In a scintillator used for radiation detection, such as an X-ray CT scanner, a scintillation crystal body having a unidirectional phase separation structure is provided which has a light guide function for crosstalk prevention without using partitions. The phase separation structure includes a first crystal phase and a second crystal phase having a refractive index larger than that of the first crystal phase and which have a first principal surface and a second principal surface, these principal surfaces being not located on the same plane, the first principal surface and the second principal surface have portions to which the second crystal phase is exposed, and a portion of the second crystal phase exposed to the first principal surface and a portion of the second crystal phase exposed to the second principal surface are connected to each other.