Provided is a scintillator used for detecting radiation in an X-ray CT scanner or the like, the scintillator having a unidirectional phase separation structure having an optical waveguide function, which eliminates the need of formation of partition walls for preventing crosstalks. The scintillator has the phase separation structure including: a first crystal phase including multiple columnar crystals having unidirectionality; and a second crystal phase filling space on the side of the first crystal phase. The second crystal phase includes a material represented by Cs3Cu2[XaY1-a]5, where X and Y are elements which are different from each other and which are selected from the group consisting of I, Br, and Cl, and 0≦a≦1 is satisfied.