JP2016008170A - Chloride, bromide, and iodide scintillator doped with europium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a halide scintillator material suitable for manufacturing a scintillation detector used in fields of medical imaging and national security.SOLUTION: A halide scintillator material is single crystalline and has a composition represented by general formula ABX(wherein A is an alkali; B is an alkaline earth; and X is a halide). Especially, a crystal represented by formula ACaEuI(wherein A=K, Rb, Cs) is doped with bivalent europium (wherein 0≤y≤1). The crystal is formed similarly to a crystal represented by formula CsAEuX(wherein A=Ca, Sr, Ba or a combination thereof; X=Cl, Br, I or a combination thereof). Eu doping is 1-10 mol%. The crystal grows in a furnace of a vertical temperature gradient coagulation method.

Description

(Cross-reference of related applications)
This application was filed on January 17, 2012, and is now a part of pending US Patent Application No. 13 / 351,748, which was filed on February 15, 2011. Claims the benefit of US Provisional Application No. 61 / 443,076 and US Provisional Application No. 61 / 491,074 filed May 27, 2011, and was filed on May 10, 2010. US Patent Application No. 13 / 098,654, filed May 2, 2011, which claims the benefit of US Provisional Patent Application No. 61 / 332,945 (currently issued April 8, 2014) U.S. Patent No. 8,692,203), all pending, Zhuravleva et al., All priority applications are hereby incorporated by reference in their entirety. Yes.

(Statement of government support)
This invention was made with government support under contract number DHS-DNDO2009-DN-077-AR1031-03 awarded by the Department of Homeland Security and DOE-NA22: DE-NA0000473 awarded by the US Department of Energy. . The government has certain rights in the invention.

(Technical field)
The present invention relates generally to new chloride, bromide and iodide scintillator crystals doped with divalent europium, and more particularly to the following formula: ACa _1-y Eu _y X ₃ (where A = K, Rb or Cs, or a combination thereof, 0 ≦ y ≦ 1) and CsA _1-y Eu _y X ₃ (where A = Ca, Sr, Ba, or a combination thereof, 0 ≦ y ≦ 1) ), And in any of the formulas, relates to a halide scintillator where X = Cl, Br or I, or a combination thereof.

Halide scintillators for radiation detection are described in US Published Patent Application No. 2011/0272585, and chloride scintillators for radiation detection are disclosed in US Published Application No. 2011/0272586 published on Nov. 10, 2011. Both are published applications of Zhuravleva et al., University of Tennessee. Halide scintillators are monocrystalline and have a composition of the formula A ₃ MBr _{6 (1-x)} Cl _6x or AM ₂ Br _{7 (1-x)} Cl _7x , where A is Li, Na , K, Rb, Cs, or any combination thereof, M, Ce, Sc, Y, La, Lu, Gd, Pr, Tb, Yb, Nd, or any combination thereof, and 0 ≦ x ≦ 1. The chloride scintillator is also monocrystalline, has the composition of the formula AM ₂ Cl ₇ , and A and M are composed of the aforementioned elements. Crystals were formed using a modified Bridgman technique. The Bridgman method is among other known instructions incorporated herein by reference for any material deemed essential to understanding the Bridgman method, such as Robertson JM, 1986, Crystal Growth of Ceramics, Bridgman-Stockbarger. method in Bever, 1986 “Encyclopedia of Materials Science and Engineering,” Pergamon, Oxford pp. 963-964.

Iodide scintillators for radiation detection are described in European Patent Application No. 2387040 published November 16, 2011, US Patent Application No. 13 / 098,654 filed May 2, 2011, and Claims priority of US Provisional Application No. 61 / 332,945, filed May 10, 2010, also from Zhuravleva et al., University of Tennessee. Disclosed iodide scintillator has 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 is an alkali Consisting essentially of an element (eg Li, Na, K, Rb, Cs), or any combination thereof, and M consisting essentially of Sr, Ca, Ba, or any combination thereof, 0 ≦ x ≦ 1. First, compounds of the above composition were synthesized, and then, these iodide scintillator crystals were produced from the synthesized compounds by, for example, forming a single crystal by the vertical temperature gradient freeze method (Vertical Gradient Freeze method). . In particular, high purity, multiple starting iodides (eg, CsI, SrI ₂ , EuI ₂ , and rare earth iodides) are handled, mixed and melted, for example, in a glove box having a pure nitrogen atmosphere. A compound of the desired composition of the material is synthesized. A single crystal of scintillator material is grown from the synthesized compound by the Bridgman method or the vertical temperature gradient solidification (VGF) method. In this method, a sealed ampoule containing the synthesized compound is transported at high speed from a hot zone to a cold zone by a controlled temperature gradient, and is simply removed from the molten synthetic compound. Forms a crystalline scintillator. The ampoule may be sealed with a hydrogen torch after creating a vacuum of about 1 × 10 ⁻⁶ mbar. The scintillator crystals may be cut, polished with sandpaper and mineral oil, and in some cases, photomultiplier tubes that are arranged to accept photons generated by the scintillator and generate a signal indicative of photon generation It may be coupled to a photon detector such as (PMT). Typically, a plate with a thickness of about 1-3 mm can be cut from the boules and a small sample can be selected for optical characterization. This scintillator crystal research continues at the University of Tennessee Scintillation Materials Laboratory in Knoxville, Tennessee.

Also, according to US Application Publication No. 2011/0165422 published July 7, 2011, as a complementary development, lanthanide doped strontium barium mixed halide scintillator crystals, such as Sr _0. It was developed at the University of California to add 5% Eu to ₂ Ba _0.75 Eu _0.05 BrI and also use the Bridgeman growth technique.

  According to US Patent Application Publication No. 2011/0024635, published February 3, 2011 by Shah et al, lithium-containing halide scintillator compositions are disclosed. This CsLiLn composition is manufactured by Radiation Monitoring Devices, Inc., Watertown, Massachusetts.

In recent years, radiation detecting materials have become national security, medical images, X-ray detection, gamma ray detection, oil well logging, and high energy physics, among other applications. Therefore, there is the most demand for materials research. Typically, the above types of crystals desirably have a high light yield, fast luminescence decay (eg, less than 1000 ns), good stopping power, high density, good energy decomposition, and growth. Shows ease, proportionality and stability under ambient conditions. La _x Br ₃ : Ce _1-x (EVD 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 today's reference materials that meet some of the desired criteria, but their application is limited by extreme hygroscopicity. Other known standards that are commercially available include bismuth germanate (BGO) and NaI: Tl, which are available from a number of sources.

  There is still a need in the art for further research and development of scintillator crystal materials for application as described above.

  This summary is provided for concept selection. These concepts are further described below in the detailed description. This summary is not intended to identify key features or basic characteristics of the claimed subject matter, nor is this summary intended to assist in determining the scope of the claimed subject matter. Absent.

The present invention has the following formula: ACa _1-y Eu _y X ₃ (wherein A = K, Rb, or Cs, or a combination thereof, and X = Cl, Br, or I, or a combination thereof) , 0 ≦ y ≦ 1) and CsA _1-y Eu _y X ₃ (where A = Ca, Sr, Ba, or a combination thereof; X = Cl, Br, or I, or a combination thereof) Satisfying the above requirements by providing an inorganic scintillator crystal such as a halide scintillator doped with a divalent europium represented by one of the following: 0 ≦ y ≦ 1). In general, one embodiment comprises ABX ₃ (A is an alkali, B is an alkaline earth, and X is a halide).

In one embodiment, the inorganic single crystal scintillator is of the formula: ACa _1-y Eu _y X ₃ , where A = K, Rb, or Cs, or combinations thereof, where X = Cl, Br, or I, or a combination thereof, comprising 0 ≦ y ≦ l). In particular, for KCaI ₃ : Eu, potassium iodide (KI) and calcium iodide (CaI) at various temperatures, for example between 200 and 800 ° C., from 0% KI to 100% CaI ₂ molarity. ₂ ) were plotted, and crystals were formed with reference to the known KI-CaI ₂ phase diagram (note that the phase diagram was obtained from the State Diagram database provided by the National Institute of Standards and Technology (NIST). Is possible). In addition, for RbCaI ₃ , CsCaI ₃ , and CsCaCl ₃ , crystals were formed using raw materials that were as pure and anhydrous as possible according to a known phase diagram. Since anhydrous RbI is not generally available, the RbI raw material was purified using known techniques. These crystals were grown using one of the vertical temperature gradient solidification method or the modified Bridgman method. Czochralski technology, or a combined Bridgman / Czochralski method, may be used as an alternative process for growing scintillator crystals.

In another embodiment, the inorganic single crystal scintillator has the formula: CsA _1-y Eu _y X ₃ (wherein A is Ca, Sr, Ba, or combinations thereof, 0 ≦ y ≦ l, X Is Cl, Br, or I, or a combination thereof. Using similar growth techniques, we studied these characteristics as a scintillator.

  Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying 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 identify identical or functionally similar elements.

  FIGS. 1, 2 and 9 comprise prior art state diagrams obtained by a state diagram database provided by the National Institute of Standards and Technology (KIST), reproduced here for the viability of those skilled in the art. Is done.

FIG. 1 is a prior art phase diagram of the KI-CaI ₂ system, where KI is shown on the left and CaI ₂ is shown on the right with a molar concentration of 0-100%, while the temperature is Shown at 200-800 ° C. along the axis. The figure shows the formation of a congruently melting compound KCaI ₃ and points out the fact that crystals of KCaI ₃ can be grown from the melt.

FIG. 2 is a prior art phase diagram from 200 ° C. to 800 ° C. for systems similar to KCaI ₃ and RbI to CaI ₂ and CsI to CaI ₂ . The three compounds, KCaI ₃ , CsCaI ₃ and RbCaI ₃ are all coincident molten compounds and these crystals can be grown from the melt.

FIG. 3 shows, from top to bottom, a typical schematic of a Bridgman apparatus configuration comprising a high temperature zone, an adiabatic zone and a low temperature zone, with the center of the furnace showing the crystal growth direction from the ampoule in the high temperature zone. .

FIG. 4 shows a graph of photoluminescence emission and excitation spectra of CsCaI ₃ : Eu and KCaI ₃ : Eu. In the figure, a broken line represents a wide excitation band, and a solid line represents an emission band of each crystal.

FIG. 5 shows a graph of radioluminescence of CsCaI ₃ : Eu, KCaI ₃ : Eu, and RbCaI ₃ : Eu crystals showing the emission of Eu ²⁺ from 5d to 4f under X-ray excitation.

FIG. 6 shows CsCaI ₃ : Eu3% (upper curve) and KCaI ₃ : Eu3% (lower curve) normalized to a reference bismuth germanate (BGO) standard with its photoelectric peak in channel 100. ) Shows a ¹³⁷ Cs energy spectrum having a 662 keV gamma ray photopeak.

FIG. 7A shows a graph of scintillation decay (count) for crystalline KCaI ₃ : Eu 1% over time measured in nanoseconds. Scintillation time profiles were recorded using a ¹³⁷ Cs gamma source. The scintillation decay constant resulting from fitting the curve to an exponential function is shown in the legend. FIG. 7B shows a graph of scintillation decay (count) for crystalline RbCaI ₃ : En 1% over time measured in nanoseconds. Scintillation time profiles were recorded using a ¹³⁷ Cs gamma source. The scintillation decay constant resulting from fitting the curve to an exponential function is shown in the legend. FIG. 7C shows a graph of scintillation decay (count) for crystalline CsCaI ₃ : Eu 1% over time measured in nanoseconds. Scintillation time profiles were recorded using a ¹³⁷ Cs gamma source. The scintillation decay constant resulting from fitting the curve to an exponential function is shown in the legend.

FIG. 8A shows a black and white view made from a photograph of a KCaI ₃ : Eu ₃ % crystal compared to a ruler. FIG. 8B shows a black and white view made from a photograph of CsCaI ₃ : Eu ₃ % crystals compared to a ruler. FIG. 8C shows a black and white view made from a photograph of RbCaCl ₃ : Eu ₃ % crystals.

FIG. 9A is a prior art phase diagram of the CsCl—CaCl ₂ system, where CsCl is shown on the left, CaCl ₂ is shown on the right with a molar concentration of 0-100%, and the temperature is between 200 ° C. and 800 ° C. Is shown along the vertical axis. FIG. 9B is a prior art state of the CsCl—SrCl ₂ system, where CsCl is shown on the left, SrCl ₂ is shown on the right in a 0-100% molar concentration, and the temperature is between 200 ° C. and 800 ° C. on the left. Shown along the vertical axis. FIG. 9C is a prior art phase diagram of the SrBr ₂ -CsBr system, where SrBr ₂ is shown on the left side, CsBr is shown on the right side in 0-100% molarity, and the temperature is between 200 ° C. and 800 ° C. on the left side. Shown along the vertical axis. The three compounds, CsCaI ₃ , CsSrI ₃ and CsSrBr ₃ are all coincident molten compounds and these crystals can be grown from the melt.

FIG. 10 is a graph of moisture absorption over time for Cs ₂ LiYCl ₆ : Ce and NaI as references and the following crystals: CsSrCl ₃ : Eu 10%, CsSrBr ₃ : Eu 10%, and CsCaCl ₃ : Eu 10%, The latter two crystals show little or no moisture absorption. Measurements were performed at the same temperature and humidity conditions.

FIG. 11 is a photoluminescence emission and excitation spectrum graph for each of the crystals of CsCaCl ₃ : Eu 10%, CsSrCl ₃ : Eu 10%, and CsSrBr ₃ : Eu 10%, in which the broken line represents a wide excitation band and a solid line Represents an emission band.

FIG. 12 provides a graph of radioluminescence for CsCaCl ₃ : Eu 10%, CsSrCl ₃ : Eu 10%, and CsSrBr ₃ : Eu 10% crystals showing Eu ²⁺ 5d-4f luminescence under X-ray excitation.

FIG. 13A represents a graph of scintillation decay over time for each crystal, specifically CsCaCl ₃ : Eu 10%. ^A scintillation time profile was recorded using a ¹³⁷ Cs gamma source. The scintillation decay constant obtained from fitting the curve to an exponential function is shown in the legend. FIG. 13B represents a graph of scintillation decay over time for each crystal, in particular CsSiCl ₃ : Eu 10%. ^A scintillation time profile was recorded using a ¹³⁷ Cs gamma source. The scintillation decay constant obtained from fitting the curve to an exponential function is shown in the legend. FIG. 13C represents a graph of scintillation decay over time for each crystal, particularly CsSrBr ₃ : Eu 10%. ^A scintillation time profile was recorded using a ¹³⁷ Cs gamma source. The scintillation decay constant obtained from fitting the curve to an exponential function is shown in the legend.

FIG. 14A represents a graph of the ¹³⁷ Cs energy spectrum with a 662 keV gamma photopeak for each crystal, in particular CsCaCl ₃ normalized to a reference bismuth germanate (BGO) standard with that photopeak in channel 100. : Eu 10%. FIG. 14B represents a graph of the ¹³⁷ Cs energy spectrum with a 662 keV gamma photopeak for each crystal, in particular CsSrCl ₃ normalized to a reference bismuth germanate (BGO) standard sample with that photopeak in channel 100. : Eu 10%. FIG. 14C represents a graph of the ¹³⁷ Cs energy spectrum with a 662 keV gamma-ray photopeak for each crystal, in particular CsSrBr ₃ normalized to a reference bismuth germanate (BGO) standard sample with that photopeak in channel 100. : Eu 10%.

FIG. 15A is a graph showing the relative light output proportionality to energy, and FIG. 15A represents CsSrBr ₃ : Eu10%. FIG. 15B is a graph showing the relative light output proportionality to energy, and FIG. 15B is a similar graph for CsCaCl ₃ : Eu.

FIG. 16A is a black and white view made from a photograph of crystals: CsSrCl ₃ : Eu 10%. FIG. 16B is a black and white view made from a photograph of crystals: CsSrBr ₃ : Eu 10%. FIG. 16C is a black and white view made from a photograph of crystals: CsCaCl ₃ : Eu 10%.

FIG. 17 shows that CsBa _x Sr _1-x I ₃ : yEu shows a decrease in moisture absorption rate (MAR) when the barium concentration increases from x = 0.03 to x = 0.24 and y = 1%. It is a graph of barium concentration in the system.

FIG. 18 is a collection of graphs showing the emission peak appearing at 445 nm to 450 nm in the radioluminescence spectrum of CsSr _1-x Ba _x I ₃ : 1% Eu at room temperature.

The present invention relates generally to new inorganic scintillator crystals derived from the concept ABX ₃ , where A is alkali, B is alkaline earth, and X is one of chlorine, bromine and iodine. A halide comprising. Also, exemplary scintillator crystals were grown and the level of divalent europium doping was investigated from 1% to 10% and their properties were recorded. The present invention also includes, for example, the formula CsSrX ₃ : Eu1-10%, CsCaX doped with divalent europium to replace one of the other divalent elements (a combination of Sr, Ca and SrBa) ₃ relates to a combined inorganic crystal scintillator that uses a combination of cesium, strontium, calcium, and barium to form a scintillator crystal of Eu 1-10% or CsSrBaX ₃ : Eu 1-10%. First, formation of an ACaI ₃ crystal doped with divalent europium will be described as an example, and then a combination crystal will be described.

Example 1 ACa _1-y Eu _y I ₃ (Where A = K, Rb and Cs)

  FIG. 1 shows a typical potassium iodide and calcium iodide system as a prior art showing the relationship between molar concentration and temperature plot. Halide salts generally absorb moisture quickly and are preferably kept dry so as not to assume a crystalline form containing water in advance. As described herein, the purification process and handling of these halide salts is carried out under a protective atmosphere to obtain pure anhydrous salts, for example, zone purification techniques in furnaces, melt-filtration, or Performed best using other known techniques, in which case the material may be sealed in a quartz ampoule either under vacuum or under nitrogen or argon gas.

FIG. 2 shows similar plots for rubidium and cesium and calcium chloride, respectively. RbI is currently not available in pure anhydrous form and must be purified using known techniques to make it as anhydrous as possible. First, as shown in FIG. 1, KCaI ₃ is a coincident molten compound having a melting point of 524 ° C.

Prior art Table 1 below provides details for each crystal formed for each of potassium, rubidium and cesium and Z _eff calculated using known equations.

From the summary of Table 1 above, all three crystals have an orthorhombic crystal structure. A precise black and white view of each Eu 3% crystal is shown in FIG. The melting point varies from 524 ° C for potassium to 686 ° C for cesium. No phase transition is shown for either potassium or cesium. A phase transition at 469 ° C. or about 470 ° C. was seen for rubidium. Z _eff did not change so much and varied from 50.0 to 52.6. The density was approximately 3.8 to 4.1 g / cm ² .

Using the vertical temperature gradient solidification method and the improved Bridgman technique shown in FIG. 3, crystals whose properties are listed in Table 1 can be formed. The method can also be used with or as an alternative to the vertical temperature gradient coagulation (VGF) method. Scintillator crystals may be grown using Czochralski technology or composite Czochralski / Bridgeman technology as an alternative. As mentioned above, halide salts are moisture sensitive. One step in the process is to synthesize CsI, KI, RbI, compounds using high purity anhydrous starting halides such 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 dried salt raw material be handled in a glove box before being transferred to the ampoule of FIG. A typical ampoule is a quartz ampoule that is vacuum sealed at a vacuum pressure of 10 ⁻⁶ . Heat can be generated using an electro-dynamic gradient (EDG) furnace manufactured by Mellen with a translation motor. The synthesized material can be further purified by filtering through a frit followed by several zone purifications. The growth parameters are suggested as follows. The temperature gradient can be 25-75 ° C. per inch of crystal growth. The translation speed can be 1 millimeter per hour (range 0.5-2 mm per hour). A typical cooling rate can be 5 ° C. per hour. The crystal growth results are shown against a ruler indicating the length of the growth, as shown in FIG.

  In addition to growth in single crystal form, the scintillator compound described herein is a polycrystalline powder by mixing particulate powder components in a stoichiometric ratio and sintering at a temperature slightly below the melting point. Can be prepared as Furthermore, these compositions can be synthesized in the form of polycrystalline ceramics by hot isostatic pressing of particulate powder.

Next, FIG. 4 shows graphs of CsCaI ₃ and KCaI ₃ crystals showing respective peaks of excitation (broken line) at 285 and 290 nm wavelengths and emission (solid line) at 460 nm wavelengths. The intensity level is shown on the vertical axis as normalized intensity. A fluorescence spectrophotometer (trade name “Florolog 3”) from Horiba Jobin Yvon was used in the measurements. The emission and excitation bands are typically Eu ²⁺ 5d to 4f emission (Eu ²⁺ 5d-4f luminescence). Ca ²⁺ ions provide substitution sites for Eu ²⁺ doping. Characteristic data confirm that Eu ²⁺ is incorporated into each crystal scintillator lattice in a stable divalent state as an alternative to calcium. Furthermore, Eu ²⁺ doping is confirmed to show excellent luminous intensity and high spectral energy decomposition at normal room temperature. CsCaCl ₃ and CsCaI ₃ are described in “Theoretical and experimental characterization of promising new scintillators: Eu ²⁺ CsCaCl ₃ and CsCaI ₃ ,” J. App. Phys. 113, incorporated herein by reference in their entirety. 203504 (2013) of Tyagi, Zhuravleva et al. And “New single crystal scintillators: CsCaCl ₃ : Eu and CsCaI ₃ : Eu,” Journal of Crystal Growth 352 (2012) pp. 115-119 .

FIG. 5 shows graphs of X-ray radioluminescence spectra of CsCaI ₃ : Eu, KCaI ₃ : Eu, and RbCaI ₃ : Eu crystals, with maximum emission peaks at 450, 470 and 470 nm, respectively. Thus, the normalized intensity is shown as a vertical axis. The radioluminescence spectrum was measured at room temperature under continuous irradiation from an X-ray generator (35 kV and 0.1 mA). The emission band is characteristic for light emission from 5d to 4f of Eu ²⁺ . The light emission is, for example, a conventional photodetector known in the art such as PMT (trade name: “XP2020Q”) manufactured by Photonis and a photomultiplier tube (PMI) such as fast timing electronics. Suitable for use with.

Next, in FIG. 6, CsCaI _3: Eu 3% and KCaI _3: Eu indicates ¹³⁷ Cs gamma-ray energy spectrum of 3% crystalline. Light output measurements were performed on samples that were directly connected to a photomultiplier tube (PMT) and covered with Teflon tape in mineral oil. PMT (“H3177-50” manufactured by Hamamatsu Photonics) may be used for absolute light measurement. Gamma-ray energy spectra were recorded using a ¹³⁷ Cs source with a 6 μs molding time. The scintillator crystal spectra of CsCaI ₃ : Eu 3% (generally, upper, indicated by diamonds) and KCaI ₃ : Eu3% (generally, lower, downward triangles) are both standards having their photoelectric peak in channel 100 It shows a 662 keV gamma-ray photopeak position with a much higher channel number than bismuth germanate (BGO) crystals, which means a much higher light output. It was found that the optimal Eu ²⁺ activator concentration was 3 mol% when different Eu doping was used at 1-10 mol%.

  The photoelectric peak in FIG. 6 was fitted with a Gaussian function to determine the peak centroid and energy resolution. The integrated quantum efficiency of the PMT was used according to the emission spectrum of the scintillator to evaluate the light output in photons per unit gamma ray energy. Table 2 below shows the absolute light output and energy decomposition for the specific sample used for the measurement compared to the 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.

As can be seen from Table 2, the sample of RbCaI ₃ : Eu ₃ % did not show a resolved gamma ray photopeak. In contrast, the KCaI ₃ : Eu ₃ % crystal significantly outperforms the reference NaI: Tl crystal at a light yield of 60,000 photons per MeV compared to 38,000 for NaI: Tl, whereas CsCaI ₃ : Eu3% crystals did not exceed the light yield of NaI: Tl, whether matched or not matched. In terms of energy decomposition, the crystals of KCaI ₃ : Eu ₃ % and CsCaI ₃ : Eu ₃ % both showed a very acceptable range from 5% (for potassium) to 7% (for cesium) at 662 keV.

The scintillation decay of each crystal is shown in FIGS. FIG. 7A shows the result of counting the scintillation decay results of KCaI ₃ : Eu1%, FIG. 7B shows the RbCaI ₃ : Eu1%, and FIG. 7C shows CsCaI ₃ : Eu1% over time. Scintillation attenuation was measured using a time-correlated single photon counting technique and using a ¹³⁷ Cs662 keV gamma source. The scintillation decay constant resulting from fitting the curve to an exponential function is shown in the legend. The first-order decay around 1 μs is characteristic of Eu ²⁺ emission from 5d to 4f.

Next, FIG. 8A shows a black and white view prepared from a photograph of a KCaI ₃ : Eu ₃ % crystal compared with a scale ruler. All single crystals shown in the drawings herein are crack free and larger than 0.1 cm in one dimension. The vertical ruler indicates that the potassium crystals have grown to a length exceeding 6 cm and the width is measured to be about 0.5 cm. Next, FIG. 8B shows a black and white view prepared from a photograph of a CsCaI ₃ : Eu ₃ % crystal compared with a ruler. A single crystal of CsCaI ₃ : Eu 1% is shown in FIG. 2 of US Patent Application No. 61 / 443,076, filed February 15, 2011, which is incorporated herein by reference in its entirety. It is shown. The vertical ruler (inch) indicates that the potassium crystals have grown to a length greater than 2 inches and the width was measured to be about 0.5 cm. CsCaCl ₃ and CsCaI ₃ are described in Tyagi, Zhuravleva et al., “Theoretical and experimental characterization of promising new scintillators: Eu ²⁺ CsCaCl ₃ and CsCaI ₃ ,” J, incorporated herein by reference in their entirety. App. Phys. 113, 203504 (2013), and also “New single crystal scintillators: CsCaCl ₃ : Eu and CsCaI ₃ : Eu,” Journal of Crystal Growth 352 (2012) pp. 115-119 . Next, FIG. 8C shows a black and white view made from a photograph of a crystal of RbCaI ₃ : Eu ₃ %.

Table 3 below, reference NaI: CsCaI was compared to that of Tl crystal _3: Eu3%, and KCaI _3: shows the summary of results Eu3% crystalline.

  This example shows that crystals that actually grow to be comparable to NaI: Tl can be obtained at reasonable costs (including coincident melting and acceptable melting points). Since the crystals are hygroscopic, conventional photodetectors such as Photomultiplier tubes such as Phototonis XP2020Q PMT and high-speed timing electronics may be used in sealed packaging. X-rays, gamma rays and optical excitation were shown. If the crystal quality (removal of raw material impurities and improved processing) is improved, both light output and energy decomposition are expected to improve beyond current levels.

Example 2 CsA doped with divalent europium (0 ≦ y ≦ 1) _1-y Eu _y X ₃ (Wherein A = Ca, Sr, Ba, or a combination thereof, and X = Cl, Br, or I, or a combination thereof)

A single crystal inorganic crystal scintillator of formula CsAX ₃ doped with divalent europium doping, investigated at 1-10 mol% as described above, is described. Here, 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 has been shown that CsSrCl ₃ : Eu 10% crystals show a light yield of about 46,000 photons per MeV and scintillation decay at 2.6 μsec, and exhibit excellent gamma and X-ray detection properties. I will. The A ²⁺ lattice site provides a substitution site for Eu ²⁺ doping.

As shown in FIGS. 9A-9C, FIG. 9A shows a prior art phase diagram of the CsCl—CaCl ₂ system, where CsCl is shown on the left, CaCl ₂ is shown on the right in 0-100% molarity, and temperature Is shown along the left vertical axis at 200-800 ° C. FIG. 9B is a similar prior art phase diagram of the CsCl—SrCl ₂ system, with CsCl shown on the left and SrCl ₂ shown on the right. FIG. 9C is a prior art phase diagram of the SrBr ₂ -CsBr system, where SrBr ₂ is shown on the left side, CsBr is shown on the right side in 0-100% molarity, and the temperature is between 200 ° C. and 800 ° C. on the left side. Shown along the vertical axis. Divalent europium is mainly doped with r (Eu ²⁺ ) = 1.20 A (CN = 7), r (Sr ²⁺ ) = 1.21 A, and r (Ca ²⁺ ) = 1.06 A as follows: Used for. The perovskite type ABX ₃ compound was obtained by coincidence melting and with actual crystal growth according to the method described above and below.

  Table 4 below (partly prior art) shows an overview of crystal growth of each scintillator crystal.

  The method of crystal growth has already been described above with respect to the description of FIG. Bridgman crystal growth may include a collection of 99.99% anhydrous pure raw material. The material may be further purified by vacuum drying and melt filtration. As described above, a quartz ampule having a high temperature region and a low temperature region may be used, so that the crystal can be grown under a vacuum seal. Heat can be generated using an electro-dynamic gradient (EDG) furnace manufactured by Mellen with a translation motor. Crystal growth parameters may be the same as described above. Temperature gradient of 75 ° C./inch, translation rate of 1 millimeter per inch, cooling rate of 5 ° C. per hour (typical example). Scintillator crystals were grown with spontaneous orientation. Ternary halide scintillators can be synthesized using vertical temperature gradient solidification (VGF), Bridgman and melt synthesis and other techniques described above.

FIG. 10 is a graph of water absorption over time for Cs ₂ LiYCl ₆ : Ce and NaI as reference and the following crystals: CsSrCl ₃ : Eu 10%; CsSrBr ₃ : Eu 10% and CsCaCl ₃ : Eu 10%. The two crystals show little or no moisture absorption. Both CsSrBr ₃ : Eu 10% and CsCaCl ₃ : Eu 10% show substantially unchanged moisture absorption over a period of 250 minutes (over 4 hours). Furthermore, CsSrCl ₃ shows a significantly improved moisture absorption of 2% over 4 hours compared to NaI above 6.5%. Samples were measured in a closed box in a controlled environment at room temperature. All samples showed significantly lower moisture sensitivity compared to NaI and CLYC scintillators.

_{11, CsCaCl 3: 10%, CsSrCl} 3: Eu10% and CsSrBr _3: represents the photoluminescence spectra for each of the EU10% scintillator crystals, in the figure, the broken line represents a broad excitation band, solid lines, emission band Represents. The emission and excitation bands are characteristic for Eu ²⁺ emission from 5d to 4f. It is thus supported that Eu ²⁺ is incorporated into the photonic structure in the stable bivalent state of the crystal. Photoluminescence excitation and emission spectra can be measured with a Horiba fluorescence spectrophotometer (trade name “Fluorolog-3”) using an Xe lamp excitation source and a scanning monochromator. Table 5 below gives an overview of the excitation (EXC) and emission (EM) bands.

_{12, CsCaCl 3: 10%, CsSrCl} 3: Eu10% and CsSrBr _3: is a graph of the normalized intensity for various nanometer wavelengths X-ray excitation of the EU10% scintillator crystals. The radioluminescence spectrum was measured at room temperature under continuous irradiation from an X-ray generator (0.1 mA, 35 kV). A monochromator manufactured by Acton can be used to disperse the spectrum as a function of wavelength. The graph shows good results of efficient radioluminescence under X-ray excitation. The emission band is characteristic for emission of Eu ²⁺ from 5d to 4f. The emission band was a wavelength suitable for capture using conventional photodetectors such as PMT (trade name: “XP2020Q”) manufactured by Photonis and a photomultiplier tube (PMT) such as high-speed timing electronics. The measured release peaks are as follows. CsCaCl _3: For EU10%, the peak is _450nm, CsSrCl 3: For EU10%, the peak is _437nm, CsSrBr 3: For EU10%, the peak was 443 nm.

13A-13C represent scintillation decay graphs over time for each crystal, FIG. 13A represents CsCaCl ₃ : Eu 10%, FIG. 13B represents CsSrCl ₃ : Eu 10%, and FIG. 13C represents CsSrBr ₃ : Eu represents 10%. Scintillation time profiles were recorded using a ¹³⁷ Cs662 keV gamma source. The scintillation decay constant obtained from fitting the curve to an exponential function is shown in the legend. The primary decay around 2-4 μs is characteristic of Eu ²⁺ emission from 5d to 4f. The measured scintillation decay time was measured as follows. For CsCaCl ₃ : Eu 10%, the decay time is 4.1 μs, for CsSrCl ₃ : Eu 10%, the decay time is 2.6 μs (fastest), and for CsSrBr ₃ : Eu 10%, the decay time is It was 3.5 μsec.

FIG 14A~14C represents a graph of ¹³⁷ Cs gamma-ray emission spectrum of each crystal, Figure _14A, CsCaCl 3: represents EU10%, FIG. 14B, CsSrCl _3: represents Eu, Figure 14C, CsSrBr _3: Eu And normalized with respect to a reference bismuth germanate (BGO) having its photoelectric peak in channel 100. Efficient scintillation properties were shown for all three crystals under excitation with ionizing radiation. Table 6 below shows the light yield and energy decomposition for each crystal compared to NaI: Tl as a reference.

As can be seen from the results, CsSrCl ₃ : Eu 10% shows an improvement in light yield over the known NaI: Tl.

Figure 15A, 15B is a graph showing the optical output proportionality, FIG. 15A, CsSrBr _3: is a graph of light output per 1keV to the energy (keV) for Eu, FIG. 15B, CsCaCl _3: About Eu It is a similar graph. FIG. 15 illustrates the importance of contributing to good energy decomposition if these proportions are good, as these graphs show good proportions for light output per keV over a wide range of energy levels from 10 to 1000 keV. Show.

FIGS. 16A to 16C are black and white diagrams prepared from photographs of CsSrCl ₃ : Eu 10%, CsSrBr ₃ , Eu 10%, and CsCaCl ₃ : Eu 10% crystals. CsSrCl ₃ : Eu 10% was grown to a length of about 2 inches. However, although it seems to be due to the phase transition, some cracks may be seen. Doping with 1% Eu was studied by the same inventors in US Patent Application No. 61 / 491,074, filed May 27, 2011, the entire contents of which are hereby incorporated by reference. It has been incorporated. The single crystal sample doped with Eu 1% is shown in FIG. 1 for CsSrBr ₃ , and in FIG. 8 is shown for CsCaCl ₃ doped with Eu 1%. Each gamma ray and X-ray scintillation characteristic is given. The crystal is about 1 cm in cross section. CsSrBr ₃ : Eu 10% grew to a length of about 2 cm, was relatively colorless and transparent, and had no cracks. Its circular cross section was slightly smaller than 2 cm in diameter. CsCaCl ₃ : Eu 10% was grown to a length exceeding 3 cm. It was also relatively colorless and transparent with no cracks. Its circular cross section was measured to be about 11/16 inch in diameter.
Table 7 shows a summary table for the following crystals compared to the reference NaI: Tl.

The table shows that when compared with NaI: Tl, the above-mentioned novel inorganic single crystal shows the expected results including good transparency, low hygroscopicity to no hygroscopicity, good light output and excellent proportionality. Indicates that It is expected that even better results will be achieved with further improvements in raw material purification and optimization of growth parameters.

A combination crystal comprising CsSr _1-x Ba _x I ₃ : Eu 1% and 3% is described below. Crystals were grown at x = 0.00, 0.03, 0.06, 0.09, 0.14 and 0.24. For example, the purpose of gradual substitution of barium in crystals doped with 1 mol% Eu with strontium was to determine whether the substitution affects the hygroscopicity of CsSrI ₃ . The latter appears to be a moisture absorber that adversely affects its ability as a scintillator. Our Phys. Status Solidi RRL 5, No 1, pp. 43-45 (2011), “Crystal growth and characterization of CsSr _1-x Eu, incorporated herein by reference in its entirety. _As reported in “ _x I ₃ high light yield scintillators”, single crystals were grown and X-ray and gamma-ray scintillations were observed. When x = 0.08, the light yield was 65000 ph / MeV. In addition, Applicants have found that certain EuIII (vs. Eu ²⁺ ) can appear on the surface and can be oxidized. On the other hand, US Patent Application No. 61 / 491,074 ("'provisional 074") of the same inventors filed on May 27, 2011, which is incorporated herein by reference in its entirety. CsBaI ₃ was studied at Eu1, ₃ and 7 mol% doping levels (Zhuravleva et al. Optical Materials 36 (2014) pp. 670-674, “The Europium, incorporated by reference in its entirety. oxidation state in CsSrI ₃ : Eu scintiallators measured by X-ray absorption spectroscopy ”). Single crystal photographs of the three samples are shown in FIG. 12 of 'tentative 074' with doping levels of Eu of 1, 3 and 7 mol% (each having a volume of about 50 mm ³ ). FIG. 13 shows three samples excited with UV light, and FIG. 14 shows data for gamma ray detection at Eu 7 mol% doping level. Furthermore, when partially substituted barium strontium, it is expected that orthorhombic crystal structure and congruent melting characteristics of CsSrI ₃ are stored, has been demonstrated. All of these composite crystals having x values of 0.03, 0.06, 0.09, 0.14 and 0.24 functioned as scintillators and were successfully produced as single crystals without cracks. However, published at 27-32 in the Journal of Crystal Growth 384 (2013) by the inventors published on 18 September 2013, which is incorporated herein by reference in its entirety. As shown in FIG. 17 quoted from FIG. 6 of the applicant's paper “Effect of Ba substitution in CsSrI ₃ : Eu ²⁺ ” (JCG2013 paper), the water absorption rate markedly decreased with increasing barium concentration. It was shown that. FIG. 18 is a collection of graphs showing the emission peak appearing at 445 nm to 450 nm in the radioluminescence spectrum of CsSr _1-x Ba _x I ₃ : 1% Eu at room temperature. The range of 445 to 450 nm is characterized by the known 5d to 4f transition. Impurity of defect luminescence is not observed. Small variations in peak position do not appear to correlate with the Ba concentration and are likely due to small variations in crystal quality and light absorption.

  FIG. 8 of the JCG2013 paper shows the emission and excitation spectrum of 1% Eu for x values from 0.03 to 0.24. The water absorption rate shown in FIG. 17 starting at 0.10% / min at zero barium concentration is improved by 35% at only 3% barium concentration and improved by 50% to 0.05% / min at 14% barium concentration. The It is clear that this improvement in hygroscopicity is critical. Table 8 below shows a table of effective densities and effective atomic numbers that increase with increasing barium concentration.

  Increasing the density and effective atomic number results in enhanced X-ray and gamma ray detection efficiency. The results of improved scintillation characteristics are described below in Table 9.

X-ray radioluminescence showed a peak at a wavelength of 445 to 450 um. The emission band is characterized by emission of Eu ²⁺ from 5d to 4f. The emission is at a wavelength suitable for use with a conventional photodetector such as a photomultiplier tube (PMT). UV / visible excitation and emission were measured with an emission peak at 446 nm. When x was 3% and Eu 1 mol%, the maximum light output was measured, measuring 28,000 photons per MeV with a decay time of 1.9 μs. When x is 24%, Eu is 3 mol%, and when the scintillation decay time is 1.5 μs, the light output is 21,000 photons per MeV, so that the light output is x Decreases with increase.

  While various aspects of the 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 those skilled in the art that various changes in form and detail can be made without departing from the spirit and scope of the invention. Accordingly, the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

  In addition, it should be understood that the accompanying drawings, which highlight the structure, method, functionality, and advantages of the present invention, are presented for illustrative purposes only. The present invention can be configured with sufficient flexibility so that it can be implemented in ways other than those shown in the accompanying drawings.

  In addition, the purpose of the abstract is to help the general public who is not familiar with U.S. national standard technical research and patent or legal terms or expressions, and especially scientists, engineers and practitioners in related fields, particularly the nature of this technical disclosure. It is to be able to judge the characteristics. The abstract is in no way intended to limit the scope of the invention in any way.

Claims (14)

Chemical composition CsCaI ₃ : yEu (where y was grown by one of the Bridgman method, the modified Bridgman method, the Czochralski method, the composite Czochralski / Bridgeman method and the vertical temperature gradient solidification method) Is from 0.01 to 0.10).   The scintillator of claim 1, comprising a single crystal larger than 0.1 cm in one dimension when y is about 0.01 to 0.03. Chemical composition RbCaI ₃ : yEu (where y is 0) grown by one of the Bridgman method, the modified Bridgman method, the Czochralski method, the composite Czochralski / Bridgeman method and the vertical gradient freezing method .01 or more and 0.03 or less).   4. The scintillator of claim 3, comprising a single crystal that is larger than 0.1 cm in one dimension when y is about 0.03. Chemical composition CsCaCl ₃ : yEu (where y was grown by one of the Bridgman method, the modified Bridgman method, the Czochralski method, the composite Czochralski / Bridgeman method and the vertical temperature gradient solidification method) Is from 0.01 to 0.10).   6. A scintillator according to claim 5, comprising a single crystal larger than 0.1 cm in one dimension. Chemical composition CsSrBr ₃ : yEtt (where y is the growth rate) grown by one of the Bridgeman method, the improved Bridgeman method, the Czochralski method, the composite Czochralski / Bridgeman method and the vertical temperature gradient solidification method. Is from 0.01 to 0.10).   The scintillator according to claim 7, comprising a single crystal larger than 0.1 cm in one dimension. Chemical composition CsSrCl ₃ : yEti (where y is the growth factor) grown by one of the Bridgman method, the modified Bridgman method, the Czochralski method, the composite Czochralski / Bridgeman method and the vertical temperature gradient solidification method. Is about 0.10).   The scintillator according to claim 9, comprising a single crystal larger than 0.1 cm in one dimension. Chemical composition CsBa _x Sr _1-x I ₃ : yEu grown by one of Bridgman method, modified Bridgman method, Czochralski method, combined Czochralski / Bridgeman method and vertical temperature gradient solidification method (Wherein y is about 0.01 to 0.03 and x is not less than 0.00 and not more than 0.24), a single crystal is formed, and the hygroscopicity decreases with increasing barium concentration Showing the scintillator.   12. A scintillator according to claim 11, comprising a single crystal of more than 0.1 cm in one dimension. Barium concentration CsSrI _3: yEu (wherein, y is about a is 0.01 to 0.03) to improve the hygroscopic properties of the scintillator according to claim 11. When x = 0.03, the water absorption rate of CsSrI ₃ : yEu is improved to a level of 0.10 to 0.065% per minute, that is, about 35%, and when x is larger than 0.14, the water absorption rate is improved. 14. The scintillator of claim 13, wherein is greater than 50%.