Optics: measuring and testing – Crystal or gem examination
Patent
1988-11-15
1990-04-24
Evans, F. L.
Optics: measuring and testing
Crystal or gem examination
356301, G01V 904, G01N 2165
Patent
active
049195336
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a detection method and more particularly relates to a method for detecting diamonds in locations which are not easily accessible.
It is often useful, for example when prospecting a site for diamond bearing ores, to examine samples of material to determine whether they contain diamonds. Such examination may be time consuming if samples have to be removed from the site and examined in a laboratory by conventional means. The examination may be further delayed if the material to be sampled is in a location which is not easily accessible.
Raman spectroscopy may be used for the separation of diamonds from a diamondiferous material and is disclosed in our UK patent no. GB 2140555B. The Raman signal of diamond is stronger than that of most other materials because diamond only contains carbon to carbon bonding and its Raman signal occurs at a position well separated from those of other minerals. Also, because diamond only contains one type of carbon to carbon bond, there is only a single Raman signal, which is readily distinguishable from associated broad band fluorescence. This means that the use of Raman spectroscopy is particularly suitable for detecting diamonds. The present invention relates to a further development of Raman spectroscopy which is suitable for detecting diamonds in locations which are not easily accessible.
Thus, according to the present invention there is provided a method for detecting diamonds in locations which are not easily accessible, the method comprising (a) irradiating material suspected of containing diamonds in a location which is not easily accessible, with laser radiation at a pre-determined wavelength, the irradiating means being adapted for access to the location and the laser radiation being capable of causing Raman radiation to be scattered from diamonds in the material, (b) collecting the scattered Raman radiation by a collecting means adapted for access to the location, (c) passing the collected Raman radiation through a filtering means adapted to pass only Raman radiation characteristic of diamonds, and (d) sensing the filtered Raman radiation by a sensing means adapted to produce a signal whenever radiation characteristic of diamonds is sensed, whereby the absence or the presence of diamonds in the location is indicated.
A device for irradiating the material with laser radiation may be a probe comprising a bundle of optical fibres which may be used to conduct the laser radiation from a laser to the material in locations which are not easily accessible, for example in crevices or down bore holes and the like. The collecting means may also be a probe comprising a bundle of optical fibres which may be used to conduct the scattered Raman radiation from the material to the filtering means. The optical fibres, which conduct the radiations to and from the location, may take the form of an integral flexible probe which may be pushed into crevices in the material or lowered down a bore hole.
Preferably the laser radiation is monochromatic and most preferably has a wavelength in the range 450 to 650 nanometers. The filtering means is preferably a narrow band pass filter and may comprise a thin glass slide having a suitable filter coating. The sensing means for the filtered Raman radiation may be based on a photocell but other forms of sensor may also be used, for example a photomultiplier tube, a diode array, a video camera, charge couple device camera, or a human eye.
It is envisaged that the apparatus used for the method according to the invention may be portable. Thus, the apparatus may be mounted on a lorry, jeep or other vehicle or may be sufficiently portable to be carried by an operator. The apparatus may be sufficiently compact to allow it to be lowered down a borehole or the like.
It is further envisaged that the apparatus may be mounted on a remote-controlled vehicle.
It is envisaged that the present invention may be used for subsea prospecting. The scattered Raman radiation in this case may be collected and filtered by a lens filter on a video ca
REFERENCES:
patent: 3371574 (1968-03-01), Dwyer
patent: 4573761 (1986-03-01), McLachlan et al.
G. D. Ferguson, "Blue Green Lasers for Underwater Applications", Oceanoptics, SPIE vol. 64 (1975) pp. 150-156.
G. Grasseli et al. "Use of Raman Spectrography in Chemistry", Moscow MIR 1984, pp. 186-187.
S. Schwab et al, "Versatile, Efficient Raman Sampling with Fiber Optics," Anal. Chem. 1984, 56, pp. 2199-2204.
Bowley Heather J.
Gerrard Donald L.
Preedy John E.
Curatolo Joseph G.
Evans F. L.
Evans Larry W.
The British Petroleum Company plc
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