USOO752.5094B2

12) United States Patent 10) Patent No.: US 7.525,0949 9 B2 Cooke et al. (45) Date of Patent: Apr. 28, 2009

(54) NANOCOMPOSITE SCINTILLATOR, 5,264,154. A 1 1/1993 Akiyama et al. DETECTOR, AND METHOD 5,952,665 A 9/1999 Bhargava 6,207,077 B1 3/2001 Burnell-Jones (75) Inventors: D. Wayne Cooke, Santa Fe, NM (US); 6,323,489 B1 11/2001 McClellan Edward A. McKigney, Los Alamos, 6,448,566 B1 9, 2002 Riedner et al.

NM (US); Ross E. Muenchausen, Los -3. W - R ck 239: SRuffet etal. al...... 428/402 Alamos, NM (US); Bryan L. Bennett, 6,599.444 B2 7/2003 Burnell-Jones Los Alamos, NM (US) 6,689,293 B2 2/2004 McClellan et al. 6,699.406 B2 3/2004 Riman et al. (73) Assignee: Los Alamos National Security, LLC, 6,734,465 B1 5, 2004 Taskar et al. Los Alamos, NM (US) 7,094,361 B2 8/2006 Riman et al. 7,145,149 B2 12/2006 Cooke et al. (*) Notice: Subject to any disclaimer, the term of this 2004/0174917. A 9 2004 Riman et al. patent is extended or adjusted under 35 2006/0231797 A1 10, 2006 Riman et al. U.S.C. 154(b) by 0 days. OTHER PUBLICATIONS (21) Appl. No.: 11/644,246 Shah et al., “CeBr3 Scintillators for Gamma-Ray Spectroscopy.” IEEE Transactions on Nuclear Science, vol. 52, No. 6, Dec. 2005, pp. (22) Filed: Dec. 21, 2006 3157-3159. Glodo et al., “Thermoluminescence of LaBr3:Ce and LaCl3:Ce crys (65) Prior Publication Data tals.” Nuclear Instruments and Methods in Physics Research A537 (2005) pp. 93-96.* US 2008/OO935.57 A1 Apr. 24, 2008 (Continued) Related U.S. Application Data Primary Examiner Constantine Hannaher (60) Provisional application No. 60/752,981, filed on Dec. (74) Attorney, Agent, or Firm—Samuel L. Borkowsky 21, 2005. (57) ABSTRACT (51) GOITInt. Cl. L/20 (2006.01) A compact includes a mixture of a solid- - binder- - and at least (52) U.S. Cl 250/361 R one nanopowder phosphor chosen from yttrium oxide, ir grrrrri. yttrium tantalate, barium fluoride, cesium fluoride, bismuth (58) Field State St. such it." R germanate, Zinc gallate, calcium magnesium pyrosilicate, pp p ry. calcium molybdate, calcium chlorovanadate, barium tita (56) References Cited nium pyrophosphate, a metaltungstate, a cerium doped nano phosphor, a bismuth doped nanophosphor, a lead doped nano U.S. PATENT DOCUMENTS phosphor, a thallium doped sodium iodide, a doped cesium 4,230,510 A 10, 1980 Cusano et al. iodide, a rare earth doped pyrosilicate, or a lanthanide halide. 4,362,946 A 12, 1982 Cusano et al. The compact can be used in a radiation detector for detecting 4,647,781 A 3/1987 Takagi et al. ionizing radiation. 4,692,266 A 9, 1987 Costa et al. 4,958,080 A 9, 1990 Melcher 31 Claims, 3 Drawing Sheets

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OTHER PUBLICATIONS Shoudu et al., “Czochralski Growth of Rare-Earth Orthosilicates YSiO, Single Crystals,” Journal of Crystal Growth, Sehgal et al., “Precipitation-Redispersion of Cerium Oxide vol. 197, Mar. 1999, pp. 901-904. Nanoparticles with Poly(acrylic acid): Toward Stable Disperions.” Rodnyi, "Physical Process in Inorganic Scintillators.” CRC Press, Langmuir, vol. 21, Sep. 2005, pp. 9359-93.64. 1997, p. 50. Pandey et al., “A Study of Optical Parameters of Amorphous Loutts et al., “Czochralski Growth and Characterization of SeoTeo Ag Thin Films Before and After Heat Treatment.” Journal (Lu Gd)SiO, Single Crystals for Scintillators,” Journal of Crystal of Ovonic Research, vol. 3, No. 2, Apr. 2007, pp. 29-38. Growth, vol. 174, Apr. 1997, pp. 331-336. Chander, “Development of Nanophosphors—A Review.” Materials Melcher et al., “Czochralski Growth or Rare Earth Oxyorthosilicate Science and Engineering R. vol. 49, issue 5, Jun. 2005, pp. 113-155. Single Crystals,” Journal of Crystal Growth, vol. 128, Mar. 1993, pp. Tong et al., Preparation of Alumina by Aqueous Gelcasting, Ceramic 1001-1005. Inter, vol. 30, Oct. 2004, pp. 2061-2066. Shmulovich et al., “Single-Crystal Rare-Earth-Doped Yttrium Inkyo et al., Kotubuki Industries, "Dispersion of Agglomerated Orthosilicate Phosphors,” J. Electrochemical Society: Solid State Nanoparticles by Micromedia Mill, Ultra Apex Mill.” J. Soc. Powder Science and Technology, vol. 135, No. 12, Dec. 1988, pp. 3141-3151. Tech. Jap., vol. 41, May 2004, pp. 1-11. Brandle et al., “Czochralski Growth of Rare-Earth Orthosilicates Khan et al., “Interaction of Binders with Dispersant Stabilised Alu (Ln2SiO3).” Journal of Crystal Growth, vol. 79, Dec. 1986, pp. 308 mina Suspensions.” Colloids and Surfaces A: Physicochemical and 3.15. Engineering Aspects, vol. 161, 2000, pp. 243-257. * cited by examiner U.S. Patent Apr. 28, 2009 Sheet 1 of 3 US 7,525,094 B2

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Fig. 3 US 7,525,094 B2 1. 2 NANOCOMPOSITE SCINTILLATOR, 135, no. 12, p. 3141-3151, 1988), incorporated by reference DETECTOR, AND METHOD herein, describes single crystals of rare-earth activated YSO (prepared according to aforementioned Brandle et al.) that RELATED APPLICATIONS include a green phosphor containing YSO activated with Tb and Gd, and ared phosphor containingYSO activated with Tb This application claims the benefit of U.S. Provisional and Eu. Patent Application Ser. No. 60/752,981 filed Dec. 21, 2005, “Czochralski Growth of Rare Earth Oxyorthosilicate hereby incorporated by reference. Single Crystals” by Melcher et al. (Journal of Crystal Growth, vol. 128, p. 1001-1005, 1993), incorporated by reference STATEMENT REGARDING FEDERAL RIGHTS 10 herein, describes the Czochralski preparation of single crys tals of GSO:Ce, LSO:Ce, and YSO:Ce. This invention was made with government Support under “Czochralski Growth and Characterization of (Lu Gd) Contract No. DE-AC51-06NA25396 awarded by the U.S. SiOs by Loutts et al. (Journal of Crystal Growth, Vol. 174, Department of Energy. The government has certain rights in p. 331-336, 1997), incorporated by reference herein, the invention. 15 describes the preparation and properties of single crystals of cerium-activated oxyorthosilicates having a crystal lattice of BACKGROUND lutetium and gadolinium. Phosphors are currently used in many important devices U.S. Pat. No. 4,647,781 to Takagi et al. entitled “Gamma Such as fluorescent lamps, RGB (red, green, blue) screens, Ray Detector,” which issued on Mar. 3, 1987, incorporated by lasers, and crystal Scintillators for radiation detectors, radio reference herein, describes a cerium-activated oxyorthosili graphic imaging and nuclear spectroscopy. Perhaps the most cate scintillator having the general formula Gd2 important property of any phosphor is its brightness, i.e. its Ln2Ce2SiOs wherein Ln is yttrium and/or lanthanum, quantum efficiency, which is the ratio of the number of pho wherein 0s xs0.5, and wherein 1x10sys0.1. U.S. Pat. No. 4,958,080 to Melcher entitled “Lutetium tons emitted by the phosphor to the number of photons 25 absorbed. Other important properties include the spectral Orthosilicate Single Crystal Scintillator Detector,” which region of maximum emission (which should match com issued on Sep. 18, 1990, describes an X-ray detector employ monly-used photodetectors), optical absorption (minimum ing a transparent, single crystal of cerium-activated lutetium self-absorption is desired), decay time of the emission (for oxyorthosilicate (LSO:Ce). Some applications fast is desired), and the density. Addition 30 U.S. Pat. No. 5.264,154 to Akiyama et al. entitled "Single ally, phosphors may be categorized as either intrinsic, when Crystal Scintillator,” which issued on Nov. 23, 1993, incor the luminescence originates from the host material, or extrin porated by reference herein, describes a single crystal cerium sic, when impurities or dopants in the host material give rise activated oxyorthosilicate Scintillator having the general for to the luminescence. mula Gd-Ln,CeSiOs wherein Ln is Sc, Tb, Lu, Dy, Ho, In general, Superior Scintillators exhibit high quantum effi 35 Er, Tm, or Yb, wherein 0.03sxs 1.9, and wherein ciency, good linearity of the spectral emission with respect to 0.001 sys0.2. incident energy, high density, fast decay time, minimal self U.S. Pat. No. 6,689,298 to McClellanet al. entitled “Crys absorption, and high effective Z-number (the probability of talline Rare-Earth Activated Oxyorthosilicate Phosphor.” photoelectric absorption is approximately proportional to which issued on Feb. 10, 2004, incorporated by reference Z). Specific scintillator applications determine the choice of 40 herein, describes a variety of single crystal phosphors such as phosphor. For example, Scintillators used for active and pas lutetium yttrium phosphor (host lattice LYSO), lutetium sive radiation detection require high density, and brightness, gadolinium phosphor (host lattice LGSO), and gadolinium whereas Scintillators used for radiographic imaging also yttrium phosphor (host lattice GYSO) that have been doped require fast decay time. with rare earth dopants Sm, Tb, Tm, Eu, Yb, and Pr. An exceptionally good Scintillatoris cerium-activated lute 45 Other exceptionally good scintillators include rare earth tium oxyorthosilicate. This material has been conveniently doped lanthanum halides, such as cerium doped lanthanum abbreviated in the art as either LSO:Ce or Ce:LSO. LSO:Ceis fluoride, cerium doped lanthanum chloride, cerium doped a crystalline solid that includes a host lattice of lutetium lanthanum bromide, and cerium doped lanthanum mixed oxyorthosilicate (Lu SiO5, abbreviated LSO) that is activated halides. by a small amount of the rare-earth metal dopant cerium (Ce). 50 While the scintillator properties of LSO:Ce are excep Cerium is an excellent activator because both its 4f ground tional, high-quality single crystals are difficult and expensive and 5d excited states lie within the band gap of about 6 eV of to prepare. The high cost, which is at least partly due to the the host LSO lattice. LSO:Ce is very bright, i.e. it has a very high cost of starting materials (high purity LuC powder) high quantum efficiency. LSO:Ce also has a high density (7.4 and equipment (iridium crucibles for containing the LuO gm/cm), a fast decay time (about 40 nanoseconds), a band 55 powder that melts at about 2150 degrees Celsius), and the emission maximum near 420 nanometers, and minimal self tendency of the crystal boule to form cracks that limit the absorption. amount of usable single crystal from the boule, limits efforts Oxyorthosilicate scintillators, including LSO:Ce, have to develop other types of crystals with an LSO host lattice. been documented in the following reports and patents. High Purity Germanium (HPGe) detectors allow for the “Czochralski Growth of Rare-Earth Orthosilicates 60 resolution of closely spaced peaks in a gamma-ray energy (Ln2SiO4) by Brandle etal (Journal of Crystal Growth, Vol. spectrum, and at this level of resolution each element has a 79, p. 308-315, 1986), incorporated by reference herein, distinctive spectrum. The number of gamma rays observed is describes yttrium oxyorthosilicate (YSO) activated with Ce, proportional to the product of the total detector efficiency and Pr, Nd, Sm, Gd, Tb, Er, Tm, or Yb. the counting time. If counting time is limited, large detector “Single-Crystal Rare-Earth doped Yttrium Orthosilicate 65 mass is needed to achieve good Statistical accuracy. Phosphors” by Shmulovich et al. (Journal of the Electro A large, inexpensive, ambient temperature gamma-ray chemical. Society:Solid-State Science and Technology, Vol. detector with the energy resolution of current HPGe detectors US 7,525,094 B2 3 4 would greatly simplify the task of finding and identifying the sion (right) for nanopowder. The overlap of the absorption isotopic composition of radiation sources. and emission curves for the nanopowder is less than for the bulk powder, which will result in longer optical attenuation BRIEF SUMMARY OF THE INVENTION length for nanophosphor composites compared to bulk phos phor composites. This effect is in addition to the longer Briefly, the present invention provides a compact that attenuation length achieved by reduced optical scattering. includes a mixture of a solid binder and at least one nanopo The additional light output of the nanopowder will contribute wder phosphor chosen from yttrium oxide, yttrium tantalate, to better energy resolution than would be achieved with the barium fluoride, cesium fluoride, bismuth germanate, Zinc bulk powder. gallate, calcium magnesium pyrosilicate, calcium molybdate, 10 FIG. 3 shows images of several solutions and mixtures calcium chlorovanadate, barium titanium pyrophosphate, a prepared using about 1 percent cerium oxide (5 nm size) metal tungstate, a cerium doped nanophosphor, a bismuth (upper images). Transparent solutions are obtained below doped nanophosphor, a lead doped nanophosphor, a thallium pH-3. The lower images show the effect of the addition of doped sodium iodide, a doped cesium iodide, a rare earth polyacrylic acid, which shifts the transparent region to a doped pyrosilicate, or a lanthanide halide 15 higher pH (pH greater than about 7). The invention also includes a radiation detection method. The method includes exposing a compact to ionizing radia DETAILED DESCRIPTION tion, wherein the compact comprises a mixture of a Solid binder and at least one nanopowder phosphor chosen from The invention is concerned with nanocomposite Scintilla yttrium oxide, yttrium tantalate, barium fluoride, cesium tors and with a detector that employs nanocomposite Scintil fluoride, bismuth germanate, Zinc gallate, calcium magne lators and that can detect photons (X-rays and gamma rays, for sium pyrosilicate, calcium molybdate, calcium chlorovana example) and/or particles (protons and neutrons, for date, barium titanium pyrophosphate, a metal tungstate, a example). Scintillators are phosphors that convert ionizing cerium doped nanophosphor, a bismuth doped nanophosphor, radiation to a light output in the UV-visible and/or infrared. a lead doped nanophosphor, a thallium doped sodium iodide, 25 The nanocomposite Scintillator is prepared using nanopow a doped cesium iodide, a rare earth doped pyrosilicate, or a ders of fast, bright, dense Scintillators. The brightness pro lanthanide halide; and detecting luminescence from the com vides an invention detector with optimum light detection, and pact. the high density provides the detector with stopping powerfor The invention also provides a radiation detector. The radia the X-rays, gamma-rays, neutrons, protons, or the like. Also, tion detector includes a compact optically coupled to a pho 30 the cost of preparing nanocomposite Scintillator of the inven todetector. The compact includes a mixture of a solid binder tion is inexpensive compared to the cost of preparing single and at least one nanopowder phosphor chosen from yttrium crystals. oxide, yttrium tantalate, barium fluoride, cesium fluoride, Embodiment nanocomposites may be prepared by mixing bismuth germanate, Zinc gallate, calcium magnesium pyro nanopowder phosphor with a polymer or glass binder. Nan silicate, calcium molybdate, calcium chlorovanadate, barium 35 titanium pyrophosphate, a metal tungstate, a cerium doped opowder is defined herein as powder with particle sizes of 100 nanophosphor, a bismuth doped nanophosphor, a lead doped nanometers or less. The binder, which is sometimes referred to herein as the matrix, is usually substantially transparent to nanophosphor, a thallium doped sodium iodide, a doped light emission from the nanopowderphosphor. The thickness cesium iodide, a rare earth doped pyrosilicate, or a lanthanide of the nanocomposite is easily controllable and can be halide. 40 adjusted depending on the particular application. BRIEF DESCRIPTION OF THE DRAWINGS Some matrix materials may have an index of refraction that closely matches the index of refraction of the phosphor and is The accompanying drawings, which are incorporated in transparent to the wavelength of emission of the phosphor. and form a part of the specification, illustrate the embodi 45 Additionally, a matrix material may also be Scintillator, ments of the present invention and, together with the descrip thereby providing light from the energy deposited into it. tion, serve to explain the principles of the invention. In the Embodiment nanopowder phosphors may be intrinsic drawings: phosphors or extrinsic phosphors. Intrinsic phosphors are FIG. 1 shows a plot of the optical attenuation length cal phosphors that do not include a dopant in order to produce culated for an embodiment nanocomposite where the index of 50 luminescence. Extrinsic phosphors include a dopant to pro refraction of the matrix (i.e. the binder) is similar to that of duce luminescence. Some non-limiting examples of intrinsic polystyrene (1.59) and the index of refraction of the phosphor phosphors include yttrium oxide, yttrium tantalate, barium is approximately that of the rare earth oxyorthosilicates fluoride, cesium fluoride, bismuth germanate, Zinc gallate, (1.80). The x-axis indicates the size of particles in nanometers calcium magnesium pyrosilicate, calcium molybdate, cal and the y-axis indicates the optical attenuation length in cen 55 cium chlorovanadate, barium titanium pyrophosphate, a timeters. The asterisk (*) represent 600 nm optical photons metal tungstate, and lanthanide halides. Some non-limiting and the plus sign (+) represent 450 nm optical photons. The examples of extrinsic phosphors include cerium doped nano calculation was performed using Software from Mishchenko phosphors, bismuth doped nanophosphors, lead doped nano et al., "Scattering, Absorption, and Emission of Light by phosphors, thallium doped sodium iodide, doped cesium Small Particles. Cambridge University Press, Cambridge 60 iodide, and rare earth doped pyrosilicates. (2002). Some embodiment host oxyorthosilicate lattices include FIG.2a shows a plot of the measured optical emission as a lutetium oxyorthosilicate (LSO), gadolinium oxyorthosili function of wavelength for powder excited by X-rays. The cate (GSO), yttrium oxyorthosilicate (YSO), lutetium nanopowder emission is more intense and shifted compared yttrium oxyorthosilicate (LYSO), gadolinium yttrium oxy to the bulk powder. FIG. 2b shows a plot of the measured 65 orthosilicate (GYSO), lutetium gadolinium oxyorthosilicate absorption (left) and emission (right) for bulk powder. FIG. (LGSO), lanthanum fluoride, lanthanum chloride, and lantha 2c shows a plot of the measured absorption (left) and emis num bromide. Some embodiment dopants with these host US 7,525,094 B2 5 6 lattices include Ce, Sm, Tb, Tm, Eu, Yb, and Pr. Mixtures of doped calcium tungstates; lead doped barium oxyorthosili these dopants into a host lattice can also be used. cates; lead doped calcium chlorosilicates; lead doped calcium Some examples of cerium doped nanophosphors include, phosphates; and lead doped calcium thiogallates. but are not limited to, cerium doped oxyorthosilicates and Some non-limiting examples of doped cesium iodide lanthanum halide compounds of the formula MX:Ce include a dopant chosen from Na and Tl. wherein M is a lanthanide chosen from lanthanum, yttrium, Some non-limiting examples of rare earth doped pyrosili cerium, praseodymium, neodymium, promethium, cates include a rare earth dopant chosen from Ce, Sm, Tb, Tm, Samarium, europium, gadolinium, terbium, dysprosium, hol Eu, Yb, and Pr. mium, erbium, thulium, ytterbium, and lutetium, and X is at Some embodiment nanopowder phosphors include rare least one halide chosen from fluoride, chloride, bromide, and 10 earth doped oxyorthosilicates (e.g. YaSiOs: RE, Lu SiOs: RE iodide. In this compound and in those that follow, when it is and GdaSiOs:RE and mixtures thereof, where RE indicates mentioned that X is at least one halide, it should understood rare earth dopant, such as Ce or Sm) and rare earth doped that mixed halide compounds are also included. For example, lanthanum halides (e.g. LaF:RE, LaCl:RE and LaBr:RE for the lanthanide halides of the formula Lax:Ce include and mixtures thereof). cerium doped LaBr, LaCl, LaF, and LaI, and also mate 15 The effective density of a scintillator may be adjusted by rials such as but not limited to LaBrisCls and altering the amount of the nanopowder phosphor used. LaBrosClos I. Other examples include cerium doped lantha Embodiments may include an amount of nanopowder phos num halosilicate of a formula LaSiOX:Ce wherein X is at phor in a range of from greater than about Zero Volume per least one halide chosen from fluoride, chloride, bromide, and cent to about 65 volume percent. Embodiments may include iodide; an alkaline earth fluoride of a formula MF:Ce an amount of nanopowder phosphor greater than about 1 wherein M is at least one alkaline earth chosen from barium, percent by Volume, or greater than about 5 percent by Volume, calcium, strontium and magnesium; an alkaline earth Sulfate or greater than about 10 percent by Volume, or greater than ofa formula MSO:Ce wherein M is at least one alkaline earth about 15 percent or by volume, or greater than about 20 chosen from barium, calcium, and strontium; an alkaline percent or by volume, or greater than about 25 percent or by earth thiogallate of a formula MGaSa:Ce wherein M is at 25 volume, or greater than about 30 percent or by volume, or least one alkaline earth chosen from barium, calcium, stron greater than about 35 percent by Volume, or greater than about tium and magnesium; alkaline earth aluminates of a formula 40 percent by volume, or greater than about 45 percent by LMAlO:Ce and CeLMAl Os:Ce wherein L, M are at volume, or greater than about 50 percent by volume, or least two alkaline earth chosen from barium, calcium, stron greater than about 55 percent by Volume, or greater than about tium and magnesium; alkaline earth pyrosilicates of a for 30 60 percent by volume. mula LMSi-O-7:Ce wherein L, M are at least two alkaline Embodiment nanocomposite Scintillators of the invention earth chosen from calcium, and magnesium; cerium doped may be prepared in a wide variety of shapes using known metal aluminum perovskites of the formula MAlO:Ce processing techniques commonly used for preparing films, wherein M is at least one metal chosen from yttrium and coatings, tubes, rods, fibers, and other structures. Nanocom lutetium; cerium doped alkaline earth sulfides of formula 35 posite Scintillators of the invention can be made very large. MS:Ce wherein M is at least one alkaline earth chosen from Importantly, the nanocomposite Scintillator can be tailored to strontium and magnesium; cerium doped yttrium borate; emit light in a spectral region that matches the optimum cerium doped yttrium aluminum borate; cerium doped response of photomultipliers (about 400 nanometers) or pho yttrium aluminum garnets; cerium doped yttrium oxychlo todiodes (about 550 nanometers), which maximizes the over rides; cerium doped calcium silicates; cerium doped calcium 40 all efficiency of the radiation detector (which includes the aluminum silicates; cerium doped yttrium phosphates; typical detector elements such as power Supplies, current cerium doped calcium aluminates; cerium doped calcium meters, photomultiplier tubes, photodiodes, etc.). pyroaluminates; cerium doped calcium phosphates; cerium Nanopowderphosphors used with some embodiments may doped calcium pyrophosphates; and cerium doped lanthanum be prepared by one or more chemical methods. Producing phosphates. 45 nanopowder by a chemical method is likely less expensive Some non-limiting examples of bismuth doped nanophos than by grinding down single crystals into powder. In addi phors include a host lattice chosen from an alkaline earth tion, the particle size, Surface characteristics, core-shell struc phosphate of a formula LM (PO):Bi wherein M is at least ture, dopant concentration and matrix material can be con one alkaline earth chosen from barium, calcium, and stron trolled more easily using chemical methods. tium; lanthanide metal oxides of a formula MO:Bi wherein 50 Nanopowder phosphor used with some embodiments has M is at least one metal chosen from yttrium and lanthanum; particle sizes of less than about 100 nanometers. Nanopowder bismuth doped yttrium aluminum borates; bismuth doped phosphorused with other embodiments has particle sizes less lanthanum oxychlorides; bismuth doped Zinc oxides; bis than 50 nanometers. Nanopowder phosphor used with yet muth doped calcium oxides; bismuth doped calcium titanium other embodiments has particle sizes less than 20 nanometers. aluminates; bismuth doped calcium sulfides; bismuth doped 55 Other embodiments may employ nanopowder phosphor hav strontium Sulfates and bismuth doped gadolinium niobates. ing particle sizes less than 10 nanometer. Some non-limiting examples of lead doped nanophosphors Nanopowder phosphor used with other embodiments has include alkaline earth sulfates of formula MSO:Pb wherein particle sizes of 5 nanometers or less. M is at least one alkaline earth chosen from calcium and Nanopowder phosphor may also be prepared by slurry ball magnesium; alkaline earthborates of formula MBO7:Pb and 60 milling of bulk scintillator powder, whereby the diluent con MBO:Pb wherein M is at least one alkaline earth chosen tains a surfactant to prevent agglomeration of the milled from calcium and strontium; alkaline earth chloroborates of a nanoparticles and afterward centrifuging or sedimentation is formula M.B.O.Ci:Pb wherein M is at least one alkaline used to separate out the desired fraction of nanoparticles. earth chosen from barium, calcium, and strontium; lead Some embodiment compacts of the invention combines the doped barium oxyorthosilicates; lead doped calcium oxides; 65 high stopping power and photoelectric cross section of inor lead doped calcium sulfides; lead doped zinc sulfides; lead ganic crystalline Scintillators with the processing costs of doped lanthanum oxides; lead doped calcium silicates; lead plastic Scintillators. US 7,525,094 B2 7 8 Improved light output and transport are expected for nano 30 nm and the presence of hard agglomerates, for example, composites prepared from nanopowder phosphors of a par requires an index matched binder (i.e. matrix material). By ticle size less than 20 nanometers (nm). FIG. 1 shows the contrast, a nanopowder of LaBr:Ce (1.0 mol%) in oleic acid calculated optical attenuation length for a nanocomposite dispersion with an average primary particle size of 10 nm scintillator of the invention. For this material, the index of 5 would not need an index matched matrix material. refraction of the matrix is similar to that of polystyrene (1.59) Particle agglomeration may be caused by a Van der Waals and the index of refraction of the phosphor is approximately type- or Coulomb type-attraction between particles. To pre that of the rare earth oxyorthosilicates (1.80). vent or at least minimize agglomeration, charge may be added It should be noted that for nanopowders having a 5 nm. or subtracted from the nanoparticle Surface to control disper particle size, and for 600 nm photon wavelengths, the optical 10 Sion. This may be accomplished, for example, by adjusting attenuation length is approximately 20 cm. The attenuation the pH of the matrix material see, for example, Sehgal et al. length is the distance through which the incident light inten “Precipitation-Redispersion of Cerium Oxide Nanoparticles sity will be reduced to 1/e or 37% of the initial value. The with Poly(acrylic acid):Toward Stable Dispersions”. Lang attenuation length takes into account both optical absorption muir, volume 21 (2005) pages 9359-9364, incorporated by and scattering losses. For a closer match of the indices of 15 reference herein). FIG. 3, which is taken from Sehgal et al., refraction between the phosphor and matrix, this attenuation shows images of several Solutions and mixtures prepared length will become longer. using about 1 percent cerium oxide (5 nm size) (upper If the indices are exactly, or nearly, matched, attenuation images). Transparent solutions are obtained below pH-3; from optical scattering will become negligible. A nanocom lower). The lower images show the effect of the addition of posite scintillator of cerium doped lanthanum fluoride (LaF: polyacrylic acid, which shifts transparent region to a higher Ce), which has an index of refraction of about 1.65, and pH (pH greater than about 7). poly(p-xylylene), known as parylene which has an index of Agglomeration may also be prevented or minimized by refraction between 1.639-1.669 and a visible light transmis adding Surfactants to the matrix see, for example, Khan et al. sion of 90% is an example of such a nanocomposite. “Interactions of Binders With Dispersant Stabilized Alumina It may be possible for the other scintillators mentioned if 25 Suspensions”. Colloids. Surf. A., vol. 161 (2000) pages 243 the matrix used is a high index of refraction optical quality 257, incorporated by reference herein), or by some other glass. For example, matrix materials such as rare-earth flint method. glasses (Pb containing) have indices of refraction between Monodisperse nanopowder phosphor with a particle size 1.70 and 1.84 and lanthanum flint glasses vary between 1.82 less than 20 nm, have a calculated optical attenuation length and 1.98 depending on the glass composition. 30 greater than 1 mm at emission wavelengths of interest, irre FIG.2a shows a plot of measured light output as a function spective of the index of refraction of the matrix (i.e. the of wavelength for bulk powder and nanopowdered YSiOs: binder) (see FIG. 1). Preferred nanopowder phosphor prop Ce, FIG.2b shows a plot of the measured light output as a erties are a primary particle size of less than about 10 nm, and function of wavelength for bulk powder, and FIG.2c show a the ability to make agglomerate free, chemically and physi similar plot for the nanopowder. According to FIG. 2a-c, the 35 cally stable dispersions. Stable dispersions of oxide nanopo light output of the nanopowdered material is about a factor of wders can be made by, for example, careful control of the pH three higher than for the bulk powder. Also, the emission of the dispersing media. For hygroscopic salts like Lax spectrum is shifted to longer wavelength, and the measured where X=Cl, Br, I, the use of surfactant modifiers such as Stokes' shift is greater for the nanopowder than for the bulk oleic acid in dry solvents such as toluene or dichloromethane powder. The Stokes' shift is the difference between the 40 will allow stable dispersions to be formed. absorption spectrum and emission spectrum of a material, and Nanoparticles with mean particle sizes below 10 nm of rare a larger value for the Stokes' shift indicates a reduced self earth doped lanthanide oxides, orthosilicates or halides may absorption and, therefore, an enhanced light output and be prepared using a variety of chemical and physical methods longer optical attenuation length, which are favorable for that include, but are not limited to, single source precursor, Scintillator applications. 45 hydrothermal, spray pyrolysis or Solution combustion meth Embodiment nanocomposite Scintillators may be prepared ods (see, for example, Chander in “Development of Nano by, for example, dispersing nanopowderphosphor in a matrix phosphors—a Review, Mat. Sci. Eng., volume R 49, (2005) material, or by hot pressing or other mechanical and thermal pages 113-155, incorporated by reference herein). treatment of nanopowder phosphor to form a monolithic Sequential mechanical processing of micron-sized powder structure. The resulting nanocomposite Scintillator must be 50 using a process known in the art as bead milling, has also been Suitably transparent, preserve the intrinsic brightness of the shown to also produce particles having a size P where Ps20 nanopowder phosphor, and homogeneously accommodate nm (see, for example, Kotobuki Industries, “Dispersion of additives such as wavelength shifting compounds, Surfac Agglomerated Nanoparticles by Micromedia Mill, Ultra tants, index matching additives, sintering inhibitors, and the Apex Mill'. J. Soc. Powder. Technol. Jap., volume 41, (2004) like. 55 pages 1-11, incorporated by reference herein). A gradual Matrix materials useful for preparing embodiment nano reduction of the size of the milling media causes a concomi composite scintillators include those where 1) the refractive tant reduction in the particle size. Milling of the resultant index of the matrix is not matched to the refractive index of particles in media less than 50 micron diameter in an appro the nanopowder phosphor; and 2) the refractive index of the priate medium to prevent agglomeration will result in a dis matrix is matched to the refractive index of the nanopowder 60 persion of nanoparticles exhibiting optical transparency. phosphor. Selection of an appropriate phosphor and binder Some unmatched index matrix materials include, but are for a nanocomposite Scintillator for a particular application is not limited to, conventional polymers such as polystyrene also based on parameters that include, but are not limited to, (PS), polyvinyl toluene (PVT), polymethylmethacrylate the mean particle size, particle size distribution, thermal sta (PMMA) or other material with the appropriate wavelength bility, chemical stability and degree and type of agglomera 65 shifters. The dispersed phosphor nanopowder may be added tion present in the nanophosphor material. A nanopowder of into the polymer directly, using an appropriate solvent that YO:Tb (1.0 mol%) with an average primary particle size of would preferably swell the polymer and support the disper US 7,525,094 B2 9 10 sion of the nanoparticles, removal of the solvent and air in a tumbled under flowing dry N, gas for about 2 hours. The vacuum oven would yield a transparent composite. In an material is charged into an injection molder at a barrel tem embodiment, for example, a nanocomposite Scintillator of the perature of 245 degrees Celsius and a pressure of 1000 atm invention is prepared by combining about 50 g of Solution and injected into a 90 degree Celsius heated mold of dimen combustion-produced, 5-nm average primary particle size 5 sion 20 cmx20 cmx3 mm in 1-2 seconds. YO:Tb (1.0 mol%) in about 150 ml of toluene with about 5 The dispersed nanopowder phosphor may also be added wt.% oleic acid, and then bead milling the mixture for about into the monomer and the Subsequent polymerization reac 1 hour using the ULTRA APEX MILL using the 30 um tion could be initiated to form the composite in a process grinding media. About 50 g of polystyrene powder (finely known as gelcasting (see, for example, Tong et al. in "Prepa ground), about 0.75 g of p-terphenyl and about 0.015 g of 10 ration of Alumina by Aqueous Gelcasting. Ceram. Inter. 3-hydroxyflavone are added into this mixture and mechani vol. 30 (2004) pages 2061-2066, incorporated by reference cally stirred and heated to 40 degrees Celsius to slowly herein). In an embodiment, about 50 g of LSO:Ce (1 mol%) remove the toluene. After two days, the resulting gel is poured is added to approximately 100 ml of a premixed solution into two 40 mmx80 mm crystallization dishes and placed into consisting of 20 wt.% deionized water, 10 wt.% DARVANC a vacuum oven. The mixture is evacuated to a pressure of 15 (surfactant), 50 wt.% methacrylamide monomer, 20 wt.% of below -20 inches of mercury and slowly heated to over 300 cross-linker. The nanophosphor powder is added stepwise degrees Celsius over the course of 8 hrs. The result is a and the mixture is ultrasonically homogenized and then de transparent nanocomposite Scintillator that contains about 50 aired for 1 hr. to make a 50 percent by volume slurry. About weight percent of the nanopowder phosphor. 0.75 g of p-terphenyl, about 0.6 g of ammonium persulfate In another embodiment, a nanocomposite Scintillator may (polymerization initiator), about 0.015 g of POPOP and about be prepared as follows. About fifty grams of YSO:Ce (1.0 mol 0.010 g of tetramethylethylene diamine (catalyst) are added %) are dispersed in about 100 ml of an alkaline solution, into this mixture and vigorously stirred to avoid coagulation. ultrasonically homogenized at 200 W for about 30 min to The slurry is then cast into the mold and gelled overnight at a yield a turbid solution. The slow addition of about 10 g temperature of about 65 degrees Celsius to yield a transparent polyacrylic acid, with stirring, is done at about 35 degrees 25 nanocomposite Scintillator that contains approximately 40 Celsius for about 2 hrs, yielding a transparent solution. The wt.% of the nanopowder phosphor. mixture is dried and the recovered powder is redispersed in a There may be cases where the conditions specified above volume of about 100 ml of acetone. About 40 g of polystyrene can not be completely met due to 1) inability to reduce pri powder (finely ground), about 0.60 g of p-terphenyland about mary particles size to below 20 nm, 2) inability to find pH/sur 0.012 g of 1,4-bis(5-phenyloxazol-2-yl)benzene (POPOP) 30 factant conditions to completely eliminate agglomerates or are added into this mixture and mechanically stirred and flocculates or 3) the presence of hard agglomerates due to heated to a temperature of about 30 degrees Celsius to slowly thermal processing of nanophosphors via pyrolysis or com remove the acetone. After about a day, the resulting gel is bustion methods. In these cases, significant advantages of the poured into two 40 mmx80 mm crystallization dishes and invention can still be realized if the matrix material can be placed into a vacuum oven. The mixture is evacuated to a 35 indexed matched, i.e., -0.02sn-ns:0.02. Since the pressure below about -20 in. Hg, and then slowly heated to a refractive index of polymers typically does not exceed 1.7 and temperature of about 300 degrees Celsius over a period of many of the nanophosphor materials of interest have n>1.8, about 8 hours. The result is a transparent plastic scintillator low-melting glasses are obvious choices for index matching containing about 50 weight percent of the nanopowder phos materials. phor. 40 Chalcogenide glasses can be processed below 1000 In an embodiment nanocomposite of the invention, a ther degrees Celsius and can have tunable refractive indices, mosetting polymer can be used as a binder. An example of depending on the glass composition and processing see, for Such a nanocomposite Scintillator may be prepared by adding example: Pandey et al. in "Optical bandgap and optical con about 60 g of La O:Pb (1.0 mol%) to 120 ml of an alkaline stants in SeosTeos, Pb, thin films. Chalcog. Lett., Vol. 2 solution and ultrasonically homogenizing at 200 Watts for 45 (2005) pages 39-44, incorporated by reference herein). These about 30 minto yield a turbid solution. The slow addition of processing conditions are compatible with the oxide-, oxy 12g polyacrylic acid, with stirring, is done at 35C for 2 hrs, orthosilicate-, and pyrosilicate-based nanopowderphosphors yielding a transparent Solution. The mixture is dried and the used with this invention. An embodiment nanocomposite recovered powder tumble coated with 1.8g of an epoxy Scintillator having a chalcogenide glass matrix may be pre silane-coupling agent. The resulting powder is mixed with 37 50 pared by mixing about 50 g of 100 nm average particle diam g of EPOTEK 301-2FL Part A (epoxy) and 13 g of EPOTEK eter sol-gel or hydrothermally processed Ga, La-Ss pow 301-2FL Part B (amine) with 0.75 g of p-terphenyl and 0.015 der with 50 g of dried YSO:Tb (1 mol %) powder. The g of 3-hydroxyflavone. The mixture is ultrasonically homog nanophosphor powder has been previously dispersed in 50 ml enized at 200W for 30 minand then placed in a vacuum oven deionized water with 5 g CALGON (surfactant) at a pH-4.0, where it is then evacuated below -20 inches of Hg and slowly 55 ultrasonically homogenized, filtered, and dried. The powder heated to a temperature of about 100 degrees Celsius over the mixture is poured into glass crystallizing dishes and fired in a course of about 2 hours. The material is left at 100 degrees tube furnace with flowing Argas. The firing temperature is Celsius for about 8hrs. The resulting transparent plastic scin between 780-880 C for 4 hours. tillator contains approximately 50 weight percent of the nan In another embodiment, chalcogenide glasses are prepared opowder phosphor. 60 in a silica tube under vacuum (10 mbar). High purity mate Alternatively, a dispersed nanophosphor could be mixed rials (Ge. As, Se, Pb, Sb, Bi and S) are used for the glass into melted polymer that is Subsequently injection molded, preparation (99.999% purity). Arsenic and selenium present directly yielding the nanocomposite. For example, 40 g of surface oxidation and need to be purified by a thermal treat LaBr:Ce (1.0 mol%) dried nanopowder is bead milled with ment before the synthesis, since arsenic oxide and selenium 40 g of 0.03 mm polystyrene beads for 2 hrs. Scintillating 65 oxide are more volatile than As and Se, respectively. The lead additives consisting of 0.60 g of p-terphenyl and 0.012 g of iodide, contaminated with water, is purified in a microwave POPOP are added into this mixture and mechanically oven before the synthesis (700 W, during 15 min). After US 7,525,094 B2 11 12 purification, the materials are placed in a silica tube, with the ing process (vide supra). For example, a mixture of 50 g of 50 oxide or oxyorthosilicate nanophosphor. Then the tube is nm average particle diameter YSO:Ce (1 mol%) and 8.5g of sealed and heated to 700-800° C. (depending on the compo finely ground manganese carbonate is added to approxi sition) in a rocking furnace. The ampoule is maintained 12h mately 100 ml of a premixed solution consisting of 20 wt.% at this temperature, to reach a good reaction between the 5 deionized water, 10 wt.% DARVANC (surfactant), 50 wt.% different elements and a good homogenization of the melt and methacrylamide monomer, 20 wt.% of cross-linker. The dispersion of the nanophosphor powder. The glass is obtained nanophosphor powder is added stepwise and the mixture is by quenching the melt and annealing the sample near its glass ultrasonically homogenized and then degassed for 1 hr. to transition temperature (T), to reduce the mechanical stress make a 50 volume percent slurry. About 0.75g of p-terphenyl, produced by cooling. The glass is then cut into disks of 1 mm 10 0.6 g of ammonium persulfate, 0.015g of POPOP and 0.010 thickness, which are polished with two parallel sides. g of tetramethylethylene diamine are added into this mixture Alternately, lower temperature hybrid glasses may be and vigorously stirred to avoid coagulation. The slurry is then formed by mixing inorganic halides, oxides, Sulfates or car cast into the mold and gelled at 65° C. overnight to yield a bonates into polystyrene or other plastic Scintillators, transparent Scintillating composite contains approximately examples of which are shown in TABLE 1 below. 15 40 wt.% of the nanophosphor. Pressed monoliths. Hot pressing of ceramics and salts is TABLE 1. known in the art, and transparent monoliths have been pro Melting Refractive duced for many materials, including the common Scintillator Material Point (C.) index 2O Sodium iodide (NaI). In using nanopowder phosphor to pre pare a pressed monolith of the invention, a verythin layer of Calcium sulfate dehydrate, CaSO-2H2O 150 53 the binder must uniformly coat the nanophosphor. A layer Ammonium sulfate, (NH4)2SO 28O 533 Copper(II) sulfate pentahydrate, 110 S43 would have a thickness of less than about 20 nanometers. In CuSO–5H2O this case the matrix material, or sintering inhibitor, need not Magnesium sulfate monohydrate, 150 S84 be index matched to the nanopowder phosphor. An embodi MgSO-H2O 25 ment of Such a monolith may be prepared by, for example, Germanium bromide GeBr 26 627 Calcium oxalate monohydrate, CaCO-H2O 2OO 6S dispersing about 200 g of LaBr:Ce (1.0 mol %) powder in Ammonium thiocyanate NHACNS 150 685 about 500 ml of an alkaline solution by ultrasonic homogeni Lithium nitrate LiNO 261 735 zation at about 200 Watts for about 30 minto yield a turbid Antimony tribromide SbBr. 97 .74 Arsenic (III) oxide, (ASOs) 274 755 30 solution. Next, a transparent solution would be prepared by Manganese (II) carbonate, MinCO 2OO 816 the slow addition to the turbid solution of about 40 grams of Mercuric Chloride HgCl2 277 859 polyacrylic acid, with stirring, at a temperature of about 35 Manganese (III) hydroxide, MnO(OH) 250 2.25 degrees Celsius over a six hour period. The mixture is then dried and the recovered powder is isostatically pressed at a The addition of these index-matching additives can be 35 pressure of about 180 MPa. done in conjunction with the nanophosphor using the tech Another approach to inhibit sintering during pressing for niques described. For example, 50g of Solution combustion nanophosphors is to synthesize the nanophosphor in a core produced 50-nm average primary particle size LSO:Ce (1.0 shell geometry. This approach to nanoparticle synthesis is mol %) in 150 ml of toluene with 5 wt.% oleic acid is bead usually done to protect the nanoparticle Surface from chemi milled for 1 hr. using the Ultra Apex Mill using the 30 um 40 cal quenching of Surface luminescence states. In our case the grinding media. Afterward, 50 g of polystyrene powder, shell properties will be chosen to obviate the need for sinter finely ground, 8.5 g of finely ground arsenic oxide, 0.75 g of ing inhibitors in the core material. A promising example p-terphenyland 0.015g of POPOP are added into this mixture would be LaBr core with a KBr shell. The core-shell mate and mechanically stirred and heated to 40° C. to slowly rials are compatible, as shown by the existence of the remove the toluene. After two days, the resulting gel is poured 45 KLaBrs scintillator. KBrhas a cubic crystal structure and can into two 40 mmx80 mm crystallization dishes and placed into easily be cold pressed. Cold pressing would eliminate the a vacuum oven. The mixture is evacuated below about -20 agglomeration and grain coarsening expected to occur in inches of Hg and slowly heated to about 300 degrees Celsius LaBr at elevated processing temperatures. over a period of about 8 hours. The resulting transparent In cases where there is no intrinsic brightness advantage to plastic Scintillator contains about 45 weight percent of nan- so the nanophosphor as compared to a bulk crystal of cubic opowder phosphor. symmetry there may be no need for a matrix material. For As another example, a dispersed nanopowder phosphor example 400 g of La Os: Bior Pb (1.0 mol%) powder with an could be mixed into melted polymer that was Subsequently average particle size of 100 nm may be pressed isostatically at injection molded, directly yielding the nanocomposite. For a pressure of about 140 MPa and at a temperature of about 250 example, 40 g of LaI:Ce (1.0 mol%) and 3 weight percent 55 degrees Celsius for about 8 hours to obtain a transparent vinyl silane coupling agent, dried nanopowder is bead milled monolith of the invention. with 40 g of 0.03 mm polystyrene beads and 6.5g of antimony Some of the possible radiation detector configurations iodide powder for 2 hrs. Scintillating additives consisting of include mounting the nanocomposite Scintillator directly 0.60 g of p-terphenyl and 0.012 g of POPOP are added into onto the face of a photomultiplier with optical coupling this mixture and mechanically tumbled under flowing dry N, 60 grease; mounting the nanocomposite Scintillator directly onto gas for 2 hrs. The material is charged into an injection molder the face of a photodiode with optical coupling grease; mount at a barrel temperature of 245° C. and a pressure of 1000 atm ing a large area nanocomposite Scintillator onto light-pipe and injected into a 90° C. heated mold of dimension 20 material that directs the scintillation light to one or more cmx20 cmx3 mm in 1-2 s. photomultiplier tubes or photodiodes; and indirect coupling Additionally, the dispersed nanopowderphosphor could be 65 of the scintillation light to fiber optics, which transmits the added into the monomer and the Subsequent polymerization light to a photodiode, photomultiplier tube or CCD camera. reaction could be initiated to form the composite in a gelcast Some of these configurations may be more easily imple US 7,525,094 B2 13 14 mented using a nanocomposite Scintillator prepared with a be used in detectors for proton and neutron radiography, for flexible binder (polydimethylsiloxane (PDMS) for example). positron emission tomography, and for medical radiography. By selecting the appropriate rare earth dopant, the light Current large-area radiographic devices are based on pix emission from the radiation detector can be tailored for either elated single crystals. These devices suffer from disadvan a photomultiplier or a photodiode. X-ray and gamma ray tages associated with non-uniform light output over the large detectors based on photomultipliers, for example, may area of the detector, and from the dark contrastlines that result employ LuSiOs doped with Ce (i.e. LSO:Ce) because the from the seams between the pixels. By contrast, the nanocom emission maximum of LSO:Ce occurs near a wavelength of posite scintillators of this invention have a relatively uniform about 420 nanometers, which is close to the maximum light output and can be made seamless over a large area, response of most photomultipliers. On the other hand, if 10 thereby providing solutions to the aforementioned existing photodiode (silicon photodiode, for example) detection is problems associated with pixelated detectors. desired, YSO:Sm would be more preferable because the Another significant problem associated with the produc maximum emission of LSO:Sm occurs near a wavelength of tion of pixelated detectors relates to the difficulty in produc about 542 nanometers, and thus is better matched to the ing pixels; some materials, such as the known Scintillator maximum response for silicon photodiodes, which have a 15 Gd2SiO5:Ce (GSO:Ce) single crystals are micaceous and maximum response at about 550 nanometers. For a radiation cannot be easily cut into pixels and polished for use in radio detector used for neutron detection, an oxyorthosilicate of graphic imaging. Large area detectors of this invention gadolinium would be employed because gadolinium has the employing a GSO:Ce Scintillating powder would not require largest known cross section for thermal neutrons; the decay GSO:Ce single crystal pixels; the bulk GSO:Ce could be scheme yields conversion electrons that excite the rare earth ground into powder, mixed with a flexible polymer binder dopant to produce scintillations. Accordingly, GdSiOs Such as PDMS, and pressed to form a large area, seamless doped with Ce (i.e. GSO:Ce) would be employed for a pho composite that can be used for radiation detection of this todetector using photomultipliers, while GSO:Sm would be invention. employed for a photodetector using photodiodes. In this In Summary, composites of fast, bright and dense rare-earth example matrix materials or nanophosphor material 25 doped Scintillating nanopowder phosphor mixed with a enhanced with Li and or 'B would further enhance the binder are prepared. These nanocomposite Scintillators are performance due to increased energy deposition in the matrix used with photomultipliers or photodiodes for inexpensive due to enhanced thermal neutron cross sections and large radiation detectors that may be useful in applications related kinetic energy release in the capture reactions. Furthermore, to, but not limited to, Homeland Security, International Safe thermalization of fast neutrons can be efficiently performed 30 guards, Scientific Research and Medical Imaging. The nano by the large hydrogenic atomic fraction that is present in composite Scintillators and detectors using them may provide many polymers, such as polyethylene. an energy resolution comparable to High Purity Germanium Nanocomposite Scintillators and detectors of the present and cost and size comparable to a plastic Scintillator. invention may be used for large-area radiation detection Such The foregoing description of the invention has been pre as portal monitors. There currently is a need for relatively 35 sented for purposes of illustration and description and is not inexpensive detectors for portal monitors related to the need intended to be exhaustive or to limit the invention to the for increased transportation security at airports, seaports, and precise form disclosed, and obviously many modifications bus and rail terminals, especially after the September 11 and variations are possible in light of the above teaching. attack on the World Trade Center. The radiation detectors of The embodiments were chosen and described in order to this invention may be used for these types of monitors. The 40 best explain the principles of the invention and its practical nanocomposite Scintillators may also be used in radiation application to thereby enable others skilled in the art to best detectors with complex and irregular shapes. utilize the invention in various embodiments and with various Embodiment nanopowder phosphors may include rare modifications as are Suited to the particular use contemplated. earth doped oxyorthosilicates. Other materials such as crys It is intended that the scope of the invention be defined by the talline NaI:Tl, BGO, semiconductors, and noncrystalline 45 claims appended hereto. organic materials may also be used. What is claimed is: In addition to LSO:Ce LSO:Sm and GSO:Ce, other pref 1. A nanocomposite Scintillator consisting essentially of a erable rare earth doped oxyorthosilicates include LYSO:Ce mixture of a Solid binder and at least one nanopowder phos (see U.S. Pat. No. 6,323,489 to McClellan entitled “Single phor of a lanthanide halide having a formula CeX or Lax: Crystal Scintillator,” which issued on Nov. 27, 2001, incor 50 Ce wherein La is selected from lanthanum (La) and yttrium porated by reference herein, which describes cerium acti (Y), and wherein X is selected from Cl, Br, and I, and wherein vated oxyorthosilicate Scintillator having the having the gen said nanopowderphosphoris an amount greater than about 30 eral formula Lue YCeSiO5, wherein 0.05sxs 1.95 and percent by Volume. 0.001szs0.02, which is abbreviated as LYSO:Ce), and the 2. The nanocomposite Scintillator of claim 1, wherein said rare earth doped oxyorthosilicates described in U.S. Pat. No. 55 binder is transparent to light emitted by the rare earth doped 6,689,298 to McClellanetal. entitled “Crystalline Rare-Earth nanopowder phosphor. Activated Oxyorthosilicate Phosphor” which issued on Feb. 3. The nanocomposite scintillator of claim 1, wherein said 10, 2004, incorporated by reference herein, which describes a binder comprises a polymer or a polymer with an index variety of single crystal phosphors such lutetium oxyortho matching additive. silicate (LSO), gadolinium oxyorthosilicate (GSO), yttrium 60 4. The nanocomposite Scintillator of claim 1, wherein said oxyorthosilicate (YSO), lutetium yttrium (LYSO) phosphor, binder comprises a chalcogenide, flint, or lanthanum flint lutetium gadolinium (LGSO) phosphor, and gadolinium glass. yttrium (GYSO) phosphor that have been doped with rare 5. The nanocomposite scintillator of claim 1, wherein said earth dopants Sm, Tb, Tm, Eu, Yb, and Pr. These rare-earth nanopowder phosphor comprises a first refractive index and doped oxyorthosilicates are preferable due to their tailorable 65 the Solid binder comprises a second refractive index, and optical emission, highlight output and high density. Not only wherein the first refractive index and second refractive index are they bright and dense, they are also fast and therefore can are equal. US 7,525,094 B2 15 16 6. The compact of claim 1, wherein said nanopowderphos 19. The radiation detection method of claim 18, wherein phor comprises a first refractive index n and the solid the amount of nanophosphor in the nanocomposite Scintilla binder comprises a second refractive index in rii and tor is greater than about 40 percent by volume. wherein -0.02sn-ns:0.02. 20. The radiation detection method of claim 18, wherein 7. The nanocomposite scintillator of claim 1, wherein the the amount of nanophosphor in the nanocomposite Scintilla nanopowder phosphor comprises a particle size P, wherein tor is greater than about 45 percent by volume. Ps 100 nanometers. 21. The radiation detection method of claim 18, wherein 8. The nanocomposite scintillator of claim 1, wherein the the amount of nanophosphor in the nanocomposite Scintilla nanopowder phosphor comprises a particle size P, wherein tor is greater than about 50 percent by volume. Ps20 nanometers. 10 22. The radiation detection method of claim 18, wherein 9. The nanocomposite scintillator of claim 1, wherein the the amount of nanophosphor in the nanocomposite Scintilla nanopowder phosphor comprises a particle size P, wherein tor is greater than about 55 percent by volume. Ps 10 nanometers. 23. The radiation detection method of claim 18, wherein 10. The nanocomposite scintillator of claim 1, wherein the the amount of nanophosphor in the nanocomposite Scintilla nanopowder phosphor comprises a particle size P, wherein 15 tor is greater than about 60 percent by volume. Ps 5 nanometers. 24. A radiation detector, comprising: 11. The nanocomposite scintillator of claim 1, wherein the nanocomposite Scintillator consisting essentially of a mix amount of nanophosphor in the nanocomposite Scintillator is ture of a solid binder and a lanthanide halide having a greater than about 35 percent by volume. formula CeX or Lax:Ce wherein La is selected from 12. The nanocomposite scintillator of claim 1, wherein the lanthanum (La) and yttrium (Y), and wherein X is amount of nanophosphor in the nanocomposite Scintillator is selected from Cl, Br, and I wherein the nanopowder greater than about 40 percent by volume. phosphor is an amount greater than about 30 percent by 13. The nanocomposite scintillator of claim 1, wherein the Volume; and amount of nanophosphor in the nanocomposite Scintillator is a photodetector optically coupled to said nanocomposite greater than about 45 percent by volume. 25 scintillator. 14. The nanocomposite scintillator of claim 1, wherein the 25. The radiation detector of claim 24, wherein said pho amount of nanophosphor in the nanocomposite Scintillator is todetector comprises a photodiode or photomultiplier. greater than about 50 percent by volume. 26. The radiation detector of claim 24, wherein the amount 15. The nanocomposite scintillator of claim 1, wherein the of nanophosphor in the nanocomposite Scintillator is greater amount of nanophosphor in the nanocomposite Scintillator is 30 greater than about 55 percent by volume. than about 35 percent by volume. 16. The nanocomposite scintillator of claim 1, wherein the 27. The radiation detector of claim 24, wherein the amount amount of nanophosphor in the nanocomposite Scintillator is of nanophosphor in the nanocomposite Scintillator is greater greater than about 60 percent by volume. than about 40 percent by volume. 17. A radiation detection method, comprising: 35 28. The radiation detector of claim 24, wherein the amount exposing a compact to ionizing radiation, wherein the com of nanophosphor in the nanocomposite Scintillator is greater pact comprises a nanocomposite Scintillator consisting than about 45 percent by volume. essentially of a mixture of a solid binder and a lanthanide 29. The radiation detector of claim 24, wherein the amount halide having a formula CeX or LaX:Ce wherein La is of nanophosphor in the nanocomposite Scintillator is greater Selected from lanthanum (La) and yttrium (Y), and 40 than about 50 percent by volume. wherein X is selected from Cl, Br, and I wherein the 30. The radiation detector of claim 24, wherein the amount nanopowder phosphor is an amount greater than about of nanophosphor in the nanocomposite Scintillator is greater 30 percent by volume; and than about 55 percent by volume. detecting luminescence from the nanocomposite Scintilla 31. The radiation detector of claim 24, wherein the amount tOr. 45 of nanophosphor in the nanocomposite Scintillator is greater 18. The radiation detection method of claim 17, wherein than about 60 percent by volume. the amount of nanophosphor in the nanocomposite Scintilla tor is greater than about 35 percent by volume.