GB2511376A

GB2511376A - A system for analysis, by laser-induced breakdown spectroscopy, of the composition of the surface layer of a material, and for the taking of samples with a vi

Info

Publication number: GB2511376A
Application number: GB201319164A
Authority: GB
Inventors: Bernard Picco; Thierry Varet
Original assignee: Areva NC SA
Current assignee: Orano Demantelement SAS
Priority date: 2013-02-27
Filing date: 2013-10-30
Publication date: 2014-09-03
Anticipated expiration: 2033-10-30
Also published as: ES2628691T3; JP6362115B2; GB2511376B; JP2016508612A; EP2962087B1; FR3002635B1; CN105074437B; EP2962087A1; WO2014131717A1; GB201319164D0; FR3002635A1; CN105074437A

Abstract

Analysing the composition of the surface layer of a material by laser-induced breakdown spectroscopy (LIBS) using a single pulsed laser 6, to generate a pulsed laser beam that interacts with the surface layer of the material 4 to produce a plasma 8 on the surface of the material. A device 10, 12 focuses the laser beam on the surface of the material and another device 18, 20 collects the light emitted by the plasma; this is then spectrally analysed by a device 22 to determine the elemental composition of the surface. A further device 30, 32, 34 sucks up and collects particles ablated from the surface layer for at least one additional qualitative or quantitative analysis. The light may be transmitted to the material and collected by optical fibres 10, 18 fitted with lenses 12, 20 and the suction device may be a cyclone 30 and pump 32 which collects particles on a filter 36. The additional analysis may be to examine for radiological contamination.

Description

A SYSTEM FOR ANALYSIS, BY LASER-INDUCED BREAKDOWN SPECTROSCOPY, OF THE COMPOSITION OF THE SURFACE LAYER OF A MATERIAL, AND FOR THE TAXING OF SAMPLES WITH A VIEW TO ADDITIONAL ANALYSES OR EXAMINATIONS OF THIS SURFACE LAYER,

AND METHOD RELATING THERETO

DESCRIPTION

TECHNICAL FIELD

The present invention relates to a system allowing the composition of the surface layer of a material to be analysed by LIBS (laser-induced breakdown spectroscopy), and the representative particles of this surface layer to be sampled for the purposes of additional qualitative or quantitative analyses, or examinations of this surface layer.

More specifically, the invention relates to a system allowing the surface contamination of a material to be analysed by LIBS, and allowing this contamination to be examined.

It applies in particular to the analysis and examination of the surface chemical contamination of a material, but more specifically to the analysis and examination of the surface radiological contamination of material, notably for the purposes of undertaking radiological investigations in workshops, buildings, and more generally nuclear installations, in particular to map their radiological condition before decontamination and/or dismantlement or after decontamination.

STATE OF THE PRIOR ART

Reference will be made to the following documents: (1] WO 95/17656, Method for determining the surface contamination of a solid, and device therefor, invention of P. Laffont et al. [2] US 5,583,634, Process for elementary analysis by optical emission spectroscopy on plasma produced by laser in the presence of argon, invention of N. André et at.

[3] US 7,106,439, Elementary analysis device by optical emission spectrometry on laser produced plasma, invention of J.L. Lacour et at.

[4] WO 2011/060404, Techniques for removing a contaminant layer from a thermal barrier coating and estimating remaining life of the coating, invention of W.T. Hassan et at.

[S] WO 2012/00577S, Laser-induced breakdown spectroscopy instrumentation for real-time elemental analysis, invention of i.E. Barefield.

Document [1] relates to the examination of the surface contamination of a solid. Documents [2] and [3] relate to the analysis of materials by the LIBS technique.

Document [4] relates to the decontamination of a coating polluted by chemical contaminants, and to the analysis of these contaminants) and uses the LlBS technique to this end. Document [5] relates to a portable device, allowing the [lBS technique to be implemented.

None of the techniques disclosed by these documents enables both analysis of the surface contamination of a material, and sampling with a view to examining this contamination, or undertaking an additional qualitative or quantitative analysis of it.

DESCRIPTION OF THE INVENTION

The aim of the present invention is to attain this dual goal.

It proposes a system allowing both an analysis of the composition of the surface layer of a material and sampling of the representative particles of this surface layer by means of a single pulsed laser, and a method of analysis and of sampling implementing this system.

It thus combines two techniques: -the LIBS technique1 which enables the chemical nature and relative concentration (in %) of the elements present at the surface of the material to be analysed, and -a sampling technique which uses the same pulsed laser as the LlBS technique, and which allows suction and collection of the ablated particles, with a view to a precise quantification of the constituent elements of the sample taken, or with a view to an additional qualitative analysis.

A brief recap of the details of the LIBS technique follows: a laser pulse at the surface of the material generates a plasma which is stretched and cooled, emitting a light radiation; the latter is collected and transmitted to a spectrometer; the lines of the spectrum obtained in this manner are recovered and analysed.

In respect of the sampling technique, a laser pulse is also sent to the surface of the material (using the same pulsed laser). This leads to an ablation of particles of the surface of the material. The ablated particles are sucked up by sampling means, and then collected on a filter.

When considering the particular application in the field of analysis and examination of surface radiological contamination of a material, quantification of the contamination (expressed in Bq/cm2) is accomplished by counting the radioactivity collected on the filter, this quantification being undertaken in situ or in the laboratory where the filter has been sent.

In precise terms, the object of the present invention is a system for analysis of the composition of the surface layer, notably a radioactive layer, of a material, by laser-induced breakdown spectroscopy, including: -a single pulsed laser, to generate a pulsed laser beam, able to interact with the surface layer and produce a plasma on the surface of the material, -a device for focusing the pulsed laser beam on to the surface of the material, -a device to collect the light emitted by the plasma, and -a device for spectral analysis of the light collected in this manner, and determination of the elemental composition of the surface layer from the spectral analysis, characterised in that it also includes a device to suck up and collect representative particles of this surface layer, extracted from the latter under the effect of the focused pulsed laser beam, with a view to at least one additional qualitative or quantitative analysis, or at least one examination, notably a radiological contamination examination, using the sucked up, collected particles.

According to one preferred embodiment of the system forming the object of the invention the pulsed laser and the focusing device are chosen to obtain a power density in the range 1 GW/cm2 to 50GW/cm2, at the surface of the material.

The focusing device is preferably chosen to obtain a focused pulsed laser beam the size of which (more accurately the focusing diameter for a roughly circular laser beam) is in the range 1 im to 10 m, at the surface of the material.

The device to suck up and collect the particles is preferably chosen to obtain a suction speed in the range 20 rn/s to 200 rn/s.

According to one preferred embodiment of the invention, the pulsed laser beam focusing device includes: -an optical fibre having a first end connected to the pulsed laser, and a second end, and -a focusing lens positioned at the second end of the optical fibre.

The device to collect the light emitted by the plasma may include an optical fibre one end of which is preferably fitted with a light-collection lens.

The system is preferably portable, and the device to suck up and collect the particles then includes: -a suction cyclone to draw in air containing the representative particles of this surface layer, -a pump to draw in the air, and -a duct which connects the pump to the cyclone.

This device may then include: -a filter, for example a paper filter, on which the particles contained in the suction air are deposited, and -a housing, which may possibly be detachable, which is installed on the duct for the purpose of placing the filter in it and removing said filter from it with a view S to the additional qualitative or quantitative analysis or the examination using the particles deposited on the filter.

Optionally, the system may also include a device for additional quantitative analysis, or for additional qualitative analysis (and therefore analysis other than the analysis resulting from the spectral analysis), or for examination, notably radiological contamination examination, using the particles deposited on the filter. In the case of the radiological contamination examination, this direct examination allows the said contamination to be assessed, with the understanding that the precise examination, which requires more substantial equipment, is then undertaken in the laboratory in non-real time.

According to another particular embodiment of the system forming the object of the invention, the device to suck up and collect the particles includes: -a suction head to draw in air containing the particles extracted from the surface layer of the material, -a pump to draw in the air, -a duct which connects the pump to the suction head, -a housing which is installed on the duct, -a grid positioned in the housing, where the latter has two apertures above the grid, respectively at both ends of this grid, -a filter, for example a paper filter, which can be moved over the grid, and which is able to traverse both apertures of the housing, and on which particles contained in the suction air are deposited, -a device for additional qualitative or quantitative analysis or examination, notably radiological contamination examination, using the particles deposited on the filter, and -a device to move the filter over the grid and at the level of the device for the additional qualitative or quantitative analysis or examination, notably radiological contamination examination.

Another oblect of the present invention is a method for analysis by LIBS of the composition of the surface layer of a material, and for taking of samples with a view to at least one additional qualitative or quantitative analysis, or at least one examination of this surface layer, and more particularly of at least one radiological contamination examination, implementing the system forming the object of the invention.

This method includes a first step of analysis by LIBS, a second step of sampling, where these first and second steps are accomplished simultaneously or sequentially, and a third step of additional qualitative or quantitative analysis, or of examination.

According to a first particular embodiment of this method, in a first step the LIBS analysis of the material is undertaken, and then, if the result of the LIBS analysis reveals the presence of at least one chemical element of interest, for example a radioactive contaminant, in a second stage a sample is taken of the surface layer of the material released by the impact of the laser beam, in order to undertake an additional qualitative or quantitative analysis, or examination, of it. The method is, in this case, implemented sequentially. One advantage of this first embodiment is that it ensures that the sampled material indeed contains the sought elements, and therefore limits the use and wastage of filters. It therefore enables less waste to be generated and, if this additional analysis or the examination is undertaken in a laboratory, enables the number of unsuccessful analyses to be limited, leading to less wasted time and use of fewer laboratory resources.

According to a second particular embodiment, otherwise called a parallel mode, the two steps of analysis by LIBS and of sampling are accomplished simultaneously. In the event of a systematic and automated examination, this can enable results of the LIBS analysis and of the analysis of the sampling filter to be obtained simultaneously, and these analyses may then be complementary.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

The present invention will be better understood on reading the description of example embodiments given below, purely as an indication and in no sense restrictively, making reference to the appended drawings in which: -figure 1 is a schematic view of a first particular embodiment of the system forming the object of the invention, in which this system is portable, and -figure 2 is a schematic view of a second particular embodiment of the system forming the object of the invention, in which this system is stationary.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

Figure 1 illustrates schematically a first example of the invention, in the application to examination of the surface radiological contamination of a material.

This is therefore a system allowing not only analysis but also examination of surface contamination 2 of a material 4. The analysis uses the LIBS technique. In the described example the system is portable, And the surface contamination of the material is of a radiological character, The system for analysis and examination of radiological contamination represented in figure 1 includes: -a single pulsed laser 6, for example a pulsed (AG laser, to cause a pulsed laser beam, able to interact with surface contamination 2 and produce a plasma S at the surface of material 4, and -a device for focusing the pulsed laser beam on to the surface of material 4.

This device includes an optical fibre 10, one end of which is optically coupled to laser 6. The other end of fibre 10 is fitted with a focusing lens 12 to focus the pulsed laser beam on to the surface of material 4.

As can be seen, the system of figure 1 includes a unit 14 fitted with a handle 16. And the end of fibre 10, which is terminated by lens 12, is roughly linear and housed in unit 14. Using handle 16 the system may be pointed towards the analysed material, and the beam focused on the surface of this material.

The system of figure 1 also includes a device to collect the light emitted by plasma 8. This device includes, in the described example, an optical fibre 18, one end of which is preferably fitted with a light collection lens 20. As can be seen, lens 20 is positioned at the level of lens 12, but underneath the latter.

The system also includes a device 22 for spectral analysis of the light collected in this manner, and determination of the elemental composition of the surface layer from the spectral analysis undertaken in this manner. This device 22 includes: -a spectrometer 24, to which the other end of fibre iSis attached, and -a device 26 for processing the spectrum provided by a spectrometer 24, to determine the elemental composition of the contamination.

This device 26 is fitted with a device 28 to display the results obtained.

In accordance with the invention, the system of figure 1 also includes a device to suck up and collect particles of surface contamination 2, extracted from the latter under the effect of the focused pulsed laser beam, with a view also to examining the surface contamination using the sucked up and collected particles.

This device includes: -a suction cyclone 30 to draw in air containing the particles of surface contamination 2, -a pump 32 to draw in the air, and -a duct 34 which connects pump 32 to cyclone 30.

The suction air is represented symbolically by arrows F in figure 1.

The device to suck up and collect the particles also includes: -a filter 36, for example a paper filter, on which particles contained in the suction air are deposited, and -a housing 38 which is installed on duct 34 to install filter 36 in it, and remove said filter from it, with a view to examining surface contamination 2 using the particles deposited on filter 36.

This examination may be undertaken in a laboratory, in which case filter 36 must then be transported. To undertake the examination a proportional counter is then used, for example, combined with electronic counting means.

As can be seen in figure 1, the roughly linear end of optical fibre 10 is within suction cyclone 30, and it is housed in a tube 40 which protects this fibre, to prevent it being disturbed by the movements of the air in the cyclone.

In addition, in the described example, housing 38 is installed permanently on duct 34. But, as a variant, a detachable housing 38 may be used. This enables the filter to be transported in the housing to the laboratory to make additional qualitative or quantitative analyses of the sample of particles collected on the filter. As an example of such additional analyses undertaken in a device-independent manner, the establishment of the isotopic spectrum may be cited. In addition, the laboratory may, for example, be in a vehicle which may be brought close to the analysed and examined material.

To return to the two techniques used: the LIBS technique and the contamination examination technique, In the invention, in particular, in the system represented in figure 1, these two techniques are combined. This poses problems concerning the choice of power density 0 which is to be deposited on the material, the choice of size T of the focused pulsed laser beam in the material, i.e. the diameter of the laser spot on the material, since the laser spot is generally roughly circular, and the choice of suction speed V. Indeed, parameters D and T have different values for the two techniques. And, as regards parameter V. choosing too high a value may be detrimental to the quality of the spectrometric analysis: there is a risk that the plasma will be "sucked up". Actually it is known that use of the LIBS technique is facilitated if a jet of air or gas, for example an inert gas, is directed at the plasma, which may require that an optimised balance is found to make each of the air or gas injection (1) or suction (2) functions effective.

When implementing the invention, in particular the system of figure 1, optimal ranges of values which are compatible with both techniques used should be used when choosing parameters 0,1 and V. The ranges of values chosen are given below.

Pulsed laser 6 and the focusing are chosen to obtain a power density 0 within the range 1 GW/cm2 to 50GW/cm2, at the surface of material 4. Purely for information, and in no way restrictively, 0 is equal to approximately 30 GW/cm2.

In addition, the focusing is chosen so as to obtain a focused pulsed laser beam the size I of which is in the range 1 pm to 10 pm, at the surface of material 4.

Purely for information, and in no way restrictively, a size I equal to approximately 5 pm is chosen.

And the device to suck up and collect the particles (pump-duct-cyclone in the example of figure 1) is chosen so as to obtain a suction speed V in the range 20 rn/s to 200 m/s, and preferably in the range 20 rn/s to 150 rn/s.

The system been described making reference to figure 1 is of the type which may be carried, and more generally transported, to the location where the contaminated material is located.

But a stationary system in accordance with the invention may be designed, in which case the contaminated material must be brought to the system.

An example of a stationary system in accordance with the invention, also related to the application to surface radiological contamination examination of a material, is illustrated schematically by figure 2.

In the case of this system the device to suck up and collect the particles includes: -a suction head 42 to draw in air containing the particles of the surface contamination, -a pump 44 to draw in the air, -a duct 46 which connects pump 44 to suction head 42, -a housing 48 which is installed on duct 46, -a grid 50 positioned in housing 48, where the latter has two apertures 52 and 54 above grid 50, respectively at both ends of this grid, -a filter 56, for example a paper filter, which can be moved over grid 50, and which is able to traverse both apertures 52 and 54 of housing 48, and on which particles contained in the suction air are deposited, -a device 58 to examine the contamination using the particles deposited on filter 56, and -a device 60 to move filter 56 over grid 50 and at the level of device 58 to examine the contamination.

Arrows f show the movement of the suction air.

In the example of figure 2, filter 56 takes the form of a strip of filter paper, which is unrolled from a reel 62. This strip is moved using drive rollers 64 controlled by an unrepresented motor.

The strip passes in succession above grid 50 which supports it, and then at the level of examination device 58. It can be seen that the strip passes over a plate 66 which supports it, and that device 58 is above this plate 66.

In the example of figure 2 this device 58 is a proportional counter. It is combined with electronic counting means 68.

A device 70 to recover the filter paper after it has passed at the level of the proportional counter can also be seen.

Figure 2 also shows the single pulsed laser used 6, for example of the YAG type, analysed material 4 which receives a focused pulsed laser beam 72, and optical fibre 10 which guides the beam to an area in proximity to material 4, traversing suction head 42 in which it is also protected by unrepresented means. The focusing lens of the laser beam is not represented.

In figure 2 the various means of recovery and analysis of the light emitted by the produced plasma are not represented. But those skilled in the art can easily adapt the corresponding means, relative to figure 1, to this figure 2.

In the case of this figure 2 it is noted that the contamination is analysed in realtime, whereas it is undertaken in non-real time in the case of figure 1.

Examples of the method which is an object of the invention are given below: Example of a method implemented in sequential mode: a Contamination examination at the end of decontamination: the LIBS analysis system is used in scanning mode to characterise the decontaminated surface in the most exhaustive manner possible, and to ensure that characteristic S chemical elements, for example uranium, are absent; if a significant signal is detected, it is switched to sampling mode; this sample is then sent to the laboratory for precise quantification of the contamination present (uranium and other radioelements, if applicable).

o Sampling for assessment of the typical spectrum: the LIBS portion of the analysis system is used in scanning mode to seek, on the surfaces of the equipment or of the structure, an area where a characteristic element, for example uranium, is present in a non-negligible quantity (several Bq.cm2 or more); if the LIBS device is correctly calibrated this can enable the quantity of uranium present in this area to be derived, but this information is not sufficient to prepare for interventions in a radioactive environment: it is important to know the distribution across the different uranium isotopes; in this case, once an area of interest has been identified in the LIBS analysis step, a sample is taken by the sampling system, and the sample taken in this manner is sent to the laboratory for analysis by a mass spectrometer. The previously undertaken LIBS analysis makes it possible to be certain that the sample taken will contain sufficient material to undertake this additional analysis.

* Example of a method implemented in parallel mode: o Systematic quality control: the quality of coating of a part, or an absence of impurities, may be required and must be demonstrated by a systematic examination; the part is then positioned in front of the system; in systematic fashion a LIBS analysis is made, and samples are taken simultaneously; the result of the [lBS analysis is used to make a first immediate sort, while the additional analysis or the examination of the sample material is used to confirm, possibly by sampling, the analysis made by LIBS.

The invention may apply to the case of radiological contamination (checking for non-contamination or qualification and quantification of surface radiological activity on an item of equipment or a structure), or to the case of chemical contamination (search for the presence of impurities on the surface of a material).

Claims

CLAIMS1. A system for analysis of the composition of the surface layer, notably a radioactive layer, of a material, by laser-induced breakdown spectroscopy, including: -a single pulsed laser (6), to generate a pulsed laser beam, able to interact with the surface layer and produce a plasma on the surface of the material (4), -a device (10, 12) for focusing the pulsed laser beam on to the surface of the material, -a device (18, 20) to collect the light emitted by the plasma, and -a device (22) for spectral analysis of the light collected in this manner, and determination of the elemental composition of the surface layer from the spectral analysis, characterised in that it also includes a device (30, 32, 34; 42, 44, 46) to suck up and collect representative particles of this surface layer, extracted from the latter under the effect of the focused pulsed laser beam, with a view to at least one additional qualitative or quantitative analysis, or at least one examination, notably a radiological contamination examination, using the sucked up, collected particles.
2. A system according to claim 1, in which the pulsed laser (6) and the focusing device (10, 12) are chosen to obtain a power density within the range 1 GW/cm2 to 50GW/cm2, at the surface of the material (4).
3. A system according to either of claims 1 and 2, in which the focusing device (10, 12) is chosen to obtain a focused pulsed laser beam the size of which is within the range 1 m to 10 m, at the surface of the material (4).
4. A system according to any one of claims 1 to 3, in which the device (30, 32, 34; 42, 44, 46) to suck up and collect the particles is chosen to obtain a suction speed within the range 20 mIs to 200 mIs.
5. A system according to any one of claims 1 to 4, in which the focusing device of the pulsed laser beam includes: -an optical fibre (10) having a first end connected to the pulsed laser (6), and a second end, and -a focusing lens (12) positioned at the second end of the optical fibre (10).
6. A system according to any one of claims 1 to 5, in which the device to collect the light emitted by the plasma includes an optical fibre (18) one end of which is preferably fitted with a lens (20) for collecting light.
7. A system according to any one of claims ito 6, characterised in that it is portable, and in which the device to suck up and collect the particles includes: -a suction cyclone (30) to draw in air containing the representative particles of this surface layer, -a pump (32) to draw in the air, and -a duct (34) which connects the pump to the cyclone.
8. A system according to claim 7, in which the device to suck up and collect the particles also includes: -a filter (36), for example a paper filter, on which particles contained in the suction air are deposited, and -a housing (38), which may possibly be detachable, which is installed on the duct (34) for the purpose of placing the filter in it and removing said filter from it with a view to the additional qualitative or quantitative analysis or the examination using the particles deposited on the filter.
9. A system according to claim 8, also including a device for additional qualitative or quantitative analysis or for examination, notably radiological contamination examination, using the particles deposited on the filter.
10. A system according to any one of claims 1 to 6, in which the device for sucking up and collecting the particles includes: -a suction head (42) to draw in air containing the particles extracted from the surface layer of the material, -a pump (44) to draw in the air, -a duct (46) which connects the pump to the suction head, -a housing (48) which is installed on the duct, -a grid (50) positioned in the housing, where the latter has two apertures (52, 54) above the grid, respectively at both ends of this grid, -a filter (56), for example a paper filter, which can be moved over the grid, and which is able to traverse both apertures of the housing, and on which particles contained in the suction air are deposited, -a device (58) for additional qualitative or quantitative analysis or examination, notably radiological contamination examination, using the particles deposited on the filter) and -a device (60) to move the filter over the grid and at the level of the device (58) for the additional qualitative or quantitative analysis or the examination, notably radiological contamination examination.
11. A method for analysis by laser-induced breakdown spectroscopy of the composition of the surface layer of a material, and for the taking of samples with a view to at least one additional qualitative or quantitative analysis or at least one examination of this surface layer, which method implements the system according to any one of claims 1 to 10, characterised in that it includes a first step of analysis by laser-induced breakdown spectroscopy, a second step of sampling, where these first and second steps are accomplished simultaneously or sequentially, and a third step of additional qualitative or quantitative analysis or of examination.