JP6037025B2 - Scintillator material, radiation detector and radiation inspection apparatus - Google Patents

Description

  The present invention relates to a scintillator material used for a radiation detector for detecting X-rays and / or a radiation detector for detecting gamma rays, and more particularly to a radiation detector used for an X-ray CT apparatus and / or a gamma-ray PET apparatus. The present invention relates to a scintillator material, a radiation detector, and a radiation inspection apparatus made of translucent ceramics or a single crystal containing an applicable complex oxide.

  A solid scintillator material that emits visible and / or near-visible light energy when excited by radiation energy (high energy electromagnetic photons) such as X-rays and gamma rays is a photoelectric conversion circuit that converts an optical signal into an electrical signal. As a radiation detector in combination with the above, it has been used for various purposes such as resource searching, security, luggage and food inspection, and high energy research. Among them, the above-mentioned solid scintillator material that converts radiation energy into visible and / or near-visible light energy, a photoelectric conversion circuit that converts light energy into an electrical signal, and the output electrical signal are digitized and calculated. X-ray CT devices and gamma-ray PET (Positron Emission Tomography) devices combined with computed tomography (CT) systems that process and image images are rapidly growing mainly in medical institutions as the aging society progresses in recent years. It is becoming popular.

  The X-ray CT apparatus and the gamma-ray PET apparatus are greatly different in the wavelength of the emitted radiation, the optical signal to be obtained and the system for processing it, and each has advantages and disadvantages. For example, an X-ray CT apparatus is less expensive than a gamma ray PET apparatus, but the exposure dose is larger than that of a gamma ray PET apparatus. On the other hand, the gamma-ray PET apparatus is capable of high-speed imaging and is suitable for detecting the position of the cancer by detecting the radioisotope specifically accumulated in the cancer cells, but is an extremely expensive apparatus. For this reason, both devices have been widely spread while being properly separated. Nonetheless, in order to further promote the spread of radiological medical devices to cope with the aging society in the future, development of new scintillator materials that contribute to the reduction of exposure dose in both X-ray CT equipment and gamma-ray PET equipment Is required.

Scintillator materials for X-ray CT apparatus include a majority amount of yttria (Y ₂ O ₃ ), up to about 50 mol% gadolinia (Gd ₂ O ₃ ), and a small amount of activity (typically about 0.02 mol%). A translucent oxide sintered scintillator having a cubic structure containing europium as a rare earth activator oxide (about 12 mol%, preferably about 1 mol% to 6 mol%, most preferably about 3 mol%). It has been known for a long time (US Pat. No. 4,421,671 (Patent Document 1)). This europium activated scintillator has been used for commercial use since it has high luminous efficiency, low afterglow level, and other desirable characteristics.

Other scintillator materials for X-ray CT apparatuses are, for example, powder scintillators that emit light by radiation in Japanese Patent Publication No. 7-97139 (Patent Document 2), and are represented by the general formula (Ln _{1 -xy} Pr _x Ce _y ) ₂ O. ₂ S: (X)
(However, Ln represents at least one element selected from the group consisting of Gd, La and Y, X represents at least one element selected from the group consisting of F and Cl, and x represents 3 × 10 ^−6. ≦ x ≦ 0.2, y is 1 × 10 ⁻⁶ ≦ x ≦ 5 × 10 ⁻³ and X is in the range of 2 to 1000 ppm) Translucent sintered scintillator formed by adding an auxiliary agent, filling in a metal container, vacuum-sealing, hot isostatic pressing, and further annealing, and photodetector for detecting light emission of the scintillator A radiation detector characterized by comprising: a scintillator material with high luminous efficiency is obtained.

  In addition, the material of this system has been widely used as a scintillator material for an X-ray CT apparatus for a long time, and continuously improved inventions have been proposed as disclosed in, for example, Japanese Patent No. 3741302 (Patent Document 3). Yes.

Furthermore, as a scintillator material for other X-ray CT apparatuses, JP 2007-169647 A (Patent Document 4) includes:
“[Claim 1]
A sintered and annealed scintillator composition comprising a garnet having the formula A ₃ B ₂ C ₃ O ₁₂ prior to annealing, wherein A is at least one of the group consisting of Tb, Ce and Lu A position having one element or a combination thereof, B is octahedral (Al), C is tetrahedral (also Al), and the garnet is
(1) In the above formula, 0.05 to 2 atoms of Al in the octahedral position B are replaced with Sc,
(2) In the above formula, 0.005 atom to 2 atoms of oxygen is replaced with fluorine, and the same number of Ca atoms are replaced at the A position,
(3) In the above formula, 0.005 atom to 2 atom at the B position is replaced with Mg, and the same number of oxygen atoms are replaced with fluorine,
(4) In the above formula, 0.005 atoms to 2 atoms at the B position were replaced with at least one combination of atoms selected from the group consisting of Mg / Si, Mg / Zr, Mg / Ti, and Mg / Hf. thing,
(5) In the above formula, 0.005 atom to 2 atoms at the B position are replaced with at least one combination of atoms selected from the group consisting of Li / Nb and Li / Ta, and (6) the above formula Wherein 0.005 atom to 2 atom at the A position is replaced with Ca, and an equal number of B or C positions are replaced with silicon,
Having at least one substitution selected from the group consisting of:
A scintillator composition. "
Is disclosed, and it is said that damage during exposure with a high energy ray can be reduced with a shorter decay time than known scintillator compositions.

A scintillator material having a garnet structure of this system has been newly invented, and recently, similar inventions have been actively proposed (for example, Japanese Patent Application Laid-Open No. 2012-72331 (Patent Document 5) and Japanese Patent Application Laid-Open No. 2012-184397). Gazette (patent document 6) etc.).
It seems that such scintillator materials are being installed in the flagship model of the latest X-ray CT system.

On the other hand, Bi ₄ Ge ₃ O ₁₂ single crystal (commonly known as BGO) has been used for a long time as a scintillator material for a gamma ray PET apparatus. BGO has a strong emission intensity to some extent and a short decay time, but has a low melting point and a low manufacturing cost. Therefore, BGO is in demand as a relatively inexpensive material for PET devices. Thereafter, a Gd ₂ SiO ₅ : Ce (commonly referred to as GSO) single crystal whose light emission amount has been increased and whose decay time has been drastically shortened has been developed and adopted in a high-end model of a gamma ray PET apparatus (for example, Japanese Patent Publication No. 62). No. 8472 (Patent Document 7)).
Thereafter, a Lu ₂ SiO ₅ : Ce (commonly referred to as LSO) single crystal having a larger light emission amount and a shorter decay time was developed, and is still mounted on a flagship machine in a gamma ray PET apparatus (for example, Japanese Patent Application Laid-Open No. Hei 9). -118593 (patent document 8)).

US Pat. No. 4,421,671 Japanese Examined Patent Publication No. 7-97139 Japanese Patent No. 3741302 JP 2007-169647 A JP 2012-72331 A JP 2012-18497A Japanese Examined Patent Publication No. 62-8472 JP-A-9-118593

However, with regard to the X-ray CT apparatus, the scintillator material based on (Y- _{major amount} Gd _{≦ 0.5} ) ₂ O ₃ : Eu based on the X-ray CT apparatus has a long decay time and a density of 6.0 g / cm ^3. The problem was that the film had to be used in the form of a thicker film.
In addition, the (Gd _1-xy Pr _x Ce _y ) ₂ O ₂ S scintillator material disclosed in Patent Documents 2 and 3 has a monoclinic crystal and has a low scintillation light transmittance of about 30%. The point and the point at which the damage at the time of exposure with a high energy ray is comparatively large have been a problem.
Further, disclosed in Patent Document _{4,5,6 (Tb 1-xy Lu x} Ce y) 3 (Al 1-z Sc z) 2 Al 3 O 12 based scintillator material is shorter decay time, Because it is cubic, the transmittance of scintillate light is as high as 80% or more, and it has very little damage when exposed to high energy rays. It is a very suitable material as a scintillator material for X-ray CT equipment. is there. However, there is a problem that a complex oxide having a very complicated composition must be processed and produced at a high temperature, which makes it extremely expensive. Or although the Example which can lower | hang a sintering process temperature is also disclosed depending on a composition, since there are many kinds of constituent elements, there also existed a problem that a yield fell considerably when it was going to manufacture with a desired composition.
On the other hand, regarding the gamma ray PET apparatus, the production cost of the BGO single crystal is reasonable, but the emission intensity and the decay time are insufficient. Further, the GSO single crystal and the LSO single crystal have a high emission intensity and a short decay time, and thus are very suitable substances as a scintillator material for a gamma ray PET apparatus. However, since the melting point is as extremely high as about 2000 ° C., there is a problem that it is much more expensive than other scintillator materials.

  The present invention has been made in view of the above circumstances, and emits scintillation light having an emission peak wavelength in the visible light region on the longer wavelength side than before by excitation of X-rays and / or gamma rays, and the transmittance of the scintillation light is To provide a novel scintillator material, a radiation detector, and a radiation inspection apparatus capable of producing a complex oxide having a high and short decay time and a relatively simple composition by a heat treatment of 1800 ° C. or less and suppressing the production cost. With the goal.

In order to achieve the above object, the present invention provides the following scintillator material, radiation detector and radiation inspection apparatus.
[1] A scintillator material comprising a translucent ceramic containing a complex oxide represented by the following formula (1) as a main component or a single crystal of a complex oxide represented by the following formula (1).
(Tb _x R _1-xy Ce _y ) ₂ B ₂ O ₇ (1)
(Wherein x is in the range of 0.2 to less than 1, y is in the range of 0.00001 to 0.01, x + y ≦ 1, R is yttrium, gadolinium, lutetium, lanthanum, holmium, thulium, europium, displo. At least one rare earth element selected from the group consisting of silicon and praseodymium, and B is at least one element selected from the group consisting of titanium, tin, hafnium, silicon, germanium, and zirconium (however, for silicon and germanium, this element Except when it is alone)
[2] The scintillator material according to [1], which emits light having an emission peak in a wavelength range of 610 to 700 nm when excited with X-rays and / or gamma rays.
[3] The scintillator material according to [1] or [2], wherein the transmittance of light having a wavelength of 633 nm at a thickness of 1 mm is 70% or more.
[4] The scintillator material according to any one of [1] to [3], wherein the main phase is a cubic crystal having a pyrochlore lattice.
[5] A radiation detector comprising the scintillator material according to any one of [1] to [4].
[6] A radiation inspection apparatus comprising the radiation detector according to [5].

  According to the present invention, a scintillator material containing terbium, a cerium active type, and a cubic rare earth oxide different from the garnet phase as a main component can be used by conventional excitation by X-rays and / or gamma rays. In addition, it emits scintillation light having an emission peak wavelength in the visible light region on the long wavelength side, has high transmittance of the scintillation light, has a short decay time, and can be manufactured at a manufacturing temperature of 1800 ° C. or lower, thereby reducing manufacturing costs. In addition, a novel scintillator material can be provided.

It is the schematic which shows the structure of the radiation detector concerning this invention, (a) is the front view, (b) is AA sectional drawing in (a).

[Scintillator materials]
Hereinafter, the scintillator material according to the present invention will be described.
The scintillator material according to the present invention is made of a translucent ceramic containing a composite oxide represented by the following formula (1) as a main component or a single crystal of the complex oxide represented by the following formula (1).
(Tb _x R _1-xy Ce _y ) ₂ B ₂ O ₇ (1)
(Wherein x is in the range of 0.2 to less than 1, y is in the range of 0.00001 to 0.01, x + y ≦ 1, R is yttrium, gadolinium, lutetium, lanthanum, holmium, thulium, europium, displo. At least one rare earth element selected from the group consisting of silicon and praseodymium, and B is at least one element selected from the group consisting of titanium, tin, hafnium, silicon, germanium, and zirconium (however, for silicon and germanium, this element Except when it is alone)

In the above formula (1), terbium is a skeletal material that is efficiently excited by irradiation with X-rays and / or gamma rays, and the excitation energy is such that the excitation energy is efficiently transferred to the cerium ions that are activators. Furthermore, the excitation energy of the energy-transferred cerium is light having a wavelength that can be photoelectrically converted by the Si photodiode, and having a light emission peak in the visible light region longer than the conventional one. It is an element that can be adjusted to a level capable of emitting light, and is an essential element in the present invention. It is preferable that energy can be efficiently transferred to the cerium ion, which is an activator, because the emission intensity increases. In addition, it is preferable that photoelectric conversion can be performed with a Si photodiode because a radiation detector can be manufactured at a much lower cost than that received with a photomultiplier tube. Furthermore, if light can be emitted with light having an emission peak in the visible light region on the longer wavelength side than before, the bias voltage can be lowered in a radiation detector using a Si photodiode, so that the circuit can be simplified. preferable.
In addition, although the light emission peak of the light which the conventional scintillator material emits changes with some compositions, it exists in the wavelength range of 510-590 nm.

  Cerium is an element that promptly receives X-ray and / or gamma ray energy absorbed by terbium and one or more other rare earth elements and enters an excited state and quickly transitions to a low energy state. It is another essential element. Use of cerium as an activator is preferable because the decay time is shorter than other activators such as europium.

  R is an element group having an action of increasing the density of the material to improve the absorption cross section of X-ray and / or gamma ray energy, and further, an element having an action of improving luminous efficiency by resonating with an electronic transition state of cerium. Groups are also included here.

As such an element, yttrium, gadolinium, lutetium, lanthanum, holmium, thulium, europium, dysprosium, and praseodymium can be suitably used.
Tb, Ce, and R are collectively referred to as elements at the A site.

B is an element having an effect of defining the crystal structure of the scintillator material as a pyrochlore type cubic crystal, and is an important element in the present invention. As a result, the scintillator material of the present invention has a cubic crystal (pyrochlore type cubic crystal) having a pyrochlore lattice as a main phase, preferably a pyrochlore type cubic crystal. The main phase means that the pyrochlore type cubic crystal accounts for 90% by volume or more, preferably 95% by volume or more, more preferably 99% by volume or more, and particularly preferably 99.9% by volume or more as a whole. Say. When the crystal structure is a cubic crystal, the effect of scattering due to birefringence is eliminated, the transmittance of scintillation light that is output when excited by X-rays and / or gamma rays is improved, and light with a wavelength of 633 nm at a thickness of 1 mm is obtained. The transmittance is preferably 70% or more.
As such an element, titanium, tin, hafnium, silicon, germanium, and zirconium can be suitably used. However, for silicon and germanium, the case where the element is used alone is excluded.
An element entering this position is referred to as an element at the B site. The Tb, Ce, and R are collectively referred to as elements at the A site. That is, the scintillator material of the present invention is mainly composed of an A ₂ B ₂ O ₇ type composite oxide.

  The above formula (1) includes terbium and cerium, and at least one rare earth element selected from the group consisting of yttrium, gadolinium, lutetium, lanthanum, holmium, thulium, europium, dysprosium, and praseodymium as R, and B It is composed of at least one element selected from the group consisting of titanium, tin, hafnium, silicon, germanium, and zirconium (provided that silicon and germanium are not included in the case of the element alone), Furthermore, other elements may be contained. As other elements, ytterbium can be exemplified, and calcium, aluminum, phosphorus, tungsten, molybdenum and the like can be typically exemplified as various impurity groups.

  The content of other elements is preferably 10 or less, more preferably 0.1 or less, and 0.001 or less (substantially zero) when the total amount of terbium is 100. Particularly preferred.

  In formula (1), x is 0.2 or more and less than 1.0. In the formula (1), when x is less than 0.2, the strongest peak wavelength when excited by X-rays and / or gamma rays is on the short wavelength side in the wavelength range assumed in the present invention, In addition, the decay time tends to be delayed as the emission wavelength shifts to the short wavelength side, which is not preferable. On the contrary, when x is 0.2 or more and less than 1.0, the strongest peak wavelength when excited by X-rays and / or gamma rays can be included in the wavelength range assumed in the present invention, and attenuation This is preferable because the time is also fast.

  In formula (1), y is 0.00001 or more and 0.01 or less, and preferably 0.0001 or more and 0.01 or less. If y is less than 0.00001, the absorbed X-ray energy and / or gamma rays are promptly received to be in an excited state, and the concentration of the activator that quickly transitions to the low energy state is too thin. This is not preferable because the decay time becomes long. If y is more than 0.01, the emission intensity starts to decrease again, which is not preferable. Further, x + y ≦ 1.

  The scintillator material of the present invention contains a composite oxide represented by the above formula (1) as a main component. That is, the scintillator material of the present invention may contain the composite oxide represented by the above formula (1) as a main component, and may contain other components as subcomponents.

  Here, containing as a main component means containing 50 mass% or more of complex oxide represented by the said Formula (1). The content of the composite oxide represented by the formula (1) is preferably 80% by mass or more, more preferably 90% by mass or more, preferably 99% by mass or more, and 99.9% by mass. The above is particularly preferable.

  Other subcomponents that are generally exemplified include dopants doped during single crystal growth, flux, and sintering aids added during ceramic production.

  As a manufacturing method of the scintillator material of the present invention, there are a single crystal manufacturing method such as a floating zone method and a micro pull-down method, and a ceramic manufacturing method, and any manufacturing method may be used. However, in general, the single crystal manufacturing method has a certain degree of restriction in the design of the concentration ratio of the solid solution, and the ceramic manufacturing method is more preferable in the present invention.

  Hereinafter, the ceramic production method will be described in more detail as an example of the production method of the scintillator material of the present invention, but the single crystal production method that follows the technical idea of the present invention is not excluded.

《Ceramics manufacturing method》
[material]
As raw materials used in the present invention, terbium and cerium, and a rare earth element R (R is at least one rare earth element selected from the group consisting of yttrium, gadolinium, lutetium, lanthanum, holmium, thulium, europium, dysprosium, and praseodymium) A metal powder that is a constituent element of the scintillator material of the present invention, further comprising B element (B is at least one element selected from the group consisting of titanium, tin, hafnium, silicon, germanium, and zirconium), Or an aqueous solution of nitric acid, sulfuric acid, uric acid or the like, or a complex oxide powder of the above elements can be suitably used. In particular, each oxide powder of each element is preferable because it is stable and safe and easy to handle. The purity of these raw materials is preferably 99.9% by mass or more.

  Moreover, it does not specifically limit about the powder shape of the said raw material, For example, square, spherical, and plate-shaped powder can be utilized suitably. Moreover, it can use suitably even if it is the powder which carried out secondary aggregation, and it can use suitably also if it is the granular powder granulated by granulation processes, such as a spray-dry process. Furthermore, there are no particular limitations on the process of adjusting these raw material powders. A raw material powder produced by a coprecipitation method, a pulverization method, a spray pyrolysis method, a sol-gel method, an alkoxide hydrolysis method, or any other synthesis method can be suitably used. Further, the obtained raw material powder may be appropriately treated by a wet ball mill, a bead mill, a jet mill, a dry jet mill, a hammer mill or the like.

  In the composite oxide powder raw material used in the present invention, a sintering suppression aid (sintering aid) may be appropriately added. In particular, in order to obtain a high translucency, it is often preferable to add a suitable sintering inhibitor that is suitable for the host material. However, the purity is preferably 99.9% by mass or more. In addition, when a sintering inhibitor is not added, it is preferable to select a raw material powder that has a primary particle size of nano-size and extremely high sintering activity. Such a selection may be made as appropriate.

  Furthermore, various organic additives may be added for the purpose of improving the quality stability and the yield in the manufacturing process. In the present invention, these are not particularly limited. That is, various dispersants, binders, lubricants, plasticizers, and the like can be suitably used.

[Manufacturing process]
In the present invention, the above raw material powder is pressed into a predetermined shape, degreased, and then sintered to produce a sintered body with a relative density of at least 92% or more. It is preferable to perform a hot isostatic pressing (HIP) process as a subsequent process.

(Press molding)
In the production method of the present invention, a normal press molding process can be suitably used. That is, it is possible to use a very general pressing process in which raw material powder is filled in a mold and pressurized from a certain direction, or a CIP (Cold Isostatic Pressing) process in which the raw material powder is sealed in a deformable waterproof container and pressurized with hydrostatic pressure. The applied pressure may be appropriately adjusted while confirming the relative density of the obtained molded body, and is not particularly limited. For example, if the pressure is controlled within a pressure range of about 300 MPa or less that can be handled by a commercially available CIP device, the manufacturing cost can be suppressed. It's okay. Alternatively, not only a molding process but also a hot press process, a discharge plasma sintering process, a microwave heating process, and the like that can be performed all at once at the time of molding can be suitably used.

(Degreasing)
In the production method of the present invention, a normal degreasing step can be suitably used. That is, it is possible to go through a temperature rising degreasing process by a heating furnace. Also, the type of atmospheric gas at this time is not particularly limited, and air, oxygen, hydrogen, and the like can be suitably used. The degreasing temperature is not particularly limited, but when a raw material mixed with an organic additive is used, it is preferable to raise the temperature to a temperature at which the organic component can be decomposed and eliminated.

(Sintering)
In the production method of the present invention, a general sintering process can be suitably used. That is, a heating and sintering process such as a resistance heating method or an induction heating method can be suitably used. The atmosphere at this time is not particularly limited, but an inert gas, oxygen, hydrogen, vacuum, or the like can be suitably used.

  The sintering temperature in the sintering step of the present invention is appropriately adjusted depending on the starting material selected. In general, using a selected starting material, a temperature that is several tens of degrees Celsius to 100 degrees Celsius or 200 degrees Celsius lower than the melting point of various composite oxide sintered bodies to be produced is suitably selected. In addition, when trying to produce a pyrochlore-type composite oxide sintered body in which there is a temperature zone in which a phase change to a phase other than a cubic crystal exists in the vicinity of the selected temperature, the conditions under which the temperature zone is strictly excluded and If controlled and sintered, the mixture of phases other than cubic crystals can be suppressed, and birefringence scattering can be reduced.

  The sintering holding time in the sintering process of the present invention is appropriately adjusted depending on the starting material selected. In general, a few hours is often sufficient. However, the relative density of the composite oxide sintered body after the sintering process must be densified to at least 92%.

(Hot isostatic pressing (HIP))
In the production method of the present invention, after the sintering process, an additional step of performing a hot isostatic pressing (HIP (Hot Isostatic Pressing) process) can be provided.

Incidentally, the pressurized gas medium type in this case, argon, an inert gas such as nitrogen or Ar-O ₂ can be used suitably. The pressure applied by the pressurized gas medium is preferably 50 to 300 MPa, and more preferably 100 to 300 MPa. If the pressure is less than 50 MPa, the translucency improvement effect may not be obtained. If the pressure exceeds 300 MPa, no further improvement in translucency can be obtained even if the pressure is increased, and the load on the device may be excessive and damage the device. There is. The applied pressure is preferably 196 MPa or less, which can be processed with a commercially available HIP device, for convenience and convenience.

  Further, the treatment temperature (predetermined holding temperature) at that time may be appropriately set depending on the type of material and / or the sintering state, and is set in the range of, for example, 1000 to 2000 ° C, preferably 1300 to 1800 ° C. At this time, as in the case of the sintering step, it is essential that the temperature be below the melting point and / or the phase transition point of the composite oxide constituting the sintered body. The composite oxide sintered body exceeds the melting point or exceeds the phase transition point, making it difficult to perform an appropriate HIP treatment. Moreover, if the heat treatment temperature is less than 1000 ° C., the effect of improving the translucency of the sintered body cannot be obtained. In addition, although there is no restriction | limiting in particular about the holding time of heat processing temperature, It is good to adjust suitably, checking the characteristic of the complex oxide which comprises a sintered compact.

  In addition, the heater material, the heat insulating material, and the processing container for HIP processing are not particularly limited, but graphite or molybdenum (Mo) can be suitably used.

(Optical polishing)
In the manufacturing method of the present invention, both ends of the light-transmitting composite oxide sintered body (translucent ceramic) that has undergone the above-described series of manufacturing steps on the optically utilized axis can be optically polished. preferable. The optical surface accuracy at this time is preferably λ / 4 or less, particularly preferably λ / 8 or less, when the measurement wavelength λ = 633 nm. Note that it is possible to further reduce the optical loss by appropriately forming an antireflection film on the optically polished surface.

  The scintillator material of the present invention obtained as described above has a cubic crystal having a pyrochlore lattice as the main phase, and is longer than the scintillation light emitted by the conventional scintillator material when excited by X-rays and / or gamma rays. Scintillation light having an emission peak in the visible light region on the wavelength side, for example, preferably has an emission peak in the wavelength range of 610 to 700 nm, more preferably 630 to 670 nm, and particularly preferably has the strongest wavelength peak in these wavelength ranges Emits light. Further, the transmittance of light having a wavelength of 633 nm when the thickness is 1 mm is 70% or more.

[Radiation detector]
The scintillator material of the present invention is suitable for X-ray CT apparatus applications and / or gamma-ray PET apparatus applications. A large number of arrays are arranged in the apparatus, and the radiation detection is excited by X-ray irradiation and / or gamma irradiation. Suitable for dexterity. Note that X-rays and gamma rays assumed in the present invention include, for example, X-rays generated in an X-ray tube using a target having an electron beam irradiation surface made of tungsten or a tungsten alloy (Re-W alloy), and radioisotopes. Examples include gamma rays generated from a gamma ray source of body cobalt 60.

The radiation detector of the present invention comprises a plate made of the scintillator material of the present invention and a light receiving element such as a Si photodiode at the subsequent stage. An example of the configuration is shown in FIG. In the radiation detector 10 of the present invention, a scintillator plate 11 made of the scintillator material of the present invention is partitioned by a reflector 12 and arranged in 36 elements in 6 rows and 6 columns, and further receives light at the subsequent stage of each scintillator plate 11. The element 13 is arranged and stored in the container 14. In this radiation detector 10, the scintillator plate 11 is excited by X-rays and / or gamma rays incident from the front, and the light emission energy output from the scintillator plate 11 is converted into an electric signal by the light receiving element 13 and amplified. It is configured to output.
The light receiving element 13 can detect light in the region of the emission peak wavelength of the scintillator material of the present invention, and is a general element used for a radiation detector mounted on an X-ray CT apparatus or a gamma ray PET apparatus. Si photodiode (PD), Si-APD (Avalanche Photodiode), CCD (Charge Coupled Device) image sensor, photomultiplier tube (PMT), and the like. As the light receiving element 13, for example, a Si-APD (avalanche photodiode) having a sensitivity wavelength range of 450 to 1050 nm and a maximum sensitivity wavelength of 550 nm or more, preferably a sensitivity wavelength range of 450 to 800 nm and a maximum sensitivity wavelength of 590 nm or more is preferable.

  A combination of the radiation detector 10 of the present invention arranged in an array in this way and a computed tomography (CT) system that digitizes an electrical signal output from the radiation detector 10 and calculates and images it. Thus, a radiation inspection apparatus such as an X-ray CT apparatus or a gamma ray PET apparatus is manufactured.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the examples. The primary particle diameter of the raw material powder was determined as a weight average value by a laser light diffraction method.

[Example 1, Comparative Example 1]
An example in which titanium, tin, or hafnium is selected as the element at the B site in the above formula (1) will be described.
Terbium oxide powder, cerium oxide powder, yttrium oxide powder, gadolinium oxide powder, lutetium oxide powder, lanthanum oxide powder, holmium oxide powder, thulium oxide, europium oxide, dysprosium oxide and praseodymium oxide powder manufactured by Shin-Etsu Chemical Co., Ltd. Was obtained. In addition, titanium oxide powder, stannic oxide powder manufactured by Kojundo Chemical Laboratory Co., Ltd., and hafnium oxide powder manufactured by American Elements were obtained. All the purity was 99.9 mass% or more.
Using the raw materials, each mixed oxide raw material having a mixing ratio as shown in Table 1 having a final composition was produced. That is, the final sum of the molar ratios of terbium, cerium, and R elements (that is, the number of moles of elements at the A site) and the number of moles of titanium, tin, or hafnium (that is, the number of moles of elements at the B site) ) And the mixed powders weighed so as to have an equimolar molar ratio. Subsequently, the mixture was dispersed and mixed in a zirconia ball mill apparatus in ethanol while preventing mixing of the test samples. The treatment time was 24 hours. Thereafter, spray drying treatment was performed to produce a granular raw material having an average particle diameter of 20 μm. Furthermore, these powders were put into an iridium crucible and fired at 1600 ° C. for 3 hours in a high-temperature muffle furnace to obtain 28 kinds of firing raw materials including comparative examples. Each obtained firing raw material was subjected to diffraction pattern analysis by a powder X-ray diffractometer manufactured by Panalytical. As a result, it was confirmed that any of the fired raw materials was an oxide raw material having a pyrochlore cubic crystal (cubic crystal having a pyrochlore lattice) as a main phase as a crystal structure.
The obtained various raw materials were again dispersed and mixed in ethanol in a zirconia ball mill apparatus. At this time, an organic dispersant and an organic binder were appropriately added. The processing time was 40 hours. Thereafter, spray drying treatment was performed again to produce granular pyrochlore oxide raw materials (starting raw materials) having an average particle diameter of 20 μm.

Next, the obtained starting material is filled into a 40 mm diameter mold, temporarily formed into a 6 mm thick rod with a uniaxial press molding machine, and then hydrostatically pressed at a pressure of 198 MPa to obtain a CIP compact. It was. Subsequently, the obtained CIP compact was put into a muffle furnace, and degreased by heat treatment in the atmosphere at 800 ° C. for 3 hours.
Next, the obtained degreased molded body was charged into a vacuum heating furnace, heated to 1500-1700 ° C. at a temperature increase rate of 100 ° C./h, held for 3 hours, and then cooled at a temperature decrease rate of 600 ° C./h. Thus, a sintered body was obtained. At this time, the sintering temperature and holding time were adjusted so that the sintered relative density of the sample was 92% or more.
Further, the sintered body was subjected to HIP treatment using an Ar gas as a pressure medium at a HIP heat treatment temperature of 1500 to 1750 ° C. and a pressure of 190 MPa for a holding time of 3 hours.

Each ceramic sintered body thus obtained was cut, ground and polished so as to have a length and width of 2 mm × 2 mm and a thickness of 1 mm to obtain a scintillator plate. Next, a reflector (made of magnesium oxide powder dispersed in a silicone paste and bonded by drying) is provided between the scintillator plates and partitioned into 36 elements in 6 rows and 6 columns. The optical end surfaces of the sample were subjected to final optical polishing with an optical surface accuracy of λ / 4 (when the measurement wavelength was λ = 633 nm).
About each obtained scintillator plate, the transmittance | permeability was measured in the following ways using HeNe laser (wavelength 633nm). At this time, care was taken so that the laser beam did not strike the reflective material between the scintillator plate and the scintillator plate.

(Measurement method of transmittance)
The transmittance was measured by the intensity of light when light having a wavelength of 633 nm was transmitted, and was determined based on the following equation.
Transmittance (%) = I / Io × 100
(In the formula, I represents transmitted light intensity (intensity of light transmitted through a sample having a thickness of 1 mm), and Io represents incident light intensity.)

Thereafter, each scintillator plate 11 was placed on the light receiving element 13 to produce the radiation detector 10 of FIG. Next, using a light output measuring device manufactured by combining the radiation detector 10 and an X-ray tube of a tungsten target, the scintillator plate 11 is irradiated with X-rays at a tube voltage of the X-ray tube of 120 kV, and the light receiving element 13 is irradiated. The value of the flowing current was obtained as the light output. In addition, Si-APD (Hamamatsu Photonics Co., Ltd. short wavelength type, model number S5343, sensitivity wavelength range 550 to 800 nm, maximum sensitivity wavelength 590 nm) was used as the light receiving element 13. In addition, the sensitivity of this Si-APD at a wavelength of 540 nm (emission peak wavelength of the CdWO ₄ single crystal (CWO single crystal) scintillator of the reference sample) is similar to that at a wavelength of 650 nm (equivalent to the emission peak wavelength of the example sample). .
At this time, the emission peak wavelength, light output, and decay time of the scintillator plate 11 were determined as follows.

(Measurement method of peak emission wavelength)
Before the light output is evaluated by the X-ray irradiation evaluation system, photoluminescence (PL) measurement is performed with a fluorescence lifetime measuring apparatus (Quantaurus-Tau: model number C11367-1 manufactured by Hamamatsu Photonics Co., Ltd.), and the emission peak wavelength is determined from the result. Asked. In other words, it is excited with light having an excitation wavelength of 280 nm, the emitted fluorescence is subjected to spectroscopy by a grating, the fluorescence wavelength spectrum is detected by a CCD camera, and the wavelength at which the fluorescence output is maximized is the emission peak wavelength during X-ray irradiation. Considered. The light having an excitation wavelength of 280 nm is ultraviolet light having the shortest wavelength that can be incident on the fluorescence lifetime measuring apparatus, that is, the maximum energy, and does not cause vibration of the skeleton material during X-ray irradiation. The excitation energy that has been gradually relaxed when excited is an excitation wavelength sufficient to confirm the wavelength at which light is finally emitted, and is used as a substitute for X-rays for measuring the emission peak wavelength during X-ray irradiation. Can be used.

(Measurement method of light output)
Here, for the purpose of facilitating the comparison, a CdWO ₄ single crystal (CWO single crystal) scintillator separately obtained in the radiation detector 10 is arranged in place of the scintillator plate 11, and an evaluation method using the light output measuring device is used. The light output in this case was obtained, and the light output ratio (to CWO ratio) of the sample when the value was “1” was shown as the light output value of each sample.

(Measurement method of decay time)
As described above, the state in which the light output of each sample is stabilized by irradiating the X-ray with the light output measuring apparatus is set to 100%, then the X-ray irradiation is stopped, and the light output intensity of each sample is stopped. Was measured until the time of decay to 5% of the stable state (decay time during X-ray irradiation).
In addition, as described above, the fluorescence lifetime measurement apparatus is used to irradiate light with an excitation wavelength of 280 nm so that the light output of each sample is stabilized to 100%, and then the light irradiation is stopped. The time until the light output intensity of the light was attenuated to 5% of the stable state was measured (attenuation time during ultraviolet irradiation).
Table 2 summarizes the above series of evaluation results.

From the above results, scintillator materials mainly composed of pyrochlore type composite oxides of the group of examples are transparent with a light transmittance of 633 nm when the thickness is 1 mm, which is 70% or more. The light emitted as the scintillator material does not wastefully scatter inside, and the strongest emission peak wavelength when excited by X-rays is in the wavelength range of 638 to 661 nm. Photoelectric conversion can be performed without any problem, and the light output is not inferior to that of the conventional material. Moreover, the decay time when the afterglow output is 5% due to X-ray irradiation is as short as 5 ms or less. The decay time when the afterglow output is 5% due to ultraviolet irradiation is 1 ns, which is the measurement lower limit level (apparatus performance limit). As a result, when the scintillator material of the present invention is used in a radiation inspection apparatus such as an X-ray CT apparatus or a gamma-ray PET apparatus, the switching cycle can be speeded up, so that the operability and safety of a low exposure dose are excellent. It is possible to finish the radiation inspection apparatus.
In the compositions of Comparative Examples 1-1 to 1-3, the strongest emission peak wavelength when excited by X-rays is shifted to the short wavelength side of less than 600 nm, so that the photoelectric conversion efficiency is reduced by the Si photodiode. Resulting in. In the composition of Comparative Example 1-4, the light output is low because the concentration of cerium, which is the activator, is too low. On the contrary, in the composition of Comparative Example 1-5, the concentration of cerium, which is the activator, is too high, so that a concentration quenching phenomenon occurs and the light output decreases.

[Example 2, Comparative Example 2]
In the above formula (1), an example where the element at the B site position is selected from the group consisting of silicon, germanium, and zirconium will be described.
Terbium oxide powder, cerium oxide powder, yttrium oxide powder, and gadolinium oxide powder manufactured by Shin-Etsu Chemical Co., Ltd. were obtained. In addition, silica powder, germanium oxide powder manufactured by Kojundo Chemical Laboratory Co., Ltd., and zirconium oxide powder manufactured by Daiichi Rare Element Chemical Industries, Ltd. were obtained. All the purity was 99.9 mass% or more.
Using the raw materials, each mixed oxide raw material having a mixing ratio having a final composition as shown in Table 3 was produced. That is, the sum of the final molar ratios of terbium, cerium, and yttrium or gadolinium (ie, the number of moles of the element at the A site) and the total molar ratio of silicon and zirconium, or germanium and zirconium, or silicon, germanium Alternatively, each of the mixed powders weighed so that the number of moles of zirconium (that is, the number of moles of the element at the B site position) was an equimolar mole ratio was prepared. Subsequently, the mixture was dispersed and mixed in a zirconia ball mill apparatus in ethanol while preventing mixing of the test samples. The treatment time was 24 hours. Thereafter, spray drying treatment was performed to produce a granular raw material having an average particle diameter of 20 μm.
Furthermore, these powders were put in an iridium crucible and fired at 1600 ° C. for 3 hours in a high-temperature muffle furnace to obtain seven kinds of firing raw materials including comparative examples. Each obtained firing raw material was subjected to diffraction pattern analysis by a powder X-ray diffractometer manufactured by Panalytical. As a result, it was confirmed that the crystal structure was an oxide raw material having pyrochlore cubic crystals (cubic crystals having pyrochlore lattices) as the main phase in Examples 2-1, 2-2, 2-3, 2-4. It was a group. Moreover, although it was a pyrochlore type, the raw materials in which the crystal system was orthorhombic were the groups of Comparative Examples 2-1 and 2-2. Furthermore, Example 2-5 was a raw material in which fluorite-type tetragonal crystals were mixed in addition to pyrochlore-type cubic crystals.
Various raw materials thus obtained were again dispersed and mixed in ethanol in a zirconia ball mill. At this time, an organic dispersant and an organic binder were appropriately added. The processing time was 40 hours. Thereafter, spray drying treatment was performed again to produce granular pyrochlore oxide raw materials (starting raw materials) having an average particle diameter of 20 μm.

Next, the obtained starting material is filled into a 40 mm diameter mold, temporarily formed into a 6 mm thick rod with a uniaxial press molding machine, and then hydrostatically pressed at a pressure of 198 MPa to obtain a CIP compact. It was. Subsequently, the obtained CIP compact was put into a muffle furnace, and degreased by heat treatment in the atmosphere at 800 ° C. for 3 hours.
Next, the obtained degreased molded body was charged into a vacuum heating furnace, heated to 1500-1700 ° C. at a temperature increase rate of 100 ° C./h, held for 3 hours, and then cooled at a temperature decrease rate of 600 ° C./h. Thus, a sintered body was obtained. At this time, the sintering temperature and holding time were adjusted so that the sintered relative density of the sample was 92% or more.
Further, the sintered body was subjected to HIP treatment using an Ar gas as a pressure medium at a HIP heat treatment temperature of 1500 to 1750 ° C. and a pressure of 190 MPa for a holding time of 3 hours.
Subsequently, the obtained ceramic sintered bodies were cut, ground, and polished so as to be 2 mm × 2 mm in length and width and 1 mm in thickness. Next, they were processed into a scintillator material consisting of 36 elements of 6 × 6 via a reflective material, and the optical end faces of the sample were subjected to final optical polishing with an optical surface accuracy of λ / 4 (when measurement wavelength λ = 633 nm).
The transmittance of each scintillator plate obtained was measured in the same manner as in Example 1 using a HeNe laser (wavelength 633 nm). At this time, care was taken so that the laser beam did not strike the reflective material between the scintillator plate and the scintillator plate.

Thereafter, each scintillator plate 11 was placed on the light receiving element 13 in the same manner as in Example 1 to produce the radiation detector 10 of FIG. Next, a light output measuring device was produced in the same manner as in Example 1, and the scintillator plate 11 was irradiated with X-rays at a tube voltage of 120 kV of an X-ray tube of a tungsten target, and the current value flowing through the light receiving element 13 was obtained as the light output. At this time, the emission peak wavelength, light output and decay time of the scintillator plate 11 were determined in the same manner as in Example 1.
Table 4 summarizes the above series of evaluation results.

From the above results, the scintillator materials mainly composed of pyrochlore-type composite oxides consisting of the group of examples have a light transmittance of 633 nm when the thickness is 1 mm, particularly 65% or more. Since -1 to 2-4 is transparent at 79% or more, the light emitted as the scintillator material does not scatter wastefully in the interior, and the strongest emission peak wavelength when excited by X-ray is 656 to Since it is in the wavelength range of 661 nm, it is possible to perform photoelectric conversion with a Si photodiode as a light receiving element without any problem. Furthermore, the optical output is comparable to that of conventional materials, and the afterglow output by X-ray irradiation. The decay time at 5% is as short as 6 ms or less. Further, the decay time when the afterglow output is 5% due to ultraviolet irradiation is 1 nm, which is the measurement lower limit level (apparatus performance limit). In Example 2-5, the light output is slightly lower than in the other examples. This is because the composition of Example 2-5 has a phase of a fluorite-type tetragonal crystal in addition to a pyrochlore-type cubic crystal. This is because the light scattering increases due to the mixture. As a result, when the scintillator material of the present invention is used in a radiation inspection apparatus such as an X-ray CT apparatus or a gamma-ray PET apparatus, the switching cycle can be speeded up, so that the operability and safety of a low exposure dose are excellent. It is possible to finish the radiation inspection apparatus.
In the compositions of Comparative Examples 2-1 and 2-2, the crystal system was orthorhombic, so that the transmittance was lowered, thereby reducing the light output.

[Example 3, Comparative Example 3]
An example in which zirconium or hafnium is selected as the element at the B site in the above formula (1) and the sintering temperature is adjusted will be described.
Terbium oxide powder, cerium oxide powder, gadolinium oxide powder, and lanthanum oxide powder manufactured by Shin-Etsu Chemical Co., Ltd. were obtained. In addition, zirconium oxide powder manufactured by Daiichi Elemental Chemical Co., Ltd. and hafnium oxide powder manufactured by American Elements were also obtained. All the purity was 99.9 mass% or more.
Using the raw materials, each mixed oxide raw material having a mixing ratio having a final composition as shown in Table 5 was produced. That is, the final sum of the molar ratios of terbium, cerium, and R elements (that is, the number of moles of the element at the A site) and the number of moles of zirconium or hafnium (that is, the number of moles of the element at the B site). Each of the mixed powders weighed so as to have an equimolar molar ratio was prepared. Subsequently, the mixture was dispersed and mixed in a zirconia ball mill apparatus in ethanol while preventing mixing of the test samples. The treatment time was 24 hours. Thereafter, spray drying treatment was performed to produce a granular raw material having an average particle diameter of 20 μm. Furthermore, these powders were put in an iridium crucible and fired at 1600 ° C. for 3 hours in a high temperature muffle furnace to obtain 12 kinds of firing raw materials including comparative examples. Each obtained firing raw material was subjected to diffraction pattern analysis by a powder X-ray diffractometer manufactured by Panalytical. As a result, it was confirmed that any of the fired raw materials was an oxide raw material having a pyrochlore cubic crystal (cubic crystal having a pyrochlore lattice) as a main phase as a crystal structure.
The obtained various raw materials were again dispersed and mixed in ethanol in a zirconia ball mill apparatus. At this time, an organic dispersant and an organic binder were appropriately added. The processing time was 40 hours. Thereafter, spray drying treatment was performed again to produce granular pyrochlore oxide raw materials (starting raw materials) having an average particle diameter of 20 μm.

Next, the obtained starting material is filled into a 40 mm diameter mold, temporarily formed into a 6 mm thick rod with a uniaxial press molding machine, and then hydrostatically pressed at a pressure of 198 MPa to obtain a CIP compact. It was. Subsequently, the obtained CIP compact was put into a muffle furnace, and degreased by heat treatment in the atmosphere at 800 ° C. for 3 hours.
Next, the obtained degreased molded body was charged into a vacuum heating furnace, heated to 1650-1750 ° C. at a temperature increase rate of 100 ° C./h, held for 10 hours, and then cooled at a temperature decrease rate of 600 ° C./h. Thus, a sintered body was obtained. At this time, the sintering temperature and the holding time were adjusted so that the sintered relative density of the sample was 99.2% or more.
Further, the sintered body was subjected to HIP treatment using an Ar gas as a pressure medium at a HIP heat treatment temperature of 1500 to 1750 ° C. and a pressure of 190 MPa for 1 hour.

Each ceramic sintered body thus obtained was cut, ground and polished so as to have a length and width of 2 mm × 2 mm and a thickness of 1 mm to obtain a scintillator plate. Next, a reflector (made of magnesium oxide powder dispersed in a silicone paste and bonded by drying) is provided between the scintillator plates and partitioned into 36 elements in 6 rows and 6 columns. The optical end surfaces of the sample were subjected to final optical polishing with an optical surface accuracy of λ / 4 (when the measurement wavelength was λ = 633 nm).
The transmittance of each scintillator plate obtained was measured in the same manner as in Example 1 using a HeNe laser (wavelength 633 nm). At this time, care was taken so that the laser beam did not strike the reflective material between the scintillator plate and the scintillator plate.

Thereafter, each scintillator plate 11 was placed on the light receiving element 13 in the same manner as in Example 1 to produce the radiation detector 10 of FIG. Next, a light output measuring device was produced in the same manner as in Example 1, and the scintillator plate 11 was irradiated with X-rays at a tube voltage of 120 kV of an X-ray tube of a tungsten target, and the current value flowing through the light receiving element 13 was obtained as the light output. At this time, in the same manner as in Example 1, the emission peak wavelength of the scintillator plate 11, the light output, and the decay time at the time of ultraviolet irradiation were obtained.
The series of evaluation results described above are summarized in Table 6.

From the above results, the scintillator materials mainly composed of pyrochlore type composite oxides of the group of examples are highly transparent with a light transmittance of 633 nm when the thickness is 1 mm. Therefore, the light emitted as the scintillator material is not scattered and lost in the interior, and the strongest emission peak wavelength when excited with ultraviolet rays is in the wavelength range of 649 to 656 nm. In addition, the photoelectric conversion can be performed without any problem, and the light output is not inferior to that of the conventional material. In addition, the decay time when the afterglow output is 5% due to ultraviolet irradiation is 15 ns in Example 3-8. Other examples are extremely short with a measurement lower limit level (apparatus performance limit). The decay time is expected to be at least as small as in Examples 1 and 2 even in the case of X-ray irradiation and gamma-ray irradiation. As a result, when the scintillator material of the present invention is used in a radiation inspection apparatus such as an X-ray CT apparatus or a gamma-ray PET apparatus, the switching cycle can be greatly accelerated, so that the operability and safety of a low exposure dose are reduced in a short time. It is possible to finish the radiation inspection apparatus excellent in.
In the compositions of Comparative Examples 3-1 and 3-2, the light output is low because the concentration of cerium as the activator is too low.

  The present invention has been described with the embodiment. However, the present invention is not limited to the above embodiment, and other embodiments, additions, modifications, deletions, and the like can be conceived by those skilled in the art. As long as the effects of the present invention are exhibited in any aspect, the present invention is included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Radiation detector 11 Scintillator plate 12 Reflector 13 Light receiving element 14 Container

Claims (6)

A scintillator material comprising a translucent ceramic containing a composite oxide represented by the following formula (1) as a main component or a single crystal of a composite oxide represented by the following formula (1).
(Tb _x R _1-xy Ce _y ) ₂ B ₂ O ₇ (1)
(Wherein x is in the range of 0.2 to less than 1, y is in the range of 0.00001 to 0.01, x + y ≦ 1, R is yttrium, gadolinium, lutetium, lanthanum, holmium, thulium, europium, displo. At least one rare earth element selected from the group consisting of silicon and praseodymium, and B is at least one element selected from the group consisting of titanium, tin, hafnium, silicon, germanium, and zirconium (however, for silicon and germanium, this element Except when it is alone)   The scintillator material according to claim 1, which emits light having an emission peak in a wavelength range of 610 to 700 nm when excited with X-rays and / or gamma rays.   The scintillator material according to claim 1 or 2, wherein the transmittance of light having a wavelength of 633 nm at a thickness of 1 mm is 70% or more.   The scintillator material according to any one of claims 1 to 3, wherein the main phase is a cubic crystal having a pyrochlore lattice.   A radiation detector comprising the scintillator material according to claim 1.   A radiation inspection apparatus comprising the radiation detector according to claim 5.

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