General Electric Company (Niskayuna, NY) scientists have created new nano-scale metal halide scintillation materials for higher resolution medical imaging and more sensitive security scanning systems. The materials may even detect subterranean radiation as well as radioactive contraband. GE’s crystalline scintillator materials are nanoparticles of metal halides less than 100 nm in size. Methods are provided for preparing the particles in which ionic liquids are used in place of water to allow precipitation of the final product. In one method, the metal precursors and halide salts are dissolved in separate ionic liquids to form solutions, which are then combined to form the nano-crystalline end product. In the other methods, micro-emulsions are formed using ionic liquids to control particle size, say inventors Brent Allen Clothier, Sergio Paulo Martins Loureiro, Alok Srivastava and Venkat Subramaniam Venkataramani in U.S. Patent 7625502.
Scintillators are materials that convert high-energy radiation, such as X-rays and gamma rays, into visible light. Scintillators are widely used in detection and non-invasive imaging technologies, such as imaging systems for medical and screening applications. In such systems, high-energy photons typically pass through the person or object undergoing imaging and, on the other side of the imaging volume, impact a scintillator associated with a light detection apparatus. The scintillator typically generates optical photons in response to the high-energy photon impacts. The optical photons may then be measured and quantified by the light detection apparatus, thereby providing a surrogate measure of the amount and location of high-energy radiation incident on the detector.
The quality of medical and other images may depend on a number of factors, including the light transmission through the scintillator, which controls the amount of light that may reach the photodetectors. Other important factors, specific to the scintillator material, are the amount of high-energy radiation that is absorbed by the scintillator, termed the stopping power, and the conversion efficiency, or quantum yield of the scintillator. Physical factors also control the image quality, including pixel size and cross-pixel isolation, among others.
Scintillators are materials that convert high-energy radiation, such as X-rays and gamma rays, into visible light. Scintillators are widely used in detection and non-invasive imaging technologies, such as imaging systems for medical and screening applications. In such systems, high-energy photons typically pass through the person or object undergoing imaging and, on the other side of the imaging volume, impact a scintillator associated with a light detection apparatus. The scintillator typically generates optical photons in response to the high-energy photon impacts. The optical photons may then be measured and quantified by the light detection apparatus, thereby providing a surrogate measure of the amount and location of high-energy radiation incident on the detector.
Additionally, scintillators may be useful in systems used to detect radioactive objects, such as contraband or contaminants, which might otherwise be difficult to detect. GE new scintillator materials may be used in all current scintillator applications. GE also developed a detector unit that may be used in oil drilling applications, as well as in other applications, such as prospecting for radioactive materials, among others.
With regard to non-invasive imaging techniques, one of the most important applications for scintillators is in medical equipment for the production of radiographic images using digital detection and storage systems. Another high-energy radiation based imaging system is positron emission tomography (PET), which generally employs a scintillator-based detector.
FIG. 7 is a block diagram of a GE process to make oxide based nano-scale scintillator particles.
FIG. 8 is a block diagram of another process to make oxide based nano-scale scintillator particles.
FIG. 11 is a block diagram of a process to make halide based nano-scale scintillator particles .
FIG. 11 is a block diagram of a process to make halide based nano-scale scintillator particles .
FIG. 12 is a block diagram of another process to make halide based nano-scale scintillator particles .
FIG. 11 is a block diagram of a procedure that utilizes ionic liquids to form nano-scale particles of a metal halide. In this procedure, a metal solution 142 is formed by dissolving one or more metal salts 144 in an ionic liquid 146. Such metal salts may include lanthanum, cerium, rubidium, gadolinium, barium, cesium, calcium, europium, indium, praseodymium, terbium, thallium, and combinations thereof.
This procedure may be used to make nano-scale particles of numerous other metal halide species, and the particular metals chosen will depend on the final product desired. Such metals may include, for example, metals, or combinations of metals, chosen from the lanthanoids, or groups 1, 2, 3, 13, 14, or 15 of the standard periodic chart. .
A halide solution 148 is prepared by dissolving a halide salt 150 in a second ionic liquid 152. This second ionic liquid may be identical to the first, or a different ionic liquid may be chosen as described above. In embodiments, the halide salt may be ammonium chloride, ammonium bromide, or a combination thereof. Other halide-type anion source compounds may be used, including materials with a general formula of NR4Y, where each R is independently chosen to be a hydride, alkyl, aryl, or halide, and Y may be a fluoride, chloride, bromide, iodide, or a combination. Further, other compounds may be used that provide anions that react in similar fashion to halides, such as, for example, sulfur. Such compounds may include, for example, ammonium sulfides, thioacetamides, thioureas, or similar compounds.
The two solutions are combined as indicated by 154 to form the final nano-scale particles 156. The mixing may be done slowly to optimize the particle size formed. Energy may be added during this process to accelerate the reaction, such as by heating, sonication, or other techniques. In embodiments of the present technique, the particles may be isolated from the solution, as shown in block 158, by filtering, phase separation, freeze-drying, or any other technique that may be used to isolate the solid product from the micro-emulsion.
FIG. 12 is a block diagram of another procedure for the formation of nano-scale particles of a metal halide. In this procedure, an organic metal solution 160 is formed by dissolving one or more organic metal salts 162 in an organic solvent 164. In an exemplary embodiment, the organic solvent is n-hexane. Any number of other organic solvents, including alkyl or aryl solvents, may be employed. Such organic metal salts may include lanthanum, praseodymium, cerium, terbium, thallium, europium, and combinations thereof. The procedure may be used to make nano-scale particles of numerous other metal halide species, and the particular metals chosen will depend on the final product desired. Such metals may include, for example, metals, or combinations of metals, chosen from the lanthanoids and groups 1, 2, 3, 13, 14, or 15 of the standard periodic chart. The organic anions used to make the metal cations soluble in an organic solution may include one or more independently selected alkoxy groups, --OR, where R represents a carbon chain containing one to ten carbons.
A halide micro-emulsion 166 is then prepared by mixing a halide solution 168 with a surfactant solution 170. The halide solution 168 is prepared using the techniques described above with respect to block 148 in FIG. 11. The surfactant solution 170 is formed by dissolving a surfactant in an organic solvent. The surfactant may be polyoxyethylene (5) nonylphenylether, available as Igepal.RTM. CO-520 from ICI Americas; aromatic ethoxylates; polyethylene glycol dodecyl ethers, available as Brij.RTM. from ICI Americas; sorbitan-fatty acid ester surfactants, available as Tween.RTM. from ICI Americas; polyoxyethylenesorbitan fatty acid ester surfactant, available as Spans from ICI Americas; or alkylphenols, among others. In an exemplary embodiment, the organic solvent is n-hexane. Any number of other organic solvents, including alkyl or aryl solvents, may be used.
The organic metal solution 160 is combined with the halide micro-emulsion 166, as indicated by 172, to form the nano-scale particles of the metal halide 174. The mixing may be done slowly to optimize the particle size formed. Energy may be added to accelerate the reaction, such as by heating, sonication, or other techniques. In embodiments of the present technique, the nano-scale particles may be isolated from the solution, as shown in block 176, by filtering, phase separation, freeze-drying, or any other technique that may be used to isolate a solid product from a micro-emulsion.
A halide solution 148 is prepared by dissolving a halide salt 150 in a second ionic liquid 152. This second ionic liquid may be identical to the first, or a different ionic liquid may be chosen as described above. In embodiments, the halide salt may be ammonium chloride, ammonium bromide, or a combination thereof. Other halide-type anion source compounds may be used, including materials with a general formula of NR4Y, where each R is independently chosen to be a hydride, alkyl, aryl, or halide, and Y may be a fluoride, chloride, bromide, iodide, or a combination. Further, other compounds may be used that provide anions that react in similar fashion to halides, such as, for example, sulfur. Such compounds may include, for example, ammonium sulfides, thioacetamides, thioureas, or similar compounds.
The two solutions are combined as indicated by 154 to form the final nano-scale particles 156. The mixing may be done slowly to optimize the particle size formed. Energy may be added during this process to accelerate the reaction, such as by heating, sonication, or other techniques. In embodiments of the present technique, the particles may be isolated from the solution, as shown in block 158, by filtering, phase separation, freeze-drying, or any other technique that may be used to isolate the solid product from the micro-emulsion.
FIG. 12 is a block diagram of another procedure for the formation of nano-scale particles of a metal halide. In this procedure, an organic metal solution 160 is formed by dissolving one or more organic metal salts 162 in an organic solvent 164. In an exemplary embodiment, the organic solvent is n-hexane. Any number of other organic solvents, including alkyl or aryl solvents, may be employed. Such organic metal salts may include lanthanum, praseodymium, cerium, terbium, thallium, europium, and combinations thereof. The procedure may be used to make nano-scale particles of numerous other metal halide species, and the particular metals chosen will depend on the final product desired. Such metals may include, for example, metals, or combinations of metals, chosen from the lanthanoids and groups 1, 2, 3, 13, 14, or 15 of the standard periodic chart. The organic anions used to make the metal cations soluble in an organic solution may include one or more independently selected alkoxy groups, --OR, where R represents a carbon chain containing one to ten carbons.
A halide micro-emulsion 166 is then prepared by mixing a halide solution 168 with a surfactant solution 170. The halide solution 168 is prepared using the techniques described above with respect to block 148 in FIG. 11. The surfactant solution 170 is formed by dissolving a surfactant in an organic solvent. The surfactant may be polyoxyethylene (5) nonylphenylether, available as Igepal.RTM. CO-520 from ICI Americas; aromatic ethoxylates; polyethylene glycol dodecyl ethers, available as Brij.RTM. from ICI Americas; sorbitan-fatty acid ester surfactants, available as Tween.RTM. from ICI Americas; polyoxyethylenesorbitan fatty acid ester surfactant, available as Spans from ICI Americas; or alkylphenols, among others. In an exemplary embodiment, the organic solvent is n-hexane. Any number of other organic solvents, including alkyl or aryl solvents, may be used.
The organic metal solution 160 is combined with the halide micro-emulsion 166, as indicated by 172, to form the nano-scale particles of the metal halide 174. The mixing may be done slowly to optimize the particle size formed. Energy may be added to accelerate the reaction, such as by heating, sonication, or other techniques. In embodiments of the present technique, the nano-scale particles may be isolated from the solution, as shown in block 176, by filtering, phase separation, freeze-drying, or any other technique that may be used to isolate a solid product from a micro-emulsion.
