An electromagnetic radiation detector comprising: a first scintillation detector comprising a first scintillator configured to output photons in response to incidence of electromagnetic radiation, the first scintillation detector configured to detect the incidence of electromagnetic radiation; a second scintillation detector configured to detect scattered electromagnetic radiation exiting out of the first scintillation detector, the scattered electromagnetic radiation that occurs inside the first scintillation detector due to Compton scattering of the electromagnetic radiation; and a multi-channel analyzer configured to perform multi-channel analysis of a result of the detection by the first scintillation detector, the result being other than results of the detection, timing of which is considered to coincide with timing of the detection by the second scintillation detector, characterized in that the second scintillation detector comprises a second scintillator that: is a thick film of scintillator paste having been solidified through compression and drying so as not to allow transmission of visible light generated by the first scintillator , and is located adjacent to the first scintillator , configured to output photons in response to incidence of the scattered electromagnetic radiation from the first scintillator , the scattered electromagnetic radiation that occurs inside the first scintillator due to Compton scattering. a first scintillation detector comprising a first scintillator configured to output photons in response to incidence of electromagnetic radiation, the first scintillation detector configured to detect the incidence of electromagnetic radiation; a second scintillation detector configured to detect scattered electromagnetic radiation exiting out of the first scintillation detector, the scattered electromagnetic radiation that occurs inside the first scintillation detector due to Compton scattering of the electromagnetic radiation; and a multi-channel analyzer configured to perform multi-channel analysis of a result of the detection by the first scintillation detector, the result being other than results of the detection, timing of which is considered to coincide with timing of the detection by the second scintillation detector, characterized in that the second scintillation detector comprises a second scintillator that: is a thick film of scintillator paste having been solidified through compression and drying so as not to allow transmission of visible light generated by the first scintillator , and is located adjacent to the first scintillator , configured to output photons in response to incidence of the scattered electromagnetic radiation from the first scintillator , the scattered electromagnetic radiation that occurs inside the first scintillator due to Compton scattering. is a thick film of scintillator paste having been solidified through compression and drying so as not to allow transmission of visible light generated by the first scintillator , and is located adjacent to the first scintillator , configured to output photons in response to incidence of the scattered electromagnetic radiation from the first scintillator , the scattered electromagnetic radiation that occurs inside the first scintillator due to Compton scattering. <EOS>