Thin film NaI(Tl) scintillators for high-resolution large-area imaging of soft x-rays

The authors are developing NaI(Tl) phosphors to use on large-area, photon-counting imaging photomultiplier tubes. An x-ray absorption uniformity of 99% is expected over an area of 133 cm2 at a film thickness of 38 ± 1.5 microm. The spatial resolution f the scintillator films, up to 61 microm thick, is consistent with a total detector resolution of less than 92 microm, given a phototube resolution of 65 microm fwhm. The fwhm for 8 keV spots is presented as a function of angle up to 40 degrees off-incidence and a simple model for the broadening of the fwhm due to parallax is presented. Improvements of 20% in the light-collection efficiency were observed for fiber optic disks coated with potassium silicate before vapor-depositing the NaI(Tl). The authors present absolute scintillating energy efficiency measurements by comparing the films to the scintillation of single crystal NaI(Tl)