A radiation detector of one embodiment includes: a scintillator configured to generate first scintillation light having a first peak wavelength and second scintillation light having a second peak wavelength in response to radiation incidence; a photodetection unit configured to detect the scintillation light generated by the scintillator; and a filter layer disposed between the scintillator and the photodetection unit and configured to selectively block the first scintillation light. The filter layer has a metasurface structure.