JP6460440B2 - X-ray phosphor plate - Google Patents

Description

  The present invention relates to a phosphor plate having high resolution used for X-ray detection.

  Inspection apparatuses using X-rays are widely used not only for medical X-ray diagnostic apparatuses but also for industrial IC inspection apparatuses. An X-ray detector used in such an inspection apparatus receives X-rays with a phosphor plate, converts this into light, and converts the light into a photoelectric conversion device (for example, a CCD image sensor, It is converted into an electrical signal imaged by a two-dimensional image sensor such as a CMOS image sensor. This X-ray detector is required to improve various performances, and most importantly, an improvement in resolution is required.

  Conventionally, the phosphor plate used in the X-ray detector is usually a particulate phosphor of about 1 μm, and the phosphor particles in the phosphor suspension are settled on the substrate, and the uniform phosphor plate on the substrate. And the like (precipitation method), and a method (vapor deposition method) for producing a uniform phosphor plate by vapor-depositing a phosphor such as cesium iodide (CsI) on a substrate. In the phosphor plate configured as described above, the X-ray image is converted into a visible light image, but the emitted photons converted from the X-rays are emitted in all solid angle directions. Among the pixels of the two-dimensional image sensor, the pixel reaches not only the pixel at the nearest position where the light emission photon is generated but also the neighboring pixel. For this reason, there is a problem that the resolution of the electric signal image is inferior to that of the original X-ray image because the image of the emitted photons becomes large.

  In order to improve this resolution, for example, to reduce the influence of light in the lateral direction, the phosphor plate is increased in filling ratio to reduce the thickness, or, for example, a columnar shape in a direction perpendicular to the substrate A method is known in which the scattering in the lateral direction is reduced by forming crystals. However, this columnar structure still causes lateral scattering, which is not a sufficient countermeasure.

As another method, using a micro electro mechanical systems (MEMS) method, a fine well-type structure is formed on the substrate 61 as shown in 6a in FIG. 6, and the well-type structure is formed in 6b in FIG. As shown, a phosphor plate that is filled with phosphor particles 62 and in which light emitted from the phosphor hardly diffuses in the horizontal direction has been proposed (see, for example, Non-Patent Document 1).
However, in this method, it is difficult to create a high aspect ratio (deep well structure), and there is a problem that the filling rate of the phosphor particles filling the well structure cannot be increased. In Non-Patent Document 1, the phosphor filling rate in the well-type structure is 30% to 50%, and high filling is an issue.

As another method, an X-ray detector comprising the following components has been proposed. That is, a network pixel is formed by digging a groove from a surface to a predetermined depth on an X-ray fluorescent substrate made of a solid phosphor such as a phosphor single crystal, and a groove between the pixels is filled with a light reflective adhesive material. . A visible light detector array is provided on the back surface of the X-ray fluorescent substrate. The solid phosphors are CdWO ₄ , Bi ₄ Ge ₃ O ₁₂ , Y ₃ Al ₅ O ₁₂ : Eu, Y ₃ Al ₅ O ₁₂ : Ce, LuTaO ₄ : Nb, Y ₂ O ₃ , CsI: Tl, CsI: _{Na, CsI, NaI, CsF,} CaF 2: Eu, LiI: Eu, Gd 2 SiO 5: an X-ray phosphor selected from the group consisting of Ce. As another form, the X-ray fluorescent substrate is configured by applying a known X-ray phosphor powder on a light guide glass substrate. The X-ray phosphor powder is selected from the group consisting of Gd ₂ O ₂ S: Tb, Gd ₂ O ₂ S: Pr, Ce, F, ZnCdS: Ag, Y ₂ O ₂ S: Eu (for example, Patent Document 1). reference).

  When the solid phosphor disclosed in Patent Document 1 is used, the problem of the filling rate is improved. However, the X-ray fluorescent substrate is composed of (1) an element having a high atomic number in order to increase the X-ray absorption coefficient. (2) The human body does not contain harmful elements, and (3) the luminous efficiency is high. It has been difficult to find a material that meets all three requirements. Furthermore, the production of solid phosphors such as single crystals has difficulties in terms of equipment and cost. In addition, when an X-ray fluorescent substrate coated with a powder phosphor according to another embodiment is used, the phosphor filling rate is naturally small, the sensitivity is low, and light scattering in the powder scintillator is unavoidable, It causes degradation of resolution. In addition, when grooving with a laser or the like, there is a concern about the problem of variation in the accuracy of the groove depth. Depth accuracy variation directly leads to resolution variation.

US Pat. No. 5,956,382A

Im Deok Junk et al., `` Flexible Gd2O2S: Tb scintillators pixelated with polyethylene microstructures for digital x-ray image sensors '', Journal of Micromechanics and Microengineering, 2009, Vol. 19, No. 1, 015014 (10pp)

  An object of this invention is to provide the fluorescent substance plate for X-ray detectors which suppresses light scattering and has high resolution.

  The present inventors use a polycrystalline phosphor ingot for the phosphor plate, and further have a through-hole structure that is discontinuous and separated from each other in a repetitive pattern shape such as a lattice shape for suppressing light scattering. The present inventors have found that the light scattering in the lateral direction parallel to the phosphor plate is suppressed, resulting in a phosphor plate for an X-ray detector having high resolution.

  An X-ray phosphor plate according to a first aspect of the present invention is a phosphor plate made of a phosphor polycrystal, wherein the phosphor plate is provided with a through hole, and the through hole has a predetermined repeating pattern. Further, the shape is discontinuous, and a light reflecting material is provided on the inner surface of each through hole. Since the phosphor plate has the above-described through-holes, the X-ray phosphor plate has high resolution while suppressing the light scattering while maintaining the mechanical strength.

  The X-ray phosphor plate according to the second invention is the X-ray phosphor plate according to the first invention, wherein the shape of the repeating pattern of the through holes is any one of a square lattice, a triangular lattice, and a hexagonal lattice. It is characterized by being. By making the shape of the repeated pattern of the through-holes into a lattice shape, an X-ray phosphor plate having higher resolution can be obtained.

  An X-ray phosphor plate according to a third invention is the X-ray phosphor plate according to the first or second invention, wherein the phosphor is a rare earth oxysulfide phosphor. By selecting a rare earth oxysulfide phosphor, an X-ray phosphor plate having excellent X-ray sensitivity is obtained.

An X-ray phosphor plate according to a fourth invention is the X-ray phosphor plate according to any one of the first to third inventions, wherein the light reflecting material is a white pigment. By selecting a white pigment as the light reflecting material, an X-ray phosphor plate having high sensitivity to X-rays and excellent resolution is obtained.
An X-ray phosphor plate according to a fifth invention is the X-ray phosphor plate according to the fourth invention, wherein the white pigment is selected from the group consisting of a titanium oxide pigment, a zinc oxide pigment, a barium sulfate pigment, and a magnesium oxide pigment. And at least one kind of pigment. By selecting these pigments, an X-ray phosphor plate having high sensitivity to X-rays and excellent resolution can be obtained.

An X-ray phosphor plate according to a sixth invention is the X-ray phosphor plate according to any one of the first to third inventions, wherein the light reflecting material is a metal film. By selecting a metal film as the light reflecting material, an X-ray phosphor plate having high sensitivity to X-rays and excellent resolution can be obtained.
An X-ray phosphor plate according to a seventh invention is the X-ray phosphor plate according to the sixth invention, wherein the metal film is selected from the group consisting of aluminum, silver, copper, gold, and zinc. It is characterized by being a metal. By selecting these metals, an X-ray phosphor plate having high sensitivity to X-rays and excellent resolution can be obtained.

  According to the phosphor plate for X-rays of the present invention, a lattice shape for increasing the density of the phosphor by increasing the density of the phosphor by using a polycrystalline phosphor ingot for the phosphor plate and further suppressing light scattering. By having a through-hole structure that is discontinuous and separated from each other in a repetitive pattern shape, etc., it suppresses light scattering in the horizontal direction parallel to the phosphor plate while maintaining mechanical strength, resulting in high resolution It is possible to provide a phosphor plate for an X-ray detector.

It is a graph which shows an example of the time change of the temperature and pressure in a hot press process in the manufacture process of the fluorescent substance plate for X-rays of this invention. It is a schematic diagram which shows the example of the through-hole pattern which deleted a part of side of the regular lattice in the fluorescent substance plate for X-rays of this invention. It is a schematic diagram which shows the cross section with an example of the fluorescent substance plate for X-rays of this invention. It is a graph which shows the relationship between the resolution MTF and the spatial frequency in the phosphor plate for X-rays of the present invention and the conventional type. It is a graph which shows the relationship between the resolution MTF and the spatial frequency in the fluorescent substance plate for X-rays of another example of this invention. It is sectional drawing of an example of the conventional fluorescent substance plate for X-rays.

  Hereinafter, an X-ray phosphor plate and its characteristics according to an embodiment of the present invention will be described. The combinations of the elements and features of the embodiments described below are merely examples, and do not limit the scope of the present invention.

The X-ray phosphor plate of the present invention is manufactured through the following steps. That is,
(1) phosphor powder synthesis step, (2) ingot creation step, (3) phosphor plate formation step, (4) through-hole creation step, (5) annealing step, and (6) reflector provision step.

In the phosphor powder synthesis step, the starting raw material powder containing the flux is mixed and prepared through a normal phosphor synthesis step such as firing and washing treatment.
The phosphor used in the present invention has a large X-ray absorption, that is, the phosphor is composed of atoms having a large atomic number, a high visible light conversion efficiency of the absorbed X-ray energy, and 2 such as a CCD. It is required to have an emission spectrum that matches the spectral sensitivity characteristics of the two-dimensional image sensor. For example, it is preferably formed of a rare earth activated rare earth oxysulfide phosphor or a europium activated alkaline earth halide phosphor. Terbium-activated gadolinium oxysulfide Gd ₂ O ₂ S: Tb is particularly preferable. In addition, europium activated alkaline earth halide phosphors such as BaFCl: Eu, rare earth activated rare earth oxyhalide phosphors such as LaOBr: Tb, and the like can be used.

  In the ingot creation step, a phosphor ingot is created from the phosphor powder by a high-temperature high-pressure sintering method. As this high-temperature and high-pressure sintering, a hot press (HP) method in which pressure is applied in a uniaxial direction or a hot isostatic press (HIP) method in which pressure is applied from all directions can be used.

  In the phosphor plate creation step, the phosphor ingot is sliced using a normal slicing machine such as a diamond cutter to obtain a phosphor plate. In consideration of mass productivity, a multi-wire saw is preferable. The thickness to be sliced can be appropriately adjusted to a thickness of several mm to several tens of μm depending on the application.

  In the through-hole creating step, the through-hole processing is performed on the phosphor plate using a laser processing apparatus in accordance with a predetermined repetitive pattern. In order to increase the strength of the phosphor plate, it is necessary that the through holes are separated from each other as shown in FIG. 2a in FIG. 2 shows a square lattice, FIG. 2b shows a triangular lattice, and FIG. 2c shows a hexagonal lattice. FIG. 2d shows an example in which through holes are processed into a square shape actually missing from the fluorescent screen. Laser processing was performed by irradiating the phosphor plate with a laser pulse having a pulse time width of several tens of nanoseconds or less. It is preferable that the typical through hole shape has a width of 10 to 50 μm and an interval between adjacent through holes is a regular lattice shape of several tens μm to several hundred μm.

  In the annealing step, a high-temperature heat treatment (annealing treatment) is performed in a reducing or neutral atmosphere in order to recover the phosphor plate that has undergone through-hole processing from damage caused by laser processing.

In the reflecting material providing step, for example, a white pigment as a reflecting material is filled and applied to at least the through hole portion of the annealed phosphor plate, or a metal film is provided by plating or vapor deposition. Examples of white pigments that can be used include titanium oxide pigments, zinc oxide pigments, barium sulfate pigments, and magnesium oxide pigments. As the metal film, aluminum, silver, gold, zinc, or the like can be used.
The X-ray phosphor plate of the present invention thus obtained has a cross section as schematically shown in FIG. The phosphor plate 10 for X-rays of the present invention is provided with a through hole in a polycrystalline phosphor plate 11 obtained by firing phosphor powder at high temperature and high pressure, and a reflective material 12 is provided inside the through hole. Yes.

In order to increase the mechanical strength of the phosphor plate of the present invention, a thin plate-like material may be bonded as a support substrate for further reinforcement. As a material of the support substrate, a thin metal plate such as aluminum, glass, a resin material, or the like can be used.
Next, as an embodiment of the present invention, an example of a method and characteristics of a phosphor plate will be described in detail with reference to the drawings.

(Phosphor powder synthesis process)
An example of the synthesis of the phosphor used for the phosphor plate of the present invention will be described. 1000 g of gadolinium oxide (Gd ₂ O ₃ ) and 3.1 g of terbium oxide (Tb ₄ O ₇ ) are weighed. Next, after stirring and dispersing in 5 liters of pure water, 270 ml of 68% nitric acid aqueous solution is added and dissolved by heating. Next, 800 g of oxalic acid is dissolved and heating is continued to obtain oxalate. The oxalate is washed with water and dried, and then calcined at 1000 ° C. in the atmosphere to obtain a coprecipitated oxide. And 1000 g of this coprecipitated oxide, 260 g of sodium carbonate (Na ₂ CO ₃ ), 30 g of lithium borate (Li ₂ B ₄ O ₇ ), and 90 g of potassium phosphate (K ₃ PO ₄ .3H ₂ O) And 300g of sulfur (S) was added and dry-mixed. Next, this raw material mixed powder was put into an alumina crucible, covered with alumina, and then fired at 1200 ° C. for 8 hours in an electric furnace. After cooling, the alumina crucible and the fired product were left in pure water for 1 hour. Thereafter, the fired product loosened in pure water was thoroughly washed with pure water, and then washed with 4N hydrochloric acid for 2 hours and 90 ° C. warm water for 1 hour using a stirrer. Thus, (Gd _0.997 Tb _0.003 ) ₂ O ₂ S phosphor powder having an average particle diameter of 20 μm was obtained.

(Ingot creation process)
Ingot preparation is obtained by subjecting the (Gd _0.997 Tb _0.003 ) ₂ O ₂ S phosphor powder to high-temperature and high-pressure treatment. As this high-temperature and high-pressure treatment, a hot press that applies pressure in a uniaxial direction was used. The phosphor powder is set in a hot press apparatus, and after evacuating, argon gas is introduced. As shown in FIG. 1, the temperature and pressure conditions are as follows. First, the temperature is raised to 1460 ° C. at a temperature rising rate of 10 ° C./min, then 1460 ° C. is maintained for 3 hours, and then the temperature is lowered to room temperature at 10 ° C./min Cooling. The pressure is increased to 40 MPa at a pressing rate of 0.67 MPa / min. And after hold | maintaining pressurization until completion | finish of said 1460 degreeC 3 hours holding | maintenance, it is pressure-reduced to 1 atmosphere at the time of temperature reduction at a pressure reduction speed of 0.67 MPa / min. At this time, pressure may be maintained until cooling to room temperature. In the ingot creation process, a small amount of sintering aid may be added to the phosphor powder. As a sintering aid, a fluoride such as lithium fluoride (LiF) or lithium hexafluorogermanate (Li ₂ GeF ₆ ) can be selected, and a sintering aid of 1% by mass or less is added to the phosphor powder. By doing so, the sintering effect can be enhanced.

(Phosphor plate forming process)
The ingot obtained by the high temperature and high pressure treatment was sliced using a multi-wire saw to obtain a phosphor plate. The slice thickness at this time was 0.25 mm.

(Through-hole creation process)
The laser processing pattern in the through hole creation step was a square lattice with 100 μm on one side, and a shape with a part of the side missing (side defect rate 40%) was used to increase the mechanical strength of the phosphor plate. An outline of the laser processing pattern is shown in FIG. 2a. Nd: YVO ₄ laser was used for laser processing. The processing conditions are as follows. Laser power: 3-4 W, beam width: 20 μm (through hole width is about 20 μm), laser pulse length: 10 ns, laser spot scanning speed: 60 mm / second, pulse frequency: 20 kHz.

(Annealing process)
The phosphor plate subjected to through-hole processing by laser processing was subjected to high-temperature annealing at 1100 ° C. for 1 hour in an argon gas containing a small amount of oxygen.

(Reflective material provision process)
As the white pigment as the reflective material, a titanium oxide pigment having a pigment particle diameter of 0.3 μm is selected, and 5 parts by mass of this white pigment is mixed with 47.5 parts by mass of deionized water, 4 parts by mass of polyvinyl alcohol, and isopropyl alcohol 42. 1.5 parts by mass of a part by weight and a nonionic surfactant (Surfinol 104S, manufactured by Nissin Chemical Industry Co., Ltd.) are added to prepare 100 parts by mass of a white pigment slurry, which is put into a plastic container. The phosphor plate subjected to the annealing treatment is immersed in this container, and ultrasonic treatment is performed for about 10 minutes, so that the white pigment slurry is filled into the through holes of the phosphor plate. Thereafter, the phosphor plate is taken out from the container, and the remaining solvent such as alcohol is evaporated to fix the white pigment in the through hole of the phosphor plate and the surface of the phosphor plate.
Next, the white pigment was removed by polishing one surface of the phosphor plate to obtain the phosphor plate of the present invention. This was designated as a phosphor plate sample 1.

  In order to evaluate the characteristics of the obtained phosphor plate sample 1, a CMOS photodiode image sensor was superimposed as a two-dimensional image sensor on the surface of the phosphor plate sample 1 from which the white pigment was removed.

In order to confirm the resolution characteristics, MTF was measured by the chart method. For comparison, instead of the phosphor plate sample 1, as an example of a conventional type, the (Gd _0.997 Tb _0.003 ) ₂ O ₂ S phosphor powder is used, and the phosphor is placed on a PET film substrate. About 180 mg / cm ² was applied as a coating amount equivalent to the phosphor amount of the plate sample 1 to prepare a phosphor coating film, which was referred to as Comparative Example 1. The result of each MTF is shown in FIG. FIG. 4 shows that the phosphor plate of the present invention has improved resolution characteristics.

  Next, as another embodiment, an example using BaFCl: Eu as a phosphor will be described.

(Phosphor powder synthesis process)
First, 780 g of barium chloride dihydrate (BaCl ₂ .2H ₂ O) and 1.65 g of europium chloride (EuCl ₃ ) are added to 1 liter of deionized water, and the solution temperature is heated to 80 ° C. to dissolve. An aqueous solution of ₂ and EuCl ₃ is prepared. This aqueous solution is returned to room temperature, and 200 ml of 5M-NH ₄ F aqueous solution is added at an addition rate of 10 ml / min to form a precipitate.

The resulting precipitate was aged at 80 ° C. for 1 hour, and then subjected to suction filtration using a 1 μm membrane filter. The precipitate was filtered off, washed with ethanol, and BaFCl: Eu precursor (Eu concentration 0. 0). 2 mol%) was obtained.
The obtained BaFCl: Eu precursor was dried in an oven at 80 ° C. for 2 hours and then baked in an electric furnace in a 1% H ₂ —N ₂ mixed gas at 850 ° C. for 3 hours to obtain a BaFCl: Eu phosphor powder. (Eu concentration 0.2 mol%) was synthesized. The obtained BaFCl: Eu phosphor powder had an average particle size of 4 μm.

(Ingot creation process)
Ingot production is obtained by subjecting the BaFCl: Eu phosphor powder to high-temperature and high-pressure treatment. As this high-temperature high-pressure treatment, a hot isostatic press (HIP) that applies pressure uniformly in all solid angle directions was used. The phosphor powder is filled into a tantalum capsule, vacuum-sealed, and set in a hot isostatic press. Furthermore, hot isostatic pressing was performed under conditions of 800 ° C. and 150 MPa for 2 hours.

(Phosphor plate forming process)
The ingot obtained by hot isostatic pressing was sliced using a multi-wire saw to obtain a phosphor plate. The slice thickness at this time was 0.25 mm.

(Through-hole creation process)
The laser processing pattern in the through-hole forming step was a triangular lattice with one side of 150 μm, and a shape with a part of the side missing (side defect rate 40%) in order to increase the mechanical strength of the phosphor plate. An outline of the laser processing pattern is shown in FIG. Nd: YVO ₄ laser was used for laser processing. The processing conditions are as follows. Laser power: 3-4 W, beam width: 20 μm (through hole width is about 20 μm), laser pulse length: 10 ns, laser spot scanning speed: 60 mm / second, pulse frequency: 20 kHz.

(Annealing process)
The phosphor plate subjected to through-hole processing by laser processing was subjected to high-temperature annealing at 750 ° C. for 1 hour in a 1% H ₂ —N ₂ mixed gas.

(Reflective material provision process)
An aluminum metal film is selected as the reflector. An aluminum metal film is formed on the surface of the phosphor plate after the high-temperature annealing and the inner surface of the through hole by vacuum deposition. Further, only the metal film adhering to one surface of the phosphor plate is removed by a polishing process, thereby forming a reflecting material.

  In order to evaluate the characteristics of the obtained phosphor plate sample 2, a CMOS photodiode image sensor was superimposed as a two-dimensional image sensor on the surface of the phosphor plate sample 2 from which the metal film was removed.

In order to confirm the resolution characteristics, MTF was measured by the chart method. For comparison, the BaFCl: Eu phosphor powder is used as an example of the conventional type instead of the phosphor plate sample 2, and the same amount of phosphor as the phosphor plate sample 2 is applied on a PET film substrate. About 145 mg / cm ² was applied as an amount to prepare a phosphor coating film, which was designated as Comparative Example 2. The result of each MTF is shown in FIG. FIG. 5 shows that the phosphor plate of the present invention has improved resolution characteristics.

  The X-ray phosphor plate of the present invention is combined with a photoelectric conversion device such as a CCD image sensor or a two-dimensional image sensor such as a CMOS image sensor to form a high-resolution X-ray image sensor. The present invention can be suitably used for X-ray diagnostic apparatuses and industrial X-ray inspection apparatuses.

10 X-ray phosphor plate 11 of the present invention Polycrystalline phosphor plate 12 Reflective material

Claims (6)

A phosphor plate made of a polycrystalline phosphor, wherein the phosphor plate is provided with a through hole, the through hole has a shape of a predetermined repeating pattern, and the shape is discontinuous. The shape of the repetitive pattern of the through holes is any of a square lattice, a triangular lattice, and a hexagonal lattice, with a part of the side missing, and a light reflecting material is provided on the inner surface of each through hole. A phosphor plate for X-rays. The phosphor, X-rays for the phosphor plate according to claim 1, characterized in that the rare earth oxysulfide phosphor. Claim 1 or 2 X-ray phosphor plate, wherein the said light reflective material is white pigment. 4. The X-ray phosphor plate according to claim 3, wherein the white pigment is at least one pigment selected from the group consisting of a titanium oxide pigment, a zinc oxide pigment, a barium sulfate pigment, and a magnesium oxide pigment. 3. The X-ray phosphor plate according to claim 1, wherein the light reflecting material is a metal film. 6. The X-ray phosphor plate according to claim 5 , wherein the metal film is at least one metal selected from the group consisting of aluminum, silver, copper, gold, and zinc.