PROBLEM TO BE SOLVED: To provide a radiation detector capable of precisely counting photon in radiation.SOLUTION: The radiation detector includes: a scintillator which has a first part including a first plane and a second part including a second plane facing the first plane a wavelength conversion part which covers a first part and is capable of converting a light beam coming at a first wavelength into a light beam of a second wavelength and outputting the same a light reflection part covering a second part excluding a second plane and a detection element that converts a light beam in a wavelength band including a second wavelength into electricity.COPYRIGHT: (C)2015,JPO&INPIT【課題】正確な放射線のフォトンカウンティングを可能とする。【解決手段】第1面を含む第1部分と、第1面と対向する第2面を含む第2部分とを有するシンチレータと、第1部分を覆い、第1の波長で入射する光を第2の波長で出射させることが可能な波長変換部と、第2面を除く第2部分を覆う光反射性の反射部と、第2の波長を含む波長帯の光を光電変換する検出素子とを設ける。【選択図】図6