as in claim 12, characterized in that the device for creating an image of the individual objects comprises the following: a second light source, which can emit UV light and/or visible and/or IR light outside the fluorescent light, and/or a second detector for detection of the transmitted light of the optional second light source or the stimulating light source, after passing between the objects, or for detection of the reflected light of the objects irradiated by the optional second light source or the stimulating light source.

14. The sorting plant as in claim 13, characterized in that the stimulating light source and the first detector are situated on the same side of the material stream.

15. The sorting plant as in claim 13, characterized in that the second detector is a detector for UV light.

16. The sorting plant as in claim 13, characterized in that a second light source that can emit visible and/or IR light is provided.

17. A computer program product, which comprises a program and can be loaded directly into a memory of a central computer of a sorting plant, with program means in order to implement all steps of the method according to claim 1 when the program is implemented by the central computer, where the steps are that the image of the fluorescent points and the image of the individual objects are processed, and that an object is defined as containing at least one specific mineral or one specific plastic when the fluorescent light of said object lies in a predetermined intensity range for at least one predetermined wavelength range, and the so defined objects are caused to be separated from the other objects of the material stream.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0086] The invention will now be explained in more detail by means of schematic drawings that represent embodiment examples of a device according to the invention. In each case, the incident light method is used for the stimulating light, i.e., the stimulating light source and detector for fluorescent radiation are disposed on the same side of the material stream.

[0087] FIG. 1 shows a sorting plant according to the invention using the incident light method for both light sources,

[0088] FIG. 2 shows a sorting plant according to the invention using the incident light method for a UV light source as stimulating light source and the backlight method for the second light source,

[0089] FIG. 3 shows an image of the fluorescent light for a specific arrangement of objects,

[0090] FIG. 4 shows an image of the reflected/transmitted light of the additional light source for the arrangement of the objects in FIG. 3,

[0091] FIG. 5 shows an image of the objects, the fluorescent portions, and their position, thus a superpositioning of FIGS. 3 and 4,

[0092] FIG. 6 shows a variant of a sorting plant according to the invention having an alternative arrangement of the device for separation of the material stream and the sensor components with a pneumatic separation device,

[0093] FIG. 7 shows a diagram representing the intensity of the stimulating light and fluorescent light in dependence on the wavelength.

EMBODIMENTS OF THE INVENTION

[0094] In FIG. 1, a UV light source 3 is built into a first housing 1 for light sources and a second light source 4 is built into a second housing 1 for light sources.

[0095] The UV light source 3 here can emit UVC light in the 200 to 280 nm range, in particular with a maximum intensity at a wavelength of 254 nm. The light intensity at the level of the objects 12 can be 1.0 to 1.5 mW/cm.sup.2. The UV light source 3 can be made in the form of a UVC light, which is also called a UVC fluorescent lamp or UVC fluorescent tube. However, the UV light source 3 here can also emit UVA light in the 330 to 400 nm range, in particular with a maximum intensity at a wavelength of 366 nm. The light intensity at the point of the objects 12 can be, for instance, 1.0 to 1.5 mW/cm.sup.2. The UV light source 3 can be made in the form of a UVA light, which is also called a UVA fluorescent lamp or UVA fluorescent tube. Or, the UV light source 3 can, for instance in the form of a fluorescent lamp or fluorescent tube, emit UVB light in the 280-330 nm range, in particular with a maximum intensity at a wavelength of 312 nm, likewise with a light intensity at the level of the objects 12 of, for instance, 1.0 to 1.5 mW/cm.sup.2.

[0096] Instead of a UV tube, it is also possible to use one or more UV LEDs (a so-called LED line). At any rate, UVA LEDs with a maximum wavelength of about 360 nm are currently available, with which a clearly higher light intensity at the site of the objects 12 of about 5.0 to 8.0 mW/cm.sup.2 can be achieved.

[0097] UVC and UVB LEDs are still very expensive and are obtainable only in limited numbers and with relatively low light intensity.

[0098] The second light source 4 here can emit light in the visible range (400-780 nm wavelength) and/or in the infrared range (780-1100 nm wavelength). If the second light source 4 emits visible light, it should also lie outside the expected fluorescent light that is produced by the UV light source 3. Typically, the fluorescent light can lie in the visible blue range, thus 400-500 nm. The second light source 4 can, for instance, as in this example, be made as a fluorescent lamp (Vis light) with wavelengths in the visible and infrared range of 520-1100 nm. Instead of the lamp (Vis light), it is also possible to use one or more color and/or infrared LEDs (LED line).

[0099] LEDs have a number of advantages over tube lights: [0100] better controllability of the intensity [0101] higher intensity [0102] many different and also narrow wavelength ranges are possible [0103] width of illumination (LED line) or illuminated area freely selectable by the arrangement of a plurality of LEDs [0104] possible to specify an intensity profile

[0105] The disadvantages, at least of LEDs in the UVC range, are the currently high purchase prices and the higher diffusion expenditure by comparison with tube lights.

[0106] The two light sources 3 and 4 could also be disposed in a common housing, but then they must be separated from each other by a light-impermeable separating wall.

[0107] In the example in FIG. 1, a UVC light 3 emits UVC radiation with a maximum intensity that is typically at a wavelength of 254 nm and is built into housing 1 so that the UV light is directed toward the objects 12 by a reflector 5 disposed behind the UVC light 3. The UV light can still pass through a filter, which absorbs a large portion of the light in the visible range emitted by the UVC light 3 and thus sends almost no visible light in the wavelength range of the fluorescent light to the detectors 7 and 8. If, for instance, blue light from the UVC light 3 reached the detector 7 for fluorescent light, it would be detected as fluorescent radiation if it likewise lies in the range of blue light.

[0108] The Vis light emitted by the second light source 4 can likewise pass through a filter, which absorbs emitted light in the UV and fluorescent range (<500 nm).

[0109] The housing 1 of the UVC light 3 consists, at least in the region of the UV light exit, of a quartz glass pane. Quartz glass has very high permeability for UVC light.

[0110] However, a quartz glass pane or panel of appropriately light-permeable materials such as standard glass, Borofloat® glass or Plexiglas can also cover the visible light exit.

[0111] The glass pane 6 serves as a slide for the tested objects 12. In the mounted state of the device according to the invention, it has a tilt of about 25° to the vertical. The objects 12 on it slide downward and in doing so are illuminated by the two light sources 3 and 4. It is important that the materials of the slide and any coverings for the light passage do not themselves fluoresce.

[0112] The spacing between the fluorescent light to be detected and the reflected light to be detected (from the second light source 4) should be as small as possible (preferably, congruent), so that both detectors 7 and 8, the one for fluorescent light and the one for reflected light, can produce an image of the moving objects 12 that matches as closely as possible. The spacing between the central axes of the light beams (represented by a dot-dash line) of the visible/IR light or the UV light, when they exit from the relevant housing 1, is, for instance, 25 mm in this example.

[0113] Both the visible/IR light of the Vis light 4 reflected by the objects 12 and the fluorescent radiation in the blue visible range induced by the UV light pass through a protective glass 11 into the additional housing 2 where, on the one hand, a detector 7 for detection of fluorescent light is accommodated and where, on the other hand, the detector 8 for detection of the reflected light of the second light source 4 is also disposed.

[0114] The protective glass 11 consists of standard glass or Borofloat® glass and protects the inside of housing 2 against dust and UVC radiation.

[0115] The detector 7 for detection of the fluorescent light is sensitive in a wavelength range of 350-1000 nm, and the sensitivity can be narrowed further to the relevant wavelength range through filters. The detector 7 as a rule will be made as a camera. It can be made, for example, as a so-called TDI camera.

[0116] To avoid distortion in the detection of the fluorescent light by another light source in this wavelength range, the second light source 4 should, as far as possible, emit only light outside of said frequency range. In practice it is often the case that even light sources in the yellow or red range, which therefore by definition “emit light in the visible range or IR light outside the wavelength range of the fluorescent light,” still have a blue component in their light, and this component must then possibly be filtered out, as explained above in the case of the filter for the second light source 4.

[0117] For detection of the reflected light from the second light source 4, it is basically sufficient if a detector 8, thus for instance a camera, can provide at least an image of objects in gray shades. From such an image it is then possible to determine the position and shape of the object 12 on the one hand, which is necessary to remove the object from the material stream, optionally by means of connected ejection devices. In addition, it is possible to determine the imaged surface area of the individual object 12, to which the fluorescent regions of the individual object can then be put into a ratio.

[0118] The detector 8, as a rule a camera, is for this reason at least sensitive in the wavelength range in which the second light source 4 emits light. In this example, a so-called RGB camera is used. In this camera an RGB signal is processed, thus the colors red, green, and blue are each transmitted or stored in a separate channel.

[0119] Basically, a highly sensitive detector is needed to detect the fluorescent light, as a rule a camera, where a so-called TDI camera 7 was used in this embodiment example. This camera contains, like the RGB camera, a CCD sensor, but it contains TDI (Time Delay Integration) elements, which are especially sensitive and nevertheless afford good pictures of moving objects.

[0120] Both detectors 7 and 8 have lenses 9 for adjusting the optical properties.

[0121] Both fluorescent light and reflected light go to a beam splitter 10, which reflects blue light, for instance in the 400-500 nm wavelength range, as completely as possible and passes visible light >500 nm (reflected light) as completely as possible. The reflected light beam is directed to the TDI camera 7, while the passed light beam goes to the RBG camera 8.

[0122] The detected data are sent to an analysis and control unit (not shown), which evaluates the two images and assigns the individual objects to the different fractions and controls the ejection units, which put the objects into the appropriate containers.

[0123] In FIG. 2, the incident light method is used only for the UV light source 3, while the backlight method is used for the second light source 4. In contrast to FIG. 1, therefore, the second light source 4 is disposed on the other side of the glass pane 6, and the light of the light source 4 thus serves as background lighting. The design and arrangement of the light sources 3 and 4 and the detectors 7 and 8 otherwise corresponds essentially to that of FIG. 1, but the second light source 4 emits NIR light in the 650-850 nm range and is designed as an LED line, the detector 7 for fluorescent light can detect visible light in the 400-650 nm range, and the detector 8 for the transmitted object detection light can detect red and infrared light in the 650-900 nm range.

[0124] It would also be conceivable to provide two UV light sources 3 with different irradiation angles for better illumination of the objects 12, as is shown in FIG. 6.

[0125] FIGS. 3 and 4 each show two-dimensional images of objects 12, which are, as a rule, generated from one-dimensional image lines. Each detector 7 and 8 registers one-dimensional image lines, thus image lines that run across the direction of travel of the objects 12. These image lines are recorded at a high rate, mostly between 1 and 20 kHz, and are assembled into a two-dimensional image, either in the form of a single image or a continuous film of the material stream.

[0126] FIG. 3 shows a record segment of the fluorescent light image of the material stream, or of specific objects 12 that have moved through the detection region of the detector 7 on the slide 6 at a specific point in time in FIG. 1 or FIG. 2, respectively, thus in the xy plane in the coordinate system indicated in FIG. 1 and FIG. 2. In this case, the x direction corresponds to the direction across the slide 6, and the negative y direction corresponds to the direction of travel of the objects 12. The speed of travel of the objects 12 is between 1 and 2 m/sec. Image lines are continuously recorded and blocked by detector 7 at a clock rate between 1 and 20 kHz and stored as a record segment. The record segments comprise between 100 and 2000 image lines, so that each object 12 will be seen in at least one record segment or an image on the slide 6.

[0127] Also, a film of the objects is divided into segments, in particular overlapping segments, and the segments are then processed further by the image processing software.

[0128] The points where fluorescence occurs are shown in dark gray. The points where no fluorescence occurs appear white in this picture, thus the slide 6 itself and the objects 12 and regions of objects 12 that do not consist of fluorescent materials, more precisely that do not exhibit any fluorescence in a wavelength range detected by detector 7. The objects 12 themselves are as a rule not discernible in FIG. 3.

[0129] For definition of the objects, one should employ FIG. 4, which shows an image of the same objects 12 (created at the same time), where here at least the geometric shape, shown in light gray, is discernible. This image is created through a record by means of the detector 8.

[0130] The creation of the image takes place in the same way as in the case of detector 7, thus through detection of one-dimensional image lines and assembly of the image lines by image processing software, and with a similar, in particular the same, clock rate. Of course, synchronization of the image lines of the two detectors 7 and 8 is useful in order to be able to combine and process the image data with respect to location and time.

[0131] Through analysis of the two images from FIGS. 3 and 4, as shown in FIG. 5, one can determine which object 12 contains how many regions with fluorescence as well as their size and thus the useful mineral or desired plastic, and in addition it is also possible to read the fluorescence intensity. Moreover, the fluorescent surface area of an object can be determined (from the first image, FIG. 3) and the total surface area of the object can be determined (from the second image, FIG. 4), and these surface areas can be put into a ratio with each other for purposes of analysis.

[0132] For instance, the entire object 13 consists of a first mineral or plastic, namely one that exhibits fluorescence in the considered wavelength range. The object 14 consists entirely of a second mineral or plastic, which does not exhibit fluorescence in the considered wavelength range. Finally, the object 15 consists partly of a first fluorescent material or plastic and partly of a second nonfluorescent material or plastic.

[0133] The exposure time for the fluorescent light detector 7 is, for example, on the order of magnitude of 100 to 1000 microseconds, the exposure time for the visible or IR detector 8 lies in the same order of magnitude or is smaller by a factor of one place, and can even be under 100 microseconds. Thereby a higher image line rate or higher resolution imaging can be achieved.

[0134] FIG. 6 shows a variant of a sorting plant according to the invention that is similar to FIG. 2, but has an alternative device for producing a single layer material stream. In FIG. 6, too, the incident light method is used for the UV light sources 3 and the backlight method is used for the second light source 4. Two UV light sources 3 with different exposure angles are arranged symmetrically to the optical axis (indicated by dot-dash line) of the detectors 7 and 8 and contribute to better illumination of the objects 12.

[0135] In contrast to FIGS. 1 and 2, in FIG. 6 the inclined glass pane 6 is made short. The background lighting in the form of light source 4, or more precisely the region where its light strikes the objects 12, and the stimulation region, where the UV light of the UV light source 3 strikes the objects 12, are provided in the direction of travel of the objects 12 (from top downward in FIG. 6) after the glass pane 6, thus under the lower edge of the glass panel 6.

[0136] This has the advantage that a light-permeable panel material is not necessary, and that the view of the objects 12 in free fall is better for the different variations in positioning of light sources and detectors. In particular, a two-sided fluorescence detection would then be more easily possible, thus a detector 7 for fluorescent light could be provided on both sides of the material stream, which in turn would have the advantage—for objects not permeable to UV light—that the presence of valuable mineral or desired plastic on the other side of the objects can also be tested.

[0137] The disadvantage of the shortened panel is that the objects 12 are guided for a shorter time, which can have a negative effect on the ejection efficiency, mainly for small objects.

[0138] The design and arrangement of the light sources 3 and 4 and the detectors 7 and 8 otherwise correspond essentially to those in FIG. 2, the second light source 4 emits NIR light in the 650-850 nm range and is made as an LED line, the detector 7 for fluorescent light can detect visible light in the 450-650 nm range, and the detector 8 for the transmitted object detection light can detect red and infrared light in the 650-85 nm range.

[0139] FIG. 6 additionally shows the connection of the detectors 7 and 8 to an analysis and control unit 16, as a rule a computer, which can form, for example, the central computer of a sorting plant, and which implements the computer program according to the invention. Said analysis and control unit 16 compiles the image lines of detectors 7 and 8 into images and conducts the analysis according to the invention, as explained in connection with FIGS. 3-5.

[0140] The ejection units, as in this case one or more blast nozzles 17, are controlled in dependence on this evaluation. The nozzles are disposed under the glass panel 6 (or a panel of nontransparent material) and below the region where the objects 12 are illuminated. Objects 13 (or additionally also objects 15), which contain sufficient amounts of a first mineral, the valuable mineral (or a desired plastic) fall downward undisturbed into a region to the right of a dividing wall 18. Objects 14, which do not (or insufficiently) contain a first mineral, the valuable mineral (or the desired plastic), rather consist entirely (or mostly) of a second mineral (or plastic) are blown by the blast nozzles 17 and deflected into a second region to the left of the dividing wall 18.

[0141] It would also be conceivable to separate the objects 12 into three fractions, where the valuable objects are divided further into a fraction with a high content of valuable material or desired plastic, like object 13 in FIG. 5, and a fraction with a low content of valuable material or desired plastic, like object 15 in FIG. 5.

[0142] FIG. 7 shows a diagram in which the wavelength of the light is plotted in nm on the horizontal axis and the relative intensity of the light is plotted on the vertical axis. The solid curve represents the stimulating light A, while the broken curve represents the fluorescent light E. In each case, only the intensity curves that contains the peak is shown. The representation concerns a specific material, and the maximum fluorescence intensity is obtained at wavelength E.sub.max when the stimulation takes place at a wavelength that corresponds to the stimulation peak A.sub.max.

[0143] The peak A.sub.max of the stimulation peak of the stimulating light A in this example is at a wavelength of 300 nm. The wavelengths at which the intensity has fallen to half of the peak A.sub.max define the width W.sub.A of the stimulation peak. In the method according to the invention, the stimulating light should lie within this width so that the fluorescent light exhibits sufficient, namely detectable, fluorescence. The wavelengths that establish the width W.sub.A of the stimulation peak here are 280 nm and 320 nm, the width W.sub.A of the stimulation peak therefore is 40 nm or relative to the peak A.sub.max±20 nm.

[0144] The peak E.sub.max of the fluorescence peak of the fluorescent light E in this example is at a wavelength of 350 nm. The wavelengths at which the intensity has fallen to half of the peak E.sub.max define the width W.sub.E of the fluorescence peak. In the method according to the invention, the fluorescent light should lie within this width, so that sufficient fluorescence is present. The wavelengths that establish the width W.sub.E of the fluorescence peak here are 325 nm and 390 nm, the width W.sub.A of the stimulation peak therefore is 65 nm or relative to the peak E.sub.max+40/−25 nm.

[0145] Examples of pairs of stimulation and fluorescence peaks for specific materials and for the case where the wavelength of the fluorescent light for specific materials can also be dependent on the deposit of origin of the materials can be seen in the following table.

[0146] Here the relevant material is listed in the first column, thus the mineral or plastic. The second column lists the stimulation wavelength or the wavelength range in which a stimulation should take place, and, in correspondence with FIG. 7, the width W.sub.A of the stimulation peak is given in the form of a positive and negative difference to the stimulation wavelength (the peak=the main peak). The third column lists the emission wavelength (wavelength of the fluorescent light) or the emission wavelength range in which a fluorescence can be detected, and, in correspondence with FIG. 7, the width W.sub.E of the fluorescence peak is given in the form of a positive and negative difference to the emission wavelength (the peak=the main peak).

TABLE-US-00001 Stimulation wavelength or Emission wavelength or wavelength range wavelength range Material (Main peak, ± delta at main (Main peak ± delta at (Mineral, plastic) peak/2) main peak/2) Scheelite 254 nm 430 nm +80/−50 (Tungsten) - Austria Fluorite - 366 nm 425 nm +20/−10 Germany Fluorite - 366 nm 500 nm +100/−80 Turkey Ruby, corundum - 410 nm +30/−30 690 nm +10/−5 Mozambique 565 nm +40/−50 Calcite 254 nm 620 nm +50/−70 (limestone) - 366 nm 620 nm +40/−70 Indonesia Calcite 254 nm 440 nm +140/−50 (limestone) - 366 nm 560 nm +90/−80 Austria Calcite 254 nm 615 nm +65/−45 (limestone) - 366 nm 600 nm +60/−40 Norway Magnesite - 366 nm 640 nm +40/−40 Brazil Magnesite - 254 nm 465 nm +105/−75 Turkey Apatite 254 nm 500 nm +40/−35 (concentration) - PET 254 nm 400 nm +30/−45 PE-HD 254 nm 405 nm +35/−30 PP 254 nm 405 nm +80/−30

[0147] For some materials such as calcite, fluorescence can be stimulated at two different wavelengths and therefore there will be two stimulation peaks. There will then be either one fluorescence peak (ruby, corundum) or two fluorescence peaks (calcite).

[0148] Should the data listed in the table not yet be known (or not known sufficiently accurately) for a specific material to be sorted, before conducting the method according to the invention, it would be appropriate to conduct a spectral measurement with narrow-band stimulation, for example in steps of 1-10 nm, in order to establish the wavelengths and intensities for the stimulating light and the fluorescent light that is to be detected.

[0149] The peak wavelengths listed in the table are fluorescence-active and are characteristic for industrially readily available stimulating light sources.

REFERENCE NUMBER LIST

[0150] 1 Housing for light source [0151] 2 Housing for detectors [0152] 3 Stimulating light source (UV light source (UVC light)) [0153] 4 Second light source (Vis light) [0154] 5 Reflector [0155] 6 Glass pane (slide) [0156] 7 Detector for detection of fluorescent light (TDI camera) [0157] 8 Detector for detection of object detection light (RGB camera) [0158] 9 Lens [0159] 10 Beam splitter [0160] 11 Protective glass [0161] 12 Object [0162] 13 Object of first mineral or plastic [0163] 14 Object of second mineral or plastic [0164] 15 Object containing first and second mineral or containing first and second plastic [0165] 16 Analysis and control unit (device for sorting out) [0166] 17 Ejection nozzle (device for sorting out) [0167] 18 Dividing wall (device for sorting out) [0168] A Stimulating light [0169] A.sub.max Peak of stimulation peak [0170] E Fluorescent light [0171] E.sub.max Peak of fluorescence peak [0172] W.sub.A Width of stimulation peak [0173] W.sub.E Width of fluorescence peak