WO1987006011A1 - Detection de la presence de materiaux - Google Patents

Detection de la presence de materiaux Download PDF

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Publication number
WO1987006011A1
WO1987006011A1 PCT/AU1986/000076 AU8600076W WO8706011A1 WO 1987006011 A1 WO1987006011 A1 WO 1987006011A1 AU 8600076 W AU8600076 W AU 8600076W WO 8706011 A1 WO8706011 A1 WO 8706011A1
Authority
WO
WIPO (PCT)
Prior art keywords
monitor
fibres
radiation
collection
fibre
Prior art date
Application number
PCT/AU1986/000076
Other languages
English (en)
Inventor
David William James
Original Assignee
University Of Queensland
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by University Of Queensland filed Critical University Of Queensland
Priority to PCT/AU1986/000076 priority Critical patent/WO1987006011A1/fr
Priority claimed from AU56299/86A external-priority patent/AU5629986A/en
Priority to IL78408A priority patent/IL78408A0/xx
Publication of WO1987006011A1 publication Critical patent/WO1987006011A1/fr

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V8/00—Prospecting or detecting by optical means
    • G01V8/10—Detecting, e.g. by using light barriers
    • G01V8/12—Detecting, e.g. by using light barriers using one transmitter and one receiver
    • G01V8/16—Detecting, e.g. by using light barriers using one transmitter and one receiver using optical fibres
    • 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
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N2021/1793—Remote sensing
    • 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
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N2021/1793—Remote sensing
    • G01N2021/1795—Atmospheric mapping of gases
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/08—Optical fibres; light guides
    • G01N2201/084—Fibres for remote transmission

Definitions

  • This invention relates to the monitoring of the presence or concentration of a chemical component in an environment of interest by stimulation of the environ ⁇ ment with electromagnetic radiation to produce scattered radiation which is collected and from which a portion or portions characteristic of the component of interest is isolated.
  • Raman scattering is a technique widely used for identifying molecules through their vibrational spectrum.
  • the principle of the technique is illustrated in FIG. 1, where both the experimental requirements (FIG. 1a) and the energy level changes (FIG. 1b) are shown, and this is described in greater detail below.
  • the major intensity is due to Rayleigh scattering, with a small contribution from the Raman scattering.
  • the difference in energy between the two is measured in the spectrum analyser which is usually a double monochromator. This difference in energy corresponds to one or more vibrational energies of the molecules in the sample.
  • the intensity at any particular energy gap corresponds to the concentration of the component vibrating with that energy.
  • the scattered light is emitted in all directions and so may be collected at any angle relative to the incident light.
  • the environment of interest may be a gas or liquid stream within a chemical plant, a fluid under pressure, a fluid at a temperature other than atmospheric temperature, a gas dissolved in a liquid or the surface of a solid.
  • the invention provides a monitor for determining the presence or concentration of a particular chemical or combination of chemical components in an environment to be monitored comprising a source of electromagnetic radiation, a means for directing the electromagnetic radiation into an environment to be monitored, a means within the environment for receiving scattered electro- magnetic radiation, a means for delivering the scattered electromagnetic radiation to a location remote from the environment to be monitored and a means sensitive to a predetermined component or combination of components within the scattered electromagnetic radiation which is characteristic of the chemical or combination of chemical components to be monitored, characterised in that the means for delivering electromagnetic radiation to the environment and the means for delivering the scattered electromagnetic radiation to the remote location comprise optical fibres, the fibres terminating in the environment to be monitored with the end of the delivery fibre or fibres being disposed relative to the end or ends of the fibres which collect scattered radiation in a relation ⁇ ship which minimises any return of the electromagnetic radiation other than scattered radiation.
  • an optical monitor ij for determining the presence or concentration of a particular chemical or combination of chemical components in an environment to be monitored comprising a laser providing monochromatic radiation, means for isolating Raman scattered radiation characteristic of the chemical or combination of chemical components to be monitored and a detection means for receiving the isolated Raman scattered radiation to provide the determination of the presence or concentration of the component characterised in that monochromatic radiation generated by the laser is delivered to the environment via one or more optical fibres and scattered radiation is collected therefrom by one or more optical fibres and transmitted thereby to the means for isolating Raman scattered radiation.
  • the invention provides a method for monitoring the presence or concentration of a particular chemical or combination of chemical components in an environment to be monitored from a remote location com ⁇ prising the supply of electromagnetic radiation to the environment, collecting and transmitting scattered radiation from the environment to a remote location, isolating Raman scattered radiation from the scattered radiation, and determining the presence or concentration of a component to be monitored by detecting a character ⁇ istic portion, or portions of the Raman spectra of that component in the collected Raman scattered radiation characterised in that the collection of Raman scattered radiation and its transmission to the remote location is achieved in isolation from the supply of monochromatic radiation by means of optic fibres.
  • FIG. 1a illustrates the basic component of a Raman scattering device.
  • FIG. 1b illustrates the energy level changes of interest in scattering.
  • FIG. a is a view of an optical fibre bundle.
  • FIG. 2b is a cross section through the bundle of FIG. 2a.
  • FIG. 3 is an axial section through a fibre bundle at the collection end.
  • FIG. is an axial section through another fibre bundle at the collection end.
  • FIG. 5 is a schematic layout illustrating the optical circuit of a monitoring device in accord ⁇ ance with the present invention.
  • FIG. 6 is a schematic layout illustrating the optical circuit of an alternate monitoring device in accordance with the present invention.
  • FIG. 7 is a schematic layout illustrating the electrical circuit of a monitoring device of the type of FIG. 5.
  • FIG. 1a shows the basic requirements for deter ⁇ mining the constitution of a sample wherein a source of monochromatic radiation such as a laser 10 is used to create a beam of radiation 11 made to pass through a sample 12 to create a transmitted beam 13 from which some energy has been lost through scattering in the sample 12, the scattered radiation 14 being collected and analysed in a spectrum analyser 15 of suitable form to identify spectral components which are characteristic of whatever material is being monitored.
  • a source of monochromatic radiation such as a laser 10
  • FIG. 1b is shown an energy level diagram indicating the two contributions to scattering caused by Rayleigh and Raman scattering.
  • the vibrational energy gap can have a number of different values for any part ⁇ icular molecule, each being associated with one of .the vibrational modes characteristic of the particular mole ⁇ cule to produce scattered Raman photons each shifted in frequency from that of the incident photon to generate a characteristic spectrum which may be viewed to identify the material generating it.
  • the technique can in principle use any monchrom- atic light source. The shorter the wavelength the greater the scattered intensity.
  • the device to be described is designed to operate most usefully with the 488nm emission from an argon ion laser. It will work with slightly decreased sensitivity from the 5l4nm emission from an argon ion laser and with increased sensitivity from the lower wavelength emissions from He/Cd and He/Sr metal vapor lasers.
  • lasers having a longer wavelength Cu vapour 578nm, He/Ne 628nm or Krypton ion 64lnm
  • the signal intensity is dependent on the power of the laser emission used. Laser powers from 10mw and greater are suitable for the technique.
  • the laser incident radiation is delivered to the sample via an optical fibre or an optical fibre bundle.
  • the scatt ⁇ ered light is collected from the sample by an optical fibre bundle.
  • Fibres having fibre diameters from 100 ⁇ ,to 500,0,with numerical apertures from 0.2 to 0.5 may be used depending on the application. Both silica and plastic fibres have been used. The choice of fibre will depend on the environment being measured and the loss character- istics of the fibre.
  • the optic fibre bundle may be of a number of different forms as set out below.
  • Concentric Assembly The simplest assembly uses a single fibre for the delivery of the incident light. Concentric with this fibre is a fibre bundle of 6, 15 or 30 fibres for collection of the scattered light. The complete probe is encased in stainless steel or other protective envelope and sealed with a flourinated polyester resin. The deliv ⁇ ery end of the fibre is polished so that the ends of all fibres are in the same optical plane. An assembly of this design using six collection fibres is shown in FIG.2 wherein an input fibre 16 is surrounded by six coll ⁇ ection fibres, such as 17, all encased in a sheath 18. Multiple Delivery Concentric Assembly. In applications where the intensity of the incident light must be dis ⁇ persed for safety reasons several fibres are used for delivery of the incident light. Each of these carries only a portion of the total light intensity and each has collection fibres as nearest neighbours. The sheathing and polishing is similar to 2a and b.
  • Acentric assembly In some applications it is necessary to separate the delivery and collection fibres.
  • the delivery fibre 19 is placed acentrically with delivery and collection bundles separately sheathed in stainless steel or other protective sheathing. This is shown in FIG. 3.
  • the delivery fibre 19 is mounted at an angle 22 to the collection bundle 20 so that the volume illuminated by the incident beam coincides with the collection cone from the collection bundle.
  • the complete acentric assembly is sheathed in stainless steel 21 or other protective envelope.
  • the scattering assembly may be integrated with the meas- urement system in which case the delivery fibre is continuous between the laser and the scattering assembly and the collection fibres are similarly con ⁇ tinuous between the scattering assembly and the detect- ion analysis system.
  • the scattering assembly may be a separate removable device.
  • the laser light is transmitted through a fibre which is then conn ⁇ ected through a standard, low loss, connector to the delivery fibre in the scattering assembly.
  • the collection fibres in the scattering assembly are fused to yield a single transmission fibre which is connected, again through a low loss connector to a single fibre which transmits the integrated collected light to the detection/ analysis system.
  • the optical coupling of the delivery fibre to the laser is preferably made through a system which is mechanically integrated to the laser in order to eliminate variations due to differential vibration.
  • the laser can be focussed by a lens which matches the numerical aperture of the particular fibre utilised. Any of the commercially available devices can be utilised for this purpose.
  • Spectrum Analysis It is necessary to examine the inten- sity of the scattered light at selected characteristic wavelengths. This may be accomplished by using a mono ⁇ chromator and in a few cases this type of system may be necessary. In a system of a few components however, better sensitivity may be achieved by examining the total scatter- ed intensity transmitted through a narrow bandpass filter. Monochromator System.
  • a monochromator When a monochromator is required for the measurement of the signal it may be either a single or double monochromator. For a single monochromator a pre- filter is required to reduce the level of the Rayleigh scattering entering the monochromator. The output from the end of the fibre would be treated as a point light source and would be coupled with appropriate optics into the monochromator.
  • FIG. 5 A block diagram for this arrangement is shown in FIG. 5.
  • laser 25 is joined by coupling optics 26 into a fibre 27 for directing monochromatic radiation to a sample or environment to be tested or monitored 28. Scattered radiation is directed by collection fibre 29, via coupling optics and a pre- filter 31 to screen Rayleigh scattered radiation, to a monochromator and detector 32.
  • Suitable signal pro ⁇ cessing and readout is catered for at 33.
  • Bandpass Filter System There are three components necessary for spectrum analysis using the bandpass filter system and these are (i) prefilter, (ii) band ⁇ pass filter system, (iii) detector.
  • the prefilter - The prefilter is necessary because the intensity of the Rayleigh scattered light is many times more intense than the scattered light of interest. This intensity gives rise to a high background signal over a wide spectral range.
  • An edge prefilter having an optical density of ⁇ -4 at the position of the Rayleigh scattering falling to low values ⁇ -15nm to the red is effective in reducing this background.
  • the effectiveness of the prefiltration is improved if the laser is chopped or pulsed and phase sensitive detection at the chopping frequency is employed. Chopping or pulse frequencies above 200hz are found to be satisfactory. Normal sectored disc choppers are used.
  • the bandpass filter system - This is made up of a series of narrow bandpass interference filters each having a bandpass between 100 cm -1 and 400cm-1. Each filter is chosen to give maximum transmission of the Raman scatter ⁇ ing of a particular component to be analysed. The choice of particular filters is dependent on the wavelength of the laser light used to produce the scattered radiation.
  • the filters In addition to the bandpass filters for the components being analysed there must be a filter to provide information on the background level at a wave- length where minimal scattering is present.
  • the filters are mounted in a turret to allow automatic changing from one to another to allow sequential recording of the scattered intensity transmitted by each filter. This filter changing is under microprocessor control.
  • the detector system The detector used to detect the scattered light may be either a photomultiplier or a diode detector depending on the sensitivity required.
  • the scattered light transmitted by the filter system is foc- ussed on the detector.
  • the signal from the detector is amplified by a phase sensitive amplifier and the result ⁇ ing voltage for each of the filter positions provides the raw data which is processed by a preprogrammed microproc ⁇ essor into concentrations of each of the components of interest.
  • Complete Analysis System The collected scattered light delivered by the collection fibre(s) is in the form of a diverging cone of light the geometry of which is dependent on the particular fibre or fibre bundle used. This diverg ⁇ ent cone of light is collimated by an appropriate lens system which is integrated with the fibre termination to optimise coupling efficiency. This collimated beam is passed through the prefilter and the filter assembly before being focussed by a further lens system onto the photomultiplier or diode.
  • An optical block diagram show- ing the arrangement of components in the system utilising the filter system is given in FIG. 6.
  • an electrical block diagram showing the relationship of the electrical components is given in FIG. 7.
  • laser 3 provides an output which may be chopped by a chopper means 35 prior to being coupled to a delivery fibre, or bundle of fibres by coupling optics 36.
  • Light scattered from the sample, or environ ⁇ ment being tested, or monitored, 37 may be processed by foreoptics 38 prior to passing prefilter 39 to remove Rayleigh scattered radiation.
  • the Raman scattered rad ⁇ iation is processed by any of one or more band pass filters 41 which may be carried into the optic path by a suitable carrier 40 such as a revolving turret.
  • a background filter 42 is provided to establish a back- ground level.
  • Focussing optics 43 may be used to focus the Raman scattered radiation on a suitable sensor 44.
  • the electrical output of a sensor 46 is fed to a microprocessor 48 with amplification 47.
  • the microprocessor 48 is fed signals which indicate the position of a filter carriage 49 so as to determine which filter is in use and from the chopper 45 to indicate the chopping rate and phase. Where phase sensitive amplific ⁇ ation is employed, signals from the chopper are also fed to the amplifier 47.
  • the above described invention may find applic ⁇ ation in environments wherein components of gases, liquids or solids are monitored.
  • A. APPLICATION TO GASES 1. Gas Mixtures at Pressures up to Two Atmospheres The method is applicable equally to static or flowing gas streams.
  • the fibreoptic system is particularly useful for the analysis of gases under pressure. Signal levels are directly proportional to the number density of gas molecules which is related to the pressure and so the determination of minor components is improved at higher pressure.
  • the fibreoptic probe may be installed dir ⁇ ectly in the gas flow path and the components may be continuously monitored with negligible delay between sampling and measurement display.
  • the Raman spectral bands observed for liquids are, in general, much broader than those of gases and the spectra are frequently much more congested than gas spectra.
  • the monitoring of one component using the bandpass filter system is dependent on having one region of scattered light unique to that component and this condition is sometimes difficult to fulfil for liquids. When this separation of one component is not possible it may be necessary to use a monochrometer for the analysis.
  • the optimisation of a synthetic process may be possible if the relative concentrations of two components can be continuously monitored. Such reacting systems are frequently corrosive which would require the use of a protected probe. Dissolved gases are frequently of importance in a continuous flow liquid system.

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  • Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Biochemistry (AREA)
  • Analytical Chemistry (AREA)
  • Chemical & Material Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geophysics (AREA)
  • Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)

Abstract

Des radiations de diffusion Raman sont détectées à une position éloignée au moyen de radiations monochromatiques envoyées (19) à la position éloignée, et les radiations diffusées sont renvoyées (20) par un faisceau de fibres optiques (27) en vue de leur traitement.
PCT/AU1986/000076 1986-03-24 1986-03-24 Detection de la presence de materiaux WO1987006011A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
PCT/AU1986/000076 WO1987006011A1 (fr) 1986-03-24 1986-03-24 Detection de la presence de materiaux
IL78408A IL78408A0 (en) 1986-03-24 1986-04-02 Method and apparatus for monitoring the presence of materials

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AU56299/86A AU5629986A (en) 1986-03-24 1986-03-24 Monitoring the presence of materials
PCT/AU1986/000076 WO1987006011A1 (fr) 1986-03-24 1986-03-24 Detection de la presence de materiaux

Publications (1)

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WO1987006011A1 true WO1987006011A1 (fr) 1987-10-08

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PCT/AU1986/000076 WO1987006011A1 (fr) 1986-03-24 1986-03-24 Detection de la presence de materiaux

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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4919533A (en) * 1987-03-18 1990-04-24 The British Petroleum Company Plc Method for detecting diamonds in remote locations
WO1990011508A1 (fr) * 1989-03-22 1990-10-04 Kidde-Graviner Limited Amenagements permettant la detection des matieres particulaires et le couplage optique
GB2241350A (en) * 1990-02-24 1991-08-28 Bruker Analytische Messtechnik Raman spectrometer
EP0447931A2 (fr) * 1990-03-20 1991-09-25 Tecsa S.P.A. Détecteur de gaz à laser I.R. avec fibres optiques
US5262644A (en) * 1990-06-29 1993-11-16 Southwest Research Institute Remote spectroscopy for raman and brillouin scattering
US5404218A (en) * 1993-11-18 1995-04-04 The United States Of America As Represented By The United States Department Of Energy Fiber optic probe for light scattering measurements
EP0767222A2 (fr) * 1995-10-05 1997-04-09 Tioxide Group Services Limited Calcination de dioxyde de titane
US5638172A (en) * 1994-05-27 1997-06-10 Eastman Chemical Company On-line quantitative analysis of chemical compositions by raman spectrometry
WO1999012019A1 (fr) * 1997-09-01 1999-03-11 Akzo Nobel N.V. Technique permettant de mesurer les proprietes de fibres polymeres
GB2339901A (en) * 1998-07-21 2000-02-09 Cambridge Imaging Ltd Improved imaging system for luminescence assays

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3625613A (en) * 1968-06-28 1971-12-07 Avco Corp Apparatus for remote sensing and analyzing of gaseous materials using raman radiation
US3768908A (en) * 1971-01-04 1973-10-30 S Zaromb Remote sensing apparatus and methods
US3973849A (en) * 1975-06-16 1976-08-10 International Business Machines Corporation Self-calibratable spectrum analyzer
US4029419A (en) * 1975-10-10 1977-06-14 International Business Machines Corporation Textile color analyzer calibration
JPS5492790A (en) * 1977-12-30 1979-07-23 Minolta Camera Co Ltd Spectral information measuring device of body
JPS55112549A (en) * 1979-02-22 1980-08-30 Nippon Steel Corp Laser raman remote analysis method and unit thereof
GB2140555A (en) * 1983-05-24 1984-11-28 British Petroleum Co Plc Diamond separation

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3625613A (en) * 1968-06-28 1971-12-07 Avco Corp Apparatus for remote sensing and analyzing of gaseous materials using raman radiation
US3768908A (en) * 1971-01-04 1973-10-30 S Zaromb Remote sensing apparatus and methods
US3973849A (en) * 1975-06-16 1976-08-10 International Business Machines Corporation Self-calibratable spectrum analyzer
US4029419A (en) * 1975-10-10 1977-06-14 International Business Machines Corporation Textile color analyzer calibration
JPS5492790A (en) * 1977-12-30 1979-07-23 Minolta Camera Co Ltd Spectral information measuring device of body
JPS55112549A (en) * 1979-02-22 1980-08-30 Nippon Steel Corp Laser raman remote analysis method and unit thereof
GB2140555A (en) * 1983-05-24 1984-11-28 British Petroleum Co Plc Diamond separation

Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4919533A (en) * 1987-03-18 1990-04-24 The British Petroleum Company Plc Method for detecting diamonds in remote locations
WO1990011508A1 (fr) * 1989-03-22 1990-10-04 Kidde-Graviner Limited Amenagements permettant la detection des matieres particulaires et le couplage optique
GB2241350A (en) * 1990-02-24 1991-08-28 Bruker Analytische Messtechnik Raman spectrometer
GB2241350B (en) * 1990-02-24 1993-11-17 Bruker Analytische Messtechnik Raman spectrometer
EP0447931A2 (fr) * 1990-03-20 1991-09-25 Tecsa S.P.A. Détecteur de gaz à laser I.R. avec fibres optiques
EP0447931A3 (en) * 1990-03-20 1992-02-26 Tecsa S.P.A. Infrared laser fibre optics gas detection device
US5262644A (en) * 1990-06-29 1993-11-16 Southwest Research Institute Remote spectroscopy for raman and brillouin scattering
US5404218A (en) * 1993-11-18 1995-04-04 The United States Of America As Represented By The United States Department Of Energy Fiber optic probe for light scattering measurements
US5652653A (en) * 1994-05-27 1997-07-29 Eastman Chemical Company On-line quantitative analysis of chemical compositions by Raman spectrometry
US5638172A (en) * 1994-05-27 1997-06-10 Eastman Chemical Company On-line quantitative analysis of chemical compositions by raman spectrometry
EP0767222A2 (fr) * 1995-10-05 1997-04-09 Tioxide Group Services Limited Calcination de dioxyde de titane
EP0767222A3 (fr) * 1995-10-05 1998-06-10 Tioxide Group Services Limited Calcination de dioxyde de titane
AU729146B2 (en) * 1995-10-05 2001-01-25 Tioxide Group Services Limited Calcination of titanium dioxide
WO1999012019A1 (fr) * 1997-09-01 1999-03-11 Akzo Nobel N.V. Technique permettant de mesurer les proprietes de fibres polymeres
US6423262B1 (en) 1997-09-01 2002-07-23 Akzo Nobel N.V. Technique for measuring properties of polymeric fibres
GB2339901A (en) * 1998-07-21 2000-02-09 Cambridge Imaging Ltd Improved imaging system for luminescence assays
GB2339901B (en) * 1998-07-21 2003-11-05 Cambridge Imaging Ltd Improved imaging system for luminescence assays

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