Patent Number: 
Section: claims

1. A scintillator plate comprising sequentially on a substrate a reflection layer and a scintillator layer containing cesium iodide and an activator and having a thickness of L, wherein the following requirement (1) is met:2≦B/A  Requirement (1)wherein A is an average activator concentration of the scintillator layer and B is an activator concentration in a region of the scintillator layer from the reflection layer side to a position of L/5. 2. The scintillator plate as claimed in claim 1, wherein the scintillator layer is comprised of columnar crystals. 3. The scintillator plate as claimed in claim 1, wherein an average activator concentration is from 0.001 to 50 mol %, based on cesium iodide. 4. The scintillator plate as claimed in claim 1, wherein the activator is a thallium compound. 5. The scintillator plate as claimed in claim 1, wherein the columnar crystals are crystals formed on the substrate by a process of heating an evaporation source containing cesium iodide and a thallium compound to perform vapor deposition onto the substrate. 6. The scintillator plate as claimed in claim 4, wherein the thallium compound is thallium bromide, thallium chloride, thallium iodide or thallium fluoride. 7. The scintillator plate comprising on a substrate a reflection layer and a scintillator layer containing cesium iodide and an activator in the sequence set for the as claimed in claim 2, wherein the following requirement is met:30≧b/a≧1.5wherein “a” is an average equivalent circular diameter of the columnar crystals of the scintillator layer at the position of 10 μm from the substrate and “b” is an average equivalent circular diameter at the top of the columnar crystals.