Powder-phosphor screens combined with interference filters for X-ray imaging with increased brightness
Powder-phosphor screens are frequently used in X-ray imaging devices. They have an angular light emission characteristic which is close to a cosine distribution (Lambertian) of photometric intensity. If interference filters are combined with these screens, the angular-emission characteristic changes. We have developed interference filters for powder-phosphor screens with increased brightness perpendicular to the screen. This is particularly advantageous for screens viewed by lens-optic or fiber-optic systems. Measurements on powder-phosphor screens (Gd 2O 2S:Tb screens, thickness 50 μm) with interference filters were carried out at X-ray photon energies of 18 keV. For an optical system with a numerical aperture of 0.25, the transmitted signal power increased by 70%. However, the spatial resolution was worse compared to the same screen without a filter; 31 μm fwhm was measured without a filter and 43 μm fwhm with a filter.