CA2155922A1 - Classification of particles according to raman response - Google Patents
Classification of particles according to raman responseInfo
- Publication number
- CA2155922A1 CA2155922A1 CA002155922A CA2155922A CA2155922A1 CA 2155922 A1 CA2155922 A1 CA 2155922A1 CA 002155922 A CA002155922 A CA 002155922A CA 2155922 A CA2155922 A CA 2155922A CA 2155922 A1 CA2155922 A1 CA 2155922A1
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- CA
- Canada
- Prior art keywords
- particles
- diamond
- laser radiation
- pulsed
- emit
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/87—Investigating jewels
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
- B07C—POSTAL SORTING; SORTING INDIVIDUAL ARTICLES, OR BULK MATERIAL FIT TO BE SORTED PIECE-MEAL, e.g. BY PICKING
- B07C5/00—Sorting according to a characteristic or feature of the articles or material being sorted, e.g. by control effected by devices which detect or measure such characteristic or feature; Sorting by manually actuated devices, e.g. switches
- B07C5/34—Sorting according to other particular properties
- B07C5/342—Sorting according to other particular properties according to optical properties, e.g. colour
- B07C5/3425—Sorting according to other particular properties according to optical properties, e.g. colour of granular material, e.g. ore particles, grain
- B07C5/3427—Sorting according to other particular properties according to optical properties, e.g. colour of granular material, e.g. ore particles, grain by changing or intensifying the optical properties prior to scanning, e.g. by inducing fluorescence under UV or x-radiation, subjecting the material to a chemical reaction
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
- B07C—POSTAL SORTING; SORTING INDIVIDUAL ARTICLES, OR BULK MATERIAL FIT TO BE SORTED PIECE-MEAL, e.g. BY PICKING
- B07C5/00—Sorting according to a characteristic or feature of the articles or material being sorted, e.g. by control effected by devices which detect or measure such characteristic or feature; Sorting by manually actuated devices, e.g. switches
- B07C5/36—Sorting apparatus characterised by the means used for distribution
- B07C5/363—Sorting apparatus characterised by the means used for distribution by means of air
- B07C5/367—Sorting apparatus characterised by the means used for distribution by means of air using a plurality of separation means
- B07C5/368—Sorting apparatus characterised by the means used for distribution by means of air using a plurality of separation means actuated independently
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/65—Raman scattering
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/85—Investigating moving fluids or granular solids
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/65—Raman scattering
- G01N2021/653—Coherent methods [CARS]
- G01N2021/655—Stimulated Raman
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- Health & Medical Sciences (AREA)
- Physics & Mathematics (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
- Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)
Abstract
In a method of classifying and sorting particles, the particles are irradiated with pulsed incident laser radiation at an intensity chosen to cause selected particles to emit a stimulated Raman signal, and the particles are classified and sorted according to whether they emit a stimulated Raman response characteristic of the selected particles. The method is particularly useful for classifying and sorting diamond particles.
Description
-` ~ 2155~22 BACKGROUND TO THE INVENTION
THIS invention relates to the classification of particles according to their Raman response to incident laser radiation. In one application the method of the invention may be used to classify diamondiferous material into diamond and non-diamond fractions.
The sorting of particles, in particular diamonds, by Raman spectroscopy has already been proposed. See, for instance, US patent 5,143,224. The application of Raman spectroscopy to diamond sorting has however proved to have a number of disadvantages, including the following:
- normal Raman scattering of incident laser radiation takes place at very low intensity levels which can be difficult to detect;
- many types of other particles normally associated with diamonds also fluoresce under the incident laser excitation, making it difficult to isolate the diamond response;
- the fluorescence which takes place is a broad band phenomenon which may swamp the weak Raman signal; and - the use of the conventional Raman scattering phenomenon in an industrial environrnent calls for verv specific requirements including very low light levels in the measuring zone, the absence of optical dispersants such as dust or smoke and expensive detection equipment to detect the weak Raman signal.
~ ~ 21S~922 SUMMARY OF THE INVENTION
According to one aspect of the invention there is provided a method of classifying particles which comprises irr~ ting the particles with pulsed incident laser radiation at an intensity chosen to cause selected particles to emit a stimulated Raman signal, and classifying the particles according to whether they emit a stimulated Raman response characteristic of the selected particles.
In one preferred application, where the particles which are to be classified comprise diamond particles and non-diamond particles, the pulsed incident laser radiation is at an intensity chosen to cause diamond particles to emit a stimulated Raman response, and the particles are classified according to whether or not they emit a stimulated Raman response characteristic of diamond.
In this application the incident laser radiation is preferably pulsed with a pulse duration shorter than the luminescence response time of diamond. The pulse duration may, for instance, be of the order of 8ns and the incident laser radiation at an intensity of about lMW/cm2.
Typically, the incident laser radiation is produced by an Nd:YAG laser operating at a wavelength of 355nm. The signals emitted by the particles in response to the incident laser radiation may be passed to a detector by a filter having a pass band centred at a characteristic Raman wavelength for diamond.
21~9 22 According to a second aspect of the invention there is provided a method of sorting particles which comprises moving the particles through an irradiation zone, irr~ tin~ the particles, in the irradiation zone, with pulsed incident laser radiation at an intensity chosen to cause selected particles to emit a stimulated Raman signal, and sorting the particles into a first fraction rich in the selected particles and a second fraction rich in other particles, according to whether they emit a stimulated Raman response characteristic of the selected particles.
To ensure a high throughput rate, the particles may be moved through the irradiation zone in a broad stream and irradiated by a laser beam which is pulsed sequentially across the width of the stream. Conveniently, the particles are transported on a belt which projects them in a broad stream through the irradiation zone.
The stream of particles can be moved, after the irradiation zone, past an ejector apparatus comprising a bank of spaced apart ejectors located adjacent the stream, a~plo~liate ejectors being activated at a~plopliate times to eject selected particles from the stream for collection as the first fraction.
The sorting method summarised above may be used to sort diamond particles from non-diamond particles.
According to a further aspect of the invention there is provided an ~pa~alus for sorting particles, the apparatus comprising:
- an irradiation zone, -` ~ 21~922 means for moving particles which are to be sorted through the irradiation zone, a pulsed laser tube for irra~ ting the particles in the irradiation zone with pulsed, incident laser radiation at an intensity chosen to cause selected particles to emit a stimulated Raman signal, a detector, a filter having a pass band centred on a characteristic Raman wavelength for the selected particles, the filter being arranged to pass ap~lopl;ate signals which are emitted by the particles in response to the incident pulsed laser radiation to the detector analysing means responsive to the detector for determining, from signals detected by the detector, which of the particles have a stimulated Raman response characteristic of the selected particles, and sorting means responsive to the analysing means for sorting the particles into a first fraction rich in the selected particles and a second fraction rich in other particles.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail, by way of example only, with reference to the accompanying diagrammatic drawings.
21~2~
In the drawings:
Figure 1 shows a side view of an apparatus which employs the method of the invention; and Figure 2 shows a plan view of the apparatus seen in Figure 1.
DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
In the following description, specific mention is made of the classification and sorting of diamonds, although it will be appreciated that the principles of the invention are also applicable to the classification and sorting of other particle types.
The Figures show a broad conveyor belt 10 which conveys diamondiferous feed material 12. The feed material is derived from mining operations and subsequent processing and contains diamond particles 14 and associated rock, i.e. non-diamond, particles 16. The feed material is discharged over a discharge pulley 18 and follows a falling trajectory 20. At an irradiation zone 22, the particles are irradiated with a pulsed laser beam generated by a laser tube 24.
The laser beam is pulsed sequentially across the width of the belt so that, at times Tl, T2, T3 Tn~ different portions of the width of the falling stream of particles are irradiated, the lateral spacing of the train of pulses being selected to accommodate the smallest expected particles. For a given wavelength, the laser beam is at an intensity chosen to activate a 21~5922 characteristic, stimulated Raman signal in the diamond particles 14, but not at an intensity high enough to have the potential to damage the crystal structure of the diamonds.
The radiation scattered by the particles at each pulse of incident radiation is collected and focused on a detector 26 by a lens system 28 and a monochromator filter 30 which has a pass band centred at a characteristic Raman wavelength for diamond. An electronic processor 32 analyses the output signal of the detector and determines whether the detected spectrum contains a stimulated Raman signal characteristic of diamond. The lateral position of a detected diamond can be ~1etermined by the processor from knowledge of the laser pulse train timing, and the longitudinal position thereof from knowledge of the belt speed.
After the irradiation zone 22, the stream of particles moves past an ejector apparatus 34 composed of a series of laterally spaced ejector valves 34.1, 34.2, 34.3.. In response to the detection of a diamond, the processor activates the approp~iate valve 34.1, 34.2, 34.3 ...., which opens to direct a puff of compressed air at the falling particle stream. The diamond particle is diverted from the normal trajectory 20 and into a concentrate collection bin 36 while non-diamond particles continue falling along the normal trajectory which directs them to waste.
Conveniently a single detector 26, rather than a number of detectors is used, but it will be appreciated in this case that the response time of the detector must be fast enough to detect the characteristic Raman signal within the excitation pulse window. The laser pulse is advantageously shorter than the luminescence response time of diamond. With this combination of features, 2 1 ~ 2 ~
interference in the scattered spectrum by background lllminescence emitted by the particles as a result of non-Raman phenomena can be elimin~ted.
As indicated previously, the intensity of the incident laser beam is selected to activate a stimulated Raman response in diamonds. The exact intensity level in a particular application and for particular particles is carefully chosen so that the intensity level is not sufficiently high to cause damage to the diamonds. When a diamond is present and irradiated with laser radiation at an intensity above an ~plopliate threshold level, the stimulated Raman signal which it emits is orders of magnitude more intense than background luminescence attributable to other phenomena and than a normal Raman signal. The stimulated Raman signal characteristic of diamond is accordingly very much easier to detect than the normal Raman signal.
The coherence of the incident laser beam makes it possible to focus the laser tube 24 so that that part of the beam which has suff1cient intensity to activate the desired stimulated Raman response narrowly covers the particle trajectory and expected lateral variations thereof, thereby ensuring that the stim~ ted response is activated if a diamond is present.
In one experiment conducted in the laboratory to test the activation of the desired stimulated response, a diarnond particle was irradiated with 8ns pulses of laser radiation at a wavelength of 355nm and at an intensity of lMW/cm2. This was achieved using an Nd:YAG laser tube and a pulse repetition frequency of 8Hz. The detector, in the experiment a H~m~m~t~u IP28 photomultiplier tube with associated focusing lens and monochromator, detected a stimulated Raman response from the diamond. An analysis of the relevant parameters indicated that diamond damage occurred at a threshold 21~2~
intensity level in excess of lGW/cm2, very much higher than the incident intensity level of 1MW/cm2 The experiment indicated that the detected stimulated Raman response was substantially more intense than the background luminescence and the normal Raman response.
It is believed that the intensity of the stimulated signal will overcome or at least reduce the problems associated with detection of low intensity normal Raman signals and swamping of the Raman signal in background luminescence or fluorescence. In addition it is believed that the stimulated response will be sufficiently intense to make it possible to conduct particle classification and sorting operations in daylight conditions as opposed to very low level light conditions.
THIS invention relates to the classification of particles according to their Raman response to incident laser radiation. In one application the method of the invention may be used to classify diamondiferous material into diamond and non-diamond fractions.
The sorting of particles, in particular diamonds, by Raman spectroscopy has already been proposed. See, for instance, US patent 5,143,224. The application of Raman spectroscopy to diamond sorting has however proved to have a number of disadvantages, including the following:
- normal Raman scattering of incident laser radiation takes place at very low intensity levels which can be difficult to detect;
- many types of other particles normally associated with diamonds also fluoresce under the incident laser excitation, making it difficult to isolate the diamond response;
- the fluorescence which takes place is a broad band phenomenon which may swamp the weak Raman signal; and - the use of the conventional Raman scattering phenomenon in an industrial environrnent calls for verv specific requirements including very low light levels in the measuring zone, the absence of optical dispersants such as dust or smoke and expensive detection equipment to detect the weak Raman signal.
~ ~ 21S~922 SUMMARY OF THE INVENTION
According to one aspect of the invention there is provided a method of classifying particles which comprises irr~ ting the particles with pulsed incident laser radiation at an intensity chosen to cause selected particles to emit a stimulated Raman signal, and classifying the particles according to whether they emit a stimulated Raman response characteristic of the selected particles.
In one preferred application, where the particles which are to be classified comprise diamond particles and non-diamond particles, the pulsed incident laser radiation is at an intensity chosen to cause diamond particles to emit a stimulated Raman response, and the particles are classified according to whether or not they emit a stimulated Raman response characteristic of diamond.
In this application the incident laser radiation is preferably pulsed with a pulse duration shorter than the luminescence response time of diamond. The pulse duration may, for instance, be of the order of 8ns and the incident laser radiation at an intensity of about lMW/cm2.
Typically, the incident laser radiation is produced by an Nd:YAG laser operating at a wavelength of 355nm. The signals emitted by the particles in response to the incident laser radiation may be passed to a detector by a filter having a pass band centred at a characteristic Raman wavelength for diamond.
21~9 22 According to a second aspect of the invention there is provided a method of sorting particles which comprises moving the particles through an irradiation zone, irr~ tin~ the particles, in the irradiation zone, with pulsed incident laser radiation at an intensity chosen to cause selected particles to emit a stimulated Raman signal, and sorting the particles into a first fraction rich in the selected particles and a second fraction rich in other particles, according to whether they emit a stimulated Raman response characteristic of the selected particles.
To ensure a high throughput rate, the particles may be moved through the irradiation zone in a broad stream and irradiated by a laser beam which is pulsed sequentially across the width of the stream. Conveniently, the particles are transported on a belt which projects them in a broad stream through the irradiation zone.
The stream of particles can be moved, after the irradiation zone, past an ejector apparatus comprising a bank of spaced apart ejectors located adjacent the stream, a~plo~liate ejectors being activated at a~plopliate times to eject selected particles from the stream for collection as the first fraction.
The sorting method summarised above may be used to sort diamond particles from non-diamond particles.
According to a further aspect of the invention there is provided an ~pa~alus for sorting particles, the apparatus comprising:
- an irradiation zone, -` ~ 21~922 means for moving particles which are to be sorted through the irradiation zone, a pulsed laser tube for irra~ ting the particles in the irradiation zone with pulsed, incident laser radiation at an intensity chosen to cause selected particles to emit a stimulated Raman signal, a detector, a filter having a pass band centred on a characteristic Raman wavelength for the selected particles, the filter being arranged to pass ap~lopl;ate signals which are emitted by the particles in response to the incident pulsed laser radiation to the detector analysing means responsive to the detector for determining, from signals detected by the detector, which of the particles have a stimulated Raman response characteristic of the selected particles, and sorting means responsive to the analysing means for sorting the particles into a first fraction rich in the selected particles and a second fraction rich in other particles.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail, by way of example only, with reference to the accompanying diagrammatic drawings.
21~2~
In the drawings:
Figure 1 shows a side view of an apparatus which employs the method of the invention; and Figure 2 shows a plan view of the apparatus seen in Figure 1.
DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
In the following description, specific mention is made of the classification and sorting of diamonds, although it will be appreciated that the principles of the invention are also applicable to the classification and sorting of other particle types.
The Figures show a broad conveyor belt 10 which conveys diamondiferous feed material 12. The feed material is derived from mining operations and subsequent processing and contains diamond particles 14 and associated rock, i.e. non-diamond, particles 16. The feed material is discharged over a discharge pulley 18 and follows a falling trajectory 20. At an irradiation zone 22, the particles are irradiated with a pulsed laser beam generated by a laser tube 24.
The laser beam is pulsed sequentially across the width of the belt so that, at times Tl, T2, T3 Tn~ different portions of the width of the falling stream of particles are irradiated, the lateral spacing of the train of pulses being selected to accommodate the smallest expected particles. For a given wavelength, the laser beam is at an intensity chosen to activate a 21~5922 characteristic, stimulated Raman signal in the diamond particles 14, but not at an intensity high enough to have the potential to damage the crystal structure of the diamonds.
The radiation scattered by the particles at each pulse of incident radiation is collected and focused on a detector 26 by a lens system 28 and a monochromator filter 30 which has a pass band centred at a characteristic Raman wavelength for diamond. An electronic processor 32 analyses the output signal of the detector and determines whether the detected spectrum contains a stimulated Raman signal characteristic of diamond. The lateral position of a detected diamond can be ~1etermined by the processor from knowledge of the laser pulse train timing, and the longitudinal position thereof from knowledge of the belt speed.
After the irradiation zone 22, the stream of particles moves past an ejector apparatus 34 composed of a series of laterally spaced ejector valves 34.1, 34.2, 34.3.. In response to the detection of a diamond, the processor activates the approp~iate valve 34.1, 34.2, 34.3 ...., which opens to direct a puff of compressed air at the falling particle stream. The diamond particle is diverted from the normal trajectory 20 and into a concentrate collection bin 36 while non-diamond particles continue falling along the normal trajectory which directs them to waste.
Conveniently a single detector 26, rather than a number of detectors is used, but it will be appreciated in this case that the response time of the detector must be fast enough to detect the characteristic Raman signal within the excitation pulse window. The laser pulse is advantageously shorter than the luminescence response time of diamond. With this combination of features, 2 1 ~ 2 ~
interference in the scattered spectrum by background lllminescence emitted by the particles as a result of non-Raman phenomena can be elimin~ted.
As indicated previously, the intensity of the incident laser beam is selected to activate a stimulated Raman response in diamonds. The exact intensity level in a particular application and for particular particles is carefully chosen so that the intensity level is not sufficiently high to cause damage to the diamonds. When a diamond is present and irradiated with laser radiation at an intensity above an ~plopliate threshold level, the stimulated Raman signal which it emits is orders of magnitude more intense than background luminescence attributable to other phenomena and than a normal Raman signal. The stimulated Raman signal characteristic of diamond is accordingly very much easier to detect than the normal Raman signal.
The coherence of the incident laser beam makes it possible to focus the laser tube 24 so that that part of the beam which has suff1cient intensity to activate the desired stimulated Raman response narrowly covers the particle trajectory and expected lateral variations thereof, thereby ensuring that the stim~ ted response is activated if a diamond is present.
In one experiment conducted in the laboratory to test the activation of the desired stimulated response, a diarnond particle was irradiated with 8ns pulses of laser radiation at a wavelength of 355nm and at an intensity of lMW/cm2. This was achieved using an Nd:YAG laser tube and a pulse repetition frequency of 8Hz. The detector, in the experiment a H~m~m~t~u IP28 photomultiplier tube with associated focusing lens and monochromator, detected a stimulated Raman response from the diamond. An analysis of the relevant parameters indicated that diamond damage occurred at a threshold 21~2~
intensity level in excess of lGW/cm2, very much higher than the incident intensity level of 1MW/cm2 The experiment indicated that the detected stimulated Raman response was substantially more intense than the background luminescence and the normal Raman response.
It is believed that the intensity of the stimulated signal will overcome or at least reduce the problems associated with detection of low intensity normal Raman signals and swamping of the Raman signal in background luminescence or fluorescence. In addition it is believed that the stimulated response will be sufficiently intense to make it possible to conduct particle classification and sorting operations in daylight conditions as opposed to very low level light conditions.
Claims (24)
1.
A method of classifying particles which comprises irradiating the particles with pulsed incident laser radiation at an intensity chosen to cause selected particles to emit a stimulated Raman signal, and classifying the particles according to whether they emit a stimulated Raman response characteristic of the selected particles.
A method of classifying particles which comprises irradiating the particles with pulsed incident laser radiation at an intensity chosen to cause selected particles to emit a stimulated Raman signal, and classifying the particles according to whether they emit a stimulated Raman response characteristic of the selected particles.
2.
A method according to claim 1 wherein the particles which are to be classified comprise diamond particles and non-diamond particles, wherein the pulsed incident laser radiation is at an intensity chosen to cause diamond particles to emit a stimulated Raman response, and wherein the particles are classified according to whether or not they emit a stimulated Raman response characteristic of diamond.
A method according to claim 1 wherein the particles which are to be classified comprise diamond particles and non-diamond particles, wherein the pulsed incident laser radiation is at an intensity chosen to cause diamond particles to emit a stimulated Raman response, and wherein the particles are classified according to whether or not they emit a stimulated Raman response characteristic of diamond.
3.
A method according to claim 2 wherein the incident laser radiation is pulsed with a pulse duration shorter than the luminescence response time of diamond.
A method according to claim 2 wherein the incident laser radiation is pulsed with a pulse duration shorter than the luminescence response time of diamond.
4.
A method according to claim 3 wherein the pulse duration is of the order of 8ns.
A method according to claim 3 wherein the pulse duration is of the order of 8ns.
5.
A method according to claim 4 wherein the incident laser radiation is at an intensity of about 1MW/cm2.
A method according to claim 4 wherein the incident laser radiation is at an intensity of about 1MW/cm2.
6.
A method according to claim 2 wherein the incident laser radiation is produced by an Nd:YAG laser operating at a wavelength of 355nm.
A method according to claim 2 wherein the incident laser radiation is produced by an Nd:YAG laser operating at a wavelength of 355nm.
7.
A method according to claim 2 wherein signals emitted by the particles in response to the incident laser radiation are passed to a detector by a filter having a pass band centred at a characteristic Raman wavelength for diamond.
A method according to claim 2 wherein signals emitted by the particles in response to the incident laser radiation are passed to a detector by a filter having a pass band centred at a characteristic Raman wavelength for diamond.
8.
A method of sorting particles which comprises moving the particles through an irradiation zone, irradiating the particles, in the irradiation zone, with pulsed incident laser radiation at an intensity chosen to cause selected particles to emit a stimulated Raman signal, and sorting the particles into a first fraction rich in the selected particles and a second fraction rich in other particles, according to whether they emit a stimulated Raman response characteristic of the selected particles.
A method of sorting particles which comprises moving the particles through an irradiation zone, irradiating the particles, in the irradiation zone, with pulsed incident laser radiation at an intensity chosen to cause selected particles to emit a stimulated Raman signal, and sorting the particles into a first fraction rich in the selected particles and a second fraction rich in other particles, according to whether they emit a stimulated Raman response characteristic of the selected particles.
9.
A method according to claim 8 wherein the particles are moved through the irradiation zone in a broad stream and wherein the particles are irradiated by a laser beam which is pulsed sequentially across the width of the stream.
A method according to claim 8 wherein the particles are moved through the irradiation zone in a broad stream and wherein the particles are irradiated by a laser beam which is pulsed sequentially across the width of the stream.
10.
A method according to claim 9 wherein the particles are transported on a belt which projects them in a broad stream through the irradiation zone.
A method according to claim 9 wherein the particles are transported on a belt which projects them in a broad stream through the irradiation zone.
11.
A method according to claim 10 wherein the stream of particles is moved, after the irradiation zone, past an ejector apparatus comprising a bank of spaced apart ejectors located adjacent the stream, and wherein appropriate ejectors are activated at appropriate times to eject selected particles from thestream for collection as the first fraction.
A method according to claim 10 wherein the stream of particles is moved, after the irradiation zone, past an ejector apparatus comprising a bank of spaced apart ejectors located adjacent the stream, and wherein appropriate ejectors are activated at appropriate times to eject selected particles from thestream for collection as the first fraction.
12.
A method according to claim 8 wherein the particles which are to be classified comprise diamond particles and non-diamond particles, wherein the pulsed incident laser radiation is at an intensity chosen to cause diamond particles to emit a stimulated Raman response, and wherein the particles are sorted into a first fraction rich in diamond particles and a second fraction rich in non-diamond particles according to whether or not they emit a stimulated Raman response characteristic of diamond.
A method according to claim 8 wherein the particles which are to be classified comprise diamond particles and non-diamond particles, wherein the pulsed incident laser radiation is at an intensity chosen to cause diamond particles to emit a stimulated Raman response, and wherein the particles are sorted into a first fraction rich in diamond particles and a second fraction rich in non-diamond particles according to whether or not they emit a stimulated Raman response characteristic of diamond.
13.
A method according to claim 12 wherein the incident laser radiation is pulsed with a pulse duration shorter than the luminescence response time of diamond.
A method according to claim 12 wherein the incident laser radiation is pulsed with a pulse duration shorter than the luminescence response time of diamond.
14.
A method according to claim 13 wherein the pulse duration is of the order of 8ns.
A method according to claim 13 wherein the pulse duration is of the order of 8ns.
15.
A method according to claim 14 wherein the incident laser radiation is at an intensity of about 1MW/cm2.
A method according to claim 14 wherein the incident laser radiation is at an intensity of about 1MW/cm2.
16.
A method according to claim 12 wherein the incident laser radiation is produced by an Nd:YAG laser operating at a wavelength of 355nm.
A method according to claim 12 wherein the incident laser radiation is produced by an Nd:YAG laser operating at a wavelength of 355nm.
17.
A method according to claim 12 wherein signals emitted by the particles in response to the incident laser radiation are passed to a detector by a filter having a pass band centred at a characteristic Raman wavelength for diamond.
A method according to claim 12 wherein signals emitted by the particles in response to the incident laser radiation are passed to a detector by a filter having a pass band centred at a characteristic Raman wavelength for diamond.
18.
An apparatus for sorting particles, the apparatus comprising:
- an irradiation zone, - means for moving particles which are to be sorted through the irradiation zone, - a pulsed laser tube for irradiating the particles in the irradiation zone with pulsed, incident laser radiation at an intensity chosen to cause selected particles to emit a stimulated Raman signal, - a detector, - a filter having a pass band centred on a characteristic Raman wavelength for the selected particles, the filter being arranged to pass appropriate signals which are emitted by the particles in response to the incident pulsed laser radiation to the detector - analysing means responsive to the detector for determining, from signals detected by the detector, which of the particles have a stimulated Raman response characteristic of the selected particles, and - sorting means responsive to the analysing means for sorting the particles into a first fraction rich in the selected particles and a second fraction rich in other particles.
An apparatus for sorting particles, the apparatus comprising:
- an irradiation zone, - means for moving particles which are to be sorted through the irradiation zone, - a pulsed laser tube for irradiating the particles in the irradiation zone with pulsed, incident laser radiation at an intensity chosen to cause selected particles to emit a stimulated Raman signal, - a detector, - a filter having a pass band centred on a characteristic Raman wavelength for the selected particles, the filter being arranged to pass appropriate signals which are emitted by the particles in response to the incident pulsed laser radiation to the detector - analysing means responsive to the detector for determining, from signals detected by the detector, which of the particles have a stimulated Raman response characteristic of the selected particles, and - sorting means responsive to the analysing means for sorting the particles into a first fraction rich in the selected particles and a second fraction rich in other particles.
19.
An apparatus according to claim 18 wherein the means for moving the particles comprises a belt for transporting the particles and for projecting theparticles in a broad stream through the irradiation zone.
An apparatus according to claim 18 wherein the means for moving the particles comprises a belt for transporting the particles and for projecting theparticles in a broad stream through the irradiation zone.
20.
An apparatus according to claim 19 wherein the sorting means comprises an ejector apparatus past which the particles move after the irradiation zone, the ejector apparatus comprising a bank of ejectors located adjacent the stream and spaced apart from one another across the width of the stream, and the ejector apparatus being arranged to operate in response to the analysing means such that appropriate ejectors are activated at appropriate times to eject selected particles from the stream for collection as the first fraction.
An apparatus according to claim 19 wherein the sorting means comprises an ejector apparatus past which the particles move after the irradiation zone, the ejector apparatus comprising a bank of ejectors located adjacent the stream and spaced apart from one another across the width of the stream, and the ejector apparatus being arranged to operate in response to the analysing means such that appropriate ejectors are activated at appropriate times to eject selected particles from the stream for collection as the first fraction.
21.
An apparatus according to claim 18 which is adapted to sort diamond particles from non-diamond particles.
An apparatus according to claim 18 which is adapted to sort diamond particles from non-diamond particles.
22.
An apparatus according to claim 21 wherein the laser tube is arranged to irradiate the particles, in the irradiation zone, with a pulsed laser beam at anintensity chosen to cause diamond particles to emit a stimulated Raman response, the pulse duration of the laser beam being shorter than the luminescence response time of diamond.
An apparatus according to claim 21 wherein the laser tube is arranged to irradiate the particles, in the irradiation zone, with a pulsed laser beam at anintensity chosen to cause diamond particles to emit a stimulated Raman response, the pulse duration of the laser beam being shorter than the luminescence response time of diamond.
23.
An apparatus according to claim 22 wherein the laser tube is arranged to irradiate the particles with laser pulses having a duration of the order of 8ns and an intensity of about 1MW/cm2.
An apparatus according to claim 22 wherein the laser tube is arranged to irradiate the particles with laser pulses having a duration of the order of 8ns and an intensity of about 1MW/cm2.
24.
An apparatus according to claim 23 wherein the laser tube is an Nd:YAG
laser tube operating at a wavelength of 355nm.
An apparatus according to claim 23 wherein the laser tube is an Nd:YAG
laser tube operating at a wavelength of 355nm.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ZA946317 | 1994-08-19 | ||
| ZA94/6317 | 1994-08-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2155922A1 true CA2155922A1 (en) | 1996-02-20 |
Family
ID=25584259
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002155922A Abandoned CA2155922A1 (en) | 1994-08-19 | 1995-08-11 | Classification of particles according to raman response |
Country Status (4)
| Country | Link |
|---|---|
| AU (1) | AU697587B2 (en) |
| CA (1) | CA2155922A1 (en) |
| GB (1) | GB2292455B (en) |
| ZA (1) | ZA955745B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2241470C (en) * | 1997-06-26 | 2005-06-21 | De Beers Consolidated Mines Limited | Diamond detection using coherent anti-stokes raman spectroscopy |
| BE1013056A3 (en) * | 1999-06-28 | 2001-08-07 | Barco Elbicon Nv | Method and device for sorting products. |
| US7608794B2 (en) | 2006-04-20 | 2009-10-27 | Sunsweet Growers, Inc. | Process and system for sorting and pitting fruit |
| BE1018705A3 (en) * | 2009-03-26 | 2011-07-05 | Best 2 N V | METHOD FOR SORTING POTATO PRODUCTS AND SORTING DEVICE FOR POTATO PRODUCTS |
| US8283589B2 (en) * | 2010-12-01 | 2012-10-09 | Key Technology, Inc. | Sorting apparatus |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4243881A (en) * | 1979-10-12 | 1981-01-06 | International Business Machines Corporation | Time-resolved infrared spectral photography |
| US4545679A (en) * | 1984-02-21 | 1985-10-08 | The United States Of America As Represented By The United States Department Of Energy | Frequency shift measurement in shock-compressed materials |
| GB2219080B (en) * | 1988-05-06 | 1992-11-04 | Gersan Ets | Identifying gemstones |
| GB2219078B (en) * | 1988-05-06 | 1992-08-26 | Gersan Ets | Identifying the position of objects or zones |
| ZA9410191B (en) * | 1993-12-30 | 1995-08-25 | De Beers Ind Diamond | Particle classification method and apparatus |
-
1995
- 1995-07-11 ZA ZA955745A patent/ZA955745B/en unknown
- 1995-08-09 AU AU28433/95A patent/AU697587B2/en not_active Ceased
- 1995-08-09 GB GB9516356A patent/GB2292455B/en not_active Expired - Fee Related
- 1995-08-11 CA CA002155922A patent/CA2155922A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| ZA955745B (en) | 1996-02-20 |
| GB9516356D0 (en) | 1995-10-11 |
| GB2292455A (en) | 1996-02-21 |
| GB2292455B (en) | 1998-09-30 |
| AU697587B2 (en) | 1998-10-08 |
| AU2843395A (en) | 1996-02-29 |
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