Abstract:
A halide scintillator material is disclosed where the halide may comprise chloride, bromide or iodide. The material is single-crystalline and has a composition of the general formula ABX 3  where A is an alkali, B is an alkali earth and X is a halide which general composition was investigated. In particular, crystals of the formula ACa 1-y Eu y I 3  where A=K, Rb and Cs were formed as well as crystals of the formula CsA 1-y Eu y X 3  (where A=Ca, Sr, Ba, or a combination thereof and X=Cl, Br or I or a combination thereof) with divalent Europium doping where 0≦y≦1, and more particularly Eu doping has been studied at one to ten mol %. The disclosed scintillator materials are suitable for making scintillation detectors used in applications such as medical imaging and homeland security.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of U. S. Provisional Application Ser. No. 61 ,443,076 filed Feb. 15, 2011 and of U. S. Provisional Application Ser. No. 61/491,074 filed May 27, 2011, and is a continuation-in-part of U. S. patent application Ser. No. 13/098,654, filed May 2, 2011 (now U. S. Pat. No. 8,692,203 issued Apr. 8, 2014) which claims the benefit of U. S. provisional patent application Ser. No. 61/332.945, filed May 10, 2010, all of Zhuravleva el al., all priority applications being incorporated by reference in their entirety. 
    
    
     STATEMENT OF GOVERNMENT SUPPORT 
     The invention was made with government support under Contract No. DHS-DNDO 2009-DN-077-AR103I-03 awarded by the Department of Homeland Security and under DOE—NA22: DE-NA0000473 awarded by the U.S. Department of Energy. The government has certain rights in the invention. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to new chloride, bromide and iodide scintillator crystals with divalent Europium doping, and, more particularly, to halide scintillators represented by one of the following formulae: ACa 1-y Eu y X 3  (where A=K, Rb or Cs, or a combination thereof, and 0≦y≦1) and CsA 1-y Eu y X 3  (where A=Ca, Sr, Ba, or a combination thereof, and 0≦y≦1) and X═Cl, Br or I or a combination thereof in either formulae. 
     BACKGROUND 
     A halide scintillator for radiation detection is described in U.S. Published Patent Application No. 2011/0272585 and a chloride scintillator for radiation detection is described in U.S. Published Application No. 2011/0272586 published Nov. 10, 2011, both published applications of Zhuravleva et al. of the University of Tennessee. The halide scintillator is single-crystalline and has a composition of the formula A 3 MBr 6(1-x) Cl 6x  or AM 2 Br 7(1-x) Cl 7x  wherein A consists of one of Li, Na, K, Rb, Cs or any combination thereof, and M consists of Ce, Sc, Y, La, Lu, Gd, Pr, Tb, Yb, Nd or any combination thereof and 0≦x≦1. The chloride scintillator is also single crystalline and has a composition of the formula AM 2 Cl 7  and A and M consist of the elements indicated above. A modified Bridgman technique was used to form the crystals. A Bridgman method is described 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” among other known tutorials incorporated by reference herein as to any material deemed essential to an understanding of the Bridgman method. 
     An iodide scintillator for radiation detection is described in EP 2387040 published Nov. 16, 2011 and claims priority to U.S. patent application Ser. No. 13/098,654 filed May 2, 2011 and to U.S. provisional patent application Ser. No. 61/332,945 filed May 10, 2010, also of Zhuravleva et al. of the University of Tennessee. The disclosed iodide scintillators have a composition of the formula AM 1-x EuI 3 , A 3 M 1-x Eu x I 5  and AM 2(1-x) Eu 2x I 5 , wherein A consists essentially of an alkali element (such as Li, Na, K, Rb, Cs) or any combination thereof, M consists essentially of Sr, Ca, Ba or any combination thereof, and 0≦x≦1. These iodide scintillator crystals were made by first synthesizing a compound of the above composition and then forming a single crystal from the synthesized compound, for example, by the Vertical Gradient Freeze method. In particular, high-purity starting iodides (such as CsI, SrI 2 , EuI 2  and rare-earth iodide(s)) are handled in a glove box with, for example, pure nitrogen atmosphere and then mixed and melted to synthesize a compound of the desired composition of the scintillator material. A single crystal of the scintillator material is then grown from the synthesized compound by the Bridgman method or Vertical Gradient Freeze (VGF) method, in which a sealed ampoule containing the synthesized compound is transported from a hot zone to a cold zone through a controlled temperature gradient at high speed to form the single-crystalline scintillator from molten synthesized compound. The ampoule may be sealed with a hydrogen torch after creating a vacuum on the order of 1×10 −6  millibars. The scintillator crystal may be cut and polished using sand papers and mineral oil and then optically coupled to a photon detector, such as a photomultiplier tube (PMT), arranged to receive the photons generated by the scintillator and adapted to generate a signal indicative of the photon generation. Typically, plates about 1-3 mm in thickness may be cut from the boules and small samples selected for the optical characterization. This scintillator crystal work has been continuing at the University of Tennessee, Scintillation Materials Research Center, Knoxville, Tenn. 
     Also, pursuant to U.S. Published Patent Application No. 2011/0165422, published Jul. 7, 2011, complimentary development of a lanthanide doped strontium barium mixed halide scintillator crystal, for example, Sr 0.2 Ba 0.75 Eu 0.05 BrI has been developed with 5% Eu doping, also using a Bridgman growth technique, at the University of California. 
     Pursuant to U.S. Published Patent Application No. 2011/0024635 published Feb. 3, 2011, of Shah et al., a lithium containing halide scintillator composition is disclosed. This CsLiLn composition appears to have been produced at Radiation Monitoring Devices, Inc. of Watertown, Mass. 
     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, gamma-ray detection, oil well logging (geological applications) and high energy physics among other applications. Typically, a crystal of the types described above desirably exhibit high light yields, fast luminescence decay (for example, below 1000 ns), good stopping power, high density, good energy resolution, ease of growth, proportionality and stability under ambient conditions. La x Br 3 :Ce 1-x  (E. V. D. van Loef et al., Applied Physics Letters, 2007, 79, 1573) and Sr x I 2 :Eu 1-x  (N. Cherepy et al., Applied Physics Letters, 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. Other known benchmarks that are commercially available include bismuth germanate (BGO) and NaI:Tl available from a number of sources. 
     There remains a need in the art for further research and development of scintillator crystal materials for the applications described above. 
     SUMMARY OF THE DISCLOSURE 
     This summary is provided to introduce a selection of concepts. These concepts are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is this summary intended as an aid in determining the scope of the claimed subject matter. 
     The present invention meets the above-identified needs by providing inorganic scintillator crystals such as halide scintillators with divalent Europium doping represented by one of the following formulae: ACa 1-y Eu y X 3  (where A=K, Rb or Cs, or a combination thereof and X═Cl, Br or I or a combination thereof and 0≦y≦1) and CsA 1-y Eu y X 3  (where A=Ca, Sr, Ba, or a combination thereof and X═Cl, Br or I or a combination thereof and 0≦y≦1). Generally, an embodiment comprises ABX 3  where A is an alkali, B is an alkali earth and X is a halide. 
     In one embodiment, an inorganic single crystal scintillator comprises the formula: ACa 1-y Eu y X 3  (where A=K, Rb or Cs, or a combination thereof and X═Cl, Br or I or a combination thereof and 0≦y≦1). In particular, crystals were formed for KCaI 3 :Eu from studying a known KI—CaI 2  phase diagram system whereby a Potassium Iodide (KI) and Calcium Iodide (CaI 2 ) graph plotted from a mole concentration of 0% KI to 100% CaI 2  versus temperature between, for example, 200 and 800° C.; (phase diagrams are available from the National Institute of Standards and Technology (NIST) phase diagrams database). Also, crystals were formed for RbCaI 3 , for CsCaI 3  and for CsCaCl 3  following known phase diagrams and by utilizing as pure and anhydrous raw materials as possible. Anhydrous RbI not being generally available, techniques were employed to purify the RbI raw material using known techniques. These crystals were grown using one of a vertical gradient freeze or a modified Bridgman method. A Czochralski technique or combination Bridgman/Czochralski method may be used as an alternative process for growing scintillator crystals. 
     In another embodiment, an inorganic single crystal scintillator comprises the formula: CsA 1-y Eu y X 3  (where A=Ca, Sr, Ba, or a combination thereof, and 0≦y≦1) and X═Cl, Br or I or a combination thereof. Similar growth techniques were employed and their characteristics studied as scintillators. 
     Further features and advantages of the present invention, as well as the structure and operation of various aspects of the present invention, are described in detail below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference numbers indicate identical or functionally similar elements. 
         FIGS. 1 ,  2  and  9  comprise PRIOR ART phase diagrams obtained via the National Institute of Standards and Technology (NIST) phase diagram database and are reproduced here for purposes of enablement of one of ordinary skill in the art. 
         FIG. 1  is a PRIOR ART phase diagram of a KI—CaI 2  system whereby KI is shown at left and CaI 2  is shown at right between 0 and 100% mol concentration while temperature is depicted along the left vertical axis between 200° C. and 800° C. The diagram shows formation of a congruently melting compound KCaI 3  and points to the fact that crystals of KCaI 3  can be grown from the melt. 
         FIG. 2  is a PRIOR ART phase diagram of KCaI 3  as well as similar systems for RbI to CaI 2  and CsI to CaI 2  also between 200° C. and 800° C. All three compounds, KCaI 3 , CsCaI 3  and RbCaI 3  are congruently melting compounds and, therefore, their crystals can be grown from the melt. 
         FIG. 3  shows typical Bridgman apparatus in diagrammatic form comprising from top to bottom, a hot zone, an adiabatic zone and a cold zone whereby the center of the furnace shows crystal growth direction from an ampoule in the hot zone. 
         FIG. 4  provides a graph for photoluminescence emission and excitation spectra for CsCaI 3 :Eu and KCaI 3 :Eu wherein dashed lines represent wide excitation bands and solid lines represent emission bands for each crystal. 
         FIG. 5  provides graphs for radio-luminescence for each crystal: CsCaI 3 :Eu, KCaI 3 :Eu, and RbCaI 3 :Eu, demonstrating Eu 2+  5d-4f luminescence under X-ray excitation. 
         FIG. 6  provides  137 Cs energy spectra with 662 keV gamma-ray photopeaks for CsCaI 3 :Eu 3% (the upper curve) and KCaI 3 :Eu 3% (the lower curve) normalized to a benchmark bismuth germanate (BGO) standard sample with its photopeak at channel  100 . 
         FIG. 7A to 7C  provides graphs of scintillation decay for each crystal KCaI 3 :Eu 1%, RbCaI 3 :Eu 1% and CsCaI 3 :Eu 1% in counts over time measured in nanoseconds. Scintillation time profiles were recorded using a  137 Cs gamma-ray source. Scintillation decay constants obtained from fitting the curves with exponential functions are shown in legends. 
         FIG. 8A to 8C  provides black and white line drawings made from photographs of the KCaI 3 :Eu 3%, CsCaI 3 :Eu 3% and RbCaCl 3 :Eu 3% crystals respectively compared with measurement rulers (except RbCaCl 3 :Eu 3%). 
         FIG. 9A  is a PRIOR ART phase diagram of the CsCl—CaCl 2  system whereby CsCl is shown at left and CaCl 2  is shown at right between 0 and 100% mol concentration while temperature is depicted along the left vertical axis between 200° C. and 800° C.;  FIG. 9B  is a PRIOR ART phase diagram of the CsCl—SrCl 2  system whereby CsCl is shown at left and SrCl 2  is shown at right between 0 and 100% mol concentration while temperature is depicted along the left vertical axis between 200° C. and 800° C.; and  FIG. 9C  is a PRIOR ART phase diagram of the SrBr 2 —CsBr system whereby SrBr 2  is shown at left and CsBr is shown at right between 0 and 100% mol concentration while temperature is depicted along the left vertical axis between 200° C. and 800° C. All three compounds, CsCaI 3 , CsSrI 3  and CsSrBr 3  are congruently melting compounds and, therefore, their crystals can be grown from the melt. 
         FIG. 10  is a graph over time of moisture intake of Cs 2 LiYCl 6 :Ce and NaI as benchmarks and the following crystals: CsSrCl 3 :Eu 10%; CsSrBr 3 :Eu 10% and CsCaCl 3 :Eu 10% where the latter two crystals exhibit little or no moisture intake. Measurements were made at the same temperature and humidity conditions. 
         FIG. 11  is a photoluminescence emission and excitation spectra graph for each of the CsCaCl 3 :Eu 10%, CsSrCl 3 :Eu 10% and CsSrBr 3 :Eu 10% crystals where dashed lines represent wide excitation bands and solid lines represent emission bands. 
         FIG. 12  provides graphs for radioluminescence for each crystal: CsCaCl 3 :Eu 10%, CsSrCl 3 :Eu 10% and CsSrBr 3 :Eu 10% demonstrating Eu 2+  5d-4f luminescence under X-ray excitation. 
         FIG. 13A to 13C  represent graphs of scintillation decay over time for each crystal whereby  FIG. 13A  represents CsCaCl 3 :Eu 10%;  FIG. 13B  represents CsSrCl 3 :Eu 10% and  FIG. 13C  represents CsSrBr 3 :Eu 10%. Scintillation time profiles were recorded using a  137 Cs gamma-ray source. Scintillation decay constants obtained from fitting the curves with exponential functions are shown in legends. 
         FIG. 14A to 14C  represent graphs of  137 Cs energy spectra with 662 keV gamma-ray photopeaks for each crystal whereby  FIG. 14A  represents CsCaCl 3 :Eu 10%;  FIG. 14B  represents CsSrCl 3 :Eu 10% and  FIG. 14C  represents CsSrBr 3 :Eu 10% normalized to a benchmark bismuth germanate (BGO) standard sample with its photopeak at channel  100 . 
         FIG. 15A to 15B  are graphs demonstrating relative light output proportionality versus energy whereby  FIG. 15A  represents CsSrBr 3 :Eu 10% and  FIG. 15B  is a similar graph for CsCaCl 3 :Eu 10%. 
         FIG. 16A to 16C  are black and white line drawings made from photographs of each respective crystal: CsSrCl 3 :Eu 10%; CsSrBr 3 :Eu 10% and CsCaCl 3 :Eu 10%. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is generally directed to new inorganic scintillator crystals from the concept ABX 3  where A is an alkali, B is an alkali earth and X is a halide comprising one of chlorine, bromine and iodine. Also, levels of divalent Europium doping were investigated between 1% and 10% with exemplary scintillator crystals grown and their characteristics recorded. It is also directed to combination inorganic crystal scintillators where Cesium, Strontium, Calcium and Barium are used in combination, for example, to form scintillator crystals of the formula CsSrX 3 :Eu 1 to 10% or CsCaX 3 :Eu 1 to 10% or CsSrBaX 3 :Eu 1 to 10% with divalent Europium doping for substitution with one of the other divalent elements (Sr, Ca and SrBa combination). First, the formation of ACaI 3  crystals with divalent Europium doping will be discussed as one example followed by a discussion of the combination crystals. 
     EXAMPLE 1 
     ACa 1-y Eu y I 3  where A=K, Rb and Cs 
     Referring to  FIG. 1 , there is shown a PRIOR ART exemplary system potassium iodide and calcium iodide showing a mol concentration versus temperature plot. Halide salts generally rapidly absorb moisture and preferably are maintained dry so as not to pre-assume a crystalline form with water. As will be explained herein, the purification process and handling of these halide salts is best performed under protective atmosphere to obtain pure, anhydrous salts, for example, using a zone refining technique in furnaces, melt-filtering or other known techniques where the material may be sealed in a quartz ampoule either under vacuum or nitrogen or argon gas. 
       FIG. 2  shows similar plots for rubidium and cesium, respectively, and calcium chloride. RbI is presently not available in pure, anhydrous form and must be purified and rendered as anhydrous as possible using known techniques. First referring to  FIG. 1 , KCaI 3  is a congruently melting compound with a melting point at 524° C. 
     The PRIOR ART table 1 below provides the details for each crystal formed for each of potassium, rubidium and cesium and Z eff  calculated using a known formula: 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 KCaI 3   
                 RbCaI 3   
                 CsCaI 3   
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 T m , ° C. 
                 524 
                 582 
                 686 
               
               
                 Crystal Structure 
                 Ortho-rhombic 
                 Ortho-rhombic 
                 Ortho-rhombic 
               
               
                 Phase transition, ° C. 
                 No 
                 470 
                 No 
               
               
                 Density, g/cm 3   
                 3.81 
                 NA 
                 4.06 
               
               
                 Z eff   
                 50.6 
                 50.0 
                 52.6 
               
               
                   
               
             
          
         
       
     
     From the table 1 summary above, all three crystals exhibit an ortho-rhombic crystal structure. Accurate black and white line drawings of the respective crystals with Eu 3% are depicted in  FIG. 8 . The melting temperature varies from 524° C. for potassium to 686° C. for Cesium. There is no phase transition exhibited for either potassium or cesium. A phase transition at 469° C. or approximately 470° C. was noted for rubidium. The Z eff  did not vary much, from 50.0 to 52.6. The density in grams per cubic centimeter was between 3.8 and 4.1 approximately. 
     The vertical gradient freeze and a modified Bridgman technique depicted in  FIG. 3  may be used to form the crystals whose characteristics are described in table 1. The method may also be used with or as a substitute for a vertical gradient freeze (VGF) method. A Czochralski technique or combined Czochralski/Bridgman technique may be used in the alternative to grow scintillator crystals. As explained above, halide salts are moisture sensitive. One step in the process is to synthesize the compound using high purity anhydrous starting halides such as CsI, KI, RbI, EuI 2  and CaI 2 . In the case of RbI, the salt was dried and purified in a glove box using known techniques. It is recommended that the dry salt raw materials be handled in a glove box prior to movement to the ampoule of  FIG. 3 . A typical ampoule is a vacuum-scaled quartz ampoule at 10 −6  vacuum pressure. A Mellen Electro-Dynamic Gradient (EDG) furnace with a translation motor may be utilized to generate heat. Synthesized material may be further purified via filtering through a frit followed by several runs of zone refining. Growth parameters are suggested as follows: a temperature gradient may be between 25-75° C. per inch of crystal growth; a translation rate may be one millimeter per hour (range of 0.5 to 2 mm per hour); a typical cool down rate may be 5° C. per hour. Crystal growth results are shown in  FIG. 8  against rulers showing length of growth. 
     In addition to growth in single crystalline form, the scintillator compounds discussed herein may be prepared as polycrystalline powders by mixing fine grain powder components in stoichiometric ratios and sintering at a temperature somewhat below the melting point. Furthermore, these compositions may be synthesized in polycrystalline ceramic form by hot isostatic pressing of fine grained powders. 
     Referring now to  FIG. 4 , there is shown a graph for CsCaI 3  and KCaI 3  with excitation at 285, 290 nm wavelength (in dashed line) and emission at 460 nm wavelength for each crystal (in solid line) shown as the respective peaks. Intensity levels are shown in the vertical axis as normalized intensity. A Flourolog3 lifetime spectrofluorometer (horiba Jobin Yvon) was used in the measurements. Emissions and excitation bands are characteristic of Eu 2+  5d to 4f luminescence. The Ca 2+  ion provides a substitution site for Eu 2+  doping. The characteristic data confirms incorporation of Eu 2+  into the lattice of each crystal scintillator in the stable divalent state as a substitute for calcium. Moreover, Eu 2+  doping is confirmed to demonstrate excellent luminosity and high spectral energy resolution at normal room temperatures. 
     Referring to  FIG. 5 , there are shown graphs for X-Ray radioluminescence spectra for each crystal: CsCaI 3 :Eu, KCaI 3 :Eu, and RbCaI 3 :Eu where the emission peak maxima are at 450, 470 and 470 nm respectively and normalized intensity shown as the vertical axis as before. Radioluminescence spectra were measured at room temperature under continuous irradiation from an X-ray generator (35 kV and 0.1 mA). Again, the emission bands are characteristic of Eu 2+  5d-4f luminescence. The emission is suitable for use with conventional photodetectors known in the art such as photomultiplier tubes (PMT&#39;s), for example, a Photonis XP2020Q PMT and fast timing electronics. 
     Referring now to  FIG. 6 , there is shown  137 Cs gamma-ray energy spectra for the CsCaI 3 :Eu 3% and KCaI 3 :Eu 3% crystals. Light output measurements were carried out on samples covered in mineral oil and directly coupled to a photomultiplier tube (PMT) and covered with Teflon tape. A Hamamatsu H3177-50 PMT may be used for the absolute light measurements. Gamma-ray energy spectra were recorded using a  137 Cs source with a 6 μsec shaping time. Both the CsCaI 3 :Eu 3% (generally upper, side-wise square) and KCaI 3 :Eu 3% (generally lower, triangle pointing down) scintillator crystal spectra exhibit the position of a 662 keV gamma-ray photopeak at a much higher channel number than a benchmark bismuth germanate (BGO) crystal with its photopeak at channel  100 , indicating much higher light output. While different Eu doping was used between 1 and 10 mol %, an optimal Eu 2+  activator concentration was found to be 3 mol %. 
     The photo peaks in  FIG. 6  were fitted with Gaussian functions to determine the centroid of the peak and the energy resolution. The integral quantum efficiency of the PMT according to the emission spectrum of the scintillators was used to estimate the light output in photons per unit gamma ray energy. All photon (light) output, temperature measurements, energy resolutions, wavelengths, durations, densities and the like in the tables are to be considered approximate measurements. Table 2 below shows the absolute light output and energy resolution for the particular samples used for the measurements compared to a NaI:Tl reference sample. The energy resolution at 662 keV was determined from the full width at half maximum (FWHM) of the 662 keV photopeak. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Light yield,  
                 Energy resolution, 
               
               
                   
                 photons/MeV 
                 %@662 keV 
               
               
                 Composition 
                 (approximate) 
                 (approximate) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 KCaI 3 :Eu 3% 
                 60,000 
                 5 
               
               
                 CsCaI 3 :Eu 3% 
                 38,500 
                 7 
               
               
                 RbCaI 3 :Eu 3% 
                 No gamma-ray photo peak 
                 NA 
               
               
                 NaI:Tl 
                 38,000 
                 ~7 
               
               
                   
               
             
          
         
       
     
     As can be seen from the table 2, the RbCaI 3 :Eu 3% sample did not provide a resolved gamma-ray photo peak. On the other hand, the KCaI 3 :Eu 3% crystal greatly exceeded the benchmark NaI:Tl crystal at a light yield of approximately 60,000 photons per Me V compared with approximately 38,000 for NaI:Tl while the CsCaI 3 :Eu 3% crystal matched, if not, exceeded the NaI:Tl light yield. As for energy resolution, both the KCaI 3 :Eu 3% and CsCaI 3 :Eu 3% crystals exhibited a very acceptable range between 5% (for KCaI 3 :Eu) and 7% for CsCaI 3 :Eu at 662 keV. 
     Scintillation decay is shown in  FIGS. 7A through 7C  for each crystal: where  FIG. 7A  represents KCaI 3 :Eu 1%;  FIG. 7B  represents RbCaI 3 :Eu 1% and  FIG. 7C  represents CsCaI 3 :Eu 1% scintillation decay results in counts over time. Scintillation decay was measured using a time-correlated single photon counting technique and using a  137 Cs 662 keV gamma-ray source. Scintillation decay constants obtained from fitting the curves with exponential functions are shown in legends. A primary decay around one μsecond is characteristic of Eu 2+  5d to 4f luminescence. 
     Referring now to  FIG. 8A , there are shown black and white line drawings prepared from photographs of a KCaI 3 :Eu 3% crystal compared with a metric ruler. The lengthwise ruler indicates that the potassium crystal was grown to a length of over six centimeters and measured approximately 0.5 centimeters in width. Referring now to  FIG. 8B , there are shown black and white line drawings prepared from photographs of a CsCaI 3 :Eu 3% crystal compared with a ruler. The lengthwise ruler in inches indicates that the potassium crystal was grown to a length of over two inches and measured approximately 0.5 centimeters in width. Referring now to  FIG. 8C , there is shown a black and white line drawing prepared from a photograph of a RbCaI 3 :Eu 3% crystal. 
     The following table 3 provides a summary of results for CsCaI 3 :Eu 3% and KCaI 3 :Eu 3% crystals compared with those of a benchmark NaI:Tl crystal: 
     
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                 LO, 
                   
               
               
                   
                   
                   
                   
                   
                   
                 Primary 
                 photons 
                   
               
               
                   
                   
                   
                 Density 
                   
                 Max 
                 sc, 
                 per 
                   
               
               
                   
                 T m , ° C. 
                 Crystal 
                 g/cm 3   
                   
                 RL, 
                 decay 
                 Mev 
                   
               
               
                 Composition 
                 (approx) 
                 structure 
                 (approx) 
                 Z eff   
                 nm 
                 μs 
                 (approx) 
                 Hygroscopic? 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 CsCaI 3 :Eu 
                 686 
                 orthorhombic 
                 4.06 
                 52.6 
                 450 
                 1.7 
                 38,500 
                 yes 
               
               
                 3% 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 KCaI 3: Eu 
                 524 
                 orthorhombic 
                 3.81 
                 50.6 
                 470 
                 .95 
                 60,000 
                 yes 
               
               
                 3% 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 NaI:Tl 
                 651 
                 cubic 
                 3.67 
                 51 
                 415 
                 .23 
                 38,000 
                 yes 
               
               
                   
               
             
          
         
       
     
     In summary for this example, it is demonstrated that practical crystal growth comparable to NaI:Tl may be obtained at reasonable cost (involving congruent melting and acceptable melting point). Since the crystals are hygroscopic, hermetic packaging may be used with conventional photodetectors such as photo-multiplier tubes such as a Photonis XP2020Q PMT and fast timing electronics. X-ray, gamma-ray, and optical excitation have been demonstrated. With improved crystal quality (removal of raw material impurity and improved processing), both light output and energy resolution are expected to improve beyond their current levels. 
     EXAMPLE 2 
     CsA 1-y Eu y X 3  (where A=Ca, Sr, Ba, or a Combination thereof and X═Cl, Br or I or a Combination thereof) with Divalent Europium Doping where 0≦y≦1 
     Now, single crystal inorganic crystal scintillators will be described of the formula CsAX 3  will be described with divalent Europium doping investigated as above between 1 and 10 mol % where A is calcium (Ca), strontium (Sr) or barium (Ba) or a combination thereof and X is a halide selected from chlorine, bromine or iodine. In particular, it will be shown that a crystal of CsSrCl 3 :Eu 10% exhibits a light yield on the order of 46,000 photons per MeV and a scintillation decay at 2.6 μseconds and provides excellent gamma-ray and X-ray detection characteristics. The A 2+  lattice site provides a substitutional site for the Eu 2+  doping. 
     Referring to  FIGS. 9A to 9C ,  FIG. 9A  shows a PRIOR ART phase diagram of the CsCl—CaCl 2  system whereby CsCl is shown at left and CaCl 2  is shown at right between 0 and 100% mol concentration while temperature is depicted along the left vertical axis between 200° C. and 800° C.;  FIG. 9B  is a similar PRIOR ART phase diagram of the CsCl—SrCl 2  system whereby CsCl is shown at left and SrCl 2  is shown at right; and  FIG. 9C  is a PRIOR ART phase diagram of the SrBr 2 —CsBr system whereby SrBr 2  is shown at left and CsBr is shown at right between 0 and 100% mol concentration while temperature is depicted along the left vertical axis between 200° C. and 800° C. Divalent europium was used primarily for doping as follows: r(Eu 2+ )=1.20 A (CN=7); r(Sr 2+ )=1.21 A and r(Ca 2+ )=1.06 A. Perovskite type ABX 3  compounds were obtained by congruently melting and with practical crystal growth according to the methods discussed above and below. 
     Table 4, in part PRIOR ART, below provides a summary of the crystal growth for each scintillator crystal: 
     
       
         
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                   
                 CsCaCl 3 :Eu 10% 
                 CsSrCl 3 :Eu 10% 
                 CsSrBr 3 :Eu 10% 
               
               
                   
               
             
             
               
                 Crystal 
                 Cubic 
                 Ortho-rhombic 
                 Ortho-rhombic 
               
               
                 structure at 
                   
                   
                   
               
               
                 room 
                   
                   
                   
               
               
                 temperature 
                   
                   
                   
               
               
                 Melting 
                 910 
                 842 
                 760 
               
               
                 point, ° C. 
                   
                   
                   
               
               
                 Density, g/cm 3   
                 3.0 
                 3.06 
                 3.76 
               
               
                 Phase 
                 445 
                 112, 443 
                 No 
               
               
                 transition, ° C. 
               
               
                   
               
             
          
         
       
     
     A method of crystal growth has already been described above with respect to a discussion of  FIG. 3 . Bridgman crystal growth may comprise a gathering of anhydrous 99.99% pure raw materials. The materials may be further purified by vacuum drying and melt filtering. As described above, a quartz ampoule may be employed having hot and cold zones whereby crystals may be grown under vacuum seal. A Mellen Electro-Dynamic Gradient (EDG) furnace with a translation motor may be utilized to generate heat. The crystal growth parameters may be the same as described above: temperature gradient at 75° C./inch, translation rate at one millimeter per inch and a cool down rate of 5° C. per hour (exemplary). The scintillator crystals were grown with spontaneous orientation. The ternary halide scintillators may be synthesized using vertical gradient freeze (VGF), Bridgman and melt synthesis and other techniques as suggested above. 
       FIG. 10  is a graph over time of moisture intake of Cs 2 LiYCl 6 :Ce and NaI as benchmarks and the following crystals: CsSrCl 3 :Eu 10%; CsSrBr 3 :Eu 10% and CsCaCl 3 :Eu 10% where the latter two crystals exhibit little or no moisture intake. CsSrBr 3 :Eu 10% and CsCaCl 3 :Eu 10% both exhibit practically flat moisture intake over a period of 250 minutes (over four hours). Moreover, CsSrCl 3  exhibits greatly improved moisture intake at 2% over four hours compared with NaI at over 6.5%. The samples were measured in a closed box with controlled environment at room temperature. All samples showed significantly lower moisture sensitivity compared to NaI and CLYC scintillators. 
       FIG. 11  represents photoluminescence spectra for each of the CsCaCl 3 : 10%, CsSrCl 3 :Eu 10% and CsSrBr 3 :Eu 10% scintillator crystals where dashed lines represent wide excitation bands and solid lines represent emission bands. The emission and excitation bands are characteristic of Eu 2+  5d to 4f luminescence. Incorporation of Eu 2+  is thus confirmed into the lattice structures in the stable divalent state of the crystals. Photoluminescence excitation and emission spectra may be measured with a Horiba Fluorolog 3 spectrofluorometer utilizing a Xe lamp excitation source and scanning monochromators. The following table 5 provides a summary of excitation (EXC) bands and emission (EM) bands: 
     
       
         
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                   
                 EXC, nanometers 
                   
               
               
                 Composition 
                 wavelength 
                 EM, nanometers wavelength 
               
               
                   
               
             
             
               
                 CsCaCl 3 :Eu 10% 
                 278 to 440 nm 
                 450 nm 
               
               
                 CsSrCl 3 :Eu 10% 
                 270 to 430 nm 
                 439 nm 
               
               
                 CsSrBr 3 :Eu 10% 
                 270 to 430 nm 
                 440 nm 
               
               
                   
               
             
          
         
       
     
       FIG. 12  is a graph of normalized intensity versus wavelength in nanometers of X-ray excitation of the CsCaCl 3 : 10%, CsSrCl 3 :Eu 10% and CsSrBr 3 :Eu 10% scintillator crystals. Radioluminescence spectra were measured at room temperature under continuous irradiation from an X-ray generator (1 mA, 35 kV). An Acton monochromator may be used to resolve the spectrum as a function of wavelength. The graph demonstrates successful results of efficient radioluminescence under X-ray excitation. The emission bands are characteristic of Eu 2+  5d-4f luminescence. The emission bands were at a wavelength suitable for capture using conventional photo detectors such as photo multiplier tubes (PMT&#39;s) such as a Photonis XP2020Q PMT and fast timing electronics. The measured emission peaks are as follows: for CsCaCl 3 :Eu 10%, the peak was at 450 nm; for CsSrCl 3 :Eu 10%, the peak was at 437 nm; and for CsSrBr 3 :Eu 10%, the peak was at 443 nm. 
       FIG. 13A to 13C  represent graphs of scintillation decay over time for each crystal whereby  FIG. 13A  represents CsCaCl 3 :Eu 10%;  FIG. 13B  represents CsSrCl 3 :Eu 10% and  FIG. 13C  represents CsSrBr 3 :Eu 10%. Scintillation time profiles were recorded using a  137 Cs 662 keV gamma-ray source. Scintillation decay constants obtained from fitting the curves with exponential functions are shown in legends. The primary decay around 2-4 μseconds is characteristic of Eu 2+  5d to 4f luminescence. The measured scintillation decay times were measured as follows: for CsCaCl 3 :Eu 10%, the decay time was at 4.1 μseconds; for CsSrCl 3 :Eu 10%, the decay time was at 2.6 μseconds (the fastest); and for CsSrBr 3 :Eu 10%, the decay time was at 3.5 μseconds. 
       FIG. 14A to 14C  represent graphs of  137 Cs gamma-ray emission spectra for each crystal whereby  FIG. 14A  represents CsCaCl 3 :Eu 10%;  FIG. 14B  represents CsSrCl 3 :Eu and  FIG. 14C  represents CsSrBr 3 :Eu normalized to benchmark bismuth germanate (BGO) with its photopeak at channel  100 . Efficient scintillation characteristics were exhibited under excitation by ionizing radiation with respect to all three crystals. The following table 6 provides light yield and energy resolution for each crystal compared with NaI:Tl as a benchmark: 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 6 
               
               
                   
               
               
                   
                 CsCaCl 3 :Eu 
                 CsSrCl 3 :Eu 
                 CsSrBr 3 :Eu 
                   
               
               
                   
                 10% 
                 10% 
                 10% 
                 NaI:Tl 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Light yield, 
                 18000 
                 46000 
                 31000 
                 38000 
               
               
                 ph/MeV 
                   
                   
                   
                   
               
               
                 (approx) 
                   
                   
                   
                   
               
               
                 Energy resol. @ 
                 8.9 
                 &gt;10 
                 6.7 
                 7.1 
               
               
                 662 keV, % 
                   
                   
                   
                   
               
               
                 (approx) 
               
               
                   
               
             
          
         
       
     
     As can be seen by the results, CsSrCl 3 :Eu 10% demonstrates improved light yield over known NaI:Tl. 
       FIG. 15A to 15B  are graphs demonstrating light output proportionality whereby  FIG. 15A  is a graph of light output per keV versus energy in keV for CsSrBr 3 :Eu and  FIG. 15B  is a similar graph for CsCaCl 3 :Eu. The importance of  FIG. 15  is that good proportionality contributes to good energy resolution as these graphs demonstrate good proportionality for light output per keV over a wide range of energy level from 10 to 1000 keV. 
       FIG. 16A to 16C  are black and white line drawings made from photographs of each respective crystal: CsSrCl 3 :Eu 10%; CsSrBr 3 :Eu 10% and CsCaCl 3 :Eu 10%. CsSrCl 3 :Eu 10% was grown to be about two inches long; however, some cracking may be seen, possibly due to phase transitions. The crystal was about one centimeter in cross-section. CsSrBr 3 :Eu 10% was gown to be about two centimeters in length and was relatively clear, colorless and crack-free. Its circular cross-section was just less than 2 centimeters in diameter. CsCaCl 3 :Eu 10% was grown to be over three centimeters in length. It too was relatively clear, colorless and crack-free. Its circular cross-section measured about 11/16 inch in diameter. 
     Table 7 provides a summary table for these crystals as follows compared with benchmark NaI:Tl: 
     
       
         
               
               
               
               
               
             
           
               
                 TABLE 7 
               
               
                   
               
               
                   
                 CsCaCl 3 :Eu 
                 CsSrCl 3 :Eu 
                 CsSrBr 3 :Eu 
                   
               
               
                   
                 10% 
                 10% 
                 10% 
                 NaI:Tl 
               
               
                   
               
             
             
               
                 Crystal 
                 Cubic 
                 Orthorhombic 
                 Orthorhombic 
                 Cubic 
               
               
                 structure 
                   
                   
                   
                   
               
               
                 Melting 
                 910 
                 842 
                 760 
                 651 
               
               
                 point, ° C. 
                   
                   
                   
                   
               
               
                 (approx) 
                   
                   
                   
                   
               
               
                 Density, g/cm 3   
                 2.9 
                 3.06 
                 3.76 
                 3.67 
               
               
                 Light yield, 
                 18,000 
                 46,000 
                 31,000 
                 38,000 
               
               
                 ph/Mev 
                   
                   
                   
                   
               
               
                 (approx) 
                   
                   
                   
                   
               
               
                 Energy 
                 8.9 
                 &gt;10 
                 6.7 
                 7.1 
               
               
                 resolution 
                   
                   
                   
                   
               
               
                 @ 662 kEv, % 
                   
                   
                   
                   
               
               
                 (approx) 
                   
                   
                   
                   
               
               
                 Primary decay 
                 4.1 
                 1.6 
                 3.5 
                 .23 
               
               
                 time, μsec 
                   
                   
                   
                   
               
               
                 (approx) 
                   
                   
                   
                   
               
               
                 Hygroscopic 
                 Low 
                 Slightly 
                 Low 
                 Very 
               
               
                   
               
             
          
         
       
     
     The table demonstrates that promising results have been obtained for new, inorganic, single crystals as indicated above when compared with NaL: TI including good transparency, low to no hygroscopicity, good light output and excellent proportionality. It is expected that with greater effort at purification of raw material and optimizing growth parameters that even better results will be achieved. 
     A combination crystal is now described comprising CsSr 1-x Ba x I 3 :Eu 1% and 3%. Crystals were grown at x=0.03, 0.06, 0.09, 0.14 and 0.24. All of these combination crystals operated as a scintillator. X-ray radioluminescence exhibited a peak at approximately 448 nm wavelength. The emission bands are characteristic of Eu 2+ 5d-4f luminescence. The emission is at a wavelength that is suitable for use with conventional photo detectors such as photo multiplier tubes (PMT&#39;s). Ultraviolet/visual excitation and emission were measured with an emission peak at 446 nm. The maximum light output was measured under 662 keV excitation when x was at 3% and Eu mol 1% and measured at approximately 28,000 photons per MeV with 1.9 μsecond decay time, the light output decreased with increasing x such that when x was 24%, the light output approximately 21,000 photons per MeV and the scinitillation decay time approximately 1.5 μseconds. 
     While various aspects of the present invention have been described above, it should be understood that they have been presented by way of example and not limitation. It will be apparent to persons skilled in the relevant art(s) that various changes in form and detail can be made therein without departing from the spirit and scope of the present invention. Thus, the present invention should not be limited by any of the above described exemplary aspects, but should be defined only in accordance with the following claims and their equivalents. 
     In addition, it should be understood that the figures in the attachments, which highlight the structure, methodology, functionality and advantages of the present invention, are presented for example purposes only. The present invention is sufficiently flexible and configurable, such that it may be implemented in ways other than that shown in the accompanying figures. 
     Further, the purpose of the foregoing Abstract is to enable the U.S. Patent and Trademark Office and the public generally and especially the scientists, engineers and practitioners in the relevant art(s) who are not familiar with patent or legal terms or phraseology, to determine quickly from a cursory inspection the nature and essence of this technical disclosure. The Abstract is not intended to be limiting as to the scope of the present invention in any way.