FR2918785A1 - RADIO ATTENUATOR MATERIAL AND METHOD FOR OBTAINING SUCH MATERIAL - Google Patents

Abstract

The invention relates to a transparent material which attenuates electromagnetic radiation and/or directly or indirectly ionising particles, of particular use for the production of transparent sheets which serve as protective screens for an operator against said electromagnetic radiation and/or particles. Said transparent attenuating material is made of a matrix of an organic glass in which at least one metal radiation-attenuating compound is dispersed (advantageously other than lead) in the form of nanoparticles, advantageously in the "core-shell" form. The metals of the nanoparticle metal compounds form at least 25 % of the mass of the material.

Description

The invention relates to the field of radiation attenuator materials

  electromagnetic and / or particulate matter directly or indirectly ionizing; More specifically, it relates to new transparent radiation attenuator materials, which are particularly suitable for the manufacture of transparent plates used as radiation protection screens. Certain sectors of activity (medical, industrial, etc.) may require the handling and use of radioactive substances that emit directly or indirectly ionizing radiation, such as electromagnetic (X, gamma) or particulate (alpha) radiation. , beta, neutron, etc.).

  Operators handling such radioactive substances, or being in the vicinity of these substances, conventionally protect themselves behind a protective screen type structure, formed of a plate made of an attenuator material or an assembly of such plates. At least some of the plates of these shields are usually made of transparent attenuator material, to give the operator direct visual access to the work area. This type of transparent plates consists of organic glass (that is to say a matrix formed of an organic material of the polymer type), or inorganic glass (that is to say for example a matrix of silicate of alkali metal); a derivative of one or more metals is integrated in this matrix to achieve the absorption of the different types of radiation emitted by the substance handled. By way of example, we mention the glasses containing a lead derivative, up to 12% to 80% by weight, introduced into the matrix during the manufacturing process; this type of leaded glass has the advantage of transmitting visible light with little absorbance, while effectively attenuating radioactive radiation. However, the use of leaded glass, organic or inorganic matrix, is not without some problems. This kind of lead material is indeed particularly brittle when the matrix is of inorganic type; this type of leaded material is not recyclable; and lead, because of its toxic nature, is brought to a maximum (especially for environmental reasons). Despite these considerations, radiation shielding screens equipped with such leaded glass plates still remain a standard today. Indeed, most lead-free radio-attenuator materials developed to date (containing at least one metal intended to replace lead), fail to reproduce the combination of the intrinsic characteristics of leaded attenuator lenses (a combination of good transmission of visible light and effective attenuation of radiation), while maintaining reasonable costs. However, the applicant has managed, despite numerous technical obstacles, to develop a new material meeting the criteria necessary for use as element constitutive transparent plates of protection. The attenuator material according to the invention consists of a matrix based on an organic glass, advantageously thermoplastic or thermosetting, in which is incorporated at least one type of metal compound radiation attenuator in the form of nanoparticles (preferably with the exception Lead). This new attenuating material has the advantage of having good transmission of visible light, without diffusion phenomena (or very little), while having radioprotection characteristics always optimal. This new material also has the advantage of being able to contain high proportions of attenuating metal compounds, advantageously other than the lead derivatives; it thus has characteristics that are close to, equivalent to, or even better than, a material of the leaded glass type. More specifically, the organic matrix of the radio-attenuator material is advantageously made based on a polymer or copolymer of acrylic or styrenic type, advantageously thermoplastic. By way of example, when it is of the acrylic type, the organic matrix may be made based on poly (methyl methacrylate), more commonly known as PMMA, or a similar polymer (for example a copolymer of poly (methacrylate) methyl)).

  By way of example, the organic matrix may be made based on polystyrene, polycarbonate or unsaturated polyester (thermosetting). The nanoparticulate metal compounds are distributed and homogeneously incorporated, or at least substantially homogeneously, in this organic matrix.

  These nanoparticulate compounds integrate a metal (or a mixture of metals, ie, so-called mixed nanoparticulate compounds) chosen (s) depending on the type of radiation to be attenuated. In this case, for the attenuation of electromagnetic ionizing radiation (X or gamma) of low or medium energy, the metal or at least one of the metals chosen advantageously has an atomic number z between 56 and 74 inclusive.

  In this case, preferably, this metal compound is more precisely chosen from the family of lanthanides (more commonly called rare earths), whose atomic number z is between 57 and 71 inclusive. In this family of lanthanides, the metal in question is still advantageously chosen from among the following elements: lanthanum (atomic number z 57), and / or - gadolinium (atomic number z 64), and / or - ytterbium ( atomic number z 70). On the other hand, for the attenuation of neutron particulate radiation, the metal of the nanoparticulate compound (s) is chosen from elements having an atomic number z of between 3 and 7 inclusive; preferably, this metal is selected from boron and lithium. In this case, the attenuator metal may also be gadolinium (atomic number z 64).

  The nanoparticulate metal compounds in question consist of at least one inorganic, organometallic or hybrid organic / inorganic metal compound. In organometallic form, the compounds are, for example, in the form of acetate, propionate, butyrate or isobutyrate; they may also be in the form of metal complexes with an organic ligand, for example di (ethylhexyl) phosphates, aminocarboxylates, hydroxycarboxylates and organophosphates. For the inorganic form, these nanoparticulate compounds may consist of a metal salt of nitrate, phosphate, fluoride, nitride or oxide type.

  The hybrid organic / inorganic form consists of nanoparticles whose structure is of the heart-bark type: the core is formed by the inorganic radio-attenuating part, and the bark constitutes the organic part improving the dispersion in the organic matrix. Preferably, the bark of these nanoparticles is formed of a multitude of grafts, connected to the inorganic part; these grafts are advantageously each formed of a spacer arm (for example of the alkyl or polyether type), terminated by an organic function chemically close to the destination matrix (in particular to optimize its affinity with the matrix). This bark is advantageously of acrylic, methacrylic and / or styrenic type.

  By way of example, the nanoparticles may be in one of the forms shown schematically below (only one of the grafts of the nanoparticle is represented for the sake of simplification). In a first embodiment, the nanoparticle is advantageously under the following general structure: OC - RR 'CH2 where C corresponds to the core, R corresponds to the spacer arm, and the organic function is of the acrylic ester type (R' = hydrogen) or methacrylic ester type (R '= methyl). In a second embodiment, the nanoparticle is advantageously under the following general structure: where C corresponds to the core, and the organic function is of the styrene type. The nanoparticulate metal compounds (and where appropriate the core portion 15 of these nanoparticles) advantageously have a maximum dimension of less than 20 nanometers. This maximum dimension of the nanoparticles has the advantage of reducing, or even eliminating, the phenomena of diffusion of the visible light passing through the attenuating material, while conferring on it radioprotection characteristics which are always optimal. It also has the advantage of allowing a high charge of the organic matrix in nanoparticles. To effectively mitigate radiation while maintaining minimal light scattering, the metal of the nanoparticulate compounds accounts for at least 25% of the scum of the attenuator material, and can reach the 80% C CH2 level.

  The matrix of the attenuator material can integrate a single type of nanoparticulate metal compound. Of course, it may also contain a combination of such nanoparticulate compounds, depending on the electromagnetic and / or particulate radiation to be attenuated.

  By way of example, the attenuating material may contain a combination of nanoparticulate compounds whose metal or metals are chosen from the following list: boron and / or lanthanum and / or gadolinium and / or ytterbium and / or bismuth. The corresponding metal (or if appropriate, the combination of metals) is chosen in particular to cover the particular energy range of electromagnetic and / or particulate radiation corresponding to certain application (s) of the medical field or research scientist. The radio-attenuator material in accordance with the invention may be obtained by a process consisting in carrying out the following steps: preparation of the nanoparticulate metal compounds, advantageously of the core-shell type, from metal salts, dispersion of said compounds nanoparticles - either in one or more polymers in solution, - or in one or more liquid monomers intended to be polymerized, in order to form the organic matrix, for example of the polymer type (poly (methyl methacrylate) type) or copolymers ( poly (methyl methacrylate-methyl-co-acrylate)). The preparation of the nanoparticle metal compounds consists, for example, of a method consisting of reacting a metal salt by heating it in a suitable synthetic solvent, in the presence of a complexing agent or an amine. The synthetic solvent in question is chosen according to the composition of the matrix and also the presentation of the nanoparticulate metal compounds (mineral, organometallic or hybrid), mainly to optimize the dispersion of these particles. The synthetic solvent used can be, for example, ethanol, methanol, tris (2-ethylhexyl) phosphate, dibutyl phosphate, tributyl phosphate, diethylene glycol, diphenyl ether, trimethyl phosphate, triphenyl phosphate, bis [2- (methacryloyloxy) ethyl] phosphate tris (2-butoxyethyl phosphate), tris (2-chloroethyl) phosphate, toluene. The complexing agent is of the trioctylamine, acrylamide, ethylene diamine tetraacetic acid, acrylic acid, methacrylic acid, dimethyl amino ethyl methacrylate, diethylaminoethyl methacrylate, N, N-dimethylacrylamide, methacrylonitrile, acrylonitrile, pyridine or amine fluoride type.

  The graft is in turn of the poly (propylene glycol), poly (propylene glycol monomethacrylate), phosphoric oxychloride, dodecanol, acrylic acid chloride, ethylene glycol methacrylate phosphate, bis (2-ethylhexyl) phosphate, hydroxyethyl methacrylate, hydroxyethyl acrylate .

  During the manufacturing process, the graft is advantageously reported on its nanoparticulate compounds, during or after the synthesis of the latter, to optimize their dispersion in the organic matrix. The nanoparticulate core-shell type compounds are thus obtained, containing, on the one hand, the core containing the radio-attenuating metal derivative, and on the other hand, the hair-type bark optimizing its dispersion in the organic matrix. In general, techniques for synthesizing nanoparticles, and grafting techniques, are known to those skilled in the art. Thus, for example, Jan W. Stouwdam and Frank C.J.M. van Veggel, Langmuir, 20 (26), 11763-11771, 2004.

  Interestingly, the Applicant has developed a technique for synthesizing in a single step rare earth phosphate nanoparticles in core-bark form, said bark being formed of ethylene glycol methacrylate phosphate. During the synthesis, the metal salt is added to a solution composed of the synthesis solvent (advantageously tris (2-ethylhexyl) phosphate) containing ethylene glycol methacrylate phosphate and phosphoric acid in a chosen proportion, as well as an amine at an adequate concentration according to the size targeted for the nanoparticles. The formation of the rare earth phosphate core will be done by having the ethylene glycol methacrylate as a graft, which will constitute the bark of the nanoparticle. Alternatively, the attenuator material according to the invention can also be obtained by extrusion of a mixture of polymer granules (s) and nanoparticulate metal compounds. In general, this attenuating material can be used for the manufacture of transparent plates serving as radioprotection screens. This type of screen can for example be an integral part of screens used by operators handling, directly or indirectly, ionizing substances, particularly in the context of certain medical interventions (nuclear medicine, radiotherapy, etc.).

  This type of plate advantageously has a thickness of at least 5 mm.

  To illustrate the efficiency and the interest of the radio-attenuator material according to the invention, examples of different materials are detailed below.

  Example 1 Preparation of nanoparticulate metal compounds, containing a mixture of lanthanum and gadolinium. We prepared a solution of a mixture of two rare earth salts: lanthanum and gadolinium (in the form of nitrates or chlorides) in a ratio 1: 1 in tris (2-ethylhexyl phosphate) at a total concentration of 1, 67 moles / liter. This mixture is then added to a solution consisting of phosphoric acid and trioctylamine in a proportion of 1: 3, in moles, respectively. The mixture is heated at 200 ° C under nitrogen with reflux for 40 hours. The obtained rare earth phosphate nanoparticles (LaPO4 and GdPO4) are then precipitated and washed with alcohol, and then recovered by centrifugation at 7800 rpm. These nanoparticles were observed using a transmission electron microscope type 1-19000NAR- 300kV (kilo Volts) at high magnification. The size of the isolated nanoparticles varies between 3 nm and 13 nm. The physico-chemical characterization confirms the composition of the nanoparticles. Preparation of nanoparticles in core-shell form The nanoparticles of rare earth phosphates (mixed lanthanum and gadolinium) prepared are treated with phosphorus oxychloride in a proportion of 1: 2 by mass, respectively. The whole is heated at 120 ° C under an inert gas atmosphere for 2 hours. After refluxing, the phosphorus oxychloride is removed under vacuum while heating at 80 ° C. for 1 hour. A solution of toluene containing a hydroxide type graft: hydroxyethyl acrylate, hydroxyethyl methacrylate or polypropylene glycol monomethacrylate is then added; and this mixture is refluxed at 140 ° C. for 2 hours. The physico-chemical characterization confirms the composition of the core-shell nanoparticles of rare earth phosphates whose core is rare earth phosphate and whose bark is made up of acrylic or methacrylic grafts.

  Dispersion of the core-shell nanoparticles in the organic matrix, then study of the optical absorption and mass attenuation characteristics The core-shell nanoparticles are easily dispersed in an acrylic-type monomer. The solution thus obtained is polymerized in the presence of azobisisobutyronitrile (AIBN) as initiator at 0.2% by weight of the monomer at 60 C. The material obtained is subjected to optical absorption and mass attenuation tests, the The results are shown in FIGS. 1 and 2. Composition Optical absorption 25% mass attenuation LaPO4 FIG. 1 FIG. 2 25% GdPO4 Percentage of the mass attenuation in 50% PMMA transmitted light in cm 2 / g according to the energy function of the length in MeV for lead-in-inorganic nm (1) wave glass, test material (2) and lead-free inorganic glass (3) PMMA / nanoparticle LaPO4 / GdPO4 material, 5 nm, medium size, 1: 1 in mass and 5 mm thick transmit at least, according to simulations of the 4-flux method, 65% of the incident light at 450 nm and 87% at 650 nm in the visible range between 450 and 650 nanometers (figure 1). Furthermore, this material exhibits a better mass attenuation than that of a lead-free inorganic attenuator glass over the entire energy range between 0.1 MeV and 1 MeV, and an attenuation close to that of the inorganic lead attenuator glass between 0 , 04 MeV and 0.09 MeV (Figure 2).

  Example 2 Preparation of nanoparticulate metal compounds containing a mixture of lanthanum, qadolinium and ytterbium. We prepared a solution of a mixture of three rare earth salts (in the form of nitrate or chloride): lanthanum, gadolinium and ytterbium, at a ratio of 1.2: 1: 1.8 in tris (2-ethylhexyl) phosphate) at a total concentration of 3 moles / liter. This solution is then added to a solution of phosphoric acid and trioctylamine in stoichiometric proportions. The mixture is heated at 200 ° C under nitrogen with reflux for 40 hours.

  The mixed nanoparticles of rare earth phosphates were precipitated and washed with alcohol and then recovered by centrifugation at 7800 rpm. These nanoparticles were observed using a transmission electron microscope of H9000NAR-300kV type at high magnification.

  The size of the isolated nanoparticles varies between 3 nm and 17 nm (the largest dimension depending on the geometrical shape). The physico-chemical characterization confirms the composition of the nanoparticles.

  Preparation of Nanoparticles in Heart-Bark Form The preparation of the nanoparticles in core-shell form is carried out according to a method identical to that described above in Example 1.

  Dispersion of the core-shell nanoparticles in the organic matrix, then study of the optical absorption and mass attenuation characteristics These nanoparticles in core-shell form are easily dispersed in an acrylic-type monomer. The solution thus obtained is polymerized in the presence of azobisisobutyronitrile (AIBN) as initiator at 0.2% by weight of the monomer at 60 C. The material obtained is subjected to optical absorption and mass attenuation tests, of which the results are shown in FIGS. 3 and 4. Composition Optical absorption Mass attenuation 15% LaPO4 FIG. 3 FIG. 4 12.5% GdPO4 Percentage of Mass Attenuation in 22.5% YbPO4 light transmitted in cm 2 / g as a function of 50% PMMA depending on the length l energy in MeV, for the wavelength in nm leaded inorganic glass (1), the test material (2) and the lead-free inorganic glass (3) The PMMA material / nanoparticles LaPO4 / GdPO4 / YbPO4 of 5 nm average size, at 1.2: 1: 1.8 in mass, and of thickness 5 mm, transmit at least, according to simulations of the 4-flux method, 65% of the incident light at 450 nm and 87% at 650 nm, in the visible range between 450 and 650 nanometers (Figure 3). The obtained material still has a better mass attenuation than the lead-free inorganic glass over the entire energy range between 0.1 MeV and 15 MeV and an attenuation identical to that of the lead inorganic glass between 0.06 MeV and 0 , 09 MeV (Figure 4).

  Example 3 One-step preparation of nanoparticulate metal compounds containing lanthanum A solution of the lanthanum salt (nitrate or chloride) in tris (2-ethylhexyl phosphate) was prepared at a total concentration of 1.67 moles / liter . This solution of lanthanum salt is then added to a solution of ethylene glycol methacrylate phosphate and trioctylamine in a proportion of 1: 3 in moles, respectively. The mixture is heated at 200 ° C under nitrogen with reflux for 40 hours. The product of the synthesis was precipitated and washed with alcohol and recovered by centrifugation at 7800 rpm. These nanoparticles of lanthanum phosphates constitute hairy nanoparticles, the core of which is lanthanum phosphate and whose bark consists of grafts of ethylene glycol methacrylate. These nanoparticles are observed using a transmission electron microscope type H9000NAR-300kV at high magnification. The size of the isolated nanoparticles varies between 3 nm and 10 nm for an average of 5 nm. The size distribution of the nanoparticles is observed by photon correlation spectroscopy, on a Beckman Coulter N4 plus apparatus. The physico-chemical characterization confirms the composition of the nanoparticles.

  Dispersion of the core-shell nanoparticles in the organic matrix, then study of the optical absorption and mass attenuation characteristics The core-shell nanoparticles obtained are dispersed in methyl methacrylate, under ultrasound. The solution is then polymerized in the presence of azobisisobutyronitrile (AIBN) as an initiator at 0.2% by weight of the monomer at 60 C.

  The material obtained is subjected to optical absorption and mass attenuation tests, the results of which are shown in FIGS. 5 and 6. Composition Optical absorption 40% mass attenuation LaPO4 FIG. 6 60% PMMA Percentage of mass attenuation in light transmitted in cm2 / g as a function of the length of the energy in MeV, for the wave in nm leaded inorganic glass (1), the test material (2) and the inorganic lead-free glass (3) The material obtained PMMA / LaPO4 nanoparticles of 5 nm average size, 1.5: 1 by mass and 5 mm thickness transmits at least, according to simulations of the 4-flux method, 76% of the incident light at 450 nm and 90% at 650 nm in the visible range between 450 and 650 nanometers (Figure 5). This material exhibits a better mass attenuation than lead-free inorganic glass over the entire energy range between 0.1 MeV and 1 MeV and attenuation close to that of inorganic lead glass between 0.04 MeV and 0.09 MeV (Figure 6).

  Example 4 Preparation of rare earth fluoride nanoparticles The rare earth fluoride nanoparticles are prepared from a 1: 1 ethanol / water solution of sodium fluoride and of an acrylic type graft (hydroxyethyl acrylate or hydroxyethyl methacrylate) each has a concentration of about 3.10-2 mol / l, in which a 1: 1 ethanol / water solution of rare earth salts (nitrates or chlorides) at a concentration between 0.5 is poured with vigorous stirring. mole / liter and 1 mole / liter. The solution thus formed is heated at 75 ° C. for 2 hours. The nanoparticles are isolated by centrifugation at 7800 rpm and dispersed in dichloromethane and then precipitated with ethanol. This washing operation is repeated several times.

  The physico-chemical characterization confirms the composition of the core-bark nanoparticles of rare earth fluorides whose core is rare earth fluoride and whose bark is composed of acrylic or methacrylic grafts.

  Dispersion of the core-shell nanoparticles in the organic matrix, then study of the optical absorption and mass attenuation characteristics The LaF3-type nanoparticles produced are mixed in methyl methacrylate under ultrasound. The solution is then polymerized in the presence of azobisisobutyronitrite (AIBN) as an initiator at 0.2% by weight of the monomer at 60 C. The material obtained is subjected to optical absorption and mass attenuation tests, the results of which are presented. Figures 7 and 8. Composition Optical absorption Mass attenuation 50% LaF3 Figure 7 Figure 8 50% PMMA Percentage of mass attenuation transmitted in cm2 / g as a function of length of energy in MeV, for the wave in nm lead inorganic glass (1), the test material (2) and the lead-free inorganic glass (3) This PMMA material / LaF3 nanoparticles of 5 nm average size, 1: 1 by mass and thickness 5 mm At least, according to simulations of the 4-flux method, 85% of the incident numeral is transmitted at 450 nm and 92% at 650 nm in the visible range between 450 and 650 nanometers (FIG. 7). This material still has a mass attenuation identical to that of the lead-free inorganic glass between 0.03 MeV and 0.037 MeV and higher attenuation beyond this range (FIG. 8).

Claims (15)

  - 1.- transparent material, attenuator of electromagnetic and / or particulate radiation directly or indirectly ionizing, used in particular for the manufacture of transparent plates serving as shields of an operator against said electromagnetic and / or particulate radiation, characterized in said attenuating transparent material is composed of a matrix based on an organic glass in which at least one radiation-attenuating metallic compound is dispersed in the form of nanoparticles.   2. A radiation attenuator material according to claim 1, characterized in that the nanoparticulate metal compounds or at least one of the nanoparticulate metal compounds consist of at least one inorganic compound, organometallic or hybrid organic / inorganic metal.   3. A radiation attenuator material according to any one of claims 1 or 2, characterized in that the nanoparticulate metal compounds or at least one of the nanoparticulate metal compounds consist of a phosphate-type metal salt, or fluoride type , or of the nitride type, or of a metal oxide.   4. attenuator material according to any one of claims 1 to 3, characterized in that the nanoparticulate metal compounds have a core-shell structure, said core consisting of a radio-attenuating inorganic part containing the attenuator metal compound and said bark being formed of grafts for optimizing the dispersion of said nanoparticles in the matrix.   5. attenuator material according to any one of claims 1 to 4 for the protection against electromagnetic radiation, characterized in that the metals or at least one of the constituent metals of the nanoparticulate metal compounds have an atomic number z between 56 and 74, terminals included.   6. attenuator material according to claim 5, characterized in that the metals or at least one of the constituent metals of the nanoparticulate metal compounds have an atomic number z between 57 and 71 inclusive.   7. attenuator material according to claim 6, characterized in that the metals or at least one of the constituent metals of the nanoparticulate metal compounds are chosen from lanthanum, ytterbium and / or gadolinium.   8. attenuator material according to any one of claims 1 to 4 for the protection against particulate radiation, characterized in that the metals or at least one of the constituent metals of the nanoparticulate metal compounds have an atomic number z between 3 and 7, terminals included.   9. Attenuator material according to any one of claims 1 to 4 for the protection against particulate radiation, characterized in that the metals or at least one of the constituent metals of the nanoparticulate metal compounds are of the gadolinium type.   10. Attenuator material according to any one of claims 1 to 9, characterized in that the nanoparticulate metal compounds have a maximum dimension of less than 20 nm.   11. attenuator material according to any one of claims 1 to 10, characterized in that the metals of the nanoparticulate metal compounds represent at least 25% of the mass of said material.   12. Radiation protection screen made of a transparent attenuator material according to any one of claims 1 to 11.   13. A method of manufacturing an attenuator material according to any one of claims 1 to 11, characterized in that it consists of the implementation of the following steps: - preparation of nanoparticulate metal compounds, optionally in the form of core-shell type, - dispersion of said nanoparticulate compounds either in one or more polymers in solution, or in one or more monomers in solution intended to be polymerized, in order to form the organic matrix.   14.- Method according to claim 13, characterized in that it consists in providing a graft on the nanoparticle metal compounds, capable of improving the solubility or dispersion of said nanoparticulate metal compounds in the organic matrix.   15. A process according to claim 14, characterized in that the grafts are reported during the synthesis of the nanoparticles, using a synthesis solvent comprising a mixture of ethylene glycol methacrylate phosphate, phosphoric acid and a amine.