In an embodiment, an X-ray detector has a transmissive fluorescence generating portion, and a reflective fluorescence generating portion. The transmissive and reflective fluorescence generating portions have at least one of an intensifying screen having a phosphor layer that contains praseodymium-activated gadolinium oxysulfide phosphor particles in which a ratio of particles having a particle diameter falling in ±30% of a center particle diameter is 45% by volume or more and their filling rate is 60% by volume or more, and an intensifying screen having a phosphor layer that contains europium-activated barium fluorochloride phosphor particles in which a ratio of particles having a particle diameter falling in ±30% of a center particle diameter is 45% by volume or more and their filling rate is 45% by volume or more.
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