JP5994149B2 - X-ray scintillator materials - Google Patents

Description

  The present invention relates to a constituent material of an X-ray scintillator used for an X-ray detector or the like.

  A scintillator is a substance that absorbs radiation such as γ-rays and X-rays and emits visible light or electromagnetic waves having a wavelength close to visible light. As its application, it is used in medical PET (Positron Emission Tomography), TOF-PET (Time of Flight Positron Emission Tomography), X-ray CT (Computer Tomography), and airports. Various radiation detectors such as personal belongings inspection equipment.

  Such a radiation detector generally includes a scintillator unit that receives radiation and converts it into visible light, and a photomultiplier tube (hereinafter referred to as an electrical signal) that detects visible light converted and transmitted by the scintillator unit. And a photodetection unit such as a photodiode. A scintillator used for this type of application is desired to be a scintillator with a high light emission output in order to reduce noise and increase measurement accuracy.

Conventionally, rare earth oxysulfide phosphors Gd ₂ O ₂ S: Pr, Ce, F and the like have been used as scintillator materials that can be used in radiation detectors.
As a new scintillator material, for example, an oxide phosphor having a garnet structure containing Ce as a light emitting element and containing Gd, Al, Ga, and O has been proposed (Patent Documents 1 to 4).

International Publication WO / 1999/033934 JP 2001-4753 A JP 2002-189080 A JP 2008-24739 A

  The present invention provides a new X-ray scintillator material that is a material for X-ray scintillators having a new composition different from those conventionally disclosed and that can constitute a scintillator with high emission output. To do.

The present invention proposes an X-ray scintillator material having a perovskite structure and containing a single-phase single crystal represented by (Y, Gd, Lu) (Al, Ga) O ₃ as a host.

  Such an X-ray scintillator material is a new single crystal material having a composition different from that of a conventionally disclosed material, and can constitute a scintillator having a high light emission output. Therefore, if the X-ray scintillator material of the present invention is used, an X-ray detector having a high light emission output can be obtained.

In an Example, it is the figure which showed the structure (outline | summary) of the apparatus used for the measurement of an output. It is the figure which showed the structure (outline | summary) of the crystal growth apparatus used in manufacture of an Example. 2 is an XRD pattern measured for the crystal obtained in Example 1. FIG. 3 is an XRD pattern measured for the crystal obtained in Example 2. FIG.

  Embodiments of the present invention will be described in detail below, but the scope of the present invention is not limited to the embodiments described below.

(Single crystal material for scintillators)
The X-ray scintillator material of the present embodiment (hereinafter referred to as “the scintillator material”) is a material containing a perovskite single crystal as a host (matrix crystal) and an activator (emission center).

The perovskite single crystal as the host (matrix) is specifically a perovskite single phase single crystal represented by (Y, Gd, Lu) (Al, Ga) O ₃ .

A perovskite single-phase single crystal represented by (Y, Gd, Lu) (Al, Ga) O ₃ can be obtained by referring to a perovskite structure represented by, for example, MBO ₃ (M and B have no particular meaning). An element composed of one or a combination of two or more selected from the group consisting of Y, Gd and Lu may exist at the position, and Al or Ga or both of them exist at the position of B. It means that it is good.
More specifically, for example, YAlO ₃ , YGaO ₃ , GdAlO ₃ , GdGaO ₃ , LuAlO ₃ , LuGaO ₃ , (Y, Gd) AlO ₃ , (Y, Gd) GaO ₃ , (Gd, Lu) AlO ₃ , ( Gd, Lu) GaO ₃ , (Y, Lu) AlO ₃ , (Y, Lu) GaO ₃ , (Y, Gd, Lu) AlO ₃ , (Y, Gd, Lu) GaO _{3 and the} like.

  This perovskite single phase single crystal is not a cubic crystal but a tetragonal crystal.

  Examples of the activator (emission center) include one or a combination of two or more selected from the group consisting of Nd, Ho, Er, Tm, Ti, and Cr. Among these, Nd, Er, and Tm are preferable from the viewpoint of obtained characteristics.

The concentration of the activator is preferably 0.0001 to 2.0000 at%. If the concentration of the activator is 0.0001 at% or more, the minimum light emission amount can be obtained, and if it is 0.0100 at% or more, the light emission efficiency for obtaining the light emission amount can be obtained more sufficiently. . On the other hand, if it is 2.000 at% or less, it is possible to avoid a decrease in the amount of light emission due to concentration quenching.
From such a viewpoint, the concentration of the activator is more preferably 0.0100 at% or more, particularly 0.0500 at% or more, and further preferably 1.0000 at% or less.
Specifically, for example, when the concentration of Nd is 0.1000 to 1.0000 at%, it is particularly preferable when the concentration of Tm is 0.5000 to 1.0000 at%.

(Use)
The scintillator material can be processed into a scintillator, and an X-ray detector can be configured by combining this scintillator with a light detection unit such as a photomultiplier or a photodiode. Among them, the scintillator material is used for various X-ray detectors such as medical PET (Positron Emission Tomography), TOF-PET (Time of Flight Positron Emission Tomography), CT (Computer Tomography). It can be suitably used as a scintillator material, and various X-ray detectors can be configured using this.

(Production method)
Next, a method for producing the present scintillator material will be described. However, the manufacturing method of this scintillator material is not limited to the method demonstrated below.

The crystal growth method at this time is not particularly limited. For example, the Bridgman-Stockbarger method (also referred to as “BS method”), Czochralski (also referred to as “CZ method”), the micro pull-down method, the zone melt method, and improvements thereof. And other known crystal growth methods such as melt growth methods can be appropriately employed.
Hereinafter, typical BS method and CZ method will be described.

  The BS method is a method in which raw materials are put in a crucible and melted, and a single crystal is grown from the bottom of the crucible while pulling down the crucible. The crystal growing apparatus is relatively inexpensive and has a feature that a single crystal having a large diameter can be grown relatively easily. On the other hand, it is difficult to control the crystal growth orientation, and excessive stress is applied during crystal growth or cooling, so that it is said that the stress distribution remains in the crystal and strain and dislocations are easily induced.

  On the other hand, the CZ method is a method in which a raw material is put in a crucible and melted, and a seed (seed crystal) is brought into contact with a molten liquid surface and grown (crystallized) while rotating a single crystal. The CZ method is said to facilitate the growth of the target crystal orientation because it is possible to identify and crystallize the crystal orientation.

More specifically explaining an example of the BS method according to an example of the crystal growth method, the dissolved solidified body crushed material obtained in the crushing step is mixed with a seed crystal as necessary, and this mixture is filled in a crucible, the crucible was placed in a crystal growth apparatus, crystal growing apparatus the vacuum degree by the vacuum exhaust system was evacuated until about 1 × 10 ^-3 ~10 ^-4 Pa, heating the crucible by the heating device, the crucible The raw material filled in is melted.
After the raw material in the crucible has melted, when the crucible is gradually pulled down vertically at a speed of about 0.1 mm / hour to 3 mm / hour, the raw material that has become a melt in the crucible begins to solidify from the bottom, Crystals are grown. When all the raw materials in the crucible are solidified, the lowering of the crucible is finished, and the crucible is cooled to about room temperature while being gradually cooled by a heating device, and an ingot-like crystal can be grown.

  The micro pulling-down method can be appropriately implemented by referring to the method described in paragraphs 0013 to 0030 of JP-A-2006-347789, for example.

  The ingot-like crystal grown as described above is preferably cut out so that a surface having a predetermined size and a predetermined orientation appears as necessary, and then heat-treated as necessary. However, heat treatment is not necessarily required.

In the heat treatment, the crystal grown in the above process is put in a container, the container is placed in a heat treatment furnace, and the heat treatment furnace is heated uniformly to 900 ° C. to 1300 ° C. Is preferably removed.
A heating temperature of 1140 ° C. or higher is not preferable because it causes structural changes. The heating time is about 20 hours or more, more preferably about 20 hours to about 30 hours.
In the heat treatment step, crystal dislocations are reduced by the heat treatment. And the temperature of a single crystal is returned to room temperature, maintaining the state where distortion was lost.
The atmosphere in the heat treatment, that is, the atmosphere in the annealing case may be a vacuum atmosphere or an inert gas atmosphere such as argon (Ar). Of these, an inert gas atmosphere such as argon is preferable, and an atmosphere obtained by mixing and injecting a fluorine-based gas into argon gas is preferable. An atmosphere in which a fluorine gas obtained by thermal decomposition of a solid fluorinating agent (for example, PbF ₂ ) is mixed with an inert gas such as argon gas is also a preferable example.

(Glossary of terms)
In the present invention, the “X-ray scintillator” absorbs X-rays and emits electromagnetic waves having visible light or a wavelength close to visible light (the wavelength range of light may extend from near ultraviolet to near infrared). It means a substance and a component of a radiation detector having such a function.

In the present invention, when “X to Y” (X and Y are arbitrary numbers) is described, it means “preferably greater than X” or “preferably greater than Y” with the meaning of “X to Y” unless otherwise specified. The meaning of “small” is also included.
Further, when “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), the intention of “preferably larger than X” or “preferably smaller than Y” Is included.

  Examples of the present invention will be described below. However, the scope of the present invention is not limited to the following examples.

<Output>
The output was measured using the measuring apparatus shown in FIG.
The measurement sample (scintillator plate) used was 4.5 mm × 4.5 mm (thickness differs for each sample) (in addition, when only the thickness is different, it has been confirmed that the output is approximately the same).
A target made of tungsten (W) is irradiated with an electron beam of 120 kV and 20 mA to generate X-rays. This X-rays are irradiated to a measurement sample, and the output of scintillation light and transmitted X-rays is a PIN photodiode (manufactured by HAMAMATSU). "S1723-5"). Next, a light shielding tape was put on the hole of the lead plate to shield the scintillation light, and the output of only the transmitted X-ray was measured. And the output by the transmitted X-ray was subtracted, and the output by the scintillation light was obtained.

<Transmissivity>
A measurement sample was prepared by optically polishing the upper and lower surfaces of the measurement sample (scintillator plate).
About each measurement sample, the linear transmittance (% T) was measured using the ultraviolet visible spectrophotometer ("V550" by JASCO Corporation).
The measurement conditions were as follows: wavelength range: 190 nm to 900 nm, scan speed: 200 nm / min, slit width: 1 nm, data mode: transmittance (% T).

<Measurement of emission spectrum by X-ray irradiation>
Using the following X-ray irradiation apparatus and detector, the luminescence vector of the measurement sample was measured.
X-ray irradiation apparatus: “RINT-2000” (40 kV, 40 mA) manufactured by RIGAKU
Detector: CCD spectrometer “QE65000”, using optical fiber.

<XRD measurement>
XRD measurement uses “RINT-2000” manufactured by Rigaku Corporation as a measuring device, uses a Cu target as a radiation source, and obtains an XRD pattern in the range of 2θ of 20 ° to 80 ° (FIGS. 3 and 4). reference).

<Example 1-6>
Y ₂ O ₃ powder raw material (99.99%), Al ₂ O ₃ powder raw material (99.99%) and Nd ₂ O ₃ powder raw material (99.99%) were weighed in predetermined amounts and mixed in a mortar. The obtained mixed raw material was transferred to a crucible made of an alloy of Ir and Re, and set in a crystal growth apparatus shown in FIG.
The crystal growth apparatus used at this time is for performing growth by the micro pull-down method. As shown in FIG. 2, a seed to be brought into contact with the crucible and the melt flowing out from the pores provided at the bottom of the crucible is used. It is provided with a moving mechanism that can be held and moved downward, and induction heating means for heating the crucible.

Crystal growth was performed by the following micro-pulling-down method. That is, after evacuating to 10 ⁻¹ Pa with a rotary pump, Ar gas was filled and Ar gas was flowed at 0.5 L / nin. High-frequency power is gradually applied and heated to the melting point of YAlO ₃ (1950 ° C.) or higher to melt the raw material, and the molten liquid is discharged from the pores provided at the bottom of the crucible, and the lower end of the molten liquid is seeded. (Composition: YAlO ₃ single crystal) is contacted, and when the melt is sufficiently familiar with and adheres to the seed crystal, the lowering shaft of the moving mechanism is lowered at 0.01 to 0.05 mm / min while maintaining the temperature, When the melted liquid disappeared, the high-frequency power was gradually lowered and cooled to room temperature with sufficient time to obtain a crystal.

All the crystals obtained in Example 1-6 were colorless and transparent. Moreover, when a part of the obtained crystal was pulverized and XRD measurement was performed, all of the crystals obtained in Example 1-6 were yttrium, aluminum, and the stoichiometric composition formula YAlO _3. It was a single phase single crystal composed of perovskite (YAP), and no other phases were confirmed.
Further, when the Nd concentration (activator) in the crystal was analyzed by glow discharge mass spectrometry (GD-MS), the concentrations shown in Table 1 were obtained.
The obtained crystal was cut out in a predetermined size and a predetermined direction, and each of the above measurement samples was used.

<Example 7-19>
Y ₂ O ₃ powder raw material (99.99%), Al ₂ O ₃ powder raw material (99.99%) and each additive raw material were weighed in predetermined amounts and mixed in a mortar. The obtained mixed raw material was transferred to a crucible made of an alloy of Ir and Re, and set in a crystal growth apparatus shown in FIG. As additive materials, Tm ₂ O ₃ powder material (99.99%), Er ₂ O ₃ powder material (99.99%), Ho ₂ O ₃ powder material (99.99%), Cr ₂ O ₃ powder The raw material (99.99%) was used.
The crystal growth apparatus used was the same as in Example 1, and crystal growth was performed in the same manner as in Example 1 to obtain a crystal.

All of the crystals obtained in Examples 7-19 were colorless and transparent. Moreover, when a part of the obtained crystal was pulverized and XRD measurement was performed, all of the crystals obtained in Example 7-19 were yttrium, aluminum, and the stoichiometric composition formula YAlO _3. It was a single phase single crystal composed of perovskite (YAP), and no other phases were confirmed.
Moreover, when the concentration of each additive element (activator) in the crystal was analyzed by glow discharge mass spectrometry (GD-MS), the concentrations shown in Table 1 were obtained.
The obtained crystal was cut out in a predetermined size and a predetermined direction, and each of the above measurement samples was used.

<Example 20-21>
Lu ₂ O ₃ powder material (99.99%), Y ₂ O ₃ powder material (99.99%), Al ₂ O ₃ powder material (99.99%) and Nd ₂ O ₃ powder material (99.99%) ) Was weighed out and mixed in a mortar. The obtained mixed raw material was transferred to a crucible made of an alloy of Ir and Re, and set in a crystal growth apparatus shown in FIG.
The crystal growth apparatus used was the same as in Example 1, and crystal growth was performed in the same manner as in Example 1 to obtain a crystal.

All the crystals obtained in Example 20-21 were colorless and transparent. A part of the obtained crystal was pulverized and subjected to XRD measurement. As a result, the crystals obtained in Examples 20 and 21 were found to have the stoichiometric composition formula Lu _0.1 Y _0.9 AlO ₃ or Lu _0.3 Y _0.7 AlO. _It was a single-phase single crystal composed of lutetium, yttrium, aluminum, and perovskite shown in FIG. ₃ , and no other phases were confirmed.
Further, when the Nd concentration (activator) in the crystal was analyzed by glow discharge mass spectrometry (GD-MS), the concentrations shown in Table 1 were obtained.
The obtained crystal was cut out in a predetermined size and a predetermined direction, and each of the above measurement samples was used.

<Examples 22-24>
Lu ₂ O ₃ powder raw material (99.99%), Gd ₂ O ₃ powder raw material (99.99%), Al ₂ O ₃ powder raw material (99.99%) and each additive raw material are weighed in predetermined amounts, and a mortar Mixed. The obtained mixed raw material was transferred to a crucible made of an alloy of Ir and Re, and set in a crystal growth apparatus shown in FIG. As the additive material, Nd ₂ O ₃ powder material (99.99%) or Tm ₂ O ₃ powder material (99.99%) was used.
The crystal growth apparatus used was the same as in Example 1, and crystal growth was performed in the same manner as in Example 1 to obtain a crystal.

The crystals obtained in Examples 22-24 were all colorless and transparent. A part of the obtained crystal was pulverized and subjected to XRD measurement. As a result, the crystals obtained in Examples 22-24 were found to have a stoichiometric composition formula of Lu _0.6 Gd _0.4 AlO ₃ and Lu _0.3 Gd _0.19 AlO. ₃ or a single phase single crystal composed of lutetium, gadolinium, aluminum, and perovskite _{represented by} Lu _0.6 Gd _0.399 AlO ₃ , and no other phases were confirmed.
Moreover, when the concentration of the additive element (activator) in the crystal was analyzed by glow discharge mass spectrometry (GD-MS), the concentrations shown in Table 1 were obtained.
The obtained crystal was cut out in a predetermined size and a predetermined direction, and each of the above measurement samples was used.

(Discussion)
As a result, by using the material obtained in Example 1-19 and containing as a host a single-phase single crystal composed of yttrium aluminum perovskite (YAP) represented by the stoichiometric composition formula YAlO ₃ , light emission was obtained. It has been found that an X-ray scintillator with high output can be constructed.
Further, it was found that the same effect can be obtained even with a perovskite containing Gd or Lu instead of Y in YAlO ₃ or in addition to Y as in Example 20-24.
Moreover, since it is considered that the same effect can be expected even with a perovskite containing Ga instead of Al, the perovskite type represented by (Y, Gd, Lu) (Al, Ga) O ₃ is used. If it is a single phase single crystal, it can be considered that the same effect as the single phase single crystal body made of yttrium, aluminum, and perovskite (YAP) represented by YAlO ₃ can be obtained.

From the results shown in Table 1, a scintillator with a high light emission output can be formed if the concentration of the activator is 0.0100 to 2.0000 at%, and more particularly 0.0500 to 1.0000 at%. Further, it has been found that an X-ray scintillator having a higher light emission output can be configured. In particular, from the viewpoint of light emission output, for example, it was found that the Nd concentration was 0.1000 at% or more and the Tm concentration was 0.5000 at% or more.
However, based on the test results so far, it can be considered that the minimum effect can be obtained if the concentration of the activator is 0.0001 at%.

DESCRIPTION OF SYMBOLS 1 Chamber 2 Induction heating coil 3 Zirconia heat insulating material 4 Alumina stage 5 Quartz tube 6 Crucible 7 Growing crystal 8 Seed crystal 9 Pulling mechanism

Claims (4)

It has a perovskite structure and M ₁ M ₂ O ₃ (M ₁ in the formula consists of Lu and Y or Gd, or Lu, Y and Gd. M ₂ in the formula is Al and a combination of Ga single phase single crystal represented by.) containing as a host, and, Nd, Ho, Er, Tm, the element consisting of one or two or more combinations selected from the group consisting of Ti and Cr A material for an X-ray scintillator, which is contained as an activator . M ₁ M ₂ O ₃ (wherein M ₁ is any one selected from the group consisting of Y, Gd, and Lu, or a combination of two or more. M having the perovskite structure) ₂ Al or Ga, or consisting of combinations. contain single-phase single crystal as a host represented by), X-ray scintillator material which contains Tm as an activator. The X-ray scintillator material according to claim 1 or 2 , wherein the concentration of the activator is 0.0001 to 2.0000 at%. A radiation detector comprising using an X-ray scintillator material according to any one of claims 1-3.

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