Patent Number: 
Section: claims

1. An oxide phosphor having the oxide consisting of at least Gd, Ce, Al, Ga, and O, wherein a crystal structure of said oxide is a garnet structure, the atomic ratio (Gd+Ce)/(Al+Ga+Gd+Ce) is more than 0.375 and 0.44 or less, and the atomic ratio Ce/(Ce+Gd) is no less than 0.0005 and no more than 0.02. 2. An oxide phosphor according to claim 1, wherein the atomic ratio Ga/(Al+Ga) is more than 0 and less than 1.0. 3. An oxide phosphor according to claim 1, further including an impurity phase of a perovskite structure. 4. An oxide phosphor according to claim 3, wherein the intensity of a main diffraction line of the perovskite structure in an X-ray diffraction measurement is 50% or less with respect to the intensity of the main diffraction line of the garnet structure. 5. An oxide phosphor according to claim 1, wherein oxide powder is synthesized by at least one of the following methods: an oxide-mixing method, a coprecipitation method, and a mechanically grinding method using material powder. 6. An oxide phosphor according to claim 5, wherein the diameters of crystal grain of the oxide-synthesized powder are 1 μm or less. 7. An oxide phosphor according to claim 5, wherein said oxide-synthesized powder is sintered by at least one of the following methods: a hot-press method, an HIP method, a pressureless sintering method, and simultaneous use of a pressureless sintering method and an HIP method. 8. An oxide phosphor according to claim 7, wherein the relative density of the sintered body of the oxide-synthesized powder is 99.0% or more. 9. A scintillator including a sintered body of the oxide phosphor according to claim 1. 10. A radiation detector in an X-ray detector including a ceramics scintillator and a light detector for detecting light emission of said scintillator, wherein the scintillator according to claim 9 is employed as said ceramics scintillator. 11. An X-ray CT apparatus comprising:an X-ray source;an X-ray detector located opposite to said X-ray source;a rotating disk holding said X-ray source and said X-ray detector, which is driven to rotate around an object to be examined; andan image reconstruction means for image-reconstructing a tomogram of said object on the basis of intensity of X-rays detected by said X-ray detector,wherein a radiation detector according to claim 10 is employed as said X-ray detector. 12. An oxide phosphor having the oxide consisting essentially of Gd, Ce, Al, Ga, and O, wherein a crystal structure of said oxide is a garnet structure, the atomic ratio (Gd+Ce)/(Al+Ga+Gd+Ce) is more than 0.375 and 0.44 or less, and the atomic ratio Ce/(Ce+Gd) is no less than 0.0005 and no more than 0.02. 13. An oxide phosphor according to claim 12, wherein the atomic ratio Ga/(Al+Ga) is more than 0 and less than 1.0. 14. An oxide phosphor according to claim 12, further including an impurity phase of a perovskite structure. 15. An oxide phosphor according to claim 14, wherein the intensity of a main diffraction line of the perovskite structure in an X-ray diffraction measurement is 50% or less with respect to the intensity of the main diffraction line of the garnet structure. 16. An oxide phosphor according to claim 12, wherein oxide powder is synthesized by at least one of the following methods: an oxide-mixing method, a coprecipitation method, and a mechanically grinding method using material powder. 17. An oxide phosphor according to claim 16, wherein the diameters of crystal grain of the oxide-synthesized powder are 1 μm or less. 18. An oxide phosphor according to claim 16, wherein said oxide-synthesized powder is sintered by at least one of the following methods: a hot-press method, an HIP method, a pressureless sintering method, and simultaneous use of a pressureless sintering method and an HIP method. 19. An oxide phosphor according to claim 18, wherein the relative density of the sintered body of the oxide-synthesized powder is 99.0% or more. 20. A scintillator including a sintered body of the oxide phosphor according to claim 12. 21. A radiation detector in an X-ray detector including a ceramics scintillator and a light detector for detecting light emission of said scintillator, wherein the scintillator according to claim 20 is employed as said ceramics scintillator. 22. An X-ray CT apparatus comprising:an X-ray source;an X-ray detector located opposite to said X-ray source;a rotating disk holding said X-ray source and said X-ray detector, which is driven to rotate around an object to be examined; andan image reconstruction means for image-reconstructing a tomogram of said object on the basis of intensity of X-rays detected by said X-ray detector,wherein a radiation detector according to claim 21 is employed as said X-ray detector. 23. An oxide phosphor according to claim 12, wherein the oxide consists of Gd, Ce, Al, Ga and O. 24. A scintillator including a sintered body of the oxide phosphor according to claim 23. 25. A radiation detector in an X-ray detector including a ceramics scintillator and a light detector for detecting light emission of said scintillator, wherein the scintillator according to claim 24 is employed as said ceramics scintillator. 26. An X-ray CT apparatus comprising:an X-ray source;an X-ray detector located opposite to said X-ray source;a rotating disk holding said X-ray source and said X-ray detector, which is driven to rotate around an object to be examined; andan image reconstruction means for image-reconstructing a tomogram of said object on the basis of intensity of X-rays detected by said X-ray detector,wherein a radiation detector according to claim 25 is employed as said X-ray detector.