JP2017036160A - Crystal material, crystal production method, radiation detector, nondestructive testing device, and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide crystal materials with a short fluorescent life.SOLUTION: The present invention provides crystal materials represented by general formula (1): (REABM)SiO, having a pyrochlore type structure, composed of a non-stoichiometric composition, a congruent melting composition, wherein, A includes at least one selected from Gd, Y, La, Sc, Yb and Lu, B includes at least one selected from La, Gd, Yb, Lu, Y and Sc, 0.1<y<0.4, RE includes at least one selected from Ce, Pr, Nd, Eu, Tb and Yb, 0<x<0.1, M includes at least one selected from Ti, Zr, Hf, Ta, Nb, Mo and W, represented by 0≤s<0.01.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a crystal material, a crystal manufacturing method, a radiation detector, a nondestructive inspection apparatus, and an imaging apparatus.

  Scintillator single crystals are used in radiation detectors that detect γ rays, X rays, α rays, neutron rays, and the like. Such radiation detectors include medical imaging devices (imaging devices) such as positron emission tomography (PET) devices and X-ray CT devices, various radiation measuring devices in the high energy physics field, and resource exploration devices ( For example, it has been widely applied to resource exploration such as oil well logging.

  In general, a radiation detector includes a scintillator that absorbs γ-rays, X-rays, α-rays, and neutron rays and converts them into scintillation light, and a photodetector such as a light receiving element that receives the scintillation light and converts it into an electrical signal or the like. Consists of For example, in high energy physics and positron emission tomography (PET) imaging systems, images are created based on the interaction between scintillators and radiation generated by radioactive decay. Here, in the positron emission tomography (PET) imaging system, gamma rays resulting from the interaction of positrons in the subject and the corresponding electrons enter the scintillator and are converted into photons that can be detected by a photodetector. Is done. Photons emitted from the scintillator can be detected using a photodiode (PD), silicon photomultiplier (Si-PM), or photomultiplier tube (PMT), or other photodetector.

  PMT has high quantum efficiency (efficiency for converting photons into electrons (current signals)) in a wavelength region near 400 nm, and is mainly used in combination with a scintillator having an emission peak wavelength in the vicinity of 400 nm. For a scintillator array in which scintillators are arranged in an array, a position sensitive PMT (PS-PMT) or the like is used in combination. Thereby, it is possible to determine in which pixel of the scintillator array the photon is detected from the centroid calculation. Further, for a short wavelength light emitting scintillator of 350 nm or less, a radiation detector can be realized by using a short wavelength PMT having a constant quantum efficiency and sensitivity even at a wavelength near 200 nm.

  On the other hand, semiconductor photodetectors such as photo diodes (PD), avalanche photo diodes (APD), and silicon photo multipliers (Si-PM) have a wide range of applications, particularly in radiation detectors and imaging devices. . Various semiconductor photodetectors are known. For example, PD and Si-PM composed of a silicon semiconductor have a quantum efficiency exceeding 50% in the wavelength band from 350 nm to 900 nm, and the quantum efficiency of PMT is 45% at the maximum. High efficiency. Among the above wavelength bands, the wavelength band with high sensitivity is 500 nm to 700 nm, and the sensitivity is highest around 600 nm, and the quantum efficiency is about 80%. For this reason, these semiconductor photodetectors are used in combination with a scintillator having an emission peak wavelength between 350 nm and 900 nm centering around 600 nm. Similar to PMT, PD, APD, and Si-PM also have a PD array having position detection sensitivity, a position-sensitive avalanche photodiode (PSAPD), and an Si-PM array. These elements can also determine in which pixel of the scintillator array the photon was detected. Furthermore, with respect to a short wavelength light emitting scintillator of 350 nm or less, a silicon semiconductor can be obtained by converting the scintillator light into light in a wavelength region where the silicon semiconductor is sensitive, such as by using a short wavelength Si-PM or a wavelength conversion element. It is possible to realize a radiation detector that performs readout by the above.

  The scintillators suitable for these radiation detectors have high density and high atomic number (high photoelectric absorption ratio) from the viewpoint of detection efficiency, high light emission from the point of high energy resolution, and the necessity of high-speed response. It is desired that the fluorescence lifetime is short. In addition, in recent systems, multiple scintillators need to be arranged densely in a long and narrow shape (for example, about 5mm x 30mm for PET) for multilayering and high resolution, making it easy to handle, workability, and large crystal production Moreover, price is also an important selection factor. It is also important that the emission wavelength of the scintillator matches the wavelength range where the detection sensitivity of the photodetector is high.

Currently, there is a scintillator Ce: Gd ₂ Si ₂ O ₇ having a pyrochlore structure as a preferable scintillator applied to various radiation detectors. The scintillator has the advantages that it is chemically stable, has no cleavage or deliquescence, and has a high light emission amount. For example, a scintillator having a pyrochlore structure that utilizes light emission from the Ce ³⁺ 4f5d level described in Non-Patent Document 1 emits light compared to Ce: Gd ₂ SiO ₅ , which is one of the widely used scintillators. The amount was 2.5 times higher. However, on the other hand, as described in Non-Patent Document 1, because of the peritectic composition on the phase diagram, single crystal growth from the melt cannot be performed, and it is difficult to obtain a large transparent body. .

  In the scintillators having the pyrochlore structure described in Patent Documents 1 and 2 and Non-Patent Document 2, attempts have been made to stabilize the structure by replacing Ce with a site of a rare earth element. As a result, this crystal can be made into a large single crystal by a melt growth method such as the floating zone method, the chocolate ski method, the micro pulling down method, the Bridgman method and the like. However, when Ce is increased at the rare earth element site, there is a problem (concentration quenching) that the amount of light emission is drastically reduced.

  In Patent Document 3 and Non-Patent Document 3, there is an attempt to stabilize the structure by replacing one or more elements selected from Y, Yb, Sc, La, and Lu with sites of rare earth elements (particularly La). Has been made. As a result, this crystal can be produced as a large single crystal by a melt growth method such as a floating zone method, a chocolate ski method, a micro pull-down method, or a Bridgman method. However, the fluorescence lifetime becomes 65 ns and 63 ns, which suggests that measurement using a PET imaging system is insufficient.

Furthermore, the emission centers such as Eu, Pr, and Ce may be Eu ³⁺ , Pr ⁴⁺ and Ce ⁴⁺ , but in this case, the ratio of Eu ²⁺ , Pr ³⁺ and Ce ³⁺ used as scintillator emission decreases, There is a possibility that the amount of luminescence is reduced and a slow fluorescence lifetime component is generated.

JP 2009-74039 A International Publication No. WO2003 / 083010 International Publication No. WO2014 / 104238

S. Kawamura, JHKaneko, M. Higuchi, T. Yamaguchi, J. Haruna, Y. Yagi, K. Susa, F. Fujita, A. Homma, S. Nishiyama, H. Ishibashi, K. Kurashige and M. Furusaka , IEEE Nuclear Science Symposium Conference Record, San Diego, USA, 29 October-5 November 2006, pp. 1160-1163. S. Kawamura, M. Higuchi, JHKaneko, S. Nishiyama, J. Haruna, S. Saeki, S. Ueda, K. Kurashige, H. Ishibashi and M. Furusaka, Crystal Growth & Design, volume 9 (3), 2009, pages 1470-1473. Akira Yoshikawa, Shunsuke Kurosawa, Yasuhiro Shoji, Valery I. Chani, Kei Kamada, Yuui Yokota, and Yuji Ohashi, Crystal Growth & Design, volume15 (4), 2015, pages 1642-1651

Examples of the luminescence activator added as the luminescence center include Ce ³⁺ and Pr ³⁺ , and these activators are those whose valence is partly larger than the target valence, for example, Ce ⁴⁺ or Pr ⁴⁺ . There exists a subject that it will exist and will inhibit light emission, and a fluorescence lifetime will become slow.

  The present invention has been made in view of the above, and it is an object of the present invention to provide a crystal material having a short fluorescence lifetime, a manufacturing method thereof, and a radiation detector, an imaging device, and a nondestructive inspection device using the crystal material. And

To solve the above problems and achieve the object, the crystalline material according to one embodiment of the present invention have the general formula _{(1) :( RE x A 1} -x-y-s B y M s) 2 Si 2 O ₇ (1)
It is characterized by having a pyrochlore type structure, a non-stoichiometric composition, and a harmonic melt composition. Here, in formula (1), A includes at least one selected from Gd, Y, La, Sc, Yb and Lu, and B is selected from La, Gd, Yb, Lu, Y and Sc. Including at least one or more, 0.1 <y <0.4, and RE includes at least one selected from Ce, Pr, Nd, Eu, Tb and Yb, and 0 <x <0.1 And M includes at least one selected from Zr, Hf, Ta, Nb, Mo and W, and is represented by 0 ≦ s <0.01.

  In the crystalline material according to one embodiment of the present invention, the ranges of the x, y, and s are further 0 <x <0.05, 0.1 <y <0.35, and 0 ≦ s <0.005. It is characterized by being expressed.

  In the crystalline material according to one embodiment of the present invention, the ranges of the x, y, and s are further represented by 0 <x <0.04, 0.1 <y <0.35, and 0 ≦ s <0.005. It is characterized by being.

  The crystal material according to one embodiment of the present invention is characterized in that, in the general formula (1), RE is Ce, A is Gd, and B is one or more selected from La and Y. .

  The crystalline material according to one embodiment of the present invention emits scintillation light when irradiated with radiation, and the predetermined fluorescent component included in the scintillation light has a fluorescence lifetime of 61 nanoseconds or less and a fluorescence peak wavelength of 170 nm or more. It is the range of 900 nm or less.

  The crystalline material according to one embodiment of the present invention emits scintillation light when irradiated with radiation, and the predetermined fluorescent component contained in the scintillation light has a fluorescence lifetime of 61 nanoseconds or less and a fluorescence peak wavelength of 300 nm or more. It is the range of 700 nm or less.

  In the crystal manufacturing method according to one aspect of the present invention, a raw material containing A, Si and RE is blended so as to have an element ratio of the crystal material according to one aspect of the present invention, and the temperature is increased until the blended raw material is melted. It is characterized in that it is cooled after being raised to form a crystal having a pyrochlore structure. The crystal manufacturing method according to one embodiment of the present invention dramatically improves the crystallization rate to 50% or more.

  The radiation detector which concerns on 1 aspect of this invention is equipped with the scintillator comprised from the crystal material which concerns on 1 aspect of this invention, and the photodetector which receives the scintillation light from the said scintillator, It is characterized by the above-mentioned.

  A radiation detector according to one embodiment of the present invention includes a scintillator including the crystal material according to one embodiment of the present invention, and scintillation light from the scintillator, and light having a wavelength of 170 nm to 350 nm included in the scintillation light. A wavelength conversion element that converts the wavelength of the light into any wavelength in the range of 320 nm to 700 nm, and a photodetector that receives the light whose wavelength has been converted by the wavelength conversion element.

  A radiation detector according to one embodiment of the present invention includes a scintillator including a crystalline material according to one embodiment of the present invention, and is provided with position sensitivity.

  An imaging device according to one embodiment of the present invention includes the radiation detector according to one embodiment of the present invention.

  A nondestructive inspection apparatus according to one aspect of the present invention includes the radiation detector according to one aspect of the present invention.

  According to the present invention, the light emission activator can be stably present at the target valence by co-adding an element having a valence larger than the valence of the target light emission activator. The crystal of the melt composition has an effect of maintaining the excellent property that the fluorescence lifetime is short.

FIG. 1 is a view showing a photograph of the produced (Ce _0.015 Gd _0.750 La _0.2349 Zr _0.0001 ) ₂ Si ₂ O ₇ crystal. FIG. 2 is a view showing a photograph of the produced (Ce _0.015 Gd _0.750 La _0.2348 Zr _0.0002 ) crystal. FIG. 3 is a view showing a photograph of the produced (Ce _0.015 Gd _0.750 La _0.2348 Hf _0.0002 ) crystal. FIG. 4 is a view showing a photograph of the produced (Ce _0.015 Gd _0.750 La _0.2348 W _0.0002 ) crystal. FIG. 5 is a view showing a photograph of the produced (Ce _0.015 Gd _0.750 La _0.2348 Ta _0.0002 ) crystal. FIG. 6 is a diagram showing a photograph of a (Ce _0.015 Gd _0.750 La _0.235 ) ₂ Si ₂ O ₇ crystal produced as a comparative example. FIG. 7 is a diagram showing the transmittance profiles of Examples 1 to 3 and Comparative Example 1. FIG. 8 is a diagram showing wave height distribution spectra (Examples 1 to 3, Comparative Examples 1 and 2) obtained by irradiation with ¹³⁷ Csγ rays (662 keV). FIG. 9 is a diagram showing a fluorescence decay curve profile of the crystal of Example 1 obtained by irradiation with ¹³⁷ Csγ rays (662 keV). FIG. 10 is a diagram showing the radiation detector according to the exemplary embodiment of the present invention. FIG. 11 is a diagram showing a nondestructive inspection apparatus according to an embodiment of the present invention. FIG. 12 is a diagram illustrating the imaging apparatus according to the embodiment of the present invention. FIG. 13 is a diagram showing a radiation detector according to the exemplary embodiment of the present invention.

  Hereinafter, embodiments of a crystal material, a crystal manufacturing method, a radiation detector, an imaging apparatus, and a nondestructive inspection apparatus according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

The crystal material according to the embodiment of the present invention has a general formula (1):
_{(1) :( RE x A 1} -x-y-s B y M s) 2 Si 2 O 7 (1)
It is a crystalline material having a pyrochlore structure, a non-stoichiometric composition, and a harmonic melt composition.
Here, in formula (1), A includes at least one selected from Gd, Y, La, Sc, Yb and Lu, and B is selected from La, Gd, Yb, Lu, Y and Sc. Including at least one or more, 0.1 <y <0.4, and RE includes at least one selected from Ce, Pr, Nd, Eu, Tb and Yb, and 0 <x <0.1 And M includes at least one selected from Ti, Zr, Hf, Ta, Nb, Mo and W, and is represented by 0 ≦ s <0.01. Regarding RE, transition metals as well as rare earth elements can be selected as the light emission activator.

  Preferably, the ranges of x, y, and s in the formula (1) are further represented by 0 <x <0.05, 0.1 <y <0.35, and 0 ≦ s <0.005.

  More preferably, the range of x, y, and s in Formula (1) is further represented by 0 <x <0.04, 0.1 <y <0.35, and 0 ≦ s <0.005.

  Thus, the crystal material according to the present embodiment is a crystal material that has a high light emission amount of scintillation light generated by radiation irradiation and has a short fluorescence lifetime. For example, in the general formula (1), RE is preferably Ce, A is Gd, and B is preferably one or more selected from La and Y.

  In addition, although the pyrosilicate crystal having a known pyrochlore structure is expected to have a high light emission amount, the stoichiometric composition is not a harmonic melting composition, so it becomes very difficult to produce a transparent bulk body, and the crystal production There is a problem that the yield sometimes worsens. On the other hand, the crystal material according to the present embodiment can be configured to solve these problems.

  Further, the crystal material according to the present embodiment can be used as the radiation detector 100 by being combined with a photodetector 102 that can receive scintillation light emitted from the crystal material 101, for example, as shown in FIG. It becomes. Further, for example, as shown in FIG. 11, the radiation detector 100 is irradiated with radiation from the radiation source 201 and the radiation that has passed through the measurement object 202 is detected by the radiation detector 100. It can also be used as a radiation measurement device or a resource exploration device as the nondestructive inspection device 200 provided.

  In addition, the crystal material according to this embodiment can have a fluorescence lifetime of a fluorescent component included in scintillation light of 10 microseconds or less and a fluorescence peak wavelength of 150 nm to 900 nm. Furthermore, the fluorescence lifetime can be set to 2 microseconds or less, and the fluorescence peak wavelength can be set to a range of 250 nm to 900 nm. As described above, since the fluorescence lifetime is short, the sampling time for fluorescence measurement can be shortened, and the high time resolution, that is, the sampling interval can be reduced. In addition, by realizing high time resolution, the number of samplings per unit time can be increased. Such a crystal material having a short-lived emission is suitable as a scintillator for PET, which is an imaging device, SPECT (Single photon emission computed tomography), and fast response radiation detection for CT. Available to: For example, as shown in FIG. 12, the radiation source 201 and the radiation detector 100 are arranged at symmetrical points of the circumference, and the measurement object 202 is scanned while scanning the circumference with the radiation source 201 and the radiation detector 100. Can be used as the imaging apparatus 300 using CT.

  Further, since the fluorescence peak wavelength of the fluorescent component is in the range of 150 nm to 900 nm, it can be detected in combination with a semiconductor photodetector such as PD, APD, or Si-PM composed of a silicon semiconductor. In particular, when the fluorescence peak wavelength of the fluorescent component is 250 nm or more and 400 nm or less, it is effective to use a wavelength conversion element to convert the wavelength to 300 nm or more and 900 nm or less, that is, the wavelength in the region where the wavelength sensitivity of the above-described photodetector is sufficient. It is. As such a wavelength conversion element, an element that converts the wavelength of light having a wavelength of 260 nm to 350 nm included in the scintillation light into any wavelength in the range of 320 nm to 700 nm can be used. For example, as shown in FIG. 13, as the wavelength conversion element 103, for example, a material using a plastic wavelength conversion optical fiber (for example, Y11 (200) MS made by Kuraray Co., Ltd.) is used. The scintillation light emitted from 101 can be received by the photodetector 104 after wavelength conversion. Further, the type of photodetector to be combined can be appropriately used according to the fluorescence peak wavelength or the like. For example, PMT or PS-PMT may be used.

  In addition, it can be used not only as a radiation detector but also as a wavelength conversion element in lighting equipment and a phosphorescent material using a long afterglow component.

Further, in the crystal material according to the present embodiment, if the fluorescence lifetime of the fluorescent component contained in the scintillation light is 61 nanoseconds or less and the fluorescence peak wavelength is in the range of 170 nm to 900 nm, further high resolution and Highly sensitive scintillation light detection can be realized. A fluorescence lifetime of 61 nanoseconds or less and a fluorescence peak wavelength in the range of 300 nm to 700 nm are preferable because scintillation light can be detected with higher resolution and sensitivity. As a luminescence activator, when bivalent such as Eu ²⁺ is added, a trivalent or higher additive is added, and when trivalent such as Ce ³⁺ is added, a tetravalent or higher ion corresponds to M in the general formula (1). It can be added to the part to be. For example, M includes Ti ⁴⁺ , Zr ⁴⁺ , Zr ⁴⁺ , W ⁴⁺ , Ta ⁵⁺ , etc., but is not limited thereto.

  Further, in the crystal material according to the present embodiment, the emission amount of the fluorescent component in the range of the ambient temperature from room temperature to 150 degrees Celsius when the ambient temperature is 0 degree Celsius is used as a reference. The attenuation rate from the reference can be less than 50%. Furthermore, the light emission amount of the fluorescent component after leaving it in an environment of 400 degrees Celsius or more for 12 hours or more does not fluctuate by 20% or more, and it does not physically break even under a pressure of 5 G or more. Therefore, the crystal material according to the present embodiment can reduce attenuation of light emission amount even under a high temperature environment, and thus is very useful as a crystal material used under a high temperature environment or under a large vibration.

  In particular, a radiation detector is configured by combining a scintillator made of a crystal material according to the present embodiment and a photodetector that receives light emitted from the scintillator and operates at an ambient temperature of room temperature to 200 degrees Celsius. By doing so, it is preferable because it can be used without cooling for resource exploration or the like which requires measurement under high temperature environment and large vibration.

  A method for producing a single crystal of crystal material according to the present embodiment (crystal production method) will be described below. In any method for producing a single crystal, a general oxide raw material can be used as a starting material. However, when used as a single crystal for a scintillator, it has a high content of 99.99% or higher (4N or higher). It is particularly preferable to use a purity raw material. These starting materials including A, Si and RE are weighed, mixed and blended so as to have a target composition (element ratio of the crystal material according to the present embodiment) at the time of forming the melt as a crystal growth material. Use. Further, among these starting materials, those having as few impurities as possible other than the target composition (for example, 1 ppm or less) are particularly preferable.

  It is desirable that the starting material composition is not stoichiometric, but is prepared taking into consideration that the melt has a ratio of the harmonic melt composition of the present embodiment. At that time, it is desirable to consider a loss in the crystal manufacturing process such as an ignition loss.

Crystal growth is preferably performed in an inert gas (eg, Ar, N ₂ , He, etc.) atmosphere. Alternatively, a mixed gas of an inert gas (for example, Ar, N ₂ , He, etc.) and oxygen gas may be used. However, when the crystal is grown in the atmosphere of this mixed gas, the partial pressure of oxygen is preferably 2% or less for the purpose of preventing oxidation of the crucible. However, when using a production method that does not use a crucible, such as the floating zone method, the oxygen partial pressure can be set to 100%. In a subsequent process such as annealing after crystal growth, oxygen gas, inert gas (eg, Ar, N ₂ , He, etc.), inert gas (eg, Ar, N 2, He, etc.), oxygen gas, The mixed gas can be used. In the subsequent process, when a mixed gas is used, the oxygen partial pressure is not limited to 2% or less, and any mixture ratio from 0% to 100% oxygen partial pressure may be used.

  As a method for producing a single crystal of the crystal material according to the present embodiment, in addition to the micro pull-down method, the Choral Ski method (pull-up method), the Bridgman method, the band melting method (zone melt method), and edge-limited thin film supply Crystal growth (EFG method), floating zone method, and the like can be mentioned, but the present invention is not limited to these, and various crystal growth methods can be used. In order to obtain a large single crystal, the chocolate ski method or the Bridgman method is preferred. By using a large single crystal, the yield of the single crystal can be improved and the processing loss can be relatively reduced. Therefore, compared with the method of taking out a single crystal from polycrystallized as described in Patent Document 1, a low-cost and high-quality crystal material can be obtained. However, the crystal material according to the present embodiment is not limited to a single crystal, and may be a polycrystalline sintered body such as ceramics that can be manufactured by a solid phase reaction method or the like.

  On the other hand, if only a small single crystal is used as the scintillator single crystal, there is no need for post-processing or there is little, so the floating zone method, the zone melt method, the EFG method, the micro pull-down method, or the chocolate ski method For reasons such as wettability with a crucible, the micro pulling method or the zone melt method is particularly preferable.

  Examples of the crucible and afterheater material that can be used include platinum, iridium, rhodium, rhenium, and alloys thereof.

  In manufacturing a scintillator single crystal, a high-frequency oscillator, a condenser heater, and a resistance heater may be used.

  Hereinafter, as an example of a method for producing a single crystal of a crystal material according to the present embodiment, a single crystal production method using a micro-pulling method, a Czochralski method, and a floating zone method will be described. The method for producing a single crystal of crystal material is not limited to this.

  The micro pull-down method can be performed using a known atmosphere control type micro pull-down apparatus using high-frequency induction heating. For example, the micro-pulling device includes a crucible containing a raw material melt, a seed crystal holder for holding a seed crystal in contact with the raw material melt flowing out from a pore provided at the bottom of the crucible, and a seed crystal holder downward. A single crystal manufacturing apparatus including a moving mechanism for moving, a moving speed control device for controlling the speed of the moving mechanism, and induction heating means (for example, a high frequency induction heating coil) for heating the crucible. According to such a single crystal manufacturing apparatus, a single crystal can be produced by forming a solid-liquid interface immediately below the crucible and moving the seed crystal downward.

  In the above-described micro-pulling-down apparatus, the crucible is made of carbon, platinum, iridium, rhodium, rhenium, or an alloy thereof. Further, an after heater which is a heating element made of carbon, platinum, iridium, rhodium, rhenium, or an alloy thereof is disposed on the outer periphery of the bottom of the crucible. By controlling the output of each induction heating means of the crucible and after-heater, the temperature of the solid-liquid boundary region of the raw material melt drawn from the pores provided at the bottom of the crucible and its distribution are controlled by adjusting the heat generation amount. Can do.

The above atmosphere control type micro pull-down apparatus employs stainless steel (SUS) as the material of the chamber and quartz as the window material, and includes a rotary pump for enabling the atmosphere control before gas replacement. This is an apparatus that makes it possible to reduce the internal vacuum to 1 × 10 ⁻³ Torr or less. In addition, Ar, N ₂ , H ₂ , O ₂ gas, etc. can be introduced into the chamber at a flow rate precisely adjusted by an accompanying gas flow meter.

Using this apparatus, the crystal growth raw material prepared by the above method is put into a crucible, the inside of the furnace is evacuated to a high vacuum, and then Ar gas or a mixed gas of Ar gas and O ₂ gas is put into the furnace. By introducing, the inside of the furnace is made an inert gas atmosphere or a low oxygen partial pressure atmosphere. Next, the crucible is heated by gradually applying high frequency power to the high frequency induction heating coil to raise the temperature until the raw material is melted, and the raw material in the crucible is completely melted.

  Subsequently, the seed crystal held in the seed crystal holder is gradually raised at a predetermined speed by the moving mechanism. Then, when the tip of the seed crystal is brought into contact with the pores at the lower end of the crucible and sufficiently blended, the seed crystal is lowered while being adjusted while the melt temperature is adjusted to grow the crystal.

  As the seed crystal, it is preferable to use a seed crystal that is equivalent to or close to the crystal growth target, but is not limited to this. Moreover, it is preferable to use a crystal having a clear crystal orientation as a seed crystal.

  Crystal growth is completed when all of the prepared crystal growth raw materials are crystallized and the melt is exhausted. On the other hand, for the purpose of keeping the composition of the crystal to be grown uniform and for the purpose of lengthening it, a device for continuously charging the crystal growth raw material may be incorporated. Thereby, the crystal can be grown while charging the crystal growth raw material.

  Next, the Czochralski method will be described. The Czochralski method can be performed using a known atmosphere-controlled pulling apparatus using high-frequency induction heating. The pulling device includes, for example, a crucible for storing the raw material melt, a seed crystal holder for holding the seed crystal in contact with the raw material melt, a moving mechanism for moving the seed crystal holder upward, and a speed of the moving mechanism. This is a single crystal manufacturing apparatus including a moving speed control device to be controlled and induction heating means (for example, a high frequency induction heating coil) for heating the crucible. According to such a single crystal manufacturing apparatus, a single crystal can be produced by forming a solid-liquid interface on the upper surface of the melt and moving the seed crystal upward.

  As the seed crystal, it is preferable to use a seed crystal that is equivalent to or close to the crystal growth target, but is not limited to this. Moreover, it is preferable to use a crystal having a clear crystal orientation as a seed crystal.

  The micro pull-down method and the Czochralski method mainly allow crystal growth of a harmonic melt composition.

  Next, the floating zone method will be described. In the floating zone method, light from a halogen lamp or the like is usually collected by 2 to 4 spheroid mirrors, a part of a sample rod made of polycrystal is placed at the elliptical focus, and the temperature is increased by light energy. By melting the crystal and moving the mirror (focal point) gradually, the melted part is moved, while the melted part is slowly cooled to change the sample rod into a large single crystal. Is the method.

  In the floating zone method, since no crucible is used, it is possible to grow higher-purity crystals, and it is also possible to grow crystals even under conditions where the crucible is oxidized in an oxygen atmosphere and crystal growth is difficult.

  Hereinafter, examples and comparative examples of the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto. In the following examples, the Ce concentration is either a concentration in a specific crystal or a concentration in a melt (preparation).

Example 1
A crystal represented by a composition of (Ce _0.015 Gd _0.750 La _0.2349 Zr _0.0001 ) ₂ Si ₂ O ₇ was produced by the Czochralski method. This crystal is a pyrochlore type oxide represented by A ₂ B ₂ O ₇ . FIG. 1 is a view showing a photograph of the produced (Ce _0.015 Gd _0.750 La _0.2349 Zr _0.0001 ) ₂ Si ₂ O ₇ crystal.

(Example 2)
A crystal represented by a composition of (Ce _0.015 Gd _0.750 La _0.2348 Zr _0.0002 ) ₂ Si ₂ O ₇ was produced by the Czochralski method. This crystal is a pyrochlore type oxide represented by A ₂ B ₂ O ₇ . FIG. 2 is a view showing a photograph of the produced (Ce _0.015 Gd _0.750 La _0.2348 Zr _0.0002 ) ₂ Si ₂ O ₇ crystal.

(Example 3)
A crystal represented by a composition of (Ce _0.015 Gd _0.750 La _0.2348 Hf _0.0002 ) ₂ Si ₂ O ₇ was produced by the Czochralski method. This crystal is a pyrochlore type oxide represented by A ₂ B ₂ O ₇ . FIG. 3 is a view showing a photograph of the produced (Ce _0.015 Gd _0.750 La _0.2348 Hf _0.0002 ) ₂ Si ₂ O ₇ crystal.

Example 4
A polycrystal represented by a composition of (Ce _0.015 Gd _0.750 La _0.2348 Zr _0.0002 ) ₂ Si ₂ O ₇ was produced by a solid phase reaction method. This crystal is a pyrochlore type oxide represented by A ₂ B ₂ O ₇ .

(Example 5)
A polycrystal represented by a composition of (Ce _0.015 Gd _0.750 La _0.2348 W _0.0002 ) ₂ Si ₂ O ₇ was produced by a solid phase reaction method. This crystal is a pyrochlore type oxide represented by A ₂ B ₂ O ₇ . FIG. 4 is a view showing a photograph of the produced (Ce _0.015 Gd _0.750 La _0.2348 W _0.0002 ) ₂ Si ₂ O ₇ crystal.

(Example 6)
A polycrystal represented by a composition of (Ce _0.015 Gd _0.750 La _0.2348 Ta _0.0002 ) ₂ Si ₂ O ₇ was produced by a solid phase reaction method. This crystal is a pyrochlore type oxide represented by A ₂ B ₂ O ₇ . FIG. 5 is a view showing a photograph of the produced (Ce _0.015 Gd _0.750 La _0.2348 Ta _0.0002 ) ₂ Si ₂ O ₇ crystal.
(Examples 7-15)
In addition to the above, crystals represented by the composition shown in Table 1 were prepared by the Czochralski method, the micro pull-down method, and the solid phase reaction method. This crystal is a pyrochlore type oxide represented by A ₂ B ₂ O ₇ .

(Comparative Example 1)
As a known comparative example, a crystal represented by a composition of (Ce _0.015 Gd _0.750 La _0.235 ) ₂ Si ₂ O ₇ was prepared by the Czochralski method. This crystal is a pyrochlore type oxide represented by A ₂ B ₂ O ₇ . FIG. 6 is a view showing a photograph of the produced (Ce _0.015 Gd _0.750 La _0.235 ) ₂ Si ₂ O ₇ crystal.

Table 1 shows M and s for Examples 1 to 15 and Comparative Example 1.

(Comparative Example 2)
As a known comparative example 2, a commercially available (Ce _0.01 Gd _0.99 ) ₂ SiO ₅ (Ce 1%: GSO) crystal having a size of 5 mm × 5 mm × 5 mm was prepared.

  Next, the crystal of Example 1 was cut to a thickness of 1 mm and mirror-polished, and then the transmittance in the direction of 1 mm thickness was measured. An ultraviolet-visible spectrophotometer (model: V-530) manufactured by JASCO Corporation was used for luminescence measurement. The same measurement was performed for the crystals of Examples 2 to 3 and Comparative Example 1. FIG. 7 is a diagram showing the transmittance profiles obtained in Examples 1 to 3 and Comparative Example 1. In FIG. 7, the horizontal axis represents wavelength (nm) and the vertical axis represents linear transmittance (%). As will be described later, it is known in Examples 1 to 3 that the maximum wavelength region of light emission is approximately 360 to 430 nm, and in this light emission region, the linear transmittance has a sufficient value of 40% or more. Even if the transmittance is low, there is sufficient utility value, for example, as an X-ray detection element.

In addition, about the crystal | crystallization of Examples 1-15, about the same sample as the transmittance | permeability measurement, ie, the sample cut to the thickness of 1 mm, and mirror-polished, using the spectroscope (model: Instrument FLS920) of Edinburgh As a result of measuring Radio-luminescence (alpha excitation of 5.5 MeV), the emission region was as shown in Table 2. Since these wavelengths are within a range that can be detected by a photo detector such as a photomultiplier tube or a Si semiconductor, they have sufficient utility value. In addition, only the wavelength range of typical light emission is shown in the light emission region of Table 2, and it is not limited to this, For example, there may be a light emission band other than this, such as light emission derived from a defect.

Furthermore, the luminescence amount of the crystals obtained in Examples 1 to 3 and Comparative Examples 1 and 2 was estimated. Here, each crystal is optically bonded to a photomultiplier tube (R7600U-200 manufactured by Hamamatsu Photonics), which is a photodetector, with optical grease (Applied Koken Co., Ltd. 6262A) and sealed with ¹³⁷ Cs having 1 MBq of radioactivity. A radiation source (gamma ray source) or a ²⁴¹ Am sealed radiation source (alpha ray source) was used to excite and emit light by irradiating gamma rays.

  Note that 700 V was applied to the photomultiplier tube to convert the scintillation light into an electrical signal. Here, the electric signal output from the photomultiplier tube is a pulse-like signal reflecting the received scintillation light, and the pulse height represents the emission intensity of the scintillation light. In this way, the electric signal output from the photomultiplier tube was shaped and amplified by the shaping amplifier, and then input to the multiple wave height analyzer for analysis to create a wave height distribution spectrum.

FIG. 8 is a diagram showing wave height distribution spectra (Examples 1 to 3, Comparative Examples 1 and 2) obtained by irradiation with ¹³⁷ Csγ rays (662 keV). In FIG. 8, the horizontal axis represents the channel number of the multi-channel analyzer (MCA) and represents the signal magnitude. The vertical axis represents the count number (arb.unit). As for the horizontal axis, the photoelectric absorption peak derived from 662 keV gamma rays is higher in the right side of the figure, indicating that the light emission amount is higher. As can be seen from FIG. 8, the crystal of Example 1 had higher light emission than the crystal of Comparative Example 2. In FIG. 8, the light emission amount of the crystal of Example 1 was 30,000 photons / MeV or more.
Regarding Examples 7 and 8, the light emission amount could be obtained as shown in Table 3. In Table 3, the light emission amount of Comparative Example 1 is also shown.

Next, the fluorescence lifetime of the crystals of Examples 1-3, 7, 8, and Comparative Example 1 was determined. Here, the crystal was optically bonded to a photomultiplier tube (R7600U-200 manufactured by Hamamatsu Photonics) with optical grease (Applied Koken 6262A), and a gamma ray was applied using a ¹³⁷ Cs sealed radiation source having a radioactivity of 1 MBq. It was excited to emit light. And the fluorescence lifetime was calculated | required by measuring the time distribution of the signal from the photomultiplier tube with an oscilloscope (Tektronix TDS 3034B).

FIG. 9 is a graph showing a fluorescence decay curve profile of the crystal of Example 1. FIG. In FIG. 9, the horizontal axis represents time, and the vertical axis represents the voltage corresponding to the emission intensity. The solid line is the result of fitting with the following function I (t) with time t as a variable in order to obtain the attenuation constant. Here, I (t) is as follows.
I (t) = 0.098 · exp (−t / 61 ns)
+ 0.040 · exp (−t / 286 ns) +0.00241
That is, the fluorescence lifetime of the crystal of Example 1 was 61 nanoseconds, and a high-speed scintillator could be configured. Table 4 shows the fluorescence lifetimes of Examples 1 to 3, 7, and 8 and Comparative Example 1.

DESCRIPTION OF SYMBOLS 100 Radiation detector 101 Crystal material 102,104 Photodetector 103 Wavelength conversion element 200 Nondestructive inspection apparatus 201 Radiation source 202 Measuring object 300 Imaging apparatus

Claims (12)

General formula (1):
_{(RE x A 1-x-} y-s B y M s) 2 Si 2 O 7 (1)
A crystal material characterized by having a pyrochlore structure, a non-stoichiometric composition, and a harmonic melting composition.
Here, in formula (1), A includes at least one selected from Gd, Y, La, Sc, Yb and Lu, and B is selected from La, Gd, Yb, Lu, Y and Sc. Including at least one or more, 0.1 <y <0.4, and RE includes at least one selected from Ce, Pr, Nd, Eu, Tb and Yb, and 0 <x <0.1 And M includes at least one selected from Ti, Zr, Hf, Ta, Nb, Mo and W, and is represented by 0 ≦ s <0.01.   The range of x, y, and s is further expressed by 0 <x <0.05, 0.1 <y <0.35, and 0 ≦ s <0.005. The crystalline material described.   The range of x, y, and s is further represented by 0 <x <0.04, 0.1 <y <0.35, and 0 ≦ s <0.005. The crystalline material described.   In the general formula (1), RE is Ce, A is Gd, and B is one or more selected from La and Y. The crystalline material described.   Scintillation light is emitted by irradiation of radiation, and the predetermined fluorescent component contained in the scintillation light has a fluorescence lifetime of 61 nanoseconds or less and a fluorescence peak wavelength in a range of 170 nm to 900 nm. The crystal material as described in any one of Claims 1-4.   Scintillation light is emitted by irradiation of radiation, and the predetermined fluorescence component contained in the scintillation light has a fluorescence lifetime of 61 nanoseconds or less and a fluorescence peak wavelength of 300 nm or more and 700 nm or less. The crystal material as described in any one of Claims 1-4.   A raw material containing A, Si, and RE is blended so as to have an element ratio of the crystalline material according to any one of claims 1 to 4, and the mixture is cooled after raising the temperature until the blended raw material is melted, A method for producing a crystal, characterized in that the crystal has a pyrochlore structure. A scintillator composed of the crystal material according to claim 1;
A photodetector for receiving scintillation light from the scintillator;
A radiation detector comprising: A scintillator composed of the crystal material according to claim 1;
A wavelength conversion element that receives the scintillation light from the scintillator and converts the wavelength of light having a wavelength of 260 nm to 350 nm contained in the scintillation light into any wavelength in the range of 320 nm to 700 nm;
A photodetector for receiving the wavelength-converted light by the wavelength conversion element;
A radiation detector comprising:   A radiation detector comprising the scintillator made of the crystal material according to claim 1 and having position sensitivity.   An imaging apparatus comprising the radiation detector according to claim 7.   A nondestructive inspection apparatus comprising the radiation detector according to claim 7.