High energy radiation detector having improved reflective backing for phosphor layer

A reflective backing member has an array of closely spaced corner reflectors adjacent to the input surface of a layer of material that absorbs high energy radiation events and converts them to light photons. The corner reflective surface causes rearward traveling light photons to be reflected along a path substantially parallel to the initial rearward path so that the reflective member provides a high quality reflective surface with less degradation of spatial resolution of an image produced by the light photons than occurs with conventional reflective backing members