WO2024118778A1 - Scintillator material and process of manufacturing - Google Patents

Abstract

Inorganic scintillator material in the form of a composite single crystal is disclosed. The crystal can have a formula including La_1-z-vCe_zC_v(Br_1-xA_x)_3-v+y+wLi_yNa_w-(LiX)_a-(NaY)_b consisting of a single-crystal matrix La_1-z-vCe_zC_v(Br_1-xA_x)_3-v+y+wLi_yNa_w and of LiX, and optionally NaY inclusions, embedded in said single-crystal matrix. A can be selected among I and Cl; C can be selected among Ca, Sr, Ba and Mg, preferably among Sr and Ca; X can be selected among F, Cl, Br, I and combinations thereof. Y can be selected among 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 and z can be molar indices for LiX, NaY, A, C, Li, Na and Ce, respectively.

Description

SCINTILLATOR MATERIAL AND PROCESS OF MANUFACTURING

TECHNICAL FIELD

The present invention concerns an inorganic scintillator material, a process for manufacturing it and the use of this material in detectors for a dual detection of gamma rays and thermal neutrons.

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

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,

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 means receives this light and produces an electrical signal proportional to the number of photons received. This signal is typically represented in the form of an energy spectrum histogram. Analysis of the spectrum makes it possible to discriminate the various peaks and deduce information about the composition of the incident radiation. The better the energy resolution ("PHR" - Pulse Height Resolution) (low PHR value), the better the peaks can be discriminated from one another.

The high performance of the inorganic scintillator materials LaCI ,:Ce (Brightness 350 TM) and LaBr^Ce (Brightness-380 TM) are reported in particular in US7479637 and US7067816. These materials are also 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, N° 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, N° 4, August 2007, or in F. Quarati et al. Quarati et al. "X-ray and gamma-ray response of a 2"x2" LaBrcCe scintillation detector" Nucl. Instr. and Meth. A574 (2007) p.l 15.

The inorganic scintillator material LaBr3:Ce:Sr is also known, in particular from US 10053624 and M.S. Alekhin et al. "Improvement ofc-ray energy resolution of LaBr₃:Ce³⁺ scintillation detectors by Sr²⁺ and Ca²⁺ co-doping" , APPLIED PHYSICS LETTERS 2013, V.102, No. 161915. However, this material does not allow a 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.

The inorganic scintillator materials CssLiLaB^Ce (CLLB) and Cs2LiYBre:Ce (CLYC), described in particular in US7525100 and in C.W.E. van Eijk et al. "Development of Elpasolite and Monoclinic Thermal Neutron Scintillators", 2005 IEEE Nuclear Science Symposium Conference Record N°13-3 are known for their double detection capability. We also know NaI:Tl:⁶Li (NAIL™). All these materials contain the isotope⁶ Li, which has a high thermal neutron absorption coefficient. However, the PHR energy resolution for a reference source in ¹³⁷Cs is around 7.0% for the latter composition.

Transparent ceramic materials based on GYGAG:Ce oxide, i.e. (Gd, Y)j (Al, Ga)s O12 (Ce) also show a PHR energy resolution in excess of 4.5% (N. J. Cherepy et al. "Comparative gamma spectroscopy with Srh (Eu), GYGAG(Ce) and Bi-loaded plastic scintillator" . IEEE Nuclear Science Symposium & Medical Imaging Conference, 2010, pp. 1288-1291).

For dual detection of gamma rays and thermal neutrons, we finally know CLLBs, i.e., CsjLiLaBre (Ce) and CS2⁶ LiLa(Br,Cl)e (Ce), also known by the acronym CLLBC, described in G.Hull et al. "Detection properties and internal activity of newly developed La-containing scintillator crystals", Nucl. Instr. & Meth Phys. Res. Sect. A. V. 925, 1 May 2019, pp. 70-75. The PHR energy resolution of these materials is always better than 3.3%. The CLYC material, i.e., Cs2LiYCle (Ce), described in N. Dinar et al. “Pulse shape discrimination of CLYC scintillator coupled with a large SiPM array" Nucl. Instr. & Meth Phys. Res. Sect. A. V. 935, Aug. 11, 2019, pp 35-39, presents a PHR energy resolution greater than 4.5% for a reference source ¹³⁷Cs.

There is therefore a continuing need for a material

- with dual detection of gamma rays and thermal neutrons,

- with a PHR energy resolution of less than 3.0% (for a reference source ¹³⁷Cs).

A purpose of the invention is to meet this need, at least in part.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and are not limited in the accompanying figures.

FIG. 1 includes an illustration of a recording of an energy spectrum with ¹³⁷Cs, in accordance with one embodiment.

FIG. 2 includes an illustration of a recording of an energy spectrum with ²⁵²Cf, in accordance with one embodiment. FIG. 3 includes an illustration of a median longitudinal section of a quartz ampoule which can be used to manufacture a composite crystal, in accordance with one embodiment.

FIG. 4 includes an illustration of a growth method and synthesis of a crystal in a Bridgman furnace, in accordance with one embodiment.

FIG. 5 includes an illustration of a FoM (Figure of Merit) measurement for the parameter of gamma ray and thermal neutron discrimination, in accordance with one embodiment.

FIG. 6 includes an illustration of after gamma-ray irradiation of the afterglow (normalized signal) of a crystal described herein, in accordance with one embodiment.

Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the invention.

SUMMARY OF THE DISCLOSURE

To meet this need, the invention proposes an inorganic scintillator material in the form of a composite single crystal Lai-z-vCezCv(Bri- Ax)3-v+y+wLiyNa_w-(LiX)a-(NaY)b consisting of a single-crystal matrix Lai-z-vCezCv(Bri-xAx)3-v+y+wLiyNa_w and LiX inclusions, and optionally NaY inclusions, embedded in said single-crystal matrix, wherein

- A is selected among the elements I and Cl ;

- C is selected among the elements Ca, Sr, Ba and Mg, preferably among Sr and Ca;

- X is selected among the elements F, Cl, Br, I and combinations thereof;

- Y is selected among the elements 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 and z are molar indices for LiX, NaY, A, C, Li, Na and Ce, respectively.

As this will be seen in greater detail later in the description, the inventors have discovered that this material, comprising a lattice of Lai-z-vCezC_v(Bri-xAx)3-v+y+wLiyNa_w and LiX inclusions, has a PHR energy resolution, at the isotopic source ¹³⁷Cs, of less than 3.0%, as well as a good gamma-ray and thermal neutron detection capability.

In the La]-z-vCe_zCv(Bri-_xAx)3-v+ +wLiyNaw lattice, Li and Na ions, if any, take up interstitial positions in the crystal.

A material according to the invention may further have one or more of the following optional features:

- the material in single crystal form preferably has a formula selected among:

- LaBr3:Ce-(LiBr)_a,

- La(Bri-_xA_x)3:Ce:C-(LiX)_a, C being selected among Ca, Sr, Ba and Mg, preferably being Sr,

- Ce(Bn._xA_x)₃-(LiX)a,

- Ce(Bri-_xA_x)3:C-(LiX)_a, C being selected among Ca, Sr, Ba and Mg, preferably being Ca, wherein

- A is selected among I and Cl;

- X is selected among I, Br, Cl, F and combinations thereof;

- 0 < x < 0.5;

- 0 < a < 0.20;

- the single-crystal matrix is selected among LaBr₃:Ce, LaBr3:Ce:Sr, CeBn and CeBr3:Ca;

- the material is LaBr3:Ce-(LiBr)_a;

- more than 10 weight%, preferably more than 50 weight% of the Li in the material is under the form 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 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 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;

- 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.

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

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. The invention also relates to a process for manufacturing a scintillator material according to the invention, comprising the following successive steps: a) preparing a starting charge having a composition suitable for the composition of said material; b) synthesizing the composite single crystal, from the starting charge, by a vertical thermal gradient crystallization method or by Edge Defined Film Fed Growth method, preferably by a vertical thermal gradient crystallization method, preferably by the Bridgman method.

This process is remarkable in that the starting charge comprises a flux providing Li, or "first flux", preferably a LiX flux, X being selected among F, Cl, Br and I, preferably a LiBr flux.

The addition of a flux is a known technique for crystal synthesis, in particular for modifying the melting temperature of the starting charge. The inventors have discovered that adding a LiX flux to a so-called single-crystal matrix provides both a double detection and a good PHR energy resolution. This result was unexpected, as Lithium Li is known to have a strong propensity to segregate and thus deteriorate the optical properties of the crystalline matrix. Surprisingly, the inventors found that, in matrices with a hexagonal structure, e.g., containing lanthanum La, inclusions originating from the flux could advantageously precipitate between the hexagonal units. Without being bound by this theory, this is how they explain that optical properties are preserved, despite lithium segregation.

Preferably, the amount of said first flux is greater than 1%, preferably greater than 3%, preferably greater than 4%, and/or less than 10%, preferably less than 8%, more preferably less than 6%, by weight percentage based on the starting charge.

Preferably, the starting charge comprises a second flux, the second flux supplying iodine I. Iodine supply by a second flux advantageously optimizes detection of the light emitted by the scintillator material by a photomultiplier tube. The second flux is preferably Nal, which avoids the use of a flux containing a rare earth, which is highly hygroscopic.

Preferably, the amount 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%, by weight percentage based on the starting charge.

The second flux may be different from or identical to the first flux, particularly when it is Lil. Lil advantageously avoids the need to use a salt such as Lals or Ceh, which are very hygroscopic. Preferably, the total amount of the first and second fluxes 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%, by weight percentage based on the starting charge.

Unless otherwise stated, when reference is made to "flux" in the rest of the description, it refers to the first flux.

The invention also concerns the use of a material according to the invention to detect gamma rays and thermal neutrons, preferably to measure the intensity of gamma rays and thermal neutrons.

The material according to the invention can be used in particular as a component of a scintillation detector, especially for applications in industry, in the medical field and/or for the detection of oil for oil drilling, for security systems, especially for the control of illicit objects, e.g. luggage in an airport or goods in containers, e.g. shipping containers. In particular, it can be used as part of a Positron Emission Tomography scanner or an Anger-type Gamma Camera.

The invention also relates to a detector of gamma rays and thermal neutrons 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 pulse of light emitted by the scintillator.

The photodetector of the detector can be a photomultiplier, a photodiode or a SiPM sensor.

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

The following description in combination with the figures is provided to assist in understanding the teachings disclosed herein. The following discussion will focus on specific implementations and embodiments of the teachings. This focus is provided to assist in describing the teachings and should not be interpreted as a limitation on the scope or applicability of the teachings.

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

As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of features is not necessarily limited only to those features but may include other features not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive-or and not to an exclusive-or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

The use of “a” or “an” is employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural, or vice versa, unless it is clear that it is meant otherwise.

The use of the word “about,” “approximately,” or “substantially” is intended to mean that a value of a parameter is close to a stated value or position. However, minor differences may prevent the values or positions from being exactly as stated. Thus, differences of up to ten percent (10%) for the value are reasonable differences from the ideal goal of exactly as described.

In the formula of a single-crystal matrix according to the invention, the sign classically separates elements that can be substituted for one another in the matrix. In the formula of a material according to the invention, a dash is used to separate the formula of the single-crystal matrix and the formula of the LiX inclusions.

Pulse Height Resolution (PHR) is measured by recording a spectrum representing the activity of a source as a function of energy. For a given incident radiation energy, PHR is the ratio of the width at half-height of the main peak corresponding to said given energy (e.g. corresponding to the main response to gamma rays or thermal neutrons), divided by the energy at the peak centroid (see in particular: G.F Knoll, "Radiation Detection and Measurement" , John Wiley and Sons, Inc, 2^nd edition, p 114).

Figure 1 shows an example of a recording of the energy spectrum obtained from an isotope source ¹³⁷Cs with energy at 667 keV, detected with a LaBr3:Ce scintillator material. This recording provides the number of counts as a function of the channel. The PHR energy resolution is equal to d/l*100%. More specifically, to obtain Figure 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. The photodetector used was an Advanced Photonix APD avalanche photodiode (type 630-70-72-510), operating at a voltage of 1600 V and cooled to 270 K. To maximize light collection, the crystal sample was wrapped in 3 layers of a Teflon film [using the technique described in J. T. M. de Haas and P. Dorenbos, IEEE Trans. Nucl. Sci. 55, 1086 (2008)], except for the polished side intended for coupling with the photodiode. The output signal from the photodetector was amplified under "shaping time" conditions of 6 s by an ORTEC 672 spectroscopic amplifier. Exposed to the gamma source, the scintillator material produces photons that are detected and counted by the photodetector.

The photodetector used is sensitive from UV to IR and can count each photon. The result is an energy spectrum, or "scintillation histogram", with values on the x-axis proportional to the quantity of emitted light detected by the photodetector, and on the y-axis the number of gamma photon interaction events with the scintillator. The higher the number of channels used to observe the scintillation peak, the higher the number of photons emitted per pulse.

Other measurement conditions are specified in the publication by O. Guillot-Noel "Optical and scintillation properties of cerium doped LaCh, LuBrs and L11CI3" in Journal of Luminescence 85 (1999) 21-35.

In the present description, and for all measurements made (unless otherwise specified), the energy resolution is always determined, as described above, for the main peak corresponding to a reference radioactive source ¹³⁷Cs at 662 keV, the energy of the main gamma emission. In this way, measurements are comparable.

The position of a peak can vary according to the size of the detector, its quality and optical properties, which determine the optical coupling with the photodetector (typically 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 scintillation detector.

The composition of the material according to the invention is classically given without taking into account the impurities usual in the technical field of the invention. The usual impurities are generally impurities originating from raw materials, the mass content of which is typically less than 0.1 %, or even less than 0.01 %, and/or parasitic phases, the volume percentage of which is notably less than 1%. A "flux" is a constituent of the starting charge that segregates, i.e., forms inclusions, without integrating into the single-crystal matrix (the crystal's host phase), i.e., without forming part of the single-crystal matrix.

LiX inclusions are "embedded" in the matrix insofar as they are arranged within the matrix. However, they form a separate phase from the matrix and are not "integrated" into the matrix.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The materials, methods, and examples are illustrative only and not intended to be limiting. To the extent not described herein, many details regarding specific materials and processing acts are conventional and may be found in textbooks and other sources within the glass, vapor deposition, and electrochromic arts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The following description is provided for illustrative purposes and does not limit the invention.

Manufacturing process

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

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

All conventional processes for preparing a starting charge for the manufacture of inorganic scintillator materials can be implemented, provided that the starting charge is adapted to the composition of the desired material. This adaptation poses no difficulty for those skilled in the art.

The starting charge, preferably each raw material source, is preferably in a powder form. The particles are typically between 50 pm and 2 mm in size. However, the particle size distribution has no effect on the material produced, as the powders are melted.

The raw materials used include:

- (Lao, 95 Ceo,s)Br powders, for example, with a particle size of between 50 pm and 2 mm;

- SrBrs powder, for example, with a particle size of between 50 pm and 2 mm;

- LiX powder, for example, with a particle size of between 50 pm and 2 mm.

Classically, prior art scintillator materials containing ⁶Li contain between 0.6% and 1.2% ⁶Li, based on Li mass. Natural Li contains 7.6% ⁶Li. Preferably, the starting charge comprises a source of Li enriched in ⁶Li, i.e. which has more ⁶Li than natural Li, the atomic ratio in ⁶Li/(⁶Li+⁷Li) preferably being 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%.

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

The introduction of a high quantity of ⁶Li considerably improves thermal neutron detection.

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.

This method and the synthesis conditions are described in detail in the article by H.Chen et al. entitled "Bridgman Growth of LaCl Ce^J+ crystal in non-vacuum atmosphere", Journal of Alloys and Compounds 449 (2008) 172-175.

However, this method does not produce a satisfactory composite single crystal. In particular, LaBn and CeBn on the one hand, and LiBr on the other, only form eutectics without forming specific phases to form a single crystal. In particular, Marcelle Gaune-Escard et al. describes 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 n°135. Generally speaking, Li does not form phases with LaBn and CeBn and therefore cannot be used, according to a conventional approach, for thermal neutron absorption so as to ensure a dual detection of thermal neutrons and gamma rays.

The inventors have sought 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 Li ions to be introduced into the structure of the crystal matrix, except in very small quantities in the interstitial positions of the crystal. They explain this result by the very high segregation of Li in the molten bath. The small amount of Li in the crystalline matrix is not sufficient for the significant absorption of thermal neutrons required for the dual detection of thermal neutrons and gamma rays.

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, notably in crystals with a cubic structure such as CaF2:Eu:Li. In fact, the inclusions enter the cubic matrix at random, which disturbs the optical transparency properties.

S. Cheng et al. have also described a Li doping for a CeCL:Li system, in "Selfassembled natLiCl-CeCh directionally solidified eutectics for thermal neutron detection", April 2020 CrystEngComm 22(19). The resulting composite does not exhibit an optical transparency suitable for the thermal photon detection in the UV spectrum. Energy resolution is also unsatisfactory.

The inventors have come up with the idea of adapting the Bridgman vertical synthesis process described by H.Chen et al. (described in "Bridgman Growth ofLaCl3:Ce^j+ crystal in non-vacuum atmosphere" , Journal of Alloys and Compounds 449 (2008) 172-175) by introducing a flux supplying Lithium (Li) into the starting charge.

Preferably, crystal growth is initiated by a seed oriented along the hexagonal crystallographic axis "c" <0001> and continues along this highly anisotropic crystallographic axis.

As shown in Figure 3, the cylindrical seed 10 is positioned in a special pocket provided for this purpose at the bottom of a bulb 12.

Preferably, the ampoule is a sealed quartz ampoule, in which the pressure is less than 10"² mbar, i.e., "under vacuum". Preferably, a mixture of (La,Ce)Br3 powders and LiBr flux is placed in the ampoule.

Surprisingly, this adapted process makes it possible to obtain an anisotropic singlecrystal matrix into which inclusions enter in an organized fashion. The matrix preferably has a hexagonal structure like that presented by LaBr?, LaCL and CeB (UC14 type) crystals 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 interfere significantly with optical properties. They can also take the form of "grains" which are inserted and aligned along lines parallel to the crystallographic axis "c" , in the space between the hexagonal structures.

A hexagonal structure differs in particular from the orthorhombic structure Cmcm, N°63, of Lab which, with a Ce doping, does not exhibit good scintillation properties. A material according to the invention can be made by any edge defined growth method, and in particular by the Edge Defined Film Fed Growth (or “EFG”) described in particular by V.A.Tatarchenko in "Stability of Crystallization in Edge-Defined Film-Fed Growth from the Mell" in Givargizov, E.I. (eds) Growth of Crystals. Springer, Boston, MA (1986), or preferably by a Bridgman growth method, especially in vacuum-sealed quartz ampoules, provided that said flux is added to the starting charge. Preferably, the single-crystal matrix has an anisotropic structure, preferably hexagonal, preferably LaBrv

According to the invention, the growth preferably results from the addition of a LiBr lithium bromide flux.

Particularly for materials of the (La,Ce)(Br,I)3-(LiX)_a type, the growth preferably results from the addition of a Lil flux.

Particularly for materials of the (La,Ce)(Br,Clh-(LiX)_a type, the growth preferably results from the addition of a LiCl flux.

During eutectic decompositions, the LiX inclusions, particularly the LiBr inclusions, solidify in a regular structure, mostly in the form of

- fine fibers and/or

- small point-like inclusions, aligned along the crystallographic axis <0001> and incorporated into the host matrix formed by the hexagonal single crystal.

Remarkably, the resulting composite single crystal retains good optical transmission properties along the crystallographic "c" axis, making it suitable as a scintillator material. In particular, the inventors found that the inclusions present the form of "fibers" oriented substantially parallel to one another, which could explain the high optical transparency of the composite single crystal according to the invention.

The synthesis method described above, using an adapted Bridgman vertical composite crystal synthesis method, can be generalized to any vertical gradient crystallization method, and in particular to the methods known by the acronym TGT (for "Temperature Gradient Technique"), 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 supplying Li is added to the starting charge.

The "EFG", "Edge Defined Film Fed Growth" method is also effective for synthesizing a scintillator material according to the invention in various forms, provided that a flux supplying Li is added to the starting charge.

Scintillator material

Preferably X = Br or I.

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. 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.

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.

Preferably 0. 15 > x and 0.05 > v and 0.40 > z.

Preferably 0.10 > x and 0.01 > v and 0.30 > z.

Preferably, x > 0.005 and v > 0.002 and z > 0.02.

Preferably, x > 0.01 and v > 0.003 and z > 0.04.

Preferably, 0.15 > x > 0.005 and 0.05 > v > 0.002 and 0.4 > z > 0.02. Preferably, 0. 10 > x > 0.01 and 0.01 > v > 0.003 and 0.30 > z > 0.04. The best performances in dual detection of gamma rays and thermal neutrons were 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.

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 10 cm³, or even greater than 100 cm³.

Detector - applications

A detector according to the invention, comprising a material according to the invention, can be used in particular:

- in a nuclear medicine apparatus, chosen in particular from Anger- type Gamma cameras and Positron Emission Tomography scanners (see for example C.W.E. 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 96); 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).

The invention also concerns such a device, and more generally, a device comprising a material according to the invention. EMBODIMENTS

The concepts as described in this specification are not limited to the particular application previously described. The radiation detector can be configured for another type of radiation. Many different aspects and embodiments are possible. Some of those aspects and embodiments are described herein. Embodiments may be in accordance with any one or more of the embodiments as listed below.

Embodiment 1. An inorganic scintillator material in the form of a composite single crystal of the formula Lai-z.-vCe_zCv(Bri-xAx)3-v+y+wLiyNa_w-(LiX)_a-(NaY)b consisting of a single-crystal matrix Lai-_z-vCe_zCv(Bri-xAx)3-v+y+wLiyNa_w and of LiX inclusions, and optionally NaY inclusions, embedded in said single-crystal matrix, wherein

A is selected among I and CI;

C is selected among Ca, Sr, Ba and Mg, preferably among Sr and Ca;

X is selected among F, CI, Br, I and combinations thereof;

Y is selected among F, CI, 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 < l ;

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.

Embodiment 2. The material according to embodiment 1 , having a formula selected among:

LaBr3:Ce-(LiBr)_a;

La(Bri-_xAx)3:Ce:C-(LiX)_a, C being selected among Ca, Sr, Ba and Mg, preferably being Sr; Ce(Bri-_xAx)₃-(LiX)_a;

Ce(Bri xA_x)3:C-(LiX)a, C being selected among Ca, Sr, Ba and Mg.

Embodiment 3. The material according to embodiment 1, where the single-crystal matrix is selected among LaBr3:Ce, LaBr3:Ce:Sr, CeBn and CeBr3:Ca. Embodiment 4. The material according to embodiment 1 , having the formula LaBr3:Ce-(LiBr)_a.

Embodiment 5. The material according to any one of the preceding embodiments, where more than 10 weight % of the Li is under the form ⁶Li.

Embodiment 6. The material according to the immediately preceding embodiment, where more than 50 weight % of the Li is under the form ⁶Li.

Embodiment 7. The material according to any one of the preceding embodiments, 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, more preferably 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, more 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.

Embodiment 8. The material according to any of the preceding embodiments, 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.

Embodiment 9. A process for manufacturing a material according to any one of the preceding embodiments, can include the following successive steps: preparing a starting charge having a composition suitable to the composition of said material; synthesizing the composite single crystal, from the starting charge, by a vertical gradient crystallization method or by Edge Defined Film Fed Growth method, the starting charge comprising a first flux providing lithium Li and of formula LiX, X being selected among F, CI, Br and I.

Embodiment 10. The process according to the immediately preceding embodiment, where X is the element Bromine Br.

Embodiment 11. The process according to any one of the two immediately preceding Embodiments, where the amount of said first flux is greater than 1%, preferably greater than 3%, more preferably greater than 4%, and/or less than 10%, preferably less than 8%, more preferably less than 6%, by weight percentage based on the starting charge.

Embodiment 12. The process according to any one of the two immediately preceding embodiments, where the starting charge comprises a second flux, the second flux supplying iodine I, and preferably being Nal.

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

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

Embodiments as described in this specification can allow for relatively large radiation detectors that can be used for inspecting cargo, vehicles, or other large objects, as well as research on high energy physics, medical imaging, small detectors, network communications, broadcast receivers, wireless transmissions, augmented reality devices, and broadcasting networks. Note that not all of the activities described above in the general description or the examples are required, that a portion of a specific activity may not be required, and that one or more further activities may be performed in addition to those described. Still further, the order in which activities are listed is not necessarily the order in which they are performed.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims.

EXAMPLES

The following non-limiting examples are given to illustrate the invention.

A composite single crystal was produced using a Bridgman method of vertical synthesis adapted by adding a flux containing Li, as follows:

A starting charge was first prepared by mixing the following powders: LaBra - 845.2 g CeBra - 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 HC1 atmosphere was required. The granulometry of the powders allowed them to be introduced into the ampoule described below, so no grinding step was necessary. Finally, it was not necessary to add activated carbon powder, as described in this article. To synthesize the composite single crystal, a quartz ampoule 12 of the type shown in Figure 3 was used. The vertically arranged ampoule 12 comprised a cylindrical part 14, with an internal diameter of 33 mm and a length of 345 mm, extended downwards by a conical part 16, whose angle at the top was 60°, defining the ampoule bottom. The internal volume of the ampoule is estimated at 300 ml.

The ampoule 12 also comprised a quartz pocket 18 located at the bottom of the ampoule.

A cylindrical seed 10, 6 mm in diameter and 40 mm in length, was cut from a single crystal (Lao.95,Ceo,o5)Br3 along axis <0001>, then placed in pocket 18 so that axis <0001> was vertical.

The mixture of powders making up the starting charge 19 was then poured into the ampoule, through a top opening 20.

The pressure was then reduced to less than 10"² mbars in the ampoule, and the ampoule was immediately sealed, by plugging the top opening 20 with an acetylene-oxygen flashlight, to prevent oxidation and volatilization.

The ampoule 12 was then placed on an ampoule holder 22 inside a Bridgman furnace 24 of the type shown in figure 4.

The furnace interior 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").

The furnace 24 comprised also electric resistors to heat the different zones to different temperatures.

The ampoule holder 22 has been placed in the furnace interior so that the starting charge is in the hot zone 30 and half of the seed 10 is in the cold zone 26 and the other half of the seed is in the intermediate zone and in the hot zone.

The setpoint temperature of the oven in the hot zone was set at 850°C to melt the charge in the ampoule and the upper part of the seed 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 seed.

After maintaining these temperatures for two hours in the oven, the ampoule 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 gradually formed in the lower part of the ampoule.

Figure 4 illustrates this synthesis operation. In the third stage, we can see the formed crystal 34, in the lower part of the ampoule, and the residual starting charge 19. The ampoule was then gradually cooled at a rate of 10°C/hour to room temperature of

20°C.

The ampoule was then cut open using a circular saw fitted with a diamond blade, in a glove box so as not to expose the resulting crystal to moisture after removal from the ampoule.

On leaving the ampoule, the crystal consists of five parts, namely, successively from bottom to top:

- the seed, devoid of inclusions;

- a cone and a cylinder trunk poor in Li;

- a cylinder trunk made of a material according to the invention;

- a cylinder trunk mainly made of solidified flux.

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

The other examples were manufactured in a similar way to Example 1, adapting the composition of the starting filler. Table 1 below summarizes the compositions of the starting charge and the corresponding material according to the invention.

In the first column, the factors indicate mass percentages. For example, "0.95Lao,95 Ceo.os Br3 + 0.05LiBr" means that the starting charge comprises 5% flux and 95% other powders, in mass percentage based on the starting charge.

Indices are atomic percentages. In the above example, the other powders supply 0.95 moles of LaB , and 0.05 moles of CeBrs per mole.

In the second column, the indices are also atomic percentages.

[Table 1]

Examples 3, 6, 9, 11 and 12 are particularly advantageous because they use a second flux, which is not a REI3 flux, where RE stands for rare earth, to achieve a partial anionic substitution of Br (or Cl) by iodine I. In fact, REI3 salts are known to be very hygroscopic. Advantageously, the manufacturing conditions are facilitated.

Furthermore, the addition of I (Iodine) by a flux advantageously moves the main scintillation emission peak closer to the spectrum of wavelengths to which photomultiplier tubes are most sensitive. In particular, substituting Br with I shifts the scintillation emission peak from 380-390 nm to 420 nm. This makes Nal and Lil fluxes particularly advantageous, as Lil can advantageously supply both Li and I.

Example 3 advantageously presents a reduced afterglow, as shown in Figure 6. This figure shows after gamma-ray irradiation the afterglow (normalized signal) of crystals LaB (Ce) - B380 (intermediate region, dark gray), LaBr3:Ce:Sr - B390 (upper region, black) and LaBrs (Ce,Li) (lower region, light gray), as a function of time (x-axis, ns). The level of afterglow or crystals synthesized with a Lil flux is advantageously reduced, making it possible, for example in the case of repeated detections, e.g., of baggage image acquisition in an airport gantry, to improve the sharpness of these images.

This advantage is particularly evident in composite single crystals according to the invention having a matrix of the LaBr3:Ce:Li type and synthesized with a Lil flux.

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 conventional "geoline" assembly, i.e., mounted in a blind metal tube whose opening was conventionally sealed with a transparent membrane.

Two detectors, A and B, were thus obtained to check that the results obtained were similar.

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

Figure 2 shows the spectrum obtained for the first detector, the spectrum obtained with the second detector being similar. The peaks corresponding to responses to gamma radiation (three peaks) and 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.

Each detector was then exposed to a source of ¹³⁷Cs so as to receive gamma radiation at 662 keV. The energy spectra obtained were analyzed to determine the energy resolution (PHR) for the two largest peaks representing the response to gamma radiation.

The results obtained are shown in Table 1 below:

[Table 2]

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

The examples thus show that a scintillator material according to the invention enables a detection of both gamma rays and thermal neutrons, with an energy resolution value (PHR), determined at 662 keV, of less than 3.0%.

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

Figure 5 illustrates the measurement of the FoM for the discrimination of gamma rays and thermal neutrons using the PSD (Pulse-Shape-Discrimination) method. It shows the PSD parameter (head/total) as a function of energy, in keV. The upper scatterplot represents the contribution of thermal neutrons. The lower scatterplot represents the contribution of gamma rays. The right-hand side shows the density of points in the framed region of interest.

The FoM was measured for both detectors. Tn both cases, it was 1 .2, confirming a good discrimination capability.

The FoM was also measured for a detector manufactured as described above, with a scintillator material manufactured as in Example 1 , but with lithium enriched in ⁶Li so that the atomic ratio in ⁶Li/(⁶Li+⁷Li) is 95%. This was 1.66, showing that an increase in ⁶Li content further improves discrimination capability.

Finally, the tests showed that the composite single crystal according to the invention has mechanical properties that make it suitable for the intended applications.

Of course, the present invention is not limited to the embodiments described in detail above, nor to the examples, provided for illustrative purposes. The specification and illustrations of the embodiments described herein are intended to provide a general understanding of the structure of the various embodiments. The specification and illustrations are not intended to serve as an exhaustive and comprehensive description of all of the elements and features of apparatus and systems that use the structures or methods described herein. Separate embodiments may also be provided in combination in a single embodiment, and conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. Further, reference to values stated in ranges includes each and every value within that range. Many other embodiments may be apparent to skilled artisans only after reading this specification. Other embodiments may be used and derived from the disclosure, such that a structural substitution, logical substitution, or another change may be made without departing from the scope of the disclosure. Accordingly, the disclosure is to be regarded as illustrative rather than restrictive.

Claims

WHAT IS CLAIMED IS:

1. An inorganic scintillator material in the form of a composite single crystal of the formula Lai-z-vCezCv(Br]-xAx)3-v+y+wLiyNa_w-(LiX)a-(NaY)b consisting of a single-crystal matrix Lai-z-vCe_zCv(Bri-xAx)3-v+y+wLiyNaw and of LiX inclusions, and optionally NaY inclusions, embedded in said single-crystal matrix, wherein

A is selected among I and CI;

C is selected among Ca, Sr, Ba and Mg, preferably among Sr and Ca;

X is selected among F, CI, Br, I and combinations thereof;

Y is selected among F, CI, 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 < l ;

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.

2. The material according to claim 1, having a formula selected among:

LaBr3:Ce-(LiBr)_a;

La(Bri-_xA_x)3:Ce:C-(LiX)a, C being selected among Ca, Sr, Ba and Mg, preferably being Sr;

Ce(Bn.xAx)3-(LiX)_a ;

Ce (Bri-_xA_x)3:C-(LiX)a, C being selected among Ca, Sr, Ba and Mg.

3. The material according to claim 1, wherein the single-crystal matrix is selected among LaBr3:Ce, LaBr3:Ce:Sr, CeBn and CeBr3:Ca.

4. The material according to claim 1, having the formula LaBr3:Ce-(LiBr)_a.

5. The material according to any one of the preceding claims, wherein more than 10 weight % of the Li is under the form ⁶Li.

6. The material according to the immediately preceding claim, wherein more than 50 weight % of the Li is under the form ⁶Li.

7. The 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, more preferably 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, more 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. The material according to any 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 process for manufacturing a material according to any one of the preceding claims, comprising the following successive steps: preparing a starting charge having a composition suitable to the composition of said material; synthesizing the composite single crystal, from the starting charge, by a vertical gradient crystallization method or by Edge Defined Film Fed Growth method, the starting charge comprising a first flux providing lithium Li and of formula LiX, X being selected among F, CI, Br and I.

10. The process according to the immediately preceding claim, wherein X is the element Bromine Br.

11. The process according to any one of the two immediately preceding claims, wherein the amount of said first flux is greater than 1%, preferably greater than 3%, more preferably greater than 4%, and/or less than 10%, preferably less than 8%, more preferably less than 6%, by weight percentage based on the starting charge.

12. The process 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 the detection for oil drilling.

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