WO2007120443A2 - Scintillateur nanocomposite, détecteur et procédé - Google Patents

Scintillateur nanocomposite, détecteur et procédé Download PDF

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Publication number
WO2007120443A2
WO2007120443A2 PCT/US2007/007615 US2007007615W WO2007120443A2 WO 2007120443 A2 WO2007120443 A2 WO 2007120443A2 US 2007007615 W US2007007615 W US 2007007615W WO 2007120443 A2 WO2007120443 A2 WO 2007120443A2
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doped
calcium
chosen
compact
alkaline earth
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PCT/US2007/007615
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WO2007120443A3 (fr
Inventor
Wayne D. Cooke
Edward A. Mckigney
Ross E. Muenchausen
Bryan L. Bennett
Rico E. Del Sesto
T. Mark Mccleskey
Kevin C. Ott
Anthony K. Burrell
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Los Alamos National Security, Llc
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Priority claimed from US11/644,246 external-priority patent/US7525094B2/en
Application filed by Los Alamos National Security, Llc filed Critical Los Alamos National Security, Llc
Publication of WO2007120443A2 publication Critical patent/WO2007120443A2/fr
Publication of WO2007120443A3 publication Critical patent/WO2007120443A3/fr

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
    • H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by potential barriers, e.g. phototransistors
    • H01L31/101—Devices sensitive to infrared, visible or ultraviolet radiation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/02—Use of particular materials as binders, particle coatings or suspension media therefor
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
    • C09K11/7772—Halogenides
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K4/00—Conversion screens for the conversion of the spatial distribution of X-rays or particle radiation into visible images, e.g. fluoroscopic screens

Definitions

  • Phosphors are currently used in many important devices such as fluorescent lamps, RGB (red, green, blue) screens, lasers, and crystal scintillators for radiation detectors, radiographic imaging and nuclear spectroscopy.
  • RGB red, green, blue
  • lasers and crystal scintillators for radiation detectors, radiographic imaging and nuclear spectroscopy.
  • the most important property of any phosphor is its brightness, i.e. its quantum efficiency, which is the ratio of the number of photons emitted by the phosphor to the number of photons absorbed.
  • Other important properties include the spectral region of maximum emission (which should match commonly-used photodetectors), optical absorption (minimum self-absorption is desired), decay time of the emission (for some applications fast is desired), and the density.
  • phosphors may be categorized as either intrinsic, when the luminescence originates from the host material, or extrinsic, when impurities or dopants in the host material give rise to the luminescence.
  • scintillators exhibit high quantum efficiency, good linearity of the spectral emission with respect to incident energy, high density, fast decay time, minimal self-absorption, and high effective Z-number (the probability of photoelectric absorption is approximately proportional to Z 5 ).
  • Specific scintillator applications determine the choice of phosphor. For example, scintillators used for active and passive radiation detection require high density, and brightness, whereas scintillators used for radiographic imaging also require fast decay time.
  • LSO:Ce cerium-activated lutetium oxyorthosilicate.
  • This material has been conveniently abbreviated in the art as either LSO:Ce or Ce:LSO.
  • LSOrCe is a crystalline solid that includes a host lattice of lutetium oxyorthosilicate (LU 2 S1O 5 , abbreviated LSO) that is activated by a small amount of the rare-earth metal dopant cerium (Ce).
  • Cerium is an excellent activator because both its 4f ground and 5d excited states lie within the band gap of about 6 eV of the host LSO lattice.
  • LSO:Ce is very bright, i.e. it has a very high quantum efficiency.
  • LSOtCe also has a high density (7.4 gm/cm 3 ), a fast decay time (about 40 nanoseconds), a band emission maximum near 420 nanometers, and minimal self-absorption.
  • Oxyorthosilicate scintillators including LSO:Ce, have been documented in the following reports and patents.
  • Detector which issued on March 3, 1987, incorporated by reference herein, describes a cerium-activated oxyorthosilicate scintillator having the general formula Gd 2 (i -x- y ) Ln 2 ⁇ Ce 2 ySi ⁇ 5 wherein Ln is yttrium and/or lanthanum, wherein 0 ⁇ x ⁇ 0.5, and wherein 1x10 ⁇ 3 ⁇ y ⁇ 0.1.
  • Other exceptionally good scintillators include rare earth doped lanthanum halides, such as cerium doped lanthanum fluoride, cerium doped lanthanum chloride, cerium doped lanthanum bromide, and cerium doped lanthanum mixed halides.
  • rare earth doped lanthanum halides such as cerium doped lanthanum fluoride, cerium doped lanthanum chloride, cerium doped lanthanum bromide, and cerium doped lanthanum mixed halides.
  • High Purity Germanium (HPGe) detectors allow for the resolution of closely spaced peaks in a gamma-ray energy spectrum, and at this level of resolution each element has a distinctive spectrum. The number of gamma rays observed is proportional to the product of the total detector efficiency and the counting time. If counting time is limited, large detector mass is needed to achieve good statistical accuracy.
  • a large, inexpensive, ambient temperature gamma-ray detector with the energy resolution of current HPGe detectors would greatly simplify the task of finding and identifying the isotopic composition of radiation sources.
  • the present invention provides a compact that includes a mixture of a solid binder and at least one nanopowder phosphor chosen from yttrium oxide, yttrium tantalate, barium fluoride, cesium fluoride, bismuth germanate, zinc gallate, calcium magnesium pyrosilicate, calcium molybdate, calcium chlorovanadate, barium titanium pyrophosphate, a metal tungstate, a cerium doped nanophosphor, a bismuth doped nanophosphor, a lead doped nanophosphor, a thallium doped sodium iodide, a doped cesium iodide, a rare earth doped pyrosilicate, or a lanthanide halide
  • the invention also includes a radiation detection method.
  • the method includes exposing a compact to ionizing radiation, wherein the compact comprises a mixture of a solid binder and at least one nanopowder phosphor chosen from yttrium oxide, yttrium tantalate, barium fluoride, cesium fluoride, bismuth germanate, zinc gallate, calcium magnesium pyrosilicate, calcium molybdate, calcium chlorovanadate, barium titanium pyrophosphate, a metal tungstate, a cerium doped nanophosphor, a bismuth doped nanophosphor, a lead doped nanophosphor, a thallium doped sodium iodide, a doped cesium iodide, a rare earth doped pyrosilicate, or a lanthanide halide; and detecting luminescence from the compact.
  • the compact comprises a mixture of a solid binder and at least one nanopowder phosphor chosen from yttrium oxide
  • the invention also provides a radiation detector.
  • the radiation detector includes a compact optically coupled to a photodetector.
  • the compact includes a mixture of a solid binder and at least one nanopowder phosphor chosen from yttrium oxide, yttrium tantalate, barium fluoride, cesium fluoride, bismuth germanate, zinc gallate, calcium magnesium pyrosilicate, calcium molybdate, calcium chlorovanadate, barium titanium pyrophosphate, a metal tungstate, a cerium doped nanophosphor, a bismuth doped nanophosphor, a lead doped nanophosphor, a thallium doped sodium iodide, a doped cesium iodide, a rare earth doped pyrosilicate, or a lanthanide halide.
  • the invention also includes a composition comprising nanophosphor particles of the formula Ce n La( 1-n )X 3 (oleic acid), wherein X is chosen from fluoride and bromide, and wherein 1 > n > 0.
  • FIGURE 1 shows a plot of the optical attenuation length calculated for an embodiment nanocomposite where the index of refraction of the matrix (i.e. the binder) is similar to that of polystyrene (1.59) and the index of refraction of the phosphor is approximately that of the rare earth oxyorthosilicates (1.80).
  • the x- axis indicates the size of particles in nanometers and the y-axis indicates the optical attenuation length in centimeters.
  • the asterisk (*) represent 600 nm optical photons and the plus sign (+) represent 450 nm optical photons. The calculation was performed using software from Mishchenko et al., "Scattering, Absorption, and Emission of Light by Small Particles," Cambridge University Press, Cambridge (2002).
  • FIGURE 2a shows a photographic image of two pieces of the cerium doped transparent nanocomposite scintillator Ce:LaF 3 (oleic acid).
  • FIGURE 2b shows a transmission electron microscope (TEM) image of the nanocomposite of FIGURE 2a.
  • TEM transmission electron microscope
  • FIGURE 3 shows an X-ray diffraction (XRD) spectrum of the nanocomposite scintillator of FIGURE 2a.
  • FIGURE 4 shows photoluminescence excitation (dashed line) and emission spectra (solid line) of the Ce doped LaF 3 doped nanocomposite of FIGURE 2a.
  • FIGURE 5 shows an energy spectrum of the nanocomposite of
  • F FIIGGUURREE 22aa aafftteerr tthhee nanocomposite is irradiated using a 57 Co source (solid line) and a 241 Am source.
  • the invention is concerned with nanocomposite scintillators and with a detector that employs nanocomposite scintillators and that can detect photons (x-rays and gamma rays, for example) and/or particles (protons and neutrons, for example).
  • Scintillators are phosphors that convert ionizing radiation to a light output in the UV-visible and/or infrared.
  • the nanocomposite scintillator is prepared using nanopowders of fast, bright, dense scintillators.
  • the brightness provides an invention detector with optimum light detection, and the high density provides the detector with stopping power for the x-rays, gamma-rays, neutrons, protons, or the like.
  • the cost of preparing nanocomposite scintillator of the invention is inexpensive compared to the cost of preparing single crystals.
  • Embodiment nanocomposites may be prepared by mixing nanopowder phosphor with a polymer or glass binder.
  • Nanopowder is defined herein as powder with particle sizes of 100 nanometers or less.
  • the binder which is sometimes referred to herein as the matrix, is usually substantially transparent to light emission from the nanopowder phosphor.
  • the thickness of the nanocomposite is easily controllable and can be adjusted depending on the particular application.
  • Some matrix materials may have an index of refraction that closely matches the index of refraction of the phosphor and is transparent to the wavelength of emission of the phosphor. Additionally, a matrix material may also be scintillator, thereby providing light from the energy deposited into it.
  • Embodiment nanopowder phosphors may be intrinsic phosphors or extrinsic phosphors.
  • Intrinsic phosphors are phosphors that do not include a dopant in order to produce luminescence.
  • Extrinsic phosphors include a dopant to produce luminescence.
  • Some non-limiting examples of intrinsic phosphors include yttrium oxide, yttrium tantalate, barium fluoride, cesium fluoride, bismuth germanate, zinc gallate, calcium magnesium pyrosilicate, calcium molybdate, calcium chlorovanadate, barium titanium pyrophosphate, a metal tungstate, and lanthanide halides.
  • extrinsic phosphors include cerium doped nanophosphors, bismuth doped nanophosphors, lead doped nanophosphors, thallium doped sodium iodide, doped cesium iodide, and rare earth doped pyrosilicates.
  • Some embodiment host oxyorthosilicate lattices include lutetium oxyorthosilicate (LSO), gadolinium oxyorthosilicate (GSO) 1 yttrium oxyorthosilicate (YSO), lutetium yttrium oxyorthosilicate (LYSO), gadolinium yttrium oxyorthosilicate (GYSO) 1 lutetium gadolinium oxyorthosilicate (LGSO), lanthanum fluoride, lanthanum chloride, and lanthanum bromide.
  • Some embodiment dopants with these host lattices include Ce, Sm, Tb, Tm, Eu, Yb, and Pr. Mixtures of these dopants into a host lattice can also be used.
  • cerium doped nanophosphors include, but are not limited to, cerium doped oxyorthosilicates and lanthanum halide compounds of the formula MX 3 ".Ce wherein M is a lanthanide chosen from lanthanum, yttrium, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium, and X is at least one halide chosen from fluoride, chloride, bromide, and iodide.
  • M is a lanthanide chosen from lanthanum, yttrium, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium
  • X is at least one halide
  • mixed halide compounds are also included.
  • the lanthanide halides of the formula LaX 3 :Ce include cerium doped LaBr 3 , LaCI 3 , LaF 3 , and LaI 3 , and also materials such as but not limited to LaBr-I -5 Ck 5 and LaBro.sClo.5l1-
  • bismuth doped nanophosphors include a host lattice chosen from an alkaline earth phosphate of a formula LM 2 (PO 4 ⁇ Bi wherein M is at least one alkaline earth chosen from barium, calcium, and strontium; lanthanide metal oxides of a formula M 2 ⁇ 3:Bi wherein M is at least one metal chosen from yttrium and lanthanum; bismuth doped yttrium aluminum borates; bismuth doped lanthanum oxychlorides; bismuth doped zinc oxides; bismuth doped calcium oxides; bismuth doped calcium titanium aluminates; bismuth doped calcium sulfides; bismuth doped strontium sulfates and bismuth doped gadolinium niobates.
  • LM 2 PO 4 ⁇ Bi wherein M is at least one alkaline earth chosen from barium, calcium, and strontium
  • lead doped nanophosphors include alkaline earth sulfates of formula MSO 4 : Pb wherein M is at least one alkaline earth chosen from calcium and magnesium; alkaline earth borates of formula MB 4 O 7 : Pb and MB 2 O 4 Pb wherein M is at least one alkaline earth chosen from calcium and strontium; alkaline earth chloroborates of a formula M 2 BsOgCIiPb wherein M is at least one alkaline earth chosen from barium, calcium, and strontium; lead doped barium oxyorthosilicates; lead doped calcium oxides; lead doped calcium sulfides; lead doped zinc sulfides; lead doped lanthanum oxides; lead doped calcium silicates; lead doped calcium tungstates; lead doped barium oxyorthosilicates; lead doped calcium chlorosilicates; lead doped calcium phosphates; and lead doped calcium thiogallates
  • doped cesium iodide include a dopant chosen from Na and Tl.
  • rare earth doped pyrosilicates include a rare earth dopant chosen from Ce, Sm, Tb, Tm, Eu, Yb, and Pr.
  • nanopowder phosphors include rare earth doped oxyorthosilicates (e.g. Y 2 SiO 5 IRE 1 Lu 2 SiO 5 IRE and Gd 2 SiO 5 :RE and mixtures thereof, where RE indicates rare earth dopant, such as Ce or Sm) and rare earth doped lanthanum halides (e.g. LaF 3 :f?E, LaCW.RE and LaBr 3 :f?E and mixtures thereof).
  • rare earth doped oxyorthosilicates e.g. Y 2 SiO 5 IRE 1 Lu 2 SiO 5 IRE and Gd 2 SiO 5 :RE and mixtures thereof, where RE indicates rare earth dopant, such as Ce or Sm
  • rare earth doped lanthanum halides e.g. LaF 3 :f?E, LaCW.RE and LaBr 3 :f?E and mixtures thereof.
  • the effective density of a scintillator may be adjusted by altering the amount of the nanopowder phosphor used.
  • Embodiments may include an amount of nanopowder phosphor in a range of from greater than about zero volume percent to about 65 volume percent.
  • Embodiments may include an amount of nanopowder phosphor greater than about 1 percent by volume, or greater than about 5 percent by volume, or greater than about 10 percent by volume, or greater than about 15 percent or by volume, or greater than about 20 percent or by volume, or greater than about 25 percent or by volume, or greater than about 30 percent or by volume, or greater than about 35 percent by volume, or greater than about 40 percent by volume, or greater than about 45 percent by volume, or greater than about 50 percent by volume, or greater than about 55 percent by volume, or greater than about 60 percent by volume.
  • Embodiment nanocomposite scintillators of the invention may be prepared in a wide variety of shapes using known processing techniques commonly used for preparing films, coatings, tubes, rods, fibers, and other structures.
  • Nanocomposite scintillators of the invention can be made very large. Importantly, the nanocomposite scintillator can be tailored to emit light in a spectral region that matches the optimum response of photomultipliers (about 400 nanometers) or photodiodes (about 550 nanometers), which maximizes the overall efficiency of the radiation detector (which includes the typical detector elements such as power supplies, current meters, photomultiplier tubes, photodiodes, etc.).
  • Nanopowder phosphors used with some embodiments may be prepared by one or more chemical methods. Producing nanopowder by a chemical method is likely less expensive than by grinding down single crystals into powder. In addition, the particle size, surface characteristics, core-shell structure, dopant concentration and matrix material can be controlled more easily using chemical methods.
  • Nanopowder phosphor used with some embodiments has particle sizes of less than about 100 nanometers. Nanopowder phosphor used with other embodiments has particle sizes less than 50 nanometers. Nanopowder phosphor used with yet other embodiments has particle sizes less than 20 nanometers. Other embodiments may employ nanopowder phosphor having particle sizes less than 10 nanometer.
  • Nanopowder phosphor used with other embodiments has particle sizes of 5 nanometers or less. 15
  • Nanopowder phosphor may also be prepared by slurry ball milling of bulk scintillator powder, whereby the diluent contains a surfactant to prevent agglomeration of the milled nanoparticles and afterward centrifuging or sedimentation is used to separate out the desired fraction of nanoparticles.
  • Some embodiment compacts of the invention combines the high stopping power and photoelectric cross section of inorganic crystalline scintillators with the processing costs of plastic scintillators.
  • FIGURE 1 shows the calculated optical attenuation length for a nanocomposite scintillator of the invention.
  • the index of refraction of the matrix is similar to that of polystyrene (1.59) and the index of refraction of the phosphor is approximately that of the rare earth oxyorthosilicates (1.80).
  • the optical attenuation length is approximately 20 cm.
  • the attenuation length is the distance through which the incident light intensity will be reduced to 1/e or 37% of the initial value.
  • the attenuation length takes into account both optical absorption and scattering losses. For a closer match of the indices of refraction between the phosphor and matrix, this attenuation length will become longer.
  • LaF 3 UCe cerium doped lanthanum fluoride
  • parylene poly(p-xylylene) which has an index of refraction between 1.639-1.669 and a visible light transmission of 90% is an example of such a nanocomposite.
  • the invention is also concerned with a composition
  • a composition comprising nanophosphor particles of the formula Cer,La(i_ n )X3(oleic acid), wherein X is chosen from fluoride and bromide, wherein 1 > n > 0.
  • An exemplary nanocomposite scintillator of lanthanum fluoride doped with cerium (20 mol percent cerium) of the invention was prepared as follows: A first solution of LaCI 3 TH 2 O (3.85 grams, 10.4 mmol) and Ce(NO 3 ) 3 6H 2 O (1.0 gram, 2.3 mmol) in deionized water (80 milliliters) was prepared.
  • a second solution of sodium fluoride (1.45 grams, 34.5 mmol) and oleic acid (ALDRICH 1 90%) in 200 ml of 1:1 water.ethanol solvent was also prepared. After the second solution was heated to a temperature of about 75 degrees Celsius, the first solution was added dropwise to the second solution over a period of about 30 minutes, resulting in the slow formation of a waxy white precipitate. The reaction mixture was allowed to stir at 75 degrees Celsius for an additional hour, after which the solid was washed by sonication in about 100 milliliters of ethanol for about 30 minutes. The resulting slurry was subjected to centrifugation at about 4000 rpm for about 30 minutes. The ethanol portion of the centrifugate was decanted from the white solid.
  • FIGURE 2a An image of two pieces of the transparent nanocomposite is shown in FIGURE 2a, and a transmission electron microscope (TEM) image is shown in FIGURE 2b. As FIGURE 2b shows, the sizes of particles of the nanocomposite are less than 10 nanometers.
  • XRD x-ray diffraction
  • FIGURE 5 shows a spectrum of the nanocomposite of FIGURE 2a after the nanocomposite is irradiated using a 57 Co source (solid line) and a 241 Am source.
  • This spectrum demonstrates that the nanocomposite scintillator may be used to detect radiation.
  • 57 Co has two dominant characteristic gamma rays at 122 keV (85.9 percent per decay) and 136 keV (10.4 percent per decay). Photoelectric interactions of these gamma rays with the nanocomposite scintillator are observed as the broad peak centered below 300 ADC counts. Compton interactions of these gamma rays form the sharply rising edge observed below 150 ADC counts.
  • the matrix used is a high index of refraction optical quality glass.
  • matrix materials such as rare-earth flint glasses (Pb containing) have indices of refraction between 1.70 and 1.84 and lanthanum flint glasses vary between 1.82 and 1.98 depending on the glass composition.
  • Embodiment nanocomposite scintillators may be prepared by, for example, dispersing nanopowder phosphor in a matrix material, or by hot pressing or other mechanical and thermal treatment of nanopowder phosphor to form a 07615
  • the resulting nanocomposite scintillator must be suitably transparent, preserve the intrinsic brightness of the nanopowder phosphor, and homogeneously accommodate additives such as wavelength shifting compounds, surfactants, index matching additives, sintering inhibitors, and the like.
  • Matrix materials useful for preparing embodiment nanocomposite scintillators include those where 1) the refractive index of the matrix is not matched to the refractive index of the nanopowder phosphor; and 2) the refractive index of the matrix is matched to the refractive index of the nanopowder phosphor. Selection of an appropriate phosphor and binder for a nanocomposite scintillator for a particular application is also based on parameters that include, but are not limited to, the mean particle size, particle size distribution, thermal stability, chemical stability and degree and type of agglomeration present in the nanophosphor material.
  • a nanopowder of LaBr 3 :Ce (1.0 mol%) in oleic acid dispersion with an average primary particle size of 10 nm would not need an index matched matrix material.
  • Particle agglomeration may be caused by a Van der Waals type- or
  • charge may be added or subtracted from the nanoparticle surface to control dispersion. This may be accomplished, for example, by adjusting the pH of the matrix material [see, for example, Sehgal et a!. "Precipitation-Redispersion of Cerium Oxide Nanoparticles with Poly(acrylic acid): Toward Stable
  • Agglomeration may also be prevented or minimized by adding surfactants to the matrix [see, for example, Khan et al. "Interactions of Binders With Dispersant Stabilized Alumina Suspensions", Colloids. Surf. A., vol. 161 (2000) pages 243-257, incorporated by reference herein), or by some other method.
  • Preferred nanopowder phosphor properties are a primary particle size of less than about 10 nm, and the ability to make agglomerate free, chemically and physically stable dispersions. Stable dispersions of oxide nanopowders can be made by, for example, careful control of the pH of the dispersing media.
  • surfactant modifiers such as oleic acid or n-butanol with cetyltrimethylammonium bromide in dry solvents such as acetone, toluene, hexane, isooctane or dichloromethane allows stable dispersions to be formed, via a reverse-micelle reaction.
  • single-source precursors containing the lanthanide and halide in the correct proportion can be thermally decomposed using hot octadecanol, dioctyl phthalate, hexadeclyamine, tri-n- octylphosphine oxide, or 4-ethylpyridine.
  • the two latter examples solvents can also augment the surfactant since they readily form capping layers on a variety of inorganic nanoparticles.
  • Nanoparticles with mean particle sizes below 10 nm of rare earth doped lanthanide oxides, orthosilicates or halides may be prepared using a variety of chemical and physical methods that include, but are not limited to, single source precursor, hydrothermal, spray pyrolysis or solution combustion methods (see, for example, Chander in “Development of Nanophosphors - a Review", Mat. Sci. Eng., volume R 49, (2005) pages 113-155, incorporated by reference herein).
  • Some unmatched index matrix materials include, but are not limited to, conventional polymers such as polystyrene (PS), polyvinyl toluene (PVT), polymethylmethacrylate (PMMA) or other material with the appropriate wavelength shifters.
  • PS polystyrene
  • PVT polyvinyl toluene
  • PMMA polymethylmethacrylate
  • the dispersed phosphor nanopowder may be added into the polymer directly, using an appropriate solvent that would preferably swell the polymer and support the dispersion of the nanoparticles, removal of the solvent and air in a vacuum oven would yield a transparent composite.
  • a nanocomposite scintillator of the invention is prepared by combining about 50 g of solution-combustion-produced, 5-nm average primary particle size Y 2 CbITb (1.0 mol%) in about 150 ml of toluene with about 5 wt. % oleic acid, and then bead milling the mixture for about 1 hour using the ULTRA APEX MILL using the 30 ⁇ m grinding media.
  • About 50 g of polystyrene powder (finely ground), about 0.75 g of p-terphenyl and about 0.015 g of 3-hydroxyflavone are added into this mixture and mechanically stirred and heated to 40 degrees Celsius to slowly remove the toluene.
  • the resulting gel is poured into two 40mm x 80mm crystallization dishes and placed into a vacuum oven.
  • the mixture is evacuated to a pressure of below -20 inches of mercury and slowly heated to over 300 degrees Celsius over the course of 8 hrs.
  • the result is a transparent nanocomposite scintillator that contains about 50 weight percent of the nanopowder phosphor.
  • a nanocomposite scintillator may be prepared as follows. About fifty grams of YSO:Ce (1.0 mol %) are dispersed in about 100 ml of an alkaline solution, ultrasonically homogenized at 200W for about 30 min to yield a turbid solution. The slow addition of about 10 g polyacrylic acid, with stirring, is done at about 35 degrees Celsius for about 2 hrs, yielding a transparent solution. The mixture is dried and the recovered powder is redispersed in a volume of about 100 ml of acetone.
  • a nanocomposite scintillator may be prepared as follows. About fifty grams of YSO:Ce (1.0 mol %) are dispersed in about 100 ml of an alkaline solution, ultrasonically homogenized at 200W for about 30 min to yield a turbid solution. The slow addition of about 1O g polyacrylic acid, 15
  • the mixture is evacuated to a pressure below about -20 inches of mercury (in. of Hg) and then slowly heated to a temperature of about 300 degrees Celsius over a period of about 8 hours.
  • the result is a transparent plastic scintillator containing about 50 weight percent of the nanopowder phosphor.
  • a thermosetting polymer can be used as a binder.
  • An example of such a nanocomposite scintillator may be prepared by adding about 60 g of La 2 ⁇ 3.Pb (1.0 mol %) to 120 ml of an alkaline solution and ultrasonically homogenizing at 200 Watts for about 30 min to yield a turbid solution. The slow addition of 12 g polyacrylic acid, with stirring, is done at 35 C for 2 hrs, yielding a transparent solution. The mixture is dried and the recovered powder tumble coated with 1.8 g of an epoxy silane-coupling agent.
  • the resulting powder is mixed with 37 g of EPOTEK 301-2FL Part A (epoxy) and 13 g of EPOTEK 301 -2FL Part B (amine) with 0.75 g of p-terphenyl and 0.015 g of 3- hydroxyflavone.
  • the mixture is ultrasonically homogenized at 200W for 30 min and then placed in a vacuum oven where it is then evacuated below -20 inches of Hg and slowly heated to a temperature of about 100 degrees Celsius over the course of about 2 hours. The material is left at 100 degrees Celsius for about 8 hrs.
  • the resulting transparent plastic scintillator contains approximately 50 weight percent of the nanopowder phosphor.
  • a dispersed nanophosphor could be mixed into melted polymer that is subsequently injection molded, directly yielding the nanocomposite.
  • 40 g of LaB ⁇ Ce (1.0 mol%) dried nanopowder is bead milled with 40 g of 0.03 mm polystyrene beads for 2 hrs.
  • Scintillating additives consisting of 0.60 g of p-terphenyl and 0.012 g of POPOP are added into this mixture and mechanically tumbled under flowing dry N2 gas for about 2 hours.
  • the material is charged into an injection molder at a barrel temperature of 245 degrees Celsius and a pressure of 1000 atm and injected into a 90 degree Celsius heated mold of dimension 20 cm x 20 cm x 3mm in 1-2 seconds.
  • the dispersed nanopowder phosphor may also be added into the monomer and the subsequent polymerization reaction could be initiated to form the composite in a process known as gelcasting (see, for example, Tong et al. in "Preparation of Alumina by Aqueous Gelcasting", Ceram. Inter., vol. 30 (2004) pages 2061-2066, incorporated by reference herein).
  • gelcasting see, for example, Tong et al. in "Preparation of Alumina by Aqueous Gelcasting", Ceram. Inter., vol. 30 (2004) pages 2061-2066, incorporated by reference herein.
  • about 50 g of LSO:Ce (1 mol%) is added to approximately 100 ml of a premixed solution consisting of 20 wt. % deionized water, 10 wt.% DARVAN C (surfactant), 50 wt. % methacrylamide monomer, 20 wt.% of cross-linker.
  • the nanophosphor powder is added stepwise and the mixture is ultrasonically homogenized and then de-aired for 1 hr. to make a 50 percent by volume slurry.
  • About 0.75 g of p-terphenyl, about 0.6 g of ammonium persulfate (polymerization initiator), about 0.015 g of POPOP and about 0.010 g of tetramethylethylene diamine (catalyst) are added into this mixture and vigorously stirred to avoid coagulation.
  • the slurry is then cast into the mold and gelled overnight at a temperature of about 65 degrees Celsius to yield a transparent nanocomposite scintillator that contains approximately 40 wt. % of the nanopowder phosphor.
  • Chalcogenide glasses can be processed below 1000 degrees
  • An embodiment nanocomposite scintillator having a chalcogenide glass matrix may be prepared by mixing about 50 g of 100 nm average particle diameter sol-gel or hydrothermally processed Ga x La ( i -X )S 3 powder with 50 g of dried YSO:Tb (1 mol%) powder.
  • the nanophosphor powder has been previously dispersed in 50 ml deionized water with 5 g CALGON (surfactant) at a pH ⁇ 4.0, ultrasonically homogenized, filtered, and dried.
  • the powder mixture is poured into glass crystallizing dishes and fired in a tube furnace with flowing Ar gas. The firing temperature is between 780-880 C for 4 hours.
  • chalcogenide glasses are prepared in a silica tube under vacuum (10 '5 mbar).
  • High purity materials Ga, As, Se, PbI 2 , Sb, Bi and S
  • Arsenic and selenium present surface oxidation and need to be purified by a thermal treatment before the synthesis, since arsenic oxide and selenium oxide are more volatile than As and Se, respectively.
  • the lead iodide, contaminated with water, is purified in a microwave oven before the synthesis (700 W, during 15 min). After purification, the materials are placed in a silica tube, with the oxide or oxyorthosil ⁇ cate nanophosphor.
  • the tube is sealed and heated to 700-800 0 C (depending on the composition) in a rocking furnace.
  • the ampoule is maintained 12 h at this temperature, to reach a good reaction between the different elements and a good homogenization of the melt and dispersion of the nanophosphor powder.
  • the glass is obtained by quenching the melt and annealing the sample near its glass transition temperature (T 9 ), to reduce the mechanical stress produced by cooling.
  • T 9 glass transition temperature
  • the glass is then cut into disks of 1 mm thickness, which are polished with two parallel sides.
  • lower temperature hybrid glasses may be formed by mixing inorganic halides, oxides, sulfates or carbonates into polystyrene or other plastic scintillators, examples of which are shown in TABLE 1 below.
  • index-matching additives can be done in conjunction with the nanophosphor using the techniques described. For example, 50 g of solution combustion produced 50-nm average primary particle size LSO:Ce (1.0 mol%) in 150 ml of toluene with 5 wt. % oleic acid is bead milled for 1 hr. using the Ultra Apex Mill using the 30 ⁇ m grinding media. Afterward, 50 g of polystyrene powder, finely ground, 8.5 g of finely ground arsenic oxide, 0.75 g of p-terphenyi and 0.015 g of POPOP are added into this mixture and mechanically stirred and heated to 40 0 C to slowly remove the toluene.
  • LSO:Ce 50-nm average primary particle size LSO:Ce (1.0 mol%) in 150 ml of toluene with 5 wt. % oleic acid is bead milled for 1 hr. using the Ultra Apex Mill using the 30
  • the resulting gel is poured into two 40mm x 80mm crystallization dishes and placed into a vacuum oven.
  • the mixture is evacuated below about -20 inches of Hg and slowly heated to about 300 degrees Celsius over a period of about 8 hours.
  • the resulting transparent plastic scintillator contains about 45 weight percent of nanopowder phosphor.
  • a dispersed nanopowder phosphor could be mixed into melted polymer that was subsequently injection molded, directly yielding the nanocomposite.
  • 40 g of LaU:Ce (1.0 mol %) and 3 weight percent vinyl silane coupling agent, dried nanopowder is bead milled with 40 g of .03 mm polystyrene beads and 6.5 g of antimony iodide, powder for 2 hrs.
  • Scintillating additives consisting of 0.60 g of p-terphenyl and 0.012 g of POPOP are added into this mixture and mechanically tumbled under flowing dry N 2 gas for 2 hrs.
  • the material is charged into an injection molder at a barrel temperature of 245 0 C and a pressure of 1000 atm and injected into a 90 0 C heated mold of dimension 20 cm x 20 cm x 3mm in 1-2 s.
  • the dispersed nanopowder phosphor could be added into the monomer and the subsequent polymerization reaction could be initiated to form the composite in a gelcasting process (vide supra).
  • a mixture of 50 g of 50 nm average particle diameter YSO:Ce (1 mol %) and 8.5 g of finely ground manganese carbonate is added to approximately 100 ml of a premixed solution consisting of 20 wt.
  • nanophosphor powder is added stepwise and the mixture is ultrasonically homogenized and then degassed for 1 hr. to make a 50 volume percent slurry. About 0.75 g of p- terphenyl, 0.6 g of ammonium persulfate, 0.015 g of POPOP and 0.010 g of tetramethylethylene diamine are added into this mixture and vigorously stirred to avoid coagulation. The slurry is then cast into the mold and gelled at 65 0 C overnight to yield a transparent scintillating composite contains approximately 40 wt. % of the nanophosphor.
  • An embodiment of such a monolith may be prepared by, for example, dispersing about 200 g of LaBr 3 :Ce (1.0 mol %) powder in about 500 ml of an alkaline solution by ultrasonic homogenization at about 200 Watts for about 30 min to yield a turbid solution.
  • a transparent solution would be prepared by the slow addition to the turbid solution of about 40 grams of polyacrylic acid, with stirring, at a temperature of about 35 degrees Celsius over a six hour period. The mixture is then dried and the recovered powder is isostatically pressed at a pressure of about 180 MPa.
  • Another approach to inhibit sintering during pressing for nanophosphors is to synthesize the nanophosphor in a core-shell geometry.
  • This approach to nanoparticle synthesis is usually done to protect the nanoparticle surface from chemical quenching of surface luminescence states.
  • the shell properties will be chosen to obviate the need for sintering inhibitors in the core material.
  • a promising example would be LaBr 3 core with a KBr shell.
  • the core-shell materials are compatible, as shown by the existence of the K 2 LaBr 5 scintillator.
  • KBr has a cubic crystal structure and can easily be cold pressed. Cold pressing would eliminate the agglomeration and grain coarsening expected to occur in LaBr 3 at elevated processing temperatures.
  • Some of the possible radiation detector configurations include mounting the nanocomposite scintillator directly onto the face of a photomultiplier with optical coupling grease; mounting the nanocomposite scintillator directly onto the face of a photodiode with optical coupling grease; mounting a large area nanocomposite scintillator onto light-pipe material that directs the scintillation light to one or more photomultiplier tubes or photodiodes; and indirect coupling of the scintillation light to fiber optics, which transmits the light to a photodiode, photomultiplier tube or CCD camera.
  • Some of these configurations may be more easily implemented using a nanocomposite scintillator prepared with a flexible binder (polydimethylsiloxane (PDMS) for example).
  • PDMS polydimethylsiloxane
  • the light emission from the radiation detector can be tailored for either a photomultiplier or a photodiode.
  • X-ray and gamma ray detectors based on photomultipliers may employ Lu2SiO 5 doped with Ce (i.e. LSOiCe) because the emission maximum of LSO:Ce occurs near a wavelength of about 420 nanometers, which is close to the maximum response of most photomultipliers.
  • YSO:Sm would be more preferable because the maximum emission of LSO:Sm occurs near a wavelength of about 542 nanometers, and thus is better matched to the maximum response for silicon photodiodes, which have a maximum response at about 550 nanometers.
  • an oxyorthosilicate of gadolinium would be employed because gadolinium has the largest known cross section for thermal neutrons; the decay scheme yields conversion electrons that excite the rare earth dopant to produce scintillations. Accordingly, Gd 2 SiOs doped with Ce (i.e.
  • GSO:Ce would be employed for a photodetector using photomultipliers, while GSO.Sm would be employed for a photodetector using photodiodes.
  • matrix materials or nanophosphor material enhanced with 6 Li and or 10 B would further enhance the performance due to increased energy deposition in the matrix due to enhanced thermal neutron cross sections and large kinetic energy release in the capture reactions.
  • thermalization of fast neutrons can be efficiently performed by the large hydrogenic atomic fraction that is present in many polymers, such as polyethylene.
  • Nanocomposite scintillators and detectors of the present invention may be used for large-area radiation detection such as portal monitors. There currently is a need for relatively inexpensive detectors for portal monitors related to the need for increased transportation security at airports, seaports, and bus and rail terminals, especially after the September 11 attack on the World Trade Center.
  • the radiation detectors of this invention may be used for these types of monitors.
  • the nanocomposite scintillators may also be used in radiation detectors with complex and irregular shapes.
  • Embodiment nanopowder phosphors may include rare earth doped oxyorthosilicates.
  • Other materials such as crystalline NaI :TI, BGO, semiconductors, and noncrystalline organic materials may also be used.
  • rare earth doped oxyorthosilicates include LYSO:Ce (see U. S. Patent 6,323,489 to McClellan entitled "Single Crystal Scintillator,” which issued on November 27, 2001, incorporated by reference herein, which describes cerium activated oxyorthosilicate scintillator having the having the general formula Lu( 2- ⁇ . z )Y ⁇ Ce z SiO 5 , wherein 0.05 ⁇ x ⁇ 1.95 and 0.001 ⁇ z ⁇ 0.02, which is abbreviated as LYSO:Ce), and the rare earth doped oxyorthosilicates described in U. S.
  • LSO lutetium oxyorthosilicate
  • GSO gadolinium oxyorthosilicate
  • YSO yttrium oxyorthosilicate
  • LYSO lutetium yttrium
  • rare-earth doped oxyorthosilicates are preferable due to their tailorable optical emission, high light output and high density. Not only are they bright and dense, they are also fast and therefore can be used in detectors for proton and neutron radiography, for positron emission tomography, and for medical radiography.
  • Current large-area radiographic devices are based on pixelated single crystals. These devices suffer from disadvantages associated with non-uniform light output over the large area of the detector, and from the dark contrast lines that result from the seams between the pixels.
  • the nanocomposite scintillators of this invention have a relatively uniform light output and can be made seamless over a large area, thereby providing solutions to the aforementioned existing problems associated with pixelated detectors.
  • Another significant problem associated with the production of pixelated detectors relates to the difficulty in producing pixels; some materials, such as the known scintillator Gd 2 SiO 5 :Ce (GSO:Ce) single crystals are micaceous and cannot be easily cut into pixels and polished for use in radiographic imaging. Large area detectors of this invention employing a GSO:Ce scintillating powder would not require GSO:Ce single crystal pixels; the bulk GSO:Ce could be ground into powder, mixed with a flexible polymer binder such as PDMS, and pressed to form a large area, seamless composite that can be used for radiation detection of this invention.
  • GSO:Ce scintillator
  • nanocomposite scintillators are used with photomultipliers or photodiodes for inexpensive radiation detectors that may be useful in applications related to, but not limited to, Homeland Security, International Safeguards, Scientific Research and Medical Imaging.
  • the nanocomposite scintillators and detectors using them may provide an energy resolution comparable to High Purity Germanium and cost and size comparable to a plastic scintillator.

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Abstract

L'invention concerne un scintillateur nanocomposite obtenu au moyen d'un phosphore en nanopoudre dopé, aux terres rares, rapide et brillant ainsi que d'un liant transparent au phosphore émis.
PCT/US2007/007615 2006-03-27 2007-03-27 Scintillateur nanocomposite, détecteur et procédé WO2007120443A2 (fr)

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CN112909117A (zh) * 2021-01-22 2021-06-04 湖北大学 一种硅掺杂铈元素红外探测器、制备方法及系统
CN112909117B (zh) * 2021-01-22 2022-08-02 湖北大学 一种硅掺杂铈元素红外探测器、制备方法及系统

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