A micro-machined retro-reflector for improving light yield in ultra-high-resolution gamma cameras

High-resolution imaging of x-ray and gamma-ray distributions can be achieved with cameras that use charge coupled devices (CCDs) for detecting scintillation light flashes. The energy and interaction position of individual gamma photons can be determined by rapid processing of CCD images of individual flashes. Here we investigate the improvement of such a gamma camera when a micro-machined retro-reflector is used to increase the light output of a continuous scintillation crystal. At 122 keV we found that retro-reflectors improve the intrinsic energy resolution (full width at half maximum (FWHM)) by 32% (from 50% to 34%) and the signal-to-noise (SNR) ratio by 18%. The spatial resolution (FWHM) was improved by about 4%, allowing us to obtain a resolution of 159 microm. The full width at tenth maximum (FWTM) improvement was 13%. Therefore, this enhancement is a next step towards realizing compact high-resolution devices for imaging gamma emitters.