Scintillator material and manufacturing process

Abstract

Scintillator material and manufacturing method Scintillator material (3) comprising quantum carbon dots with a graphitic core dispersed in a matrix, said material comprising aromatic units capable of emitting UV radiation in response to irradiation, in particular of the beta type, this UV radiation causing luminescence of the carbon dots and the emission by them of radiation in the visible range Figure for the abstract: Fig. 1

Description

Title of the invention: Scintillator material and manufacturing method Technical field

[0001] The present invention relates to scintillators capable of emitting light photons under the effect of radiation of nuclear origin, in particular radiation [3. Prior art

[0002] The detection of emissions in the form of waves such as gamma or X rays, or particles such as beta rays or neutrons, represents an increasingly current challenge, as the dismantling of first generation nuclear installations is carried out. It is likely that these needs will increase with the increase in the number of dismantling sites.

[0003] Scintillation materials with increasingly lower detection limits will be necessary in the future in order to ensure the best possible radiation protection of dismantling operators.

[0004] While current gamma scintillators cover radiation protection needs relatively well, feedback from personnel in charge of dismantling operations shows that progress still needs to be made regarding alpha or beta detection. This is mainly due to the low energy involved, which makes these radiations difficult to detect.

[0005] Existing beta scintillators generally use inorganic crystals (Csl, GaO, CaF2) or plastic matrices (POPOP, benzene derivatives) as luminescent agents capable of transforming incident particles (electrons or positrons for [3 or |3+) into light photons.

[0006] They are relatively complex to produce and require the use of exhaustible resources in the case of certain inorganic crystals such as those based on gallium for example. Statement of the invention

[0007] There is therefore a need for a scintillator material that is relatively simple to produce, making it possible to avoid the use of rare inorganic compounds if desired, and having good detection sensitivity to beta radiation in particular. Summary of the invention

[0008] The invention aims to meet this need and achieves this by means of a scintillator material comprising dispersed graphitic core quantum carbon dots in a matrix, said material comprising aromatic units capable of emitting UV radiation in response to irradiation, in particular of the beta type, this UV radiation causing luminescence of the carbon points and the emission by the latter of radiation in the visible range.

[0009] Such a material does not require the use of rare inorganic compounds and has good sensitivity to the detection of beta radiation in particular.

[0010] The invention also relates, according to another of its aspects, to a method for detecting radiation originating from a radioactive source, in particular beta radiation, in which a scintillator material according to the invention is exposed to said radiation, and an emission of light photons by said material is detected, in response to this exposure.

[0011] The invention also relates to a radiation detector, in particular beta radiation, comprising a scintillator material according to the invention, arranged so as to be able to be exposed to said radiation, and at least one sensor of light photons emitted by said scintillator material in response to this exposure. Matrix

[0012] The matrix may be thermoplastic or thermosetting. In particular, it may be cast or injected in a fluid state into a mold, then demolded after cooling.

[0013] The matrix may have any shape, in particular polyhedral, for example cubic or parallelepiped, solid or hollow cylindrical, conical, toric, among other possibilities. It may be machined, if necessary, to the desired shape.

[0014] The matrix can also be in the form of a layer serving as a binder for the carbon dots.

[0015] The matrix is preferably transparent, but may be translucent.

[0016] The matrix may be colorless and the material may have a brown color due to the presence of carbon dots.

[0017] The matrix may further include one or more colorants.

[0018] It can integrate a light collecting element, if necessary, or form a light guide.

[0019] The matrix occupies any volume appropriate to the conditions of use. Its thickness ranges, for example, from 1 mm to 100 mm.

[0020] In particular when it is polymeric, the polymer of the matrix can have the aforementioned aromatic units.

[0021] The matrix may in particular be a styrenic polymer, in particular polystyrene (PS), acrylonitrile butadiene styrene (ABS) or methylmethacrylate butadiene styrene (MBS), or be chosen from aromatic polyethers (PAE), in particular poly(phenylene oxide) (PPO), polyvinyltoluene (PVT) or a mixture of these. The matrix may in particular contain polystyrene or be made of polystyrene, this polymer allows good results to be obtained.

[0022] The matrix may be polymeric. The polymer may be a homopolymer or a copolymer. Aromatic motifs

[0023] The aromatic units may be phenyl rings, but any aromatic unit capable of generating UV emission under the action of the incident radiation to be detected, then by transfer, in particular radiative, an emission of visible light by the carbon points, may be suitable.

[0024] The aromatic units can thus be cycles other than phenyl, for example.

[0025] The aromatic units may be present within the matrix. The matrix may thus be a plastic material having aromatic units, as mentioned above.

[0026] The aromatic units may comprise one or more heteroatoms, where appropriate, and / or be condensed in the form of aromatic polycyclic compounds. Carbon points

[0027] Carbon dots are also known by the Anglo-Saxon designation “Carbon Dots” or “CD”.

[0028] They are in the form of luminescent nanoparticles with a graphitic core, the size of which is less than or equal to 50nm, and preferably less than or equal to 10nm.

[0029] The carbon dots are preferably hydrophobic, which can facilitate their dispersion in the polymerization precursor of the matrix.

[0030] In exemplary embodiments, the carbon dots have traces of nitrogen, which originate from the synthesis process used. These traces of nitrogen can contribute to improving the emission efficiency of the carbon dots. Indeed, the nitrogen groups act as exciton traps, which results in an increase in the quantum efficiency of the carbon dots.

[0031] The carbon points may have a non-zero nitrogen content, in particular an atomic % content of Nls of between 10 and 15%.

[0032] The carbon dots may have a non-zero oxygen content, in particular an atomic % content of Ois of between 15 and 20%. The carbon dots may have an atomic % content of Cls of between 65 and 75%.

[0033] The mass content of carbon dots may be between 0.01% and 0.5% relative to the total weight of the scintillator material (carbon dots plus matrix). Synthesis process

[0034] Carbon dots can be produced from the degradation (for example hydrothermal or by microwave) of molecules used as precursors. These precursor molecules are preferably extracted from biomass, which constitutes an advantage in view of the inexhaustible nature of the resources allowing their production.

[0035] The carbon points advantageously result from a synthesis process involving the decomposition of trinitropyrene, previously solubilized in an organic solvent, which may be toluene, dimethylformamide (DMF), or better still a toluene / DMF mixture.

[0036] The presence of DMF in a DMF / toluene mixture makes it possible to obtain a better mass yield of carbon points.

[0037] Manufacturing method The invention also relates to a method for manufacturing the scintillator material according to the invention, in which the carbon dots are synthesized by implementing the above synthesis method, in particular a synthesis method in which the decomposition of trinitropyrene, previously solubilized in an organic solvent, is carried out, this organic solvent comprising a mixture of toluene and dimethylformamide (DMF).

[0038] As mentioned above, the matrix can be polymerized in the presence of the carbon dots. Alternatively, the matrix can be dissolved in a solution containing the carbon dots suspended in an organic solvent, and then the organic solvent is evaporated, this evaporation taking place, for example, in a mold of the desired shape.

[0039] It is thus possible to prepare a suspension of carbon dots in an organic solvent, in particular consisting of or containing toluene, dissolve polystyrene with this solution and then evaporate the solvent. Brief description of the drawings

[0040] The invention may be better understood by reading the detailed description which follows, non-limiting examples of its implementation, and by examining the attached drawing, in which:

[0041] [Fig. 1] schematically and partially represents a test installation for a scintillator material according to the invention,

[0042] [Fig.2] represents two raw images obtained from a 90Sr source on a PS matrix alone (left image) and on a scintillator material according to the invention (right image), with a PS matrix loaded with 0.015% by weight of carbon points,

[0043] [Fig.3] represents transmission electron microscopy (TEM) images of carbon dots (images A and B) and a diffractogram of the carbon dots (image C),

[0044] [Fig.4] illustrates the effect of scintillator thickness on the intensity of the radioluminescence,

[0045] [Fig.5] illustrates the effect of carbon dot concentration on the intensity of the radioluminescence,

[0046] [Fig.6] illustrates the effect of the presence of carbon dots in a PS matrix for a source 90Sr (left image) and 14C (right image),

[0047] [Fig.7] illustrates the XPS spectrum of the carbon dots used for scintillation (at left) and the associated content of Carbon (C), Nitrogen (N) and Oxygen (O), and

[0048] [Fig.8] illustrates the deconvolution of XPS spectra associated with carbon points used for scintillation and identification of functions present in carbon dots using fitting curves (Fits). Detailed description

[0049] [Fig.l] shows an installation 1 (also called a measuring bench) for testing a scintillator material 3 according to the invention, comprising a radioactive source 2 arranged on one side of the scintillator material 3 and a camera 4 arranged on the opposite side, to observe the scintillator material 3, the assembly being placed in a black enclosure 5.

[0050] The camera 4 is equipped with a photosensitive detector making it possible to count photons in a spectral range covering the UV-visible domain of light (180-900 nm).

[0051] The radioactive source 2 used for the tests is for example a pure beta emitting source, such as a 90Sr source delivering an energy of 546 keV and having an activity of 12 kBq, or a 14C source delivering an energy of 156 keV and having an activity of 33 kBq.

[0052] The scintillator material 3 may be in the form of a solid block, of parallelepiped or cylindrical shape, any shape being however possible.

[0053] The manufacture of the scintillator material 3 can be done in two stages.

[0054] In a first step, the carbon dots are synthesized in the form of a powder. In a second step, this powder is dispersed in a liquid monomer in the presence of a polymerization initiator. After a waiting time necessary for the polymerization of the monomer, the carbon dots are found fixed in a transparent plastic matrix, for example polystyrene.

[0055] It is also possible to avoid the waiting time associated with the polymerization of the monomer. In this case, it is sufficient to first prepare a suspension of carbon dots in toluene. 5g of polystyrene are then dissolved in 10mL of this suspension. Finally, the mixture is placed in a mold of the desired shape and left for the toluene to evaporate. After waiting 48 hours, a polystyrene scintillator loaded with carbon dots is obtained.

[0056] Carbon dots can be synthesized from trinitropyrene of the following formula:

[0057] [Chem.l]

[0058] A solution of trinitropyrene is prepared, for example, at a concentration of 10 mg / mL in dimethylformamide (DMF). This solution can then be placed either in a microwave oven at 200°C for 1 hour, or in an autoclave at 200°C for 8 hours. At the end of the reaction, a blackish purple solution is obtained. This solution is slowly evaporated, for example, at 70°C for 72 hours. Following the evaporation step, a black powder is collected. This black powder can be redispersed in 5 mL of ethanol. These 5 mL are then dialyzed, for example, for 24 hours in a tube specific to IkDa to remove the species that have not reacted. The ethanol solution containing the purified carbon dots is then evaporated, for example, at 70°C overnight.

[0059] After this final evaporation step, a black powder of purified carbon dots is obtained. It is this black powder which can then be used for the preparation of the scintillator material.

[0060] The synthesis is preferably carried out in DMF because it is preferable to obtain hydrophobic carbon points, which are easier to disperse subsequently in the monomer which serves as a precursor to the transparent plastic matrix.

[0061] [Fig.3] shows TEM images as well as the diffractogram relating to the carbon dots thus prepared. The size of the carbon dots is polydisperse, between a few nm and 50nm (images A and B). The DRX analysis (image C) gives a classic diffractogram of what is generally obtained with carbon dots, with a broad peak around 25° relative to the (002) plane of the graphitic core of the carbon dots.

[0062] To produce the block of scintillator material 3, a mass of, for example, between 5 mg and 15 mg of carbon dots is taken and then dispersed in 20 mL of styrene with stirring. Then, a mass of a polymerization initiator such as benzoyl peroxide, for example, between 0 and 20 mg, is added. Then the viscous liquid is placed in a mold intended to give its shape to the scintillator material, and left to mature at a temperature of, for example, between 70°C and 110°C for a time of, for example, between 5 and 25 days.

[0063] The installation of [Fig.l] makes it possible to test the radioluminescence properties of the scintillator materials 3 according to the invention thus obtained.

[0064] The radioactive source 2 illuminates the scintillator material 3, which is in an excited energetic state. When it is de-excited, the scintillator material 3 emits a light photon which is captured by the detector of the camera 4. The signal recovered by the camera in the form of an image is then analyzed by a computer 7 running image processing software to obtain a curve allowing the efficiency of each scintillator material to be compared.

[0065] [Fig.2] shows the results of the radioluminescence tests carried out with the measuring bench of [Fig.l]. It can be seen that the samples containing carbon dots (right image) emit much more light photons than the PS matrix alone (left image). There is therefore clearly a carbon dot effect involved in the radioluminescence mechanisms of the scintillator material according to the invention.

[0066] We see in [Fig.6] that the intensity of the detected signal can depend on the energy of the radiation considered, since for the same exposure time, the 90Sr source (left image) causes the emission of more light photons in the visible range of light than the 14C source (right image).

[0067] [Fig. 5] shows the influence of the concentration of carbon dots in the matrix on the radioluminescence intensity of the scintillator material according to the invention. In this example, the scintillator material is 9 mm thick and 13 mm on each side, and the concentration is respectively 0.045% (highest intensity), 0.027% (intermediate intensity) and 0.015% by weight (lowest intensity).

[0068] [Fig.4] shows the effect of the thickness of the scintillator material placed on the path of the incident radiation on the intensity of the 90Sr radioluminescence. It can be seen that the radioluminescence effect is indeed due to the presence of the scintillator material, increasing with its thickness, and therefore to the presence of the carbon dots in this material. The highest intensity is obtained in this figure for a thickness of 9mm, and the lowest for a thickness of 2mm, for the same concentration of 0.027% by weight of the carbon dots.

[0069] [Fig.7] shows the XPS spectrum of the carbon dots and their calculated content in Carbon (69.5%), Nitrogen (12.4%) and Oxygen (18.1%). The deconvolution of the peaks of the XPS spectrum presented in [Fig.8] allows the identification of the various groups present on the surface of the carbon dots.

[0070] Of course, the invention is not limited to the exemplary embodiments which have just been described.

[0071] For example, the scintillator material may be used for the detection of radiation other than beta radiation, for example alpha or gamma radiation.

[0072] The matrix can be made with other polymers, and the aromatic units can be present in another form.

[0073] The scintillator material can be combined with other scintillator materials aimed at detecting other radiation, for example neutron.

Claims

Claims

1. Detector of radiation of radioactive origin, in particular beta, comprising: - a scintillator material (3) arranged so as to be able to be exposed to said radiation, comprising quantum carbon dots with a graphitic core dispersed in a matrix, said material comprising aromatic units capable of emitting UV radiation in response to irradiation, in particular of the beta type, this UV radiation causing luminescence of the carbon dots and the emission by them of radiation in the visible range. - and at least one sensor (4) of light photons emitted by said scintillator material in response to this exposure.

2. Detector according to claim 1, the matrix of the scintillator material being polymeric and the polymer of the matrix having said aromatic units.

3. Detector according to claim 2, the aromatic units being phenyl rings.

4. Detector according to one of claims 2 and 3, the matrix comprising or being made of polystyrene.

5. Detector according to any one of claims 1 to 4, the carbon points having a non-zero nitrogen content, in particular an atomic % content of NI s of between 10 and 15%.

6. Detector according to any one of claims 1 to 5, the carbon points having a non-zero oxygen content, in particular an atomic % content of Ois of between 15 and 20%.

7. Detector according to any one of claims 1 to 6, the carbon points having an atomic % content of Cls of between 65 and 75%.

8. Detector according to any one of the preceding claims, the mass content of carbon points being between 0.01% and 0.5% relative to the weight of the material.

9. A detector according to any preceding claim, the carbon dots resulting from a decomposition of trinitropyrene.

10. A detector according to any preceding claim, the carbon dots being hydrophobic.

11. A method of detecting radiation from a radioactive source, in particular beta radiation, in which a detector according to any one of the preceding claims is exposed to said radiation.

12. A detector according to any one of claims 1 to 10, the radiation being beta radiation.

13. Process for the preparation of carbon dots, in particular with a view to their use for the manufacture of a scintillator material for a detector according to any one of claims 1 to 10 or 12, in which the decomposition of trinitropyrene, previously solubilized in an organic solvent, is carried out, this organic solvent comprising a mixture of toluene and dimethylformamide (DMF).

14. A method of manufacturing a scintillator material of a detector according to any one of claims 1 to 10 or 12, wherein the carbon dots are synthesized by implementing the method according to claim 13.

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