SPARKLING MATERIAL, PROCESS FOR MANUFACTURING AND APPLICATION OF THIS MATERIAL

Abstract

Inorganic scintillator material in a composite single crystal of formula La1-z-vCezCv(Br1-xAx)3-v+y+wLiyNaw-(LiX)a-(NaY)b consisting of a single-crystal matrix La1-z-vCezCv(Br1-xAx)3-v+y+wLiyNaw and LiX inclusions, and optionally NaY inclusions, incorporated into said single-crystal matrix, where - A is chosen from I and Cl; - C is chosen from Ca, Sr, Ba and Mg, preferably from Sr and Ca; - X is chosen from F, Cl, Br, I and their combinations; - Y is chosen from F, Cl, Br, I and their combinations; - 0 ≤ x ≤ 0.5; - 0 ≤ y ≤ 0.02; - 0 ≤ v ≤ 0.1; - 0 ≤ w ≤ 0.02, preferably w = 0; - 0 ≤ z ≤ 1; - 0 ≤ z +v ≤ 1 - 0 < a ≤ 0.20 - 0 ≤ b ≤ 0.20 - a, b, x, v, y, w and z are molar indices for LiX, NaY, A, C, Li, Na and Ce, respectively.

Description

Title of the invention: SPARKLING MATERIAL, METHOD FOR MANUFACTURING AND APPLICATION OF THIS MATERIAL technical field

[0001] The present invention relates to an inorganic scintillator material, a method for its manufacture and the use of this material in detectors for dual detection of gamma rays and thermal neutrons. Previous technique

[0002] Inorganic scintillator materials are widely used in detectors of gamma rays, X-rays, cosmic rays and particles with energies greater than 1 keV. Such detectors are used in particular in industry for thickness or weight measurements, in the fields of nuclear medicine, physics, chemistry, security systems, particularly for the control of illicit objects, or the search for oil deposits and other geophysical applications.

[0003] Inorganic scintillator materials consist of a crystal that responds to incident radiation by emitting a light pulse. This crystal is transparent in the wavelength range of the light pulse,

[0004] A detector incorporating such a crystal can be manufactured. In response to incident radiation, the crystal emits light, preferably in the UV or visible spectrum. An optical detection device receives this light and produces an electrical signal proportional to the number of photons received. This signal is conventionally represented as an energy histogram. Analysis of the spectrum allows the different peaks to be distinguished, providing information about the composition of the incident radiation. The peaks can be distinguished from one another more effectively when the power height resolution (PHR) is good (low PHR value).

[0005] The high performance of the inorganic scintillator materials LaCl3:Ce (Brillance 350 TM) and LaBr3:Ce (Brillance-380 TM) are disclosed in particular in US7479637 and US7067816. These materials are further described in S. Kraft et al. “Development and Characterization of Large La-Halide Gamma-Ray Scintillators for Future Planetary Missions”. IEEE TRANSACTIONS ON NUCLEAR SCIENCE, V. 54, No. 4, August 2007, in W. Drozdowski et al. “Gamma-Ray Induced Radiation Damage in LaBr3:5%Ce and LaCl3:10%Ce Scintillators” IEEE TRANSACTIONS ON NUCLEAR SCIENCE, V. 54, No. 4, August 2007, or in F. Quarati et al. “X-ray and gamma-ray response of a 2”x2” LaBr3:Ce scintillation detector” Nucl.Instr.and Meth. A574 (2007) p.115.

[0006] The inorganic scintillator material LaBr3:Ce:Sr is also known, in particular from US 10053624 and from MS Alekhin et al. “Improvement of c-ray energy resolution of EaBr3:Ce3+ scintillation detectors by Sr2+ and Ca2+ co-doping”, APPLIED PHYSICS LETTERS 2013, V.102, N° 161915. However, this material does not allow dual detection of gamma rays and thermal neutrons due to the absence, in the crystalline matrix, of an isotope with a high thermal neutron absorption capacity.

[0007] For dual detection, the inorganic scintillator materials Cs2LiLaBr6:Ce (CLLB) and Cs2LiYBr6:Ce (CLYC) are known, notably described in US7525100 and in CWE van Eijk et al., “Development of Elpasolite and Monoclinic Thermal Neutron Scintillators,” 2005 IEEE Nuclear Science Symposium Conference Record No. 13-3. NaI:Tl:6Li (NAIL™) is also known. All these materials contain a 6Li isotope, which has a high thermal neutron absorption coefficient. However, the PHR energy resolution for a 137Cs reference source is approximately 7.0% for the latter composition.

[0008] Transparent ceramic materials based on GYGAG:Ce oxide, i.e. (Gd, Y)3(Al, Ga)5O i2 (Ce) also exhibit a PHR energy resolution greater than 4.5% (NJ Cherepy et al. “Comparative gamma spectroscopy with Srl2 (Eu), GYGAG(Ce) and Bi-loadedplastic scintillator”. IEEE Nuclear Science Symposium & Medical Imaging Conference, 2010, pp. 1288-1291).

[0009] For a double detection of gamma rays and thermal neutrons, we finally know the CLLBs, that is to say the Cs2LiLaBr6(Ce) and the Cs26LiLa(Br,Cl)6(Ce), also known under the acronym CLLBC, described in G.Hull et al. “Detection properties and internal activity of newly developed Ea-containing scintillator crystals,” Nucl. Instr. & Meth Phys. Res. Sect. AV 925, 1 May 2019, pp. 70–75. These materials exhibit a PHR energy resolution consistently greater than 3.3%. The CLYC material, i.e., Cs₂LiYCl₆(Ce), described in N. Dinar et al., “Puse shape discrimination of CEYC scintillator coupled with a large SiPM array,” Nucl. Instr. & Meth Phys. Res. Sect. AV 935, 11 August 2019, pp. 35–39, exhibits a PHR energy resolution greater than 4.5% for a ¹³⁷Cs reference source.

[0010] There is therefore a permanent need for a material - with dual detection of gamma rays-thermal neutrons, - with a PHR energy resolution of less than 3.0% (for a reference source 137Cs).

[0011] One object of the invention is to meet, at least partially, this need. Summary of the invention

[0012] To meet this need, the invention proposes an inorganic scintillator material in the form of a composite single crystal Lai.z.vCezCv(Bri.xAx)3.v+y+wLiyNaw-(LiX)a-(NaY)b consisting of a single-crystal matrix Lai.z.vCezCv(Bri.xAx)3.v+y+wLiyNaw and LiX inclusions, and optionally NaY inclusions, incorporated into said single-crystal matrix, where - A is chosen from among the elements I and Cl; - C is chosen from the elements Ca, Sr, Ba and Mg, preferably from Sr and Ca; - X is chosen from the elements F, Cl, Br, I and their combinations; - Y is chosen from the elements F, Cl, Br, I and their combinations; - 0 < x < 0.5; - 0 < y < 0.02; -0< v<0,l ; - 0 < w < 0.02, preferably w = 0; -0 <z< 1 ; - 0 < z +v < 1 - 0 < a < 0.20 - 0 < b < 0.20 - a, b, x, v, y, w and z are molar indices for LiX, NaY, A, C, Li, Na and Ce, respectively.

[0013] As will be seen in more detail in the rest of the description, the inventors discovered that this material comprising a network of Lai.z.vCezCv(Bri.xAx)3.v+y+wLiyNaw and LiX inclusions, has a PHR energy resolution, at the 137Cs isotopic source, of less than 3.0%, as well as a good ability to detect gamma rays and thermal neutrons.

[0014] In the Lai.z.vCezCv(Bri.xAx)3.v+y+wLiyNaw network, the possible Li and Na ions take interstitial positions in the crystal.

[0015] A material according to the invention may also have one or more of the following optional characteristics: - the material in single-crystal form preferably has a formula chosen from: - LaBr3:Ce-(LiBr)a, - La(BrbxAx)3:Ce:C-(LiX)a, where C is chosen from Ca, Sr, Ba and Mg, preferably Sr, - Ce(Brl xAx)3-(LiX)a, - Ce(BrbxAx)3:C-(LiX)a, where C is chosen from Ca, Sr, Ba and Mg, preferably Ca, where - A is among I and Cl; - X is among I, Br, Cl, F and their combinations; - 0 < x < 0.5; - 0 < a < 0.20; - the single-crystal matrix is ​​chosen from LaBr3:Ce, LaBr3:Ce:Sr, CeBr3 and CeBr3:Ca; - the material is LaBr3:Ce-(LiBr)a; - more than 10%, preferably more than 50% by mass of the Li in the material is in the form of 6Li; - x is less than or equal to 0.10, preferably less than or equal to 0.04, preferably less than or equal to 0.03, preferably is zero; - v is preferably greater than 0.001, and / or less than or equal to 0.05, preferably less than or equal to 0.004, preferably less than or equal to 0.003, preferably is equal to 0.003; - a is greater than 0.01, preferably greater than or equal to 0.05, and / or less than or equal to 0.2, preferably less than or equal to 0.18.

[0016] z can be greater than 0.005. In a preferred embodiment, z is less than or equal to 0.30, preferably less than or equal to 0.10, preferably less than or equal to 0.05. In another preferred embodiment, z is greater than 0.9, greater than 0.95, preferably equal to 1.

[0017] In one embodiment, x is greater than 0.02, or even greater than 0.04.

[0018] Preferably, x = 0 and 0.005 > v > 0.001 and 0.10 > z > 0.02 and 0.17 > a > 0.12; or x = 0 and 0.005 > v > 0.001 and z > 0.9 and 0.17 > a > 0.12.

[0019] The invention also relates to a method for manufacturing a scintillator material according to the invention, comprising the following successive steps: a) preparation of a starting charge having a composition adapted to the composition of said material; b) synthesis of the composite single crystal, from the starting charge, by a vertical thermal gradient crystallization method or by a shape-controlled capillary growth method in contact with the edge, preferably by a vertical thermal gradient crystallization method, preferably by the Bridgman method.

[0020] This process is remarkable in that the starting charge includes a flux bringing Li, or "first flux", preferably a flux of LiX, X being chosen from F, Cl, Br, and I, preferably a flux of LiBr.

[0021] The addition of a flux is a known technique for crystal synthesis, particularly for modifying the melting temperature of the starting charge. The inventors discovered that adding a flux of LiX to a so-called single-crystal matrix makes it possible to obtain both dual detection and good energy resolution. PHR. This result was unexpected because lithium (Li) is known to have a strong propensity to segregate and thus degrade the optical properties of the crystal matrix. Surprisingly, the inventors found that, in matrices with a hexagonal structure, for example containing lanthanum (La), inclusions originating from the flux could advantageously precipitate between the hexagonal motifs. While not bound by this theory, this is how they explain that the optical properties are preserved, despite the lithium segregation.

[0022] Preferably, the quantity of said first flow is greater than 1%, preferably greater than 3%, preferably greater than 4%, and / or less than 10%, preferably less than 8%, preferably less than 6%, as a mass percentage based on the starting charge.

[0023] Preferably, the starting charge includes a second flux, the second flux supplying iodine (I). The supply of iodine by a second flux advantageously optimizes the detection of the light emitted by the scintillator material by a photomultiplier tube. The second flux is preferably Na₂, which avoids the use of a flux containing a rare-earth element, which is highly hygroscopic.

[0024] Preferably, the quantity of said second flux is greater than 1%, preferably greater than 3%, preferably greater than 4%, and / or less than 10%, preferably less than 8%, preferably less than 6%, as a mass percentage based on the starting charge.

[0025] The second flux may be different from or identical to the first flux, particularly when it is Lil. Lil advantageously avoids having to use a salt such as Lal3 or Cel3, which are highly hygroscopic.

[0026] Preferably, the total quantity of the first and second streams is greater than 1%, preferably greater than 3%, preferably greater than 4%, and / or less than 10%, preferably less than 8%, preferably less than 6%, as a mass percentage based on the starting charge.

[0027] Unless otherwise indicated, when reference is made to "flow" in the rest of the description, it refers to the first flow.

[0028] The invention also relates to the use of a material according to the invention for detecting gamma rays and thermal neutrons, preferably for measuring the intensity of gamma rays and thermal neutrons.

[0029] The material according to the invention can in particular be used as a component of a scintillation detector, especially for applications in industry, in the medical field and / or for oil detection in oil drilling, for security systems, particularly for the screening of illicit objects, for example, luggage at an airport or goods in containers, for example, shipping containers. In particular, it can be used as an element of a scanner Position Emission Tomography or Gamma Camera of the Anger type.

[0030] The invention also relates to a gamma ray and thermal neutron detector comprising: - a scintillator made of a material according to the invention and - a photodetector optically coupled to the scintillator to produce an electrical signal in response to the reception of a light pulse emitted by the scintillator.

[0031] The photodetector of the detector may in particular be a photomultiplier, or a photodiode, or a SiPM sensor.

[0032] The invention relates in particular to a security detector, in particular for the identification of objects comprising a material emitting both gamma radiation and thermal neutrons, in particular illicit objects, comprising a material according to the invention. Definitions

[0033] An inorganic scintillator material according to the invention, sometimes referred to as a "composite single crystal" in the description, consists of a single-crystal "host" matrix, preferably with a hexagonal structure, and inclusions incorporated into said matrix and preferably aligned parallel to the growth axis of the matrix. Unless otherwise specified, "matrix" refers to this single-crystal host matrix.

[0034] In the formula of a single-crystal matrix according to the invention, the sign “:” classically separates elements that are interchangeable with each other in the matrix.

[0035] In the formula of a material according to the invention, a dash “-” serves to separate the formula of the single-crystal matrix and the formula of the LiX inclusions.

[0036] Power Height Resolution (PHR) is measured from the recording of a spectrum representing the activity of a source as a function of energy. For a given incident radiation energy, the PHR is the ratio of the full width at half maximum (FWHM) of the principal peak corresponding to said given energy (e.g., corresponding to the principal response to gamma rays or thermal neutrons), divided by the energy at the centroid of the peak (see in particular: GF Knoll, John Wiley and Sons, Inc., 2nd edition, p. 114).

[0037] Figure 1 shows an example of an energy spectrum recording obtained from a 137Cs isotope source with an energy of 667 keV, detected with a LaBr3:Ce scintillator material. This recording provides the count as a function of the channel. The energy resolution PHR is equal to d / 1 * 1QQ%.

[0038] More specifically, to obtain [Fig. 1], the scintillation intensity was recorded at room temperature in a glove box (atmospheric humidity in the glove box less than 0.3 ppm) using a 137Cs gamma source at 662 keV. An Advanced Photonix avalanche photodiode was used as the photodetector. APD (type 630-70-72-510), under 1600 V voltage and cooled to 270 K. To maximize light collection, the crystal sample was wrapped with three layers of Teflon film (according to the technique described in JTM by Haas and P. Dorenbos, IEEE Trans. Nucl. Sci. 55, 1086 (2008)), except for the polished face intended for coupling with the photodiode. The photodetector's output signal was amplified with a shaping time of 6 ps using an ORTEC 672 spectroscopic amplifier. When exposed to the gamma source, the scintillator material produces photons that are detected and counted by the photodetector.

[0039] The photodetector used is sensitive from the UV to the IR and allows each photon to be counted. This yields an energy spectrum, or "scintillation histogram," with the x-axis representing values ​​proportional to the amount of emitted light detected by the photodetector and the y-axis representing the number of gamma photon interaction events with the scintillator. The higher the number of channels observed for the scintillation peak, the greater the number of photons emitted per pulse.

[0040] The other measurement conditions are specified in the publication by O. Guillot-Noël “Optical and scintillation properties of cerium doped LaCl3, LuBr3 and LuCl3” in Journal of Luminescence 85 (1999) 21-35.

[0041] In the present description, and for all measurements performed (unless otherwise indicated), the energy resolution is always determined, as described above, for the main peak corresponding to a 137Cs reference radioactive source at 662 keV, the energy of the main gamma emission. The measurements are thus comparable.

[0042] The position of a peak can vary depending on the size of the detector, its quality and its optical properties, which determine the optical coupling with the photodetector (classically a photomultiplier tube (“PMT”, or “Photo-Multiplier Tube”) or a silicon photomultiplier (“SiPM”, or “Silicon Photo-Multiplier”). The lower the energy resolution, the better the quality of the scintillator detector.

[0043] The composition of the material according to the invention is conventionally given without taking into account the usual impurities in the technical field of the invention. The usual impurities are generally impurities originating from the raw materials, the mass content of which is conventionally less than 0.1%, or even less than 0.01%, and / or parasitic phases whose volume percentage is in particular less than 1%.

[0044] A “flux” is a constituent of the starting charge which segregates, that is to say forms inclusions, without integrating into the single-crystal matrix (host phase of the crystal), that is to say without constituting a part of the single-crystal matrix.

[0045] The LiX inclusions are “incorporated” into the matrix insofar as they are arranged within the matrix. However, they form a distinct phase of the matrix and are therefore not "integrated" into the matrix.

[0046] “Contain”, “understand” or “present” must be interpreted in such a way non-exhaustive list. Brief description of the figures

[0047] Other features and advantages of the invention will become apparent upon examination of the following description and with regard to the accompanying drawing in which: - the [Fig. 1][Fig. 1] represents an example of recording an energy spectrum with 137Cs; - Fig. 2 represents an example of recording an energy spectrum with a 252Cf source; - [Fig.3] [Fig.3] schematically represents a median longitudinal section of a quartz bulb, usable for manufacturing a composite crystal according to the invention; - Fig. 4 [Fig. 4] schematically represents the synthesis of the material according to the invention in a Bridgman furnace; - Fig. 5 illustrates the measurement of the FoM (Figure of Merit) for the parameter of discrimination of gamma rays and thermal neutrons. Detailed description

[0048] The following description is provided for illustrative purposes only and does not limit the invention. Manufacturing process

[0049] A scintillator material according to the invention can be manufactured following steps a) to b) described above.

[0050] In step a), a starting charge is prepared having a composition adapted to the composition of said material.

[0051] All conventional methods for preparing a starting charge for the manufacture of inorganic scintillator materials can be used, provided that the starting charge is adapted to the composition of the desired material. This adaptation presents no difficulty for those skilled in the art.

[0052] The starting material, preferably each source of raw material, is preferably in powder form. The particles typically have a size between 50 µm and 2 mm. However, the particle size distribution has no effect on the manufactured material, as the powders are melted.

[0053] As raw materials, one can in particular use - a powder of (Lao^Ceo^Br,, for example whose particle size varies between 50 pm and 2 mm; - a powder of SrBr2, for example, whose particle size varies between 50 pm and 2 mm; - a LiX powder, for example, whose particle size varies between 50 pm and 2 mm.

[0054] Classically, prior art scintillator materials which contain 6Li contain between 0.6% and 1.2% of 6Li, based on the mass of Li.

[0055] Natural Li contains 7.6% of 6Li. Preferably, the starting charge comprises a Li source enriched in 6Lr, i.e., which has more 6Li than natural Li, the atomic ratio in 6Li / (6Li+7Li) being preferably greater than 8%, preferably greater than 10%, preferably greater than 30%, preferably greater than 40%, preferably greater than 50%, preferably greater than 60%, preferably greater than 70%, preferably greater than 80%, preferably greater than 90%, preferably greater than or equal to 95% or preferably greater than or equal to 98%.

[0056] The 6Li of the starting charge is found mainly in the inclusions (LiX) and in small quantities in interstitial sites of the single-crystal matrix (Liy).

[0057] The introduction of a high amount of 6Li considerably improves the detection of thermal neutrons.

[0058] In step b), the composite single crystal is synthesized from the starting charge, preferably by a vertical thermal gradient crystallization method, in a sealed ampoule.

[0059] This method and the synthesis conditions are described in detail in the article by H. Chen et al. entitled “Bridgman Growth of LaCls:Ce3+ crystal in non-vacuum atmosphere”, Journal of Alloys and Compounds 449 (2008) 172-175.

[0060] However, this method does not allow for obtaining a satisfactory composite single crystal. In particular, LaBr3 and CeBr3 on the one hand, and LiBr on the other, only form eutectics without forming specific phases to constitute a single crystal. Marcelle Gaune-Escard et al. describe this behavior of Li in "Compound formation in lanthanide-alkali metal halide systems," Mineral Processing and Extractive Metallurgy (Trans. Inst. Min Metall. C) 2014 Vol. 123 No. 135. In general, Li does not form phases with LaBr3 and CeBr3 and therefore cannot be used, according to a classical approach, for the absorption of thermal neutrons in order to ensure dual detection of thermal neutrons and gamma rays.

[0061] The inventors attempted to grow LaBr3:Ce crystals by adding a flux of LiBr using the Czochralski method, well known to those skilled in the art. However, these tests showed that this method does not allow the introduction of Li ions into the crystal matrix structure, except in very small quantities in the interstitial positions of the crystal. They explain this result by a very strong segregation of Li in the molten bath. The small amount of Li in the crystal matrix is ​​insufficient for significant absorption of thermal neutrons, necessary for the dual detection of thermal neutrons and gamma rays.

[0062] The article “Growth and characterization of directionally solidified eutectic systems for scintillator applications”, February 2018, Journal of Crystal Growth 498, by A. Yoshikawa et al., also describes an unsuccessful attempt to introduce inclusions of a Li-containing eutectic system into crystals, particularly into cubic crystals such as CaF2:Eu:Li. The inclusions enter the cubic matrix randomly, which disrupts the optical transparency properties.

[0063] S. Cheng et al. also described Li doping for a CeCl3:Li system in "Self-assembled natLiCl-CeCf directionally solidified eutectics for thermal neutron detection," April 2020, CrystEngComm 22(19). The resulting composite does not exhibit optical transparency suitable for detecting thermal photons in the UV spectrum. The energy resolution is also unsatisfactory.

[0064] The inventors conceived of adapting the Bridgman vertical synthesis process described by H. Chen et al. (described in “Bridgman Growth of LaCl::Cei+ crystal in non-vacuum atmosphere”, Journal of Alloys and Compounds 449 (2008) 172-175) by introducing a flux bringing Lithium (Li) into the starting charge.

[0065] Preferably, crystal growth is initiated by a seed oriented along the hexagonal crystallographic axis “c” <0001> and continues along this strongly anisotropic crystallographic axis.

[0066] As shown in [Fig.3], the cylindrical germ 10 is positioned in a pocket provided for this purpose at the bottom of an ampoule 12.

[0067] Preferably, the ampoule is a sealed quartz ampoule, in which the pressure is less than 102 mbar, i.e., "under vacuum". Preferably, a mixture of (La,Ce)Br3 powders and a LiBr stream are placed in it.

[0068] Surprisingly, this adapted process makes it possible to obtain an anisotropic single-crystal matrix in which inclusions are arranged in an organized manner. The matrix preferably has a hexagonal structure like that exhibited by LaBr3, LaCl3, and CeBr3 crystals (UC14 type) with space group P6_3m, No. 176. Doping does not change the organization of the crystallographic structures of these compounds. With a hexagonal structure, the inclusions take the form of fibers which, advantageously, do not significantly disrupt the optical properties. They can also take the form of "grains" which are inserted, aligned along lines parallel to the crystallographic axis "c", into the space between the hexagonal structures.

[0069] A hexagonal structure is particularly distinguished from the orthorhombic Cmcm structure, No. 63, of Lal3, which, with Ce doping, does not exhibit good scintillation properties. A material according to the invention can be fabricated by any method of Edge growth, and in particular by the edge-defined film-fed growth (EFG) method described notably by VATatarchenko in "Stability of Crystallization in Edge-Defined Film-Fed Growth from the Melt" in Givargizov, E.I. (ed.) Growth of Crystals. Springer, Boston, MA. (1986), or preferably by a Bridgman growth method, particularly in vacuum-sealed quartz ampoules, provided that said flux is added to the starting charge. Preferably, the single-crystal matrix has an anisotropic, preferably hexagonal, LaBr3 structure.

[0070] According to the invention, growth preferably results from the addition of a lithium bromide LiBr stream.

[0071] In particular for (La,Ce)(Br,I)3-(LiX)a type materials, growth preferably results from the addition of a LiX flux.

[0072] In particular for (La,Ce)(Br,Cl)3-(LiX)a type materials, growth preferably results from the addition of a LiCl flux.

[0073] During eutectic decompositions, LiX inclusions, in particular LiBr, solidify into a regular structure predominantly taking the form - fine fibers and / or - small, localized inclusions, aligned along the crystallographic axis <0001> and incorporated into the host matrix formed by the hexagonal single crystal.

[0074] Remarkably, the resulting composite single crystal retains good optical transmission properties along the crystallographic axis "c", making it suitable as a scintillator material. The inventors have observed in particular that the inclusions have the form of "fibers" oriented substantially parallel to each other, which could explain the high optical transparency of the composite single crystal according to the invention.

[0075] The synthesis method described above, implementing an adapted Bridgman method for vertical synthesis of composite crystals, can be generalized to any vertical gradient crystallization method, and in particular to the methods known under the acronym TGT (for "Temperature Gradient Technique" in English), described in particular by ZHOU Yongzong in "Growth of High Quality Large Nd:YAG Crystals by Temperature Gradient Technique (TGT)", in Journal of Crystal Growth 78 (1986) 31–35, provided that a flux bringing Li is added to the starting charge.

[0076] The edge-contact capillary shape-controlled growth method (or "EFG," for "Edge Defined Film Fed Growth") is also effective for synthesizing a scintillator material according to the invention in various forms, provided that a flux carrying Li be added to the starting charge. Scintillator material

[0077] Preferably X = Br or I.

[0078] Preferably, x < 0.40, preferably x < 0.30, preferably x < 0.20, preferably x < 0.15, preferably x < 0.10, preferably x < 0.05, preferably x < 0.02, preferably x < 0.01, preferably x is zero. In one embodiment, x > 0.005.

[0079] Preferably, v > 0.001, v > 0.002 and / or preferably v < 0.05, preferably v < 0.01, preferably v < 0.005, preferably v < 0.004, preferably v < 0.003.

[0080] Preferably, z > 0.02. In one embodiment, z < 0.90, preferably z < 0.70, preferably z < 0.50, preferably z < 0.40, less than or equal to 0.30, preferably less than or equal to 0.10, preferably less than or equal to 0.05, preferably less than or equal to 0.04. In another embodiment, z is greater than 0.9, preferably equal to 1.

[0081] Preferably, 0.15 > x and 0.05 > v and 0.40 > z.

[0082] Preferably, 0.10 > x and 0.01 > v and 0.30 > z.

[0083] Preferably, x > 0.005 and v > 0.002 and z > 0.02.

[0084] Preferably, x > 0.01 and v > 0.003 and z > 0.04.

[0085] Preferably, 0.15 > x > 0.005 and 0.05 > v > 0.002 and 0.4 > z > 0.02.

[0086] Preferably, 0.10 > x > 0.01 and 0.01 > v > 0.003 and 0.30 > z > 0.04.

[0087] The best performance in dual detection of gamma rays and thermal neutrons was obtained for the following two cases: 1) x = 0, and 0.005 > v > 0.001, and 0.10 > z > 0.02, preferably 0.07 > z > 0.03, the preferred indices being x = 0 and v = 0.003 and z = 0.05; and 2) x = 0, and 0.005 > v > 0.001, and z > 0.9, preferably z > 0.95, the preferred indices being x = 0 and v = 0.003 and z = 1.

[0088] The dimensions of the composite single crystal constituting the material according to the invention are chosen to effectively stop and detect the radiation to be detected. The single crystal preferably has a volume greater than 10 mm³, or even greater than 1 cm³, or even greater than 100 cm³. Detector - applications

[0089] A detector according to the invention, comprising a material according to the invention, can in particular be used - in a nuclear medicine device, specifically chosen from among Anger-type gamma cameras and Positron Emission Tomography scanners (see, for example, CWE Van Eijk, “Inorganic Scintillator for Medical Imaging”, International Seminar New Types of Detectors, 15-19 May 1995 - Archamp, France. Published in "Physica Medica", Vol. XII, Supplement 1, June 1996); or - in a detection device for oil drilling (see for example “Applications of scintillation counting and analysis”, in “Photomultiplier tube, principle and application”, chapter 7, Philips).

[0090] The invention also relates to such an apparatus, and more generally, an apparatus comprising a material according to the invention. Examples

[0091] The following non-limiting examples are given for the purpose of illustrating the invention.

[0092] A composite single crystal was fabricated using an adapted Bridgman vertical synthesis method by adding a flux containing Li, in the following manner:

[0093] A starting charge was first prepared by mixing the following powders: LaBr3 - 845.2 g CeBr3 - 44.6 g LiBr - 10.2 g Due to the choice of these powders, and unlike the process described in “Bridgman Growth of LaCl3:Ce3+ crystal in non-vacuum atmosphere”, Journal of Alloys and Compounds 449 (2008) 172-175, no dehydration step or heating to 200-230°C in an HCl atmosphere was required. The powders' particle size allowed their introduction into the ampoule described below, eliminating the need for grinding. Finally, the addition of activated carbon powder, as described in that article, was unnecessary.

[0094] For the synthesis of the composite single crystal, a quartz ampoule 12 of the type shown in [Fig. 3] was used. The ampoule 12, positioned vertically, comprised a cylindrical portion 14, with an internal diameter of 33 mm and a length of 345 mm, extended downwards by a conical portion 16, the apex angle of which was 60°, defining the base of the ampoule. The internal volume of the ampoule is estimated at 300 ml.

[0095] The bulb 12 also had a quartz pocket 18 arranged at the bottom of the bulb.

[0096] A cylindrical seed 10, 6 mm in diameter and 40 mm in length, was cut from a single crystal (La0j95,Ce0j05)Br3 along the axis <0001> , then placed in pocket 18 so that the axis <0001> either vertical.

[0097] The mixture of powders constituting the starting charge 19 was then poured into the ampoule, through a top opening 20.

[0098] Then the pressure was reduced to less than 102 mbar in the ampoule and the ampoule was immediately sealed by plugging the upper opening 20 with an acetylene-oxygen torch to prevent oxidation and volatilization.

[0099] The bulb 12 was then placed on a bulb holder 22 in the enclosure of a Bridgman oven 24 of the type shown in [Fig.4].

[0100] The furnace enclosure 24 comprised a lower "cold" zone 26, an intermediate gradient zone 28 and an upper "hot" zone 30. The intermediate zone was defined by a horizontal wall 32 separating the hot and cold zones ("baffle").

[0101] Oven 24 also included electric heating elements to heat the different zones to different temperatures.

[0102] The bulb holder 22 was placed in the enclosure so that the starting load was in the hot zone 30 and half of the germ 10 was in the cold zone 26 and the other half of the germ was in the intermediate zone and in the hot zone.

[0103] The setpoint temperature of the hot zone oven was set at 850°C to fuse the charge in the bulb and the upper part of the germ 10. The temperature in the cold zone was controlled so as not to exceed 770°C and not to melt the lower part of the germ.

[0104] After maintaining these temperatures for two hours in the oven, the bulb was moved downwards for three weeks at a speed of 0.5 mm / h, corresponding to the crystallization rate, so that the solid-liquid interface remained in the hot zone. A crystal then gradually formed in the lower part of the bulb.

[0105] Figure 4 illustrates this synthesis operation. In the third step, the crystal 34 formed in the lower part of the bulb and the residual starting charge 19 can be distinguished.

[0106] The bulb was then cooled gradually at a rate of 10°C / hour until it reached an ambient temperature of 20°C.

[0107] The ampoule was then opened by cutting with a circular saw equipped with a diamond blade, in a glove box so as not to expose the crystal obtained to humidity after its removal from the ampoule.

[0108] Upon exiting the ampoule, the crystal consists of five parts, namely, successively from bottom to top: - the germ, free of inclusions; - a cone and a truncated cylinder poor in Li, - a truncated cylinder made of a material according to the invention; - a truncated cylinder mainly composed of solidified flux.

[0109] The cylinder trunk in a material according to the invention constitutes a composite single crystal according to the invention, rich in Li and 6Li due to the progressive segregation in Li during growth.

[0110] The other examples were manufactured in a similar manner to example 1, in adapting the composition of the starting charge. Table 1 below summarizes the compositions of the starting charge and the material according to the corresponding invention.

[0111] In the first column, the factors indicate mass percentages. For example, "0.95La0j95Ce0j05Br3+ 0.05LiBr" means that the starting charge comprises 5% flux and 95% other powders, as a mass percentage based on the starting charge.

[0112] The indices are atomic percentages. In the example above, the other powders thus provide, for one mole, 0.95 moles of LaBr3 and 0.05 moles of CeBr3.

[0113] In the second column, the indices are also atomic percentages.

[0114] [Tables 1] No. Charge composition + flux Composition of synthesized composite single crystal 1 0.95La0j95Ce0j05Br3 + 0.05LiBr Lao,94Lio,i7Ceo,o6Br3,i7 2 O.95Lao 95SiooiCeo 05613 02"h0.05Li6i Lao^SrO'OovLium, 17Cc(M)6B r3| Lao,946Leo, 16Ceo,o6Br3.16 5 0.95La0.95Sr0.01Ce0.05Br302+0.056LiBr Laoj94Srojoo66Leo, 16Ce0j06Br3> ! 0.95La0.95Sr0.01Ce0.05Br302+0.056LiI Laoj94Srojoo66Lio, 16Ce0j06Br3> ! O,95Ceo,99Cao,oiBr2.99 +0.05LiBr CeCao.ooeLio, O,95Ceo,99Cao,oiBr2.99 +0.056LiBr CeCao,oo66Li o,i5Br3ji62 11 O^OLao^SrixoïCeoxisBr^+O^SLiBr-iTfOSNal Laoj94Srojoo7Lio, 12N a0> ioCeo>o6Br3, !m 10.07 12 O,9OCeOj99CaOjoiBr3 +0.05LiBr+0.05NaI CeCao.ooeLio, 12N a0> ioBr3> 162lo,o7 13 OjOSLao^sCeO'OsB^ + 0.05LiCl Lao,94Lio, . i7Ceo,o6Br3,o9Clo,o8 14 O.95Ceo.99Cao,oiBr2.99 +0.05LiCl CeCao.ooeLio, 1 eBr3 >O92Clo.o8 .

[0115] Examples 3, 6, 9, 11, and 12 are particularly advantageous because they employ a second flux, which is not a rare earth element (REI3) flux, to achieve a partial anionic substitution of Br (or Cl) by iodine I. REI3 salts are known to be highly hygroscopic. Advantageously, this simplifies their manufacture.

[0116] Furthermore, the supply of I (Iodine) by a flux advantageously makes it possible to bring the main scintillation emission peak closer to the spectrum of wavelengths to which Photomultiplier tubes are the most sensitive. In particular, substituting Br with I shifts the scintillation emission peak from 380-390 nm to 420 nm. NaL and LIL fluxes are thus particularly advantageous, as LIL can effectively provide both Li and I.

[0117] Example 3 advantageously exhibits reduced afterglow, as shown in [Fig. 6]. This figure represents, after gamma irradiation, the afterglow (normalized signal) of LaBr3(Ce)-B380 crystals (intermediate region, dark gray), LaBr3:Ce:Sr-B390 crystals (upper region, black), and LaBr3(Ce,Li) crystals (lower region, light gray), as a function of time (abscissa, ns). The afterglow level for crystals synthesized with a flux of Lil is advantageously reduced, which makes it possible, for example, in the case of repeated detections, such as acquiring images of luggage in an airport security gate, to improve the sharpness of these images.

[0118] This advantage is found in particular in the composite single crystals according to the invention having a LaBr3:Ce:Li type matrix and synthesized with a Lil flux.

[0119] The single crystal of Example 1 was cut in two, and each part of the initial single crystal, with a volume of 18.5 cm3, was encapsulated in the form of a classic "geoline" assembly, i.e. mounted in a blind metal tube whose opening was conventionally sealed by a transparent membrane.

[0120] Two detectors A and B were thus obtained in order to verify that the results obtained were similar.

[0121] The detectors were exposed to the same 252Cf neutron source and an energy spectrum was determined from the light signal returned by the detectors.

[0122] Figure 2 shows the spectrum obtained for the first detector; the spectrum obtained with the second detector is similar. The peaks corresponding to the responses to gamma radiation (three peaks) and to thermal neutrons (thermalized by a layer of PMMA plastic (1" thick) around the source), indicated by arrows Fl and F2 respectively, are well formed and visible.

[0123] Each detector was then exposed to a 137Cs source so as to receive gamma radiation at 662 keV. The resulting energy spectra were analyzed to determine the power-to-resolve (PHR) of the two largest peaks representing the gamma radiation response.

[0124] The results obtained are provided in Table 1 below:

[0125] [Tables2] Gamma radiation peak detector PHR, % A First main peak 2.79% Second main peak 2.98% B First main peak 2.81% Second main peak 2.89%

[0126] This table shows that the results obtained are consistent for both detectors. The PHR values ​​are remarkably low compared to those obtained with the LaBr3:Ce (Brillance-380 TM) material mentioned in the preamble, measured with the same apparatus.

[0127] The examples thus show that a scintillator material according to the invention allows detection of both gamma rays and thermal neutrons, with a power-resolved potential (PHR) value, determined at 662 keV, of less than 3.0%.

[0128] The ability of a detector to detect both gamma rays and thermal neutrons, that is, the ability to properly discriminate responses to these two incident radiations, is classically measured by means of a measurement called "Figure of Merit" (FoM), as described in B, S, Buddena et al, “Handheld Readout Electronics to Fully Exploit the Particle Discrimination Capabilities of El-pasolite Scintillators”, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment Volume 795, 21 September 2015, Pages 213-218.

[0129] Figure 5 illustrates the measurement of the FoM for the discrimination of gamma rays and thermal neutrons by the PSD method (in English "Pulse-Shape-Discrimination"). It provides the PSD parameter ("head" (or "front part") / total) as a function of energy, in keV. The upper scatter plot represents the contribution of thermal neutrons. The lower scatter plot corresponds to the contribution of gamma rays. The right-hand side shows the point density in the boxed region of interest.

[0130] The FoM was measured for both detectors. In both cases, it was 1.2, which confirms a good discrimination capability.

[0131] The FoM was also measured for a detector made as described above, with a scintillator material made like that of Example 1, but enriching the lithium in 6Li so that the atomic ratio of 6Li / (6Li+7Li) is 95%. It was 1.66, which shows that an increase in the 6Li content further improves the discrimination capability.

[0132] Finally, tests have shown that the composite single crystal according to the invention presents mechanical properties that make it suitable for the intended applications.

[0133] Of course, the present invention is not limited to the embodiments described in detail above, nor to the examples provided for illustrative purposes.

Claims

Demands

1. Inorganic scintillator material in a composite single crystal of formula Lai.z.vCezCv(Bri.xAx)3.v+y+wLiyNaw-(LiX)a-(NaY)b consisting of a single-crystal matrix Lai_z_vCezCv(Bri_xAx)3_v+y+wLiyNaw and LiX inclusions, and optionally NaY inclusions, incorporated into said single-crystal matrix, where - A is selected from I and Cl; - C is selected from Ca, Sr, Ba and Mg, preferably from Sr and Ca; - X is selected from F, Cl, Br, I and combinations thereof; - Y is selected from F, Cl, Br, I and combinations thereof; - 0 < x < 0.5; - 0 < y < 0.02; -0 < v < 0.1; - 0 < w < 0.02, preferably w = 0; -0 <z< 1 ; - 0 < z +v < 1 - 0 < a < 0,20 - 0 < b < 0,20 - a, b, x, v, y, w et z sont des indices molaires pour LiX, NaY, A, C, Li, Na et Ce, respectivement.

2. Material according to claim 1, having a formula selected from: - LaBr3:Ce-(LiBr)a, - La(Bri_xAx)3:Ce:C-(LiX)a,, C being selected from Ca, Sr, Ba and Mg, preferably being Sr, - Ce(Brl xAx)3-(LiX)a, - Ce(Bri_xAx)3 :C-(LiX)a, C being selected from Ca, Sr, Ba and Mg.

3. Material according to claim 1, wherein the single-crystal matrix is ​​selected from LaBr3:Ce, LaBr3:Ce:Sr, CeBr3, and CeBr3:Ca.

4.

5. Material according to claim 1, having the formula LaBr3:Ce-(LiBr)a. Material according to any one of the preceding claims, wherein more than 10% by mass of the Li is in the form 6Li.

6. Material according to the immediately preceding claim, wherein more than 50% by mass of the Li is in the form of 6Li.

7. Material according to any one of the preceding claims, characterized in that - x is less than or equal to 0.10, preferably less than or equal to 0.04, preferably less than or equal to 0.03, preferably is zero; and / or - v is greater than 0.001, and / or less than or equal to 0.05, preferably less than or equal to 0.004, preferably less than or equal to 0.003; and / or - a is greater than 0.01, preferably greater than or equal to 0.05, and / or less than or equal to 0.2, preferably less than or equal to 0.

18.

8. Material according to any one of the preceding claims, characterized in that: x = 0 and 0.005 > v > 0.001 and 0.10 > z > 0.02 and 0.17 > a > 0.12; or x = 0 and 0.005 > v > 0.001 and z > 0.9 and 0.17 > a > 0.

12.

9. A method for manufacturing a material according to any one of the preceding claims, comprising the following successive steps: a) preparation of a starting charge having a composition adapted to the composition of said material; b) synthesis of the composite single crystal, from the starting charge, by a vertical gradient crystallization method or by a shape-controlled capillary growth method in contact with the edge, the starting charge comprising a first flux supplying Lithium Li and of formula LiX, X being selected from F, Cl, Br, and I.

10. Method according to the immediately preceding claim, in which X is the element Bromine Br.

11. A method according to any one of the two immediately preceding claims, wherein the quantity of said first stream is greater than 1%, preferably greater than 3%, preferably greater than 4%, and / or less than 10%, preferably less than 8%, preferably less than 6%, as a mass percentage based on the starting charge.

12. A method according to any one of the two immediately preceding claims, wherein the starting charge comprises a second flux, the second flux supplying iodine I, and preferably being Nal.

13. Use of a material according to any one of claims 1 to 8, or manufactured according to any one of claims 9 to 12, as a component of a scintillation detector, in particular for applications in industry, the medical field and / or detection for oil drilling.

14. Security detector, in particular for the identification of objects containing a material emitting both gamma radiation and thermal neutrons, in particular illicit objects, containing a material according to any one of claims 1 to 8 or manufactured according to any one of claims 9 to 12.

Images