An apparatus and method, the apparatus comprising: a plurality of layers of scintillator material configured to generate photons in response to incident radiation; and a plurality of layers of spacer material wherein the scintillator material and spacer material are arranged in alternate layers so that a plurality of interfaces are provided between layers of scintillator material and layers of spacer material; wherein the scintillator material has a different refractive index to the spacer material and the thickness of layers within the plurality of layers is arranged to enable constructive interference of photons emitted by the scintillator material and reflected by the interfaces.