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Definitions

• the rare earth halides in the following, Ln is used to designate a rare earth
• LnBr 3 doped with Cerium and LnCl ⁇ doped with Cerium have very interesting scintillation properties especially for applications in nuclear imaging and spectroscopy (Positron-Emission-Tomography known as PET, Gamma camera, oil prospecting and other).
• PET nuclear imaging and spectroscopy
• these compounds must be obtained in the form of large crystals.
• these crystals are single crystals. In certain particular cases they can also be polycrystals inside which the crystals have a dimension of the order of one or more centimeters.
• rare earth halides are very hygroscopic compounds which react with water and air as soon as they are heated to form very stable oxyhalides. It has generally been considered that oxyhalide levels of the order of 0.1% by weight are acceptable, the crystals obtained at these contents being apparently sufficiently transparent.
• certain crystals such as Csl: Tl accommodate high oxygen contents (for example around 0.2% of CsOH) as far as the scintillation properties are concerned.
• the Applicant has discovered that the scintillation properties, in particular the light yield, that is to say the number of UV-Visible photons emitted by MeV of energy from an incident particle, rare earth halides could be drastically improved by making lower the level of oxyhalide in a rare earth halide crystal below this value.
• the Applicant has therefore sought to develop manufacturing processes leading to the purest rare earth halides possible (in particular in oxygen), that is to say of which the water content is much less than 0.1% by weight and the oxyhalide content is less than 0.2% by weight, and even less than 0.1% by weight, or even less than 0.05% by weight.
• any installation is always more or less sealed and on the other hand always contains a little adsorbed water, so that partial pollution is usual in this kind of preparation, and one generally expects a strong oxidation by impurities from the gaseous environment, especially at high temperatures such as above 300 ° C.
• the invention also provides a solution from this point of view since the process according to the invention leads to a very pure rare earth halide, even with an installation initially containing water, adsorbed, absorbed, or in the condensed phase, and even in the presence of a reasonable amount of water and oxygen in the atmosphere during heating leading to the melting.
• a LaC ⁇ produced according to the invention has a crystallization temperature of 880 ° C while the values published by the prior art range between 852 and 860 ° C.
• a LaBr 3 manufactured according to the invention has a crystallization temperature of 820 ° C., while the values published in the prior art are between 777 ° C. and 789 ° C.
• the invention allows in particular the preparation of single crystals having a particularly short scintillation decay time. We are looking for crystals whose scintillation peaks have the lowest possible decay time, because thus the temporal resolution is improved. To make this measurement, the light intensity of the main peak is recorded over time. Thus, the invention allows the production of single crystals whose decay time of the main component is less than 40, and even less than 30 and even less than 20 nanoseconds.
• X represents a halogen atom chosen from Cl, Br, I.
• Rare earth fluorides are not concerned by the present invention taking into account that they are not hygroscopic and taking into account that their chemistry is very specific.
• the single crystals prepared according to the invention also have a particularly low energy resolution, in particular less than 5%, or even less than 4%, or even less than 3.5%.
• the ammonium-bromide route to anhydrous rare earth bromides MBr 3 ; J. of the Less-common Metals, 127 (1987) 155-160 ” teaches the preparation of a rare earth halide / ammonium bromide complex and its thermal decomposition at less than 20 ° C / hour to form a halide of rare earth, but never reaching fusion. By doing so, the halide retains a high specific surface, greater than 0.1 m 2 / g, which is suitable for absorbing moisture and forming oxychloride.
• the fact of working at less than 400 ° C. greatly limits the problems of corrosion of the materials, and this is one of the reasons why it is preferred in the prior art to use such low temperatures.
• the invention solves the above-mentioned problems.
• the invention makes it possible to obtain a very pure rare earth halide in the form of a polycrystalline block, in particular having a rare earth oxyhalide content of less than 0.2% by weight, or even less than 0.1% by weight, or even less than 0.05% by weight, or even less than 0.02% by weight and a water content less than 0.1% by weight.
• the preparation process according to the invention comprises a step of heating a mixture on the one hand of at least one compound comprising at least one Ln-X bond and on the other hand of NH 4 X, in which Ln represents a rare earth and X is chosen from Cl, Br and I, said compound and NH X being able to be combined at least partially within a complex, said step leading to a molten phase comprising the targeted halide, then a cooling step leading at least one solid block comprising said halide.
• the method according to the invention makes it possible in particular to prevent the water present in the mixture or the crucible or the apparatus, in adsorbed, absorbed or complexed form, from combining definitively in rare earth oxychloride with the halide of rare earth.
• the process according to the invention leads to a final block having much less oxyhalogenide than the same process without NH 4 X at the start.
• the polycrystalline block obtained according to the invention is very pure.
• the invention combines in a single heating step the oxygen scavenging action conferred by the presence of the ammonium halide, and the fact of going immediately to the melting of the rare earth halide of so as to drastically reduce its specific surface, which makes it all the less sensitive to moisture during its storage and handling.
• the halide is therefore firstly purified, to be secondly melted so as to become much less sensitive to oxidation by water and oxygen, this first and second stage being carried out in one and the same heating step, which means that once the mixture has reached the temperature of 300 ° C, its temperature is not brought back to room temperature or even to a temperature below 200 ° C before reaching the fusion of the desired rare earth halide.
• This preparation of the block according to the invention is carried out under an inert or neutral atmosphere (nitrogen or argon for example) but this atmosphere may even contain relatively high contents of water and oxygen, that is to say so that the sum of the mass of water and oxygen in the gaseous atmosphere is less than 200 ppm by weight.
• the water content of the inert atmosphere ranges from 10 to 180 ppm by weight and the oxygen content of the atmosphere ranges from 0.5 to 2 ppm by weight.
• the block Due to its low specific surface, compared to a powder, the block absorbs less impurities from the air (humidity and oxygen) and can therefore be stored and handled in a very pure state. Under these conditions, this block can be used for the preparation of crystals (generally single crystals) of very pure and high quality rare earth halides.
• the invention also relates to a method for preparing the blocks according to the invention in a crucible rich in carbon.
• a method for preparing the blocks according to the invention in a crucible rich in carbon is provided.
• the growth of Ba 2 Y ⁇ - Er ⁇ CI 7 (o ⁇ x ⁇ 1) in a vitreous carbon crucible leads to pollution of the crystal because of the crucible, it turned out that the compositions which are the subject of the present invention were advantageously melted in a crucible rich in carbon as is the case with vitreous carbon, to make the block according to the invention.
• the rare earths Ln concerned by the present invention are those of column 3 (according to the new notation) of the periodic table of the elements, including Se, Y, La, and the Lanthanides from Ce to Lu.
• the halides of Y are more particularly concerned. , La, Gd and Lu, which can in particular be doped with Ce or Pr.
• the rare earth halides more particularly concerned with being manufactured in a block according to the present invention can be represented by the general formula A e Ln f X (3f + e) in which Ln represents one or more rare earth (s), X represents one or more halogen atom (s) chosen from Cl, Br or I, and A represents one or more alkali (s) such as K, Li, Na, Rb or Cs, e and f representing values as
• - e which can be zero, is less than or equal to 3f, - f is greater than or equal to 1.
• the method according to the invention is all the more effective the lower the atomic number of X.
• the effectiveness of the process according to the invention in reducing the level of oxyhalide in the final block goes, depending on the nature of X, in the following increasing direction: I ⁇ Br ⁇ Cl.
• the process according to the invention is all the more effective as the ionic radius of Ln is large.
• the efficiency of the process according to the invention in reducing the rate of oxyhalide in the final block goes, depending on the nature of Ln, in the following increasing direction: Se ⁇ Lu ⁇ Y ⁇ Gd ⁇ Pr ⁇ Ce ⁇ The.
• the rare earth halides more particularly concerned are in particular the following: ALn 2 X 7 in which Ln represents one or more rare earth (s), X represents one or more halogen atom (s) chosen from Cl, Br or I, A representing an alkali such as Rb and Cs,
• LaBr 3 which can in particular be doped with 0.1 to 50% by weight of CeBr 3 ,
• GdBr 3 which can in particular be doped with 0.1 to 50% by weight of CeBr 3 ,
• the x Gd (- ⁇ -X ) Br 3 which can in particular be doped with 0.1 to 50% of CeBr 3 , x which can range from 0 to 1,
• RbLn 2 Br 7 which can in particular be doped with 0.1 to 50% by weight of CeBr 3 ,
• - K 2 LaCI 5 which can in particular be doped with 0.1 to 50% by weight of CeCI 3 .
• - K 2 Lal 5 which can in particular be doped with 0.1 to 50% by weight of Cel 3 .
• dopant or “doped” refers to a rare earth rare which replaces one or more majority rare earths, the minority and majority being included under the acronym Ln.
• the invention can in particular lead to a block in which Ln is La or Ce and X is Cl or Br.
• the invention relates in particular to a method for preparing a block characterized in that it comprises a step of heating a mixture on the one hand of at least one compound comprising at least one Ln-X bond and on the other share of NH 4 X, said compound and NH 4 X can be combined at least partially within a complex, said step leading to a melt comprising the halide of formula A e LnfX (3f + e ), said heating step being followed by a cooling step after obtaining the melt, said heating step, after reaching 300 ° C never falling below 200 ° C before obtaining said melt.
• the compound comprising at least one Ln-X bond can be of formula
• Ln has the degree of oxidation 3 and, if it is present, A has the degree of oxidation 1.
• r can be zero.
• u can be zero.
• the amount of oxygen bound to Ln is such that the amount of oxyhalogenide obtained by the dissolution method is less than 100 ppm by weight.
• the compound comprising at least one Ln-X bond can be a rare earth halide or a hydrated rare earth halide. He can by example be of formula LnX 3 or LnX 3. (H 2 O) n with n ranging from 1 to 10, or a mixture of several of the compounds whose formulas have just been given.
• the compound comprising at least one Ln-X bond can also be a rare earth oxyhalide. It can be of formula LnXO or a mixture of several of the compounds whose formulas have just been given. It is preferred to avoid the presence of LnXO in the starting mixture. Thus, preferably, the starting mixture contains less than 100 ppm by weight of LnXO. In general, it is a powdered rare earth halide containing a small proportion of oxyhalogenide and water. The mixture can also comprise a complex of a rare earth oxyhalide and NH 4 X.
• the mixture can also comprise water, in free form or in complex form, for example with the rare earth halide. Surprisingly, the amount of water can be very large, without this resulting in obtaining a higher rate of oxyhalide in the final polycrystalline block according to the invention, as soon as the mixture contains a sufficient amount of NH 4 X.
• the mixture can even comprise for example up to 20% by weight of water, or even more. It can also include, for example, less than 16% by weight of water, or even less than 5% by weight of water.
• the mixture on the one hand of at least one compound comprising at least one Ln-X bond and on the other hand of NH 4 X, these two compounds being optionally at least partially in complexed form, comprises sufficient NH X for that the final block comprises less than 0.2% by weight of rare earth oxyhalide, or even less than 0.1%> by weight of rare earth oxyhalide, or even less than 0.05% by weight of oxyhalide rare earth, or even less than 0.02% by weight of rare earth oxyhalide.
• the Ln atoms in the compound are only linked to X atoms or oxygen atoms or A atoms.
• an amount of NH 4 X is introduced into the mixture which is at least the sum of the following two amounts:
• the number of moles of oxygen atoms bonded to Ln is identical to the number of moles of oxyhalogenide of formula LnOX as obtained by the dissolution method described below. From the mass of oxyhalide obtained by the dissolution method, it is therefore easy to calculate the number of moles of oxygen atoms bound to Ln, considering that the oxyhalide has the formula LnOX. In the case of the presence of A (generally Rb or Cs), taking into account that this atom has a very weak tendency to combine with oxygen, its presence does not intervene for the calculations of the quantities of NH 4 X.
• A generally Rb or Cs
• the mixture can comprise a complex of the compound comprising at least one Ln-X bond and of NH 4 X.
• This complex can for example be prepared by wet chemistry on the following principle: first a rare earth salt such as a rare earth oxide or a hydrated rare earth halide is dissolved in the corresponding hydracid (i.e. HCI if one wishes to obtain a chloride, HBr if one wishes to obtain bromide). At this stage, AX (A being generally Rb or Cs) is added if a halide containing A is targeted. Ammonium halide, preferably 1 to 4 moles of halide d, is added to the solution. ammonium per mole of rare earth halide, so as to obtain a solution.
• the mixture on the one hand of at least one compound comprising at least one Ln-X bond and on the other hand of NH 4 X is then subjected to a heat treatment.
• the mixture is generally loaded into a crucible, which can be made of platinum, carbon such as graphite or molybdenum or tantalum or boron nitride or silica.
• the crucible can also be made of graphite coated with pyrolytic carbon or of graphite coated with silicon carbide or of graphite coated with boron nitride.
• a crucible is used for demolding the block when cold.
• a crucible made of a material comprising at least 20% by weight of carbon is preferably used.
• a material may for example be made of carbon or graphite, or of amorphous carbon (or vitreous carbon), or of graphite coated with pyrolytic carbon (also vitreous carbon), or of graphite coated with silicon carbide, or of graphite coated with boron nitride (possibly pyrolytic).
• the crucible can therefore be coated with a layer of pyrolytic carbon.
• the material can comprise on the one hand a graphite substrate and on the other hand a coating, this coating may be pyrolytic carbon or silicon carbide or boron nitride (may be pyrolytic). The coating is used in particular to plug the porosity of the graphite.
• the crucible is then positioned in a sealed oven whose atmosphere is purged to make it inert, for example purged under primary vacuum and then swept by a stream of dry nitrogen.
• the oven temperature is then gradually increased to at least 400 ° C.
• the water in the complex is eliminated, then NH 4 X sublimes and settles on the cold parts downstream from the oven. It is important that the mixture is protected from ambient air and is well under an inert atmosphere, in particular from 300 ° C. and preferably from 200 ° C. This is why the potential air inlets in the installation are beyond the place where the NH 4 X is deposited so that the air cannot go up to the mixture to be purified.
• the actual temperature of the mixture generally shows a plateau corresponding to the elimination temperature of NH 4 X, even if the set temperature is constantly increasing. In the case of NH 4 CI, this level is between 300 and 400 ° C. This applies not only if the NH X is initially in free form but also if it is in complexed form. Taking into account that the heated mass contains much less NH X after this plateau, one would have expected that the mixture would then be easily oxidized from the impurities present in the gaseous environment (presence of water and d 'oxygen), and all the more that the temperatures are higher (at this stage, the temperature of the heated mass is generally higher than 300 ° C). The Applicant has discovered that this was not the case and that it was possible to control the oxidation of the rare earth halide.
• the temperature must then quickly rise to a temperature sufficient to melt the desired rare earth halide (for example 880 ° C for LaCI 3 ).
• a temperature sufficient to melt the desired rare earth halide for example 880 ° C for LaCI 3 .
• the mixture already transformed compared to the origin can be heated with a speed greater than 50 ° C / hour and even greater than 100 ° C / hour and even greater than 150 ° C / hour and even higher than 200 ° C / hour.
• the heating rate is less than 600 ° C / hour taking into account that it is generally necessary to protect the materials of the installation according to their resistance to thermal shock.
• the mixture For heating the mixture, once the mixture is at a temperature above 300 ° C., its temperature is not brought back to ambient temperature or even to a temperature below 200 ° C. before having reached the melting of the desired rare earth halide. It is preferable to heat the mixture until it melts in a single heating step, without lowering the temperature even momentarily before obtaining the melt comprising the molten halide.
• the entire heating step (from room temperature to melting) can generally be carried out in less than 10 hours, or even less than 6 hours, even less than 4 hours.
• An anhydrous rare earth halide block is thus recovered, comprising less than 0.1% by weight of water and less than 0.2% by weight of rare earth oxyhalide, or even less than 0.1% by weight. of rare earth oxyhalide, even less than 0.05% by weight of rare earth oxyhalide, or even less than 0.02%> by weight of rare earth oxyhalide.
• This block is easy to handle and store. Generally, blocks of at least 1 g per unit or even at least 10 g per unit, or even at least 50 g per unit, or even at least 500 g per unit, can be produced.
• the blocks generally have an apparent density of at least 75%, or even at least 80%>, or even at least 85% of the theoretical density, it being understood that the theoretical density is that corresponding to the same material free of porosity .
• the block according to the invention is polycrystalline and contains a multitude of grains which are each of small single crystals.
• a block generally contains at least 100 grains and even at least 1000 grains. No grain of the block represents more than 10% of the mass of the whole block.
• the ammonium halide condensed on the cold parts downstream of the furnace can at least partly be reused, for example in the process according to the invention.
• oxyhalide in a rare earth halide, it is sufficient to separate them by water (for example at room temperature) since the oxyhalides are insoluble in water while the halides are.
• the oxyhalides can be recovered by filtration, for example on a polypropylene (PP) filter, then dried at 120 ° C.
• PP polypropylene
• this method leads to the dissolution of AX since A does not form an oxyhalide.
• This so-called “dissolution method” or “insoluble method” leads well, even in the presence of A in the halide, to the determination of the oxyhalogenide level of formula LnXO.
• the block according to the invention can be used as a raw material used for the growth of crystals (generally single crystals) according to techniques known as so-called Bridgman growths, or Kyropoulos or Czochralski or growth by the gradient displacement method (“gradient freeze method "in English). These single crystals are very pure and can be used as a scintillator material.
• This preparation of crystals is carried out under a neutral atmosphere (nitrogen or argon for example) but this atmosphere can even contain relatively high contents of water and oxygen, that is to say so that the sum of the masses of water and d oxygen in the gaseous atmosphere is less than 200 ppm by weight.
• the content of the inert atmosphere in water ranges from 10 to 180 ppm by weight and the oxygen content of the atmosphere ranges from 0.5 to 2 ppm by weight.
• the invention also relates to a single crystal of formula A e Ln f X ( 3f + e ) whose symbols have the meanings already given, said single crystal comprising less than 0.2%> and even less than 0.1%, or even less than 0.05% or even less than 0.02% by weight of rare earth oxyhalide.
• Ln is chosen from La, Gd, Y, Lu and Ce
• X is chosen from Cl and Br.
• Gd, Y, Lu in particular chosen from lanthanides or mixtures of lanthanides from the group: La, Gd, and in which x is the molar rate of substitution of Ln by cerium, with x greater than or equal to 0.01 mole
• Ln- ⁇ -x Ce x CI 3 in which Ln is chosen from lanthanides or mixtures of lanthanides from the group: Y, La, Gd,
• Lu in particular among the elements or mixtures of elements of the group: La, Gd, Lu, and in which x is the molar rate of substitution of Ln by cerium, with x greater than or equal to 1 mole% and strictly less than 100 moles%.
• the aforementioned growth processes can lead to a large single crystal, that is to say at least 1 cm 3 , or even at least 10 cm 3 . and even at least 200 cm 3 .
• This single crystal can then be cut to sizes suitable for the desired applications.
• the single crystal according to the invention because of its high purity has a particularly high light output. This light output can in particular be measured relative to that of a Nal crystal doped with 600 ppm by weight of Tl iodide whose energy resolution at 622 KeV is 6.8% o, the integration time being 1 ⁇ s and the radioactive source being Cs 137 at 622 KeV.
• the coupling between the crystals (Nal or rare earth halide) and the photomultiplier is carried out using a transparent silicone grease up to 320 nm.
• the outlet face of the Nal towards the photomultiplier is polished.
• the invention makes it possible to obtain light yields of at least 90% of that of the Tl doped Nal crystal, in any event greater than that obtained on crystals which are not according to the invention.
• the crystal or single crystal can in particular be produced in a crucible made of platinum or graphite or graphite coated with pyrolytic carbon.
• the energy resolution was measured as follows: a piece of 10 ⁇ 10 ⁇ 5 mm is cut from the single crystal. All the faces of the part except one of the large 10 * 10 mm faces are left uncut and the face on which the photomultiplier (PMT) is coupled is polished. The crystal is wrapped in several thicknesses of PTFE (Teflon) tape except on the face which is coupled to the PMT. The crystal is prepared in a glove box with a dew point below - 40 ° C.
• LaCI 3 complex (NH 4 CI) 3.5 which contains 0.7% by weight of water by measurement with Karl Fischer.
• the LaCI complex 3. (NH CI) 3.5 is indeed a compound comprising at least one Ln-X bond since it contains La-CI bonds. It is also in itself a mixture within the meaning of the invention, comprising on the one hand an Ln-X-linked compound and on the other hand NH X (in this case NH CI).
• the quantity of NH 4 X is such that the ratio of the number of moles of NH 4 X to the number of moles of Ln not bound to oxygen is 3.5, which corresponds well to a preferred ratio according to the invention. Furthermore, there is no NH X to be introduced as oxygen linked to Ln since the starting mixture does not contain this type of bond.
• the nitrogen atmosphere contained about 50 ppm by weight of water and between 1 and 2 ppm by weight of oxygen.
• the oxychloride content in the final block measured by dissolution, is 0.01% by weight.
• the water content is less than 0.1% by weight (detection limit of the method used).
• the resulting block has a mass of 651g
• Example 2 (comparative): anhydrous LaCI 3
• the procedure is exactly as for Example 1 except that the complex is replaced by an anhydrous LaCI 3 powder whose oxychloride content is less than 0.02%, the particle size submillimetric and the water content is not detectable at Karl Fischer.
• the oxychloride content in the final block measured by dissolution, is 0.23% or by weight.
• the water content is less than 0.1% by weight.
• the nitrogen atmosphere contained about 50 ppm by weight of water and between 1 and 2 ppm by weight of oxygen.
• the molten pellet weighs 76.61 g and contains 0.035%) only of LaOBr oxybromide (measured by the insoluble method).
• the water content is more than 0.1% by weight.
• the hydrostatic density of this block, measured by immersion in hexane is approximately 4.92 g / cm 3 , or 87% of the theoretical density, which proves good densification.
• This molten block is then used for growth in a Bridgman furnace in a graphite crucible under a nitrogen sweep.
• the nitrogen atmosphere contained about 50 ppm by weight of water and between 1 and 2 ppm by weight of oxygen.
• the crystal obtained is clear and free of white inclusions of oxybromides and bubbles.
• the oxybromide content of this crystal is 0.05% by weight. More than 80% of the mass of this crystal is suitable for use as a scintillator.
• EXAMPLE 4 Anhydrous LaBr from a Wet Complex
• the LaBr 3 complex (NH 4 Br) 3 ⁇ 5 is used as prepared in the previous example but by humidifying it so that it contains 14.7%> by weight of water by measurement with Karl Fischer. 124 g of this mixture (complex + water) are then taken, which is heated to 200 ° C./h under nitrogen sweeping in a graphite crucible, up to 860 ° C. We make a plateau of 4:30 at 860 ° C.
• the nitrogen atmosphere contained about 50 ppm by weight of water and between 1 and 2 ppm by weight of oxygen.
• the molten pellet weighs 64.1 g and contains 0.034%> by weight only of oxybromide (measured by the insoluble method). The water content is less than 0.1% by weight.
• the nitrogen atmosphere contained about 50 ppm by weight of water and between 1 and 2 ppm by weight of oxygen.
• the sintered but not melted pellet weighs 104.9 g. It is therefore a powdery solid which is brought back to ambient conditions.
• the oven is recharged with 92.7 g of the previous sintered pellet which is heated to 200 ° C./h under nitrogen sweeping in a graphite crucible. We make a step of 1 h 30 at 840 ° C.
• the nitrogen atmosphere contained about 50 ppm by weight of water and between 1 and 2 ppm by weight of oxygen.
• the molten pellet weighs 92.7 g and contains 0.65%> by weight of GdOBr (measured by the insoluble method), which demonstrates that bringing the block to room temperature before melting is contraindicated.
• EXAMPLE 7 Anhydrous GdBr 3
• Example 8 Single crystal from LaCI 3 powder
• the same batch of anhydrous LaCI 3 powder is used as that used for Example 2 for growth in a Bridgman oven in graphite crucible under a nitrogen sweep.
• the nitrogen atmosphere contained about 50 ppm by weight of water and between 1 and 2 ppm by weight of oxygen.
• the Crystal obtained has numerous white inclusions of oxychlorides and bubbles organized in filaments along the axis of drawing.
• the oxychloride content of this crystal is 0.25% by weight. About 90% of the mass of this crystal is unsuitable for use as a scintillator.
• the following mixture is produced in a vitreous carbon crucible: 0.5874 g of LaOBr, 1.3585g of NH 4 Br (i.e. 5.5 moles) and 10.0678g of complex (NH 4 Br) 3 ⁇ 5 LaBr 3 .
• the mixture is heated with a speed of 200 ° C / h to 830 ° C with a 2h stage at this temperature.
• the nitrogen atmosphere contained about 50 ppm by weight of water and between 1 and 2 ppm by weight of oxygen.
• the insoluble level in the final block is 0.19% by weight.
• a block of 1 kg of LaCI 3 at 10% is used) by weight of CeCI 3 , manufactured according to the invention and whose LaOCI content is less than 0.05%> by weight.
• This block is then used for growth of the Bridgman type in graphite crucible.
• the nitrogen atmosphere contained about 50 ppm by weight of water and between 1 and 2 ppm by weight of oxygen.
• the crystal obtained is very clear. Its oxychloride content by the insoluble method is less than 0.05%).
• a 10 ⁇ 10 ⁇ 5 mm piece is then cut from this crystal, the scintillation yield of which is compared to a piece of Nal: TI (Nal doped with 600 ppm by weight of Tl iodide) according to the following protocol:
• Radioactive source Cs 137 to 622 KeV
• the light emission of the LaCI 3 crystal is 93% of that of the reference Nal crystal. Its energy resolution is 3.6% o.
• the main component of the scintillation decay time is 27 nanoseconds.
• Example 12 Single crystal from LaCI: 1 kg of commercial LaCI 3 and CeCI 3 powders are used (LaOX content and water of Example 2). The mass of CeCI 3 represents 10%) of the mass of the mixture of these two powders. They are melted in a graphite crucible and growth is made of the Kyropoulos type (KC 01). The nitrogen atmosphere contained about 50 ppm by weight of water and between 1 and 2 ppm by weight of oxygen. The crystal obtained is slightly milky. Its insoluble content is 0.1% by weight. A 10x10x5 mm piece is then cut from this crystal, the scintillation yield of which is compared to a Nal: TI piece according to the same protocol as for the previous example. The light emission of the LaCI 3 crystal is 83% of that of the reference Nal crystal. Its energy resolution is 3.9%>.
• a Bridgman type crystal is produced in a silica crucible in accordance with the teaching of the IEEE Transaction on Nuclear science publication: "Scintillation properties of LaCI 3 crystals: Fast, efficient and High Energy resolution scintillators".
• the mass of CeCI 3 represents 10%> of the mass of the mixture before growth of the crystal.
• a 10x10x5 mm piece is then cut from this crystal, the scintillation yield of which is compared to a Nal: TI piece according to the same protocol as for the two previous examples.
• the light emission of the LaCI 3 crystal is 87%> that of the reference Nal crystal. Its Energy resolution is 4.2%>.
• Photomultiplier Hamamatsu R-1306 - Reference: Nal crystal: TI (Nal doped with 600 ppm by weight of iodide of Tl) 50mm in diameter and 50mm in length.
• the light emission of the LaBr 3 crystal is 147% of that of the reference Nal crystal. Its energy resolution is 4.2%.
• the main component of the scintillation decay time is 39 nanoseconds.
• Example 15 (comparative): LaBr ⁇ single crystal:
• This crystal also contains 0.5% by weight of CeBr 3.
• a 10x10x5 mm piece is then cut from this crystal, the scintillation efficiency of which is compared to a Nal: TI piece according to the same protocol as for the previous example.
• the crystal is slightly milky.
• LaBr 3 crystal is 102% "of that of the reference Nal crystal.
• the main component of the scintillation decay time is 38 nanoseconds.
• Example 16 Monocrystal of LaCI3: Three blocks of LaCI 3 are doped with 5% by weight of CeCI 3 of 1 kg each manufactured according to the invention and such that the LaOCI content is ⁇ 0.05% or by weight. This block is then used for growth of the Bridgman type in graphite crucible. The nitrogen atmosphere contained about 50 ppm by weight of water and between 1 and 2 ppm by weight of oxygen. The crystal obtained is very clear. The oxychloride content of this block cannot be measured by the insoluble method. It is less than 0.05% by weight. Then cut in this crystal a piece of 10x10x5 mm including the scintillation yield is compared to a piece of Nal: TI according to the following protocol:
• Nal crystal Nal crystal: TI (Nal doped with 600 ppm by weight of iodide deTI) 50mm in diameter and 50mm long.
• the light emission of the LaCI 3 crystal is 98% of that of the reference Nal crystal. Its energy resolution is 4.6%>.
• the main component of the scintillation decay time is 28 nanoseconds.
• Example 1 The procedure is as for Example 1 except that the block is prepared in a platinum crucible. The final block sticks to the crucible and is much more difficult to unmold than in the case of the graphite crucible coated with pyrolytic carbon.

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