There is provided a radiation detector including: a plurality of photoelectric conversion devices, each photoelectric conversion device formed at least partially within an embedding layer and having a light receiving surface situated at least partially outside of the embedding layer, and a plurality of scintillator crystals, at least a first scintillator crystal of the plurality of scintillator crystals in contact with at least one light receiving surface at a proximal end, wherein a cross-section of the first scintillator crystal at the proximal end is smaller than a cross-section of the first scintillator crystal at a distal end.