Inventors: Stephen M. Hanrahan, Gautam Gundiah, Gregory Bizarri, Anurag Chaudhry, Andrew Canning, Edith Bourret-Courchesne, Stephen E. Derenzo

RELATEDPATENTAPPLICATIONS

[0001] The application claims priority to U.S. Provisional Patent Application Ser. No. 61/176,454, filed May 7, 2009, which is herein incorporated by reference in its entirety.

STATEMENT OF GOVERNMENTAL SUPPORT

[0002] The invention was made with government support under Grant No. HSHQDC-07-X- 00170 awarded by the U.S. Department of Homeland Security, and Contract No. DE-AC02- 05CH11231 awarded by the U.S. Department of Energy. The government has certain rights in the invention.

FIELD OF THE INVENTION

[0003] The present invention is in the field of inorganic crystals with scintillation properties useful as gamma-ray detectors.

BACKGROUND OF THE INVENTION

[0004] The need for radiation detecting materials has been at the forefront of materials research in recent years due to applications in national security, medical imaging, X-ray detection, oil well logging, and high-energy physics. Essential qualities that a scintillator must possess are high light yields, fast luminescence decay (below 1000 ns), good stopping power, high density, good energy resolution, ease of growth, proportionality, and stability under ambient conditions. La _x Br ₃ :Cei_ _x (E.V.D. van Loef et al, Appl. Phys. Lett., 2001, 79, 1573) and Sr _x I ₂ :Eui_ _x (N. Cherepy et al, Appl. Phys. Lett. 2007, 92, 083508) are present day benchmark materials that satisfy some of the desired criteria, but their application is limited due to the extreme hygroscopic nature.

[0005] Barium mixed halides, such as barium fluoride iodide (BaFI) doped with Eu, have been studied as a photostimulable phosphor since the mid 1980's for applications in computed radiology (K. Takahashi et al, J. Electrochem. Soc, 1985, 132, 1492). However, none of these have been identified as candidate scintillators for detecting gamma rays.

SUMMARY OF THE INVENTION

[0006] The present invention provides for a composition comprising an inorganic scintillator comprising a lanthanide-doped barium mixed halide useful for detecting nuclear material.

[0007] The present invention provides for an inorganic scintillator having the formula:

Bai_ _y X _X X ₂ - _x :Ln _y ;

wherein X ¹ is a first halogen element, X ² is a second halogen element, X ¹ and X ² are not the same halogen element, Ln is a lanthanide with a valence of 2+, x has a value having the range 0<x<2, and y has a value having the range 0<y<l, and the inorganic scintillator is a single crystal having at least one dimension of a length of at least 1 mm, at least 5 mm, at least 1 cm, or at least 3 cm, or a length at least sufficient to stop or absorb gamma-radiation.

[0008] The present invention provides for an inorganic scintillator having the formula:

Bai_ _y X _X X ₂ - _x :Ln _y ;

wherein X ¹ is a first halogen element, X ² is a second halogen element, X ¹ and X ² are not the same halogen element, Ln is a lanthanide with a valence of 2+, x has a value having the range 0<x<2, and y has a value having the range 0<y<l; with the proviso that the inorganic scintillator is not BaFChEu ²⁺ , BaFBnEu ²⁺ , BaFLEu ²⁺ , BaBrChEu ²⁺ , BaClLEu ²⁺ , BaBrLEu ²⁺ , EuFCl, EuFBr, and/or EuFI.

[0009] The present invention provides for an inorganic scintillator having the formula:

Bai_ _y X _X X ₂ - _x :Ln _y ;

wherein X ¹ is a first halogen element, X ² is a second halogen element, X ¹ and X ² are not the same halogen element, Ln is a lanthanide with a valence of 2+ and it is not Eu ²⁺ , x has a value having the range 0<x<2, and y has a value having the range 0<y<l .

[0010] The present invention provides for an inorganic scintillator having the formula: wherein X ¹ is a first halogen element, X ² is a second halogen element, X ¹ and X ² are not the same halogen element, Ln is a lanthanide with a valence of 3+, M is an alkaline metal with an atomic number smaller than the atomic number of Ba, x has a value having the range 0<x<2, and y has a value having the range 0<y<0.5; or,

(b) Ba _1-2 X ¹ _X X ² ^Ln ₂ ;

wherein X ¹ is a first halogen element, X ² is a second halogen element, X ¹ and X ² are not the same halogen element, Ln is a lanthanide with a valence of 3+, x has a value having the range 0<x<2, and z has a value having the range 0<z<0.1.

[0011] The present invention provides for an inorganic scintillator described and/or having the properties described in Examples 1, 2, and 3.

[0012] The present invention also provides for a composition comprising essentially of a mixture of halide salts useful for producing the inorganic scintillator. When the Ln has a valence of 2+, the mixture comprises essentially of a solid BaX ^x ₂ , optionally a solid BaX ² ₂ , optionally a solid LnX^, and optionally a solid LnX ² ₂ ; wherein the mixture has a stoichiometry of about (1-y) number of Ba atoms: x number of X ¹ atoms: (2-x) number of X ² atoms: y number of Ln atoms, x has a value having the range 0<x<2, and y has a value having the range 0<y<l; X ¹ is a first halogen element; X ² is a second halogen element; and X ¹ and X ² are not the same halogen element. When the Ln has a valence of 3+, the mixture comprises essentially of a solid BaX ^x ₂ , optionally a solid BaX ² ₂ , optionally a solid LnX^, optionally a solid LnX ² ₃ , optionally a solid MX ¹ , and optionally a solid MX ² ; wherein the mixture has a stoichiometry of about (a) (l-2y) number of Ba atoms: x number of X ¹ atoms: (2-x) number of X ² atoms: y number of Ln atoms: y number of M atoms, x has a value having the range 0<x<2, and y has a value having the range 0<y<0.5; X ¹ is a first halogen element; X ² is a second halogen element; and X ¹ and X ² are not the same halogen element; or (b) (1-z) number of Ba atoms: x number of X ¹ atoms: (2-x) number of X ² atoms: z number of Ln atoms, x has a value having the range 0<x<2, and z has a value having the range 0<y<0.1; X ¹ is a first halogen element; X ² is a second halogen element; and X ¹ and X ² are not the same halogen element.

[0013] The halide salts can be powdered crystals. The halide salts are essentially pure. Such halide salts are commercially available. [0014] The present invention further provides for a method for producing the composition comprising an inorganic scintillator as described herein comprising: (a) providing a composition comprising essentially of a mixture of halide salts useful for producing the inorganic scintillator as described herein, (b) heating the mixture so that the halide salts start to react, and (c) cooling the mixture to room temperature such that the composition comprising an inorganic scintillator is formed.

[0015] The invention provides for a device comprising a composition comprising an inorganic scintillator or lanthanide-doped barium mixed halide of the present invention and a photodetector. The device is useful for the detection of an ionizing radiation, such as gamma radiation. The device is useful for industrial, medical, protective and defensive purpose or in the oil and nuclear industry.

[0016] In some embodiments of the invention, the device is a gamma ray (or like radiation) detector which comprises a single crystal of lanthanide-doped barium mixed halide. When assembled in a complete detector, the scintillator crystal is optically coupled, either directly or through a suitable light path, to the photosensitive surface of a photodetector for generation of an electrical signal in response to the emission of a light pulse by the scintillator. The inorganic scintillator of the invention possesses certain important characteristics, most notably high light output, very short decay time and high detection efficiency, that make it superior to prior scintillators as a gamma ray or like radiation detector, in particular for homeland security applications, such as nuclear material detection.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The foregoing aspects and others will be readily appreciated by the skilled artisan from the following description of illustrative embodiments when read in conjunction with the accompanying drawings.

[0018] Figure 1 shows the X-ray luminescence for a BaFLEu ²⁺ single crystal sample.

[0019] Figure 2 shows the decay curves for a BaFLEu ²⁺ single crystal sample.

[0020] Figure 3 shows a BaBrLEu ²⁺ single crystal: inside the quartz ampoule (panel A), and out of the ampoule (panel B). The cross-sectional width of the crystal is about 1 cm.

[0021] Figure 4 shows the photo luminescence spectrum showing an emission wavelength at 450 nm for a BaBrLEu ²⁺ single crystal.

[0022] Figure 5 shows the X-ray luminescence decay curves for a BaBrLEu ²⁺ single crystal.

[0023] Figure 6 shows the response of the crystal to gamma radiation (pulse height measurement) of a BaBrLEu ²⁺ single crystal.

[0024] Figure 7 is a diagrammatic view of one embodiment of a scintillation detector in accordance with the present invention.

[0025] Figure 8 shows the plot of luminescent intensity (estimated photons/MeV) as a function OfEu ²⁺ concentration in BaBrI.

[0026] Figure 9 shows the plot of the amount of luminescence with decay times of less than 500 ns (estimated photons/MeV) as a function OfEu ²⁺ concentration in BaBrI.

[0027] Figure 10 shows the photoluminescence spectrum for a BaClLEu ²⁺ sample.

[0028] Figure 11 shows the decay curves for a BaClL5% Eu ²⁺ sample.

[0029] Figure 12 shows the fraction of luminescence intensity decaying in the first 1,000 ns as a function of the Eu ²⁺ concentration in BaClI.

DETAILED DESCRIPTION OF THE INVENTION

[0030] Before the present invention is described, it is to be understood that this invention is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

[0031] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.

[0032] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited.

[0033] As used in the specification and the appended claims, the singular forms "a", "an", and "the" include plural references unless the context clearly dictates otherwise. Thus, for example, reference to a "crystal" includes a single crystal as well as a plurality of crystals.

[0034] The terms "optional" or "optionally" as used herein mean that the subsequently described feature or structure may or may not be present, or that the subsequently described event or circumstance may or may not occur, and that the description includes instances where a particular feature or structure is present and instances where the feature or structure is absent, or instances where the event or circumstance occurs and instances where it does not.

[0035] These and other objects, advantages, and features of the invention will become apparent to those persons skilled in the art upon reading the details of the invention as more fully described below.

The Inorganic Scintillators

[0036] The inorganic scintillator can be in a polycrystalline powder or a single crystal form. The crystal can be any size with an average volume of at least 0.001 mm ³ , at least 1 mm ³ , at least 5 mm , at least 10 mm , at least 100 mm , at least 3 cm , or at least 1 cm . The crystal can be any size with at least one dimension of the crystal having a length of at least 100 μm, at least 1 mm, at least 2 mm, at least 5 mm, at least 1 cm, at least 3 cm, at least 5 cm, or at least 10 cm. In some embodiments of the invention, the crystal has at least one dimension having a length that is of sufficient length, or depth, to stop or absorb gamma-radiation in order to electronically detect the gamma-radiation.

[0037] The lanthanide atoms in the inorganic scintillator substitute for the barium atoms.

[0038] The inorganic scintillators of the present invention are useful as they are scintillators and they produce a useful bright and fast scintillation in response to irradiation by short- wavelength high energy light, such as x-ray or gamma rays. The crystals of the inorganic scintillator also have the added advantage of having the property of readily growing into crystals. Large size crystals can be grown by the following technique: Bridgman growth and related techniques, Czochralski growth and related techniques, the traveling heater method and related techniques.

[0039] In some embodiments of the invention, the lanthanide-doped barium mixed halide has the formula:

wherein X ¹ is a first halogen element, X ² is a second halogen element, X ¹ and X ² are not the same halogen element, Ln is a lanthanide with a valence of 2+, x has a value having the range 0<x<2, and y has a value having the range 0<y<l;

(b) Ba _LZy X ¹ _X X ² _Z-X iLH _y ^ _y ;

wherein X ¹ is a first halogen element, X ² is a second halogen element, X ¹ and X ² are not the same halogen element, Ln is a lanthanide with a valence of 3+, M is an alkaline metal with an atomic number smaller than the atomic number of Ba, x has a value having the range 0<x<2, and y has a value having the range 0<y<0.5; or,

(c) Ba ₁ . _z X ¹ _x X ² ₂ . _x :Ln _z ;

wherein X ¹ is a first halogen element, X ² is a second halogen element, X ¹ and X ² are not the same halogen element, Ln is a lanthanide with a valence of 3+, x has a value having the range 0<x<2, and z has a value having the range 0<z<0.1.

[0040] X ¹ and X ² are each independently F, Cl, Br, or I. Ln can be La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu. M can be Li, Na, K, Rb, or Cs. Examples of lanthanides with a valence of 2+ are Eu and Yb. Examples of lanthanides with a valence of 3+ are Ce and Yb. The inorganic scintillator is a scintillator that produces a bright luminescence upon irradiation by a suitable radiation, such as gamma radiation.

[0041] In some embodiments of the invention, the lanthanide-doped barium mixed halide has the formula:

wherein X ¹ is Cl, Br, or I, X ² is Cl, Br, or I, X ¹ and X ² are not the same halogen element, Ln is a lanthanide with a valence of 2+ (such as Eu ²⁺ ), x has a value having the range 0<x<2, and y has a value having the range 0<y<l;

(b) Ba _LZy X ¹ _X X ² _Z-X iLH _y ^ _y ;

wherein X ¹ is Cl, Br, or I, X ² is Cl, Br, or I, X ¹ and X ² are not the same halogen element, Ln is a lanthanide with a valence of 3+ (such as Ce ³⁺ ), M is an alkaline metal with an atomic number smaller than the atomic number of Ba (such as Li ⁺ or Na ⁺ ), x has a value having the range 0<x<2, and y has a value having the range 0<y<0.5; or,

(c) Ba _L2 X ¹ _X X ² ^Ln ₂ ;

wherein X ¹ is Cl, Br, or I, X ² is Cl, Br, or I, X ¹ and X ² are not the same halogen element, Ln is a lanthanide with a valence of 3+ (such as Ce ³⁺ ), x has a value having the range 0<x<2, and z has a value having the range 0<z<0.1.

[0042] In some embodiments of the invention, the mixed halide combination is: (i) X ¹ is Cl and X ² is Br; (ii) X ¹ is Cl and X ² is I; or, (iii) X ¹ is Br and X ² is I.

[0043] In some embodiments of the invention, the lanthanide-doped barium mixed halide has the formula:

(a) Bai_ _y F _x X ₂ _ _x :Ln _y ;

wherein X is Cl, Br, or I, Ln is a lanthanide with a valence of 2+ (such as Eu ²⁺ ), x has a value having the range 0<x<2, and y has a value having the range 0<y<l;

(b) Bai_ _2y F _x X ₂ .χ:Ln _y ,M _y ;

wherein X is Cl, Br, or I, Ln is a lanthanide with a valence of 3+ (such as Ce ), M is an alkaline metal with an atomic number smaller than the atomic number of Ba (such as Li ⁺ or Na ⁺ ), x has a value having the range 0<x<2, and y has a value having the range 0<y<0.5; or,

(c) Bai_ _z F _x X ₂ - _x :Ln _z ;

wherein X is a Cl, Br, or I, Ln is a lanthanide with a valence of 3+ (such as Ce ³⁺ ), x has a value having the range 0<x<2, and z has a value having the range 0<z<0.1.

[0044] In some embodiments of the invention, x has a value having the range 0.1<x<1.9, or 0.9<x<l .1. In some embodiments of the invention, x has a value of 1.

[0045] In some embodiments of the invention, when the Ln has a valence of 2+, y has a value having the range 0.001<y<l . In some embodiments of the invention, when the Ln has a valence of 2+, y has a value having the range 0.001<y<0.5. In some embodiments of the invention, when the Ln has a valence of 2+, y has a value having the range 0.001<y<0.3. In some embodiments of the invention, when the Ln has a valence of 2+, y has a value having the range 0.05<y<0.15. In some embodiments of the invention, when the Ln has a valence of 2+, y has a value having the range 0.05<y<0.1.

[0046] In some embodiments of the invention, when the Ln has a valence of 3+, y has a value having the range 0.001<y<0.5. In some embodiments of the invention, when the Ln has a valence of 3+, y has a value having the range 0.001<y<0.2. In some embodiments of the invention, when the Ln has a valence of 3+, y has a value having the range O.Ol≤y≤O.l.

[0047] In some embodiments of the invention, when the Ln has a valence of 3+, z has a value having the range 0.001<z<0.1. In some embodiments of the invention, when the Ln has a valence of 3+, z has a value having the range O.Ol≤z≤O.l. In some embodiments of the invention, when the Ln has a valence of 3+, z has a value having the range 0.001<z<0.05. In some embodiments of the invention, when the Ln has a valence of 3+, z has a value having the range O.OOl≤z≤O.01.

Characterization of the Inorganic Scintillators

[0048] The crystals of the invention can be characterized using a variety of methods. The crystals can be characterized regarding X-ray diffractometry, X-ray luminescence spectra, X- ray fluorescence for concentration of activators, and/or pulsed X-ray time response. X-ray diffractometry determines the composition of crystalline solids, such as crystalline phase identification. X-ray luminescence spectra determines the spectra components. Pulsed X-ray time response determines luminosity, decay times, and fractions. X-ray luminescence is used to determine the relative luminosity of a crystal. An X-ray excited emission spectra is obtained of a crystal by irradiating the crystal with an X-ray and collecting the emission light at 90° by a CCD detector.

[0049] In some embodiments of the invention, the luminosity of the inorganic scintillator is more than the luminosity of yttrium aluminium perovskite (YAP) and/or bismuth germanate (BGO). In further embodiments of the invention, the luminosity of the inorganic scintillators is more than double the luminosity of YAP and/or BGO.

[0050] The inorganic scintillator crystals which contain fluorine are not sensitive to moisture and can be handled and stored under ambient conditions. The inorganic scintillator crystals which do not contain fluorine are less sensitive to moisture than SrI ₂ IEu.

[0051] In some embodiments of the invention, the single crystal inorganic scintillators, such as BaFLEu, which contain fiuroine, have a luminescence output of about 30,000, 40,000, or 50,000 photons/MeV, and a decay of about 99% in less than 1 μs.

[0052] In some embodiments of the invention, the single crystal inorganic scintillators, such as BaBrLEu, which do not contain fluorine, have a luminescence output of at least 75,000 photons/MeV, and a decay of about 98% in less than 700 ns or 1 μs.

Preparation of the Inorganic Scintillators

[0053] The inorganic scintillators of the invention can be prepared using a variety of methods. For example, the crystals useful for fabrication of luminescent screens can be prepared by a solid-state reaction aided, or optionally not aided, by a flux of halides as described herein. In some embodiments, the single crystals are prepared by providing a composition comprising essentially of a mixture of halide salts useful for producing the inorganic scintillator as described herein. The mixture is heated to a temperature of up to about 900°C using a simple programmable furnace to produce a reactive molten mixture. The reaction is maintained at temperature for the mixture to fully react and produce the desired melt. The resultant molten product of reaction is then cooled slowly at about 2 to 5°C/minute.

[0054] A particular method of preparing the inorganic scintillator of the invention is as follows: Bridgman growth and related techniques, Czochralski growth and related techniques, the traveling heater method and related techniques. These methods can be used to produce the inorganic scintillator as single crystals on a one-by-one basis. The crystals containing fluorine can be produced using the Bridgman growth technique. The Czochralski growth method may not be suitbale for producing the crystals containing fluorine.

[0055] The Bridgman growth technique is a directional solidification process. The technique involves using an ampoule containing a melt which moves through an axial temperature gradient in a furnace. Single crystals can be grown using either seeded or unseeded ampoules. The Bridgman growth technique is taught in Robertson J. M., 1986, Crystal growth of ceramics: Bridgman-Stockbarger method in Bever: 1986 "Encyclopedia of Materials Science and Engineering" Pergamon, Oxford pp. 963-964, which is incorporated by reference.

[0056] The Czochralski growth technique comprises a process of obtaining single-crystals in which a single crystal material is pulled out of the melt in which a single-crystal seed is immersed and then slowly withdrawn; desired optical properties and doping level is accomplished by adding dopants to the melt. The Czochralski growth technique is taught in J. Czochralski, "Ein neues Verfahren zur Messung der Kristallisationsgeschwindigheit der Metalle" [A new method for the measurement of the crystallization rate of metals], Z. Phys. Chemie 92 (1918) 219-221, which is incorporated by reference. The method is well-know to those skilled in the art in producing a wide variety of componds, including semiconductors and scintillator materials (such as LaBr ₃ ICe).

[0057] The traveling heater method is described in Triboulet, Prog. Cryst. Gr. Char. Mater., 128, 85 (1994) and Funaki et al, Nucl. Instr. And Methods, A 436 (1999), which are incorporated in their entireties by reference.

[0058] A particular method of preparing inorganic scintillators of the invention is the ceramic method which comprises the following steps: The reactant mixture is placed in a container, such as a glove box, filled with one or more inert gas, such as nitrogen gas. The container is under a very dry condition. The dry condition is required due to the hygroscopic nature of the halides within the reactant mixture. The two or more powder reactants are ground together, such as with a mortar and pestle, for a sufficient period, such as about 10 minutes, to produce a reactant mixture. When Ln halide is added to the powder reactants for grinding, methanol can be further added, and grinding can take place until the mixture appears dry. The reactant mixture is sintered under high temperature and pressure.

[0059] In some embodiment of the invention, the single crystals of the inorganic scintillator can be grown by melting and re-solidifying the pre-synthesized compounds in powder form, such as described herein, or directly from melting the mixtures of the halides salts and lanthanide halides used as activators. To grow best performing crystals the starting compounds might need to be purified further by zone refining.

[0060] Growing the single crystal involves loading the mixtures, such as described herein, in a quartz ampoule in a dry environment and sealing the ampoule using a high temperature torch, maintaining the dry environment at a reduced pressure, in the ampoule. The ampoule is then placed in a furnace. The growth of the crystal can be performed by a variation of the known vertical "Bridgman" technique. The compound is melted, let to homogenized at a temperature above the melting point and the compound is solidified in a directional manner in a temperature gradient. The ampoule is shaped to provide a nucleation site at the bottom (conical shape). The solidification front moves upward. Horizontal configurations and other growth techniques such as Czochralski (may need to pressurized the growth chamber) could be used.

[0061] The resulting crystals are then characterized by the methods described herein. The resulting crystals also have properties similar to those described herein.

Application of the Inorganic Scintillators

[0062] The present invention provides for a gamma ray or x-ray detector, comprising: a scintillator composed of a transparent single crystal of the inorganic scintillator of the present invention, and a photodetector optically coupled to the scintillator for producing an electrical signal in response to the emission of a light pulse by the scintillator.

[0063] The inorganic scintillators of this invention have many advantages over other known crystals. The inorganic scintillators produce a luminescence in response irradiation, such as irradiation by alpha-, beta-, or gamma-radiation, that is brighter and faster than known and commercially used scintillators. The scintillating crystals have a number of applications as detectors, such as in the detection of gamma-ray, which has use in national security, such as for detection of nuclear materials, and medical imaging applications. [0064] The invention is useful for the detection of ionizing radiation. Applications include medical imaging, nuclear physics, nondestructive evaluation, treaty verification and safeguards, environmental monitoring, and geological exploration. This will be a major improvement, providing much finer resolution, higher maximum event rates, and clearer images.

[0065] Also, Ce activated inorganic scintillator crystals of the present invention can be useful in positron emission tomography (PET).

[0066] The invention also relates to the use of the scintillating material above as a component of a detector for detecting radiation in particular by gamma rays and/or X-rays. Such a detector especially comprises a photodetector optically coupled to the scintillator in order to produce an electrical signal in response to the emission of a light pulse produced by the scintillator. The photodetector of the detector may in particular be a photomultiplier, photodiode, or CCD sensor.

[0067] A particular use of this type of detector relates to the measurement of gamma or x-ray radiation, such a system is also capable of detecting alpha and beta radiation and electrons. The invention also relates to the use of the above detector in nuclear medicine apparatuses, especially gamma cameras of the Anger type and positron emission tomography scanners (see, for example C. W. E. Van Eijk, "Inorganic Scintillator for Medical Imaging", International Seminar New types of Detectors, 15 19 May 1995—Archamp, France. Published in "Physica Medica", Vol. XII, supplement 1, June 96; hereby incorpoaretd by reference).

[0068] In another particular use, the invention relates to the use of the above detector in detection apparatuses for oil drilling, (see, for example "Applications of scintillation counting and analysis", in "Photomultiplier tube, principle and application", chapter 7, Philips; hereby incorporated by reference).

[0069] One embodiment of the invention is shown in Figure 7 which shows a gamma ray detector. The detector can be one as described in U.S. Patent No. 4,958,080, hereby incorporated by reference. It will be understood, of course, that the utility of the novel single crystal inorganic scintillator of the invention is not limited to the detection of gamma radiation but that it has general application to the detection of other types of like radiation, e.g. X-rays, cosmic rays, and energetic particles. [0070] In Figure 7, a single crystal inorganic scintillator 10 is shown encased within the housing 12 of a gamma ray detector. One face 14 of the scintillator is placed in optical contact with the photosensitive surface of a photomultiplier tube 16. Alternatively, the light pulses could be coupled to the photomultiplier via light guides or fibers, lenses, mirrors, or the like. The photomultiplier can be replaced by any suitable photodetector such as a photodiode, microchannel plate, etc. In order to direct as much of each light flash to the photomultiplier as possible, the other faces 18 of the inorganic scintillator are preferably surrounded or covered with a reflective material, e.g. Teflon tape, magnesium oxide powder, aluminum foil, or titanium dioxide paint. Light pulses emitted by the crystal inorganic scintillator upon the incidence of radiation are intercepted, either directly or upon reflection from the surfaces 18, by the photomultiplier, which generates electrical pulses or signals in response to the light pulses. These electrical output pulses are typically first amplified and then subsequently processed as desired, e.g. in a pulse height amplifier, to obtain the parameters of interest regarding the detected radiation. The photomultiplier is also connected to a high voltage power supply, as indicated in Figure 7. Other than the inorganic scintillator, all of the components and materials referred to in connection with Figure 7 are conventional, and thus need not be described in detail.

[0071] It is to be understood that, while the invention has been described in conjunction with the preferred specific embodiments thereof, the foregoing description is intended to illustrate and not limit the scope of the invention. Other aspects, advantages, and modifications within the scope of the invention will be apparent to those skilled in the art to which the invention pertains.

[0072] All patents, patent applications, and publications mentioned herein are hereby incorporated by reference in their entireties.

[0073] The invention having been described, the following examples are offered to illustrate the subject invention by way of illustration, not by way of limitation.

EXAMPLE 1

Characterization of BaFIrEu

[0074] Single crystals of the composition BaFLEu are obtained by the Bridgman growth technique using commercial chemicals without further purification. A melting temperature of 96O ⁰ C and a homogenization time of 2 hours is used. The cooling rate (or directional solidification rate) is 1 mm/hour in a temperature gradient of 5O ⁰ C/ cm. Presented in Figures 1 and 2 are X-ray luminescence and decay curves for a BaFLEu sample. The emission maximum is at -405 nm and the estimated luminosity several tens of thousands photons/MeV. Luminescence decay measurements indicate that the scintillators response is fast with nearly the entire amount of light decaying within 620 ns. In addition, BaFLEu is not sensitive to moisture and the samples can be handled and stored under ambient conditions.

[0075] These inorganic scintillator crystals are useful for national security purposes, such as detecting nuclear material.

EXAMPLE 2

Synthesis and Characterization of BaBrIrEu

[0076] Eu ²⁺ and Ce ³⁺ -activated barium halides of the form BaX ₂ (X=Cl, Br, I) have been investigated and found to be attractive candidates (N. Cherepy et al, Appl. Phys. Lett. 2007, 92, 083508; J. Selling et al, IEEE Trans. Nucl. Sci. 2008, 55, 1183). Some of the mixed halides componds are known x-ray phosphors, but have never been used for gamma detection.

[0077] Micro-crystalline powder and single crystal compositions BaBrI doped with Eu ²⁺ for scintillator applications are synthesized. A crystal is obtained by the Bridgman growth technique starting with a mixture of stoichiometric amounts of the respective halides in a sealed quartz tube (See Figure 3). A melting temperature of 850°C and a homogenization time of 2 hours is used. The cooling rate (or directional solidification rate) is 1 mm/hour in a temperature gradient of 5O ⁰ C/ cm. Reactants are used as obtained from the manufacturer without any purification. Figures 4-6 shows the photoluminescence spectrum showing an emission wavelength at 410 nm for the single crystal, the X-ray luminescence decay curves and the response of the crystal to gamma radiation (pulse height measurement). The new inorganic scintillator crystal properties are compared to those Of SrI ₂ IEu reported by others. The new inorganic scintillator crystal has a higher stopping power for stopping gamma-rays than SrI ₂ :Eu, and a faster luminescence decay time. [0078] Depending on the activator concentration, measurements show that the range of response and light decay encompass the following: a luminescence decay of 83% of the light decaying within 700 ns, and a luminescence decay of 98% of the light decaying within 500 ns. This crystal has a high luminescence output (over 75,000 ph/MeV), fast decay and ease of growth at low cost.

[0079] Figures 8 and 9 show the plots of luminescent intensity (estimated photons/Me V) and the amount of luminescence with decay times of less than 500 ns (estimated photons/MeV), respectively, as functions of the Eu ²⁺ concentration (up to 30%) in BaBrI.

[0080] These inorganic scintillator crystals are useful for national security purposes, such as detecting nuclear material.

EXAMPLE 3

Synthesis and Characterization of BaClIrEu

[0081] Crystals of BaClI doped with Eu ²⁺ for scintillator applications are synthesized using the techniques described herein.

[0082] Figure 10 shows the photo luminescence spectrum showing an emission wavelength between 420 nm and 440 nm, or at about 430 nm, for a BaClLEu ²⁺ sample. Figure 11 shows the decay curves for a BaClI:5% Eu ²⁺ sample. Figure 12 shows the fraction of luminescence intensity decaying in the first 1,000 ns as a function of the Eu ²⁺ concentration in BaClI.

[0083] These inorganic scintillator crystals are useful for national security purposes, such as detecting nuclear material.

[0084] While the present invention has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process step or steps, to the objective, spirit and scope of the present invention. All such modifications are intended to be within the scope of the claims appended hereto.