JP2013040274A - Garnet type crystal for scintillator and radiation detector using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a garnet type crystal for a scintillator suitably applied to a radiation detector and having a short fluorescent lifetime.SOLUTION: The garnet type crystal for the scintillator is represented by general formula (I): LuPrYAlGaO, provided that 0.0001≤x≤0.15, 0.3≤Y≤3, and 1≤z≤3.

Description

  The present invention relates to a garnet crystal for a scintillator and a radiation detector using the same.

  Scintillator single crystals are used in radiation detectors that detect γ-rays, X-rays, α-rays, neutrons, etc., and such radiation detectors can be used for positron emission tomography (PET) devices or X-ray computed tomography devices (CT). It is widely applied to medical imaging devices such as devices, various radiation measuring devices in the field of high energy physics, and resource exploration devices. Generally, a radiation detector is composed of a scintillator that absorbs γ rays, X rays, α rays, and neutron rays and converts them into scintillation light, and a light receiving element that receives the scintillator light and converts it into an electrical signal or the like. For example, in high energy physics and PET imaging systems, an image is created based on a collision between a scintillator and radiation generated by nuclear decay. Also, in positron emission tomography, 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. . For example, photons emitted from a specific location within the subject can be detected using a photodiode (PD), silicon photomultiplier (Si-PM), or photomultiplier tube (PMT), or other photodetector. Can be detected.

  Therefore, the scintillators suitable for these radiation detectors have a high density and a high atomic number (high photoelectric absorption ratio) from the viewpoint of detection efficiency, and a light emission level from the viewpoint of high-speed response and high energy resolution. In many cases, it is desired that the fluorescence lifetime (fluorescence decay time) is short.

Currently, there is a scintillator having a garnet structure as a preferable scintillator applied to various radiation detectors. A scintillator having a garnet structure has the advantages that it is chemically stable, has no cleavage and deliquescence, and has excellent workability. For example, scintillators having a garnet structure that utilizes light emission from the 4f5d level of Pr ³⁺ described in Patent Document 1 and Non-Patent Document 2 have a short fluorescence lifetime of about 40 ns or less. For example, Pr-added Lu ₃ Al ₅ O ₁₂ (Pr: LuAG) exhibits excellent characteristics such as a light emission amount of about 19000 photon / MeV, a fluorescence lifetime of about 20 ns, and a density of 6.7 g / cm ³ . Non-Patent Document 2 discloses a technique for reducing defects by replacing Ga with an Al site of Pr: LuAG to reduce a long-life light-emitting component.

International Publication No. 2006/049284 Pamphlet

Winicjuz Drozdowski, Pieter Dorenbos, Johan T. M.M. de Haas, Renata Drozdowska, Alan Owens, Kei Kamada, Kosuke Tsusumumi, Yoshiyuki Uuki, Takayuki Yanagida ECL ESC 55, NO. 4, (2008) 2420-2424 H. Ogino, K .; Kamada and A.K. Yoshikawa, et al. , IEEE Trans. Nucl. Sci. 55 (2008) 1197

  However, according to the knowledge of the present inventor, in the technique of Patent Document 1, a long-lived light emitting component of 100 ns or more is present at a ratio of 70% or more with respect to the total light emission amount simultaneously with a fluorescent life component of about 20 ns. The problem became clear.

  Although the technique described in Non-Patent Document 1 can reduce defects by substituting Ga for the Al site of Pr: LuAG and reduce the long-life light-emitting component, there is a problem that the light emission amount is reduced.

  The present invention has been made in view of the above circumstances, and provides a garnet-type crystal for a scintillator that can be suitably applied to a radiation detector, has a high emission amount, a short fluorescence lifetime, and a long lifetime emission component. .

According to the present invention for solving the above problems,
General formula (1):
_{Lu 3-x-Y Pr x} Y y Al 5-z Ga z O 12 (I)
(In the formula (I), 0.0001 ≦ x ≦ 0.15, 0.3 ≦ y ≦ 3, 1 ≦ z ≦ 3)
A garnet-type crystal for a scintillator represented by:

  Moreover, according to this invention, a radiation detector provided with the scintillator comprised from said garnet-type crystal | crystallization for scintillators, and the light receiver which detects light emission of the said scintillator is provided.

According to the present invention, Pr is a light emitting element, Al and O are essential components, and Y or Lu is contained in a garnet-type crystal containing Ga, thereby optimizing the energy band structure. ³⁺ 4f5d light emission is promoted, and as a result, the fluorescence lifetime is shortened, the long-life light emission component is decreased, and the light emission amount is increased. Therefore, it is possible to realize a garnet crystal for a scintillator that can be suitably applied to a radiation detector and has a short fluorescence lifetime, a high light emission amount and a long lifetime light emission component.

  ADVANTAGE OF THE INVENTION According to this invention, the garnet-type crystal | crystallization for scintillators which can be applied suitably for a radiation detector and has a high light emission amount, a short fluorescence lifetime, and a long lifetime light emission component is provided.

It is a figure explaining an example of the apparatus which measures the light-emission quantity and fluorescence decay time when the garnet-type crystal for scintillators of this invention is excited by a gamma ray. It is a figure explaining the principle that the emitted light amount becomes high when the garnet-type crystal for scintillators of the present invention is excited by γ-rays, the fluorescence lifetime of light emission is short, and the long-life component is reduced. Is a graph showing an emission spectrum of _{Lu 1.97 Pr 0.03 Y 1 Al 4} Ga 1 O 12 crystals was produced and _{Lu 1.97 Pr 0.03 Y 1 Al 3} Ga 2 O 12 crystals in the micro-pulling-down method.

Hereinafter, embodiments of the present invention will be described.
The scintillator garnet-type crystal according to the embodiment of the present invention is represented by the following general formula (I).
_{Lu 3-x-Y Pr x} Y y Al 5-z Ga z O 12 (I)
(In the formula (I), 0.0001 ≦ x ≦ 0.15, 0.3 ≦ y ≦ 3, and 1 ≦ z ≦ 3.)

In the garnet-type crystal for scintillator represented by the above formula (I), the Pr concentration x is 0.0001 ≦ x ≦ 0.15, preferably 0.001 ≦ x ≦ 0.10. Preferably, 0.015 ≦ x ≦ 0.09. Thus, by taking a suitable Pr value in the general formula (I), the emission of light from the 4f5d level of Pr ³⁺ is promoted, and as a result, the fluorescence lifetime is shortened and the long-life emission component is reduced. The amount of luminescence increases.

In the garnet-type crystal for scintillator represented by the above formula (I), the Ga concentration z is 1 ≦ z ≦ 3, and a more preferable range of z is 1 ≦ z ≦ 2.5.
Thus, by taking Y and Ga suitable in the general formula (I), the fluorescence lifetime is shortened, the long-life luminescence component is decreased, and the light emission amount is increased.

Further, the light emission amount of the garnet-type crystal represented by the above formula (I) can be obtained at 18000 photon / MeV or more, and more preferably at 20000 phototon / MeV or more.
In the present invention, the light emission amount refers to a crystal of φ3 × 2 mm size measured at 25 ° C., and can be measured using, for example, a measuring apparatus as shown in FIG. In this measurement apparatus, a Cs137γ ray source 11, a scintillator 12 as a measurement sample, and a photomultiplier tube 14 are provided in a dark box 10. The scintillator 12 is physically fixed to the photomultiplier tube 14 using a Teflon tape 13 and optically bonded by an optical adhesive or the like. The Cs ¹³⁷ γ-ray source 11 irradiates the scintillator 12 with 622 keV γ-rays, and the pulse signal output from the photomultiplier tube 14 is input to the preamplifier 15 and the waveform shaping amplifier 16 to be amplified and amplified. The waveform is shaped and input to the multi-channel analyzer 17, and the energy spectrum of Cs ¹³⁷ γ-ray excitation is acquired using the personal computer 18. The position of the photoelectric absorption peak in the obtained energy spectrum is compared with Ce: LYSO (light emission amount: 30000 photon / MeV), which is a known scintillator, and the light emission amount is determined in consideration of the wavelength sensitivity of the photomultiplier tube 14 respectively. Calculate automatically.
In this measurement method, the amount of light emitted by the scintillation counting method is measured, and the photoelectric conversion efficiency with respect to radiation can be obtained. Therefore, it is possible to measure the specific light emission amount of the scintillator.

  Since the garnet-type crystal represented by the above formula (I) has 0.3 ≦ y ≦ 3 and 1 ≦ z ≦ 3, the fluorescence lifetime (fluorescence decay time) of fluorescence emission by γ-ray excitation is 25 nanoseconds or less. , Preferably 22 nanoseconds or less, more preferably 20 nanoseconds or less. In addition, since this garnet-type crystal satisfies 0.3 ≦ y ≦ 3 and 1 ≦ z ≦ 3, the long-life component can be remarkably reduced. For example, the long-life component having a fluorescence lifetime exceeding 100 nanoseconds The light emission amount of the fluorescent component can be 40% or less with respect to the total light emission amount of the fluorescent component, but can be preferably 10% or less, and has no long-life component with a fluorescence lifetime exceeding 100 nanoseconds. Is particularly preferred.

The reason why 1 ≦ z, that is, when Ga is 1 or more, can shorten the fluorescence lifetime, reduce the long-life component, and increase the light emission amount can be inferred as follows.
In general, a garnet-type crystal has a cubic crystal structure represented by a chemical formula C ₃ A ₂ D ₃ O ₁₂ , and is represented by a schematic diagram as shown in FIG. Here, C is a DodechahedrAl site, A is an OctahedrAl site, D is a TetrahedrAl site, and each site is surrounded by O ²⁻ ions. For example, in a lutetium aluminum garnet composed of Lu, Al, and O, it is expressed as Lu ₃ Al ₂ Al ₃ O ₁₂ . More generally, it is simply expressed as Lu ₃ Al ₅ O _12, and it is known that Lu is arranged at the dodecahedral site and Al is arranged at the octahedral and tetrahedral sites. Here, for example, when Ga is substituted at the site of Al in Lu ₃ Al ₅ O _12, it is known that Ga is randomly substituted with octahedral and tetrahedral sites. Further, it is known that when a rare earth element such as Y, Lu, Yb, or Gd is replaced with a Lu site, it is replaced with a dodecahedral site. For example, when Ga is substituted at the Al site in Lu ₃ Al ₅ O ₁₂ , the crystal lattice changes, and the lattice constants are 11.90 Å for Lu ₃ Al ₅ O ₁₂ and 12.18 で for Lu ₃ Ga ₅ O _12. To change. Thus, when the crystal lattice changes due to the substitution of Ga to the Al site, the crystal field changes and the energy band structure also changes. As the Ga concentration is increased, the band gap is reduced and the 5d ₁ level of Pr ³⁺ is closer to the conductor. Further, as the Y concentration increases, the 5d ₁ level of Pr ³⁺ leaves the conductor.
In the garnet-type crystal represented by the general formula (I), the energy band structure is optimized by taking the optimum amount of Y and Ga substitution, and light emission from the energy level of Pr ³⁺ 4f5d is promoted. The amount becomes higher. Further, it is considered that the fluorescence lifetime is shortened and the long-life component is reduced.

In the present invention, the fluorescence decay time of fluorescence emission by γ-ray excitation can be measured using, for example, the measurement apparatus shown in FIG. More specifically, the scintillator 12 is irradiated with γ-rays from the Cs ¹³⁷ γ-ray source 11, the pulse signal output from the photomultiplier tube 14 is acquired using the digital oscilloscope 19, and the fluorescence decay component is analyzed. Thus, the fluorescence decay time of each fluorescence decay component and the ratio of the light emission amount of each fluorescence decay component to the light emission amount of the entire fluorescence lifetime component can be calculated.

Specifically, when a nonlinear regression curve is drawn using the function of the following formula (II) for the fluorescence lifetime component of the voltage pulse signal measured using the measuring apparatus shown in FIG. The square value of the correlation coefficient R is 0.98 or more.
I (t) = A1 * exp (−t / t ₁ ) + A2 * exp (−t / t ₂ ) + y ₀ (II)
Wherein, t is time, the intensity of the first component of A1 is fluorescence lifetime, t ₁ is the life of the first component, A2 is the intensity of the second component of the fluorescence lifetime, t ₂ is the lifetime of the second component, y ₀ Is the background value. ]
Emission amount A1 * _{t 1} of the first component of the fluorescence _lifetime, the light emission amount of the second component of the fluorescence lifetime is expressed by A2 * _{t 2,} the light emission amount of the whole fluorescent components represented by _{A1 * t 1 + A2 * t} 2 It is.

  The garnet-type crystal of the present invention can be suitably used for radiation detection with a fast response when the fluorescence wavelength emitted by being excited by gamma rays is 200 to 350 nm, preferably 200 to 320 nm.

  Next, the method for producing the garnet-type crystal of the present invention will be described below. In any method for producing a crystal, a general oxide raw material can be used as a starting material, but when used as a single crystal for a scintillator, it has a high purity of 99.99% or higher (4N or higher). It is particularly preferable to use raw materials, and these starting materials are weighed and mixed so as to have a target composition when forming a melt. Further, among these raw materials, those having particularly few impurities (for example, 1 ppm or less) other than the target composition are particularly preferable. In particular, it is preferable to use a raw material that contains as little an element (such as Tb) that emits light near the emission wavelength.

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. Note that in post-processes such as annealing after crystal growth, oxygen gas, inert gas (eg, Ar, N ₂ , He, etc.), inert gas (eg, Ar, N ₂ , He, etc.), and oxygen gas A mixed gas can be used. When a mixed gas is used, the oxygen partial pressure is not limited to 2% or less, and any mixture ratio of oxygen partial pressure from 0% to 100% may be used.

  The oxide garnet-type crystal manufacturing method of the present embodiment includes a micro pull-down method, a chocolate lasky method (pull-up method), a Bridgman method, a band melting method (zone melt method), and an edge-limited thin film supply crystal growth (EFG method) and hot isostatic pressing method, and the like, but are not limited thereto.

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

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

  Hereinafter, a method for producing a single crystal for an oxide scintillator of the present embodiment will be described by way of example of a crystal production method using a micro pull-down method, but is not limited thereto.

  The micro pull-down method can be performed using an atmosphere control type micro pull-down apparatus using high-frequency induction heating. The micro pull-down device includes a crucible, a seed holder that holds the seed that comes into contact with the melt flowing out from the pores provided at the bottom of the crucible, a moving mechanism that moves the seed holder downward, and a moving speed control of the moving mechanism This is a single crystal manufacturing apparatus comprising an apparatus and induction heating means for heating the crucible. According to such a single crystal manufacturing apparatus, a 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 adjusting the output of the induction heating means of the crucible and afterheater, the temperature of the solid-liquid boundary region of the melt drawn from the pores provided at the bottom of the crucible and its distribution can be controlled by adjusting the heat generation amount.

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 is equipped with a rotary pump to enable the atmosphere control. It is an apparatus that enables the degree to be 0.13 Pa (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 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 introduced into the furnace. Thus, the inside of the furnace is set to an inert gas atmosphere or a low oxygen partial pressure atmosphere, and the crucible is heated by gradually applying high-frequency power to the high-frequency induction heating coil to completely melt the raw material in the crucible.

  Subsequently, the seed crystal is gradually raised at a predetermined speed, and its tip is brought into contact with the pores at the lower end of the crucible and is sufficiently blended. Then, the crystal is lowered by lowering the pulling shaft while adjusting the melt temperature. Grow.

  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 with a clear orientation as a seed crystal.

  Crystal growth is completed when all of the prepared materials are crystallized and the melt is gone. On the other hand, for the purpose of keeping the composition uniform and for the purpose of lengthening, a device for continuously charging raw materials may be incorporated.

The melting point of the garnet-type crystal for scintillator represented by the above formula (I) can be in the range of 1700 to 1900 ° C. For example, the melting point of Lu ₃ Al ₅ O ₁₂ is as high as 1980 ° C., but the melting point of the crystal of the present invention is low, so that damage to the heat insulating material can be reduced, and when using a crucible for crystal production In addition, damage to the crucible can be reduced. In addition, the effect of reducing evaporation of gallium oxide, which is a constituent element, can also be obtained. Furthermore, in the formula (I), it is preferable that z is 1 or more because more industrial mass production is possible.

Another example of the method for producing a garnet-type crystal for scintillator according to the present invention is a method for producing transparent ceramics using a hot isostatic pressing apparatus. In this method, first, each powder raw material is put into an alumina crucible, covered with alumina, and calcined at 1500 ° C. for 2 hours. After cooling, the scintillator powder washed with pure water and dried is ball milled for 24 hours to obtain a scintillator powder having a particle size of 1 to 2 μm. Next, 5% by weight of pure water was added to the pulverized powder, uniaxial press molding was performed at a pressure of 500 kg / cm ² , and then cold isostatic pressing was performed at a pressing force of 3 ton / cm ² to obtain the theoretical density. A molded body of about 64% is obtained. Thereafter, the obtained molded body is put into a mortar, capped, and subjected to primary sintering at 1750 ° C. for 3 hours to obtain a sintered body having a theoretical density of 98.5% or more.

  Here, when sintering in a hydrogen, nitrogen or argon atmosphere, it is preferable to use an alumina stag as the stag, but when sintering in vacuum, it is preferable to use boron nitride. By doing so, a desired scintillator crystal can be obtained efficiently.

  Moreover, it is preferable that the temperature increase rate of 1350 degreeC or more shall be 50 degreeC / hour. By doing so, a uniform sintered body having a high density can be obtained.

  Finally, hot isostatic pressing is performed under the conditions of 1550 ° C., 3 hours, and 1000 atm. Thereby, a sintered body having the same density as the theoretical density can be obtained.

  The scintillator crystal having a garnet structure according to the present invention can be used as a radiation detector by being combined with a light receiver. Furthermore, it can be used as a radiation inspection apparatus characterized by including these radiation detectors as radiation detectors. Examples of the radiation inspection apparatus include PET, SPECT, and CT.

  The garnet-type crystal of the present invention emits a fluorescent component having a fluorescence lifetime (fluorescence decay time) of 25 nanoseconds or less, and emits a long-lived component with a fluorescence lifetime of more than 100 nanoseconds. It can be 40% or less based on the amount. Therefore, the radiation detector provided with the garnet-type crystal of the present invention requires a short sampling time for fluorescence measurement, and can reduce the high time resolution, that is, the sampling interval.

  Thus, since the garnet-type crystal for scintillators of the present invention has a high light emission amount, high energy resolution, high density, and short lifetime, these radiation inspection apparatuses including the scintillator crystal of the present invention have a high-speed response. Radiation detection is possible.

  Hereinafter, specific 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 Pr concentration is described as either a concentration in a specific crystal or a concentration in a melt (preparation). In each example, the Pr concentration is 1 in the crystal. On the other hand, there was a relationship such that the concentration at the time of preparation was about 1 to 10.

Example 1
A garnet-type crystal represented by a composition of Lu _1.97 Pr _0.03 Y ₁ Al ₄ Ga ₁ O ₁₂ was produced by the micro-pulling down method.

(Example 2)
A garnet-type crystal represented by a composition of Lu _1.97 Pr _0.03 Y ₁ Al ₃ Ga ₂ O ₁₂ was produced by a micro-pulling-down method.

(Example 3)
A garnet-type crystal represented by a composition of Lu _0.97 Pr _0.03 Y ₂ Al ₃ Ga ₂ O ₁₂ was produced by the micro-pulling down method.

Example 4
A garnet-type crystal represented by a composition of Pr _0.03 Y _2.97 Al ₄ Ga ₁ O ₁₂ was produced by a micro-pulling down method.

(Example 5)
A garnet-type crystal represented by a composition of Pr _0.03 Y _2.97 Al ₃ Ga ₂ O ₁₂ was produced by a micro-pulling-down method.

(Example 6)
A garnet-type crystal represented by a composition of Lu _1.97 Pr _0.03 Y ₁ Al ₃ Ga ₂ O ₁₂ was produced by hot isostatic pressing.

(Example 7)
A garnet-type crystal represented by a composition of Lu _1.97 Pr _0.03 Y ₁ Al ₃ Ga ₂ O ₁₂ was prepared by the Czochralski method.

(Comparative Example 1)
A garnet-type crystal represented by a composition of Lu _2.97 Pr _0.03 Al ₅ O ₁₂ was produced by the micro-pulling down method.

(Comparative Example 2)
A garnet-type crystal represented by a composition of Lu _1.97 Pr _0.03 Y ₁ Al ₁ Ga ₄ O ₁₂ was produced by a micro-pulling-down method.

(Comparative Example 3)
A garnet-type crystal represented by a composition of Lu _0.97 Pr _0.03 Y ₂ Al ₁ Ga ₄ O ₁₂ was produced by the micro-pulling down method.

The crystals obtained in Examples 1 to 7 and Comparative Examples 1 to 3 were processed and polished to a size of φ3 × 2 mm, and each scintillator characteristic was evaluated. Further, the emission spectra of the crystals obtained in Examples and Comparative Examples were measured by X-ray excitation emission spectrum method. Specifically, each sample was irradiated with X-rays, and the generated scintillation light was obtained using a spectroscope to obtain a profile as shown in FIG. FIG. 3 shows the emission spectra obtained in Examples 1 and 2.
Further, γ-rays from ¹³⁷ Cs were irradiated, and the fluorescence decay time and the amount of luminescence were measured. For light emission measurement, the position of the photoelectric absorption peak in the obtained energy spectrum is compared with Ce: LYSO (light emission: 30000 photon / MeV), which is a known scintillator, and the wavelength sensitivity of the photomultiplier tube is considered. The amount of luminescence was calculated. The measurement temperature was 25 ° C.
As for the fluorescence lifetime, a nonlinear regression curve is drawn using the function of the above formula (II) for the fluorescence lifetime component of the voltage pulse signal measured using the measuring apparatus shown in FIG. The amount of luminescence and the amount of luminescence of the second component of the fluorescence lifetime were calculated, and the ratio of each luminescence amount was calculated.

  Tables 1 and 2 summarize the various characteristics relating to the crystals obtained in Examples 1 to 7 and Comparative Examples 1 to 3.

As shown in FIG. 3, in Examples 1 to 7 and Comparative Example 1, an emission peak derived from 4f5d emission of Pr ³⁺ was confirmed around 310 nm. As shown in FIG. 3 and Tables 1 and 2, the emission peak shifts to the short wavelength side when the Ga concentration increases, and the emission peak shifts to the long wavelength side when the Y concentration increases. This is because the band gap decreases as the Ga concentration increases, and 5d ₁ level of the Pr ³⁺ is closer to the conductor. Further, when the Y concentration is increased, the 5d ₁ level of Pr ³⁺ is separated from the conductor.

  Thus, it was found that the praseodymium-activated garnet-type crystal in the present invention has a high light emission amount, a short fluorescence decay time, and a long life component by taking the optimum Ga concentration and Y concentration.

  In addition, all the crystals obtained in Examples 1 to 6 and Comparative Examples 1 to 3 were single crystals, and the crystals of Example 7 were transparent ceramics.

DESCRIPTION OF SYMBOLS 10 Dark box 11 ¹³⁷ Cs radiation source 12 Scintillator 13 Teflon tape 14 Photomultiplier tube 15 Preamplifier 16 Waveform shaping amplifier 17 Multichannel analyzer 18 Personal computer 19 Digital oscilloscope

Claims (5)

Formula (I):
_{Lu 3-x-y Pr x} Y y Al 5-z Ga z O 12 (I)
(In the formula (I), 0.0001 ≦ x ≦ 0.15, 0.3 ≦ y ≦ 3, 1 ≦ z ≦ 3)
A garnet-type crystal for a scintillator represented by The garnet-type crystal for scintillators according to claim 1, wherein the fluorescent component derived from Pr ³⁺ 4f5d emission has a fluorescence lifetime of 25 nanoseconds or less.   The garnet-type crystal for a scintillator according to claim 1 or 2, wherein the light emission amount of the long-lived fluorescent component exceeding 100 nanoseconds is 40% or less with respect to the light emission amount of the entire fluorescent component.   The garnet-type crystal for scintillators according to any one of claims 1 to 3, wherein the light emission amount is 18000 photon / MeV or more.   A radiation detector, comprising: a scintillator composed of the garnet-type crystal for scintillators according to any one of claims 1 to 4; and a light receiver that detects light emission of the scintillator.