New needle-crystalline CR detector

The storage phosphor RbBr:Tl+ can be grown in needles via vacuum deposition. Thanks to reduced lateral light diffusion thick needle screens still offer acceptable resolution. Due to its low intrinsic X-ray absorption, however, a RbBr:Tl+ needle screen does not lead to a better absorption/resolution compromise than a BaFBr1-xIx:Eu2+ powder screen. CsBr:Eu2+ does combine high specific X-ray absorption and the possibility of needle growth. Its blue emission, peaking at 440 nm and near I.R. stimulation band, with maximum at 685 nm, make it well suited for use in CR systems. Sensitivity and sharpness of a 500 mu thick CsBr:Eu2+ needle screen were measured in a flying-spot scanner. The number of photostimulated light quanta per absorbed X-ray quantum is higher than for BaFBr1-xIx:Eu2+. At 70 kVp and 0.5 mm Cu filtration, equal sharpness is obtained for 85% vs. 46% X-ray absorption in BaFBr1-xIx:Eu2+ screens. DQE was measured at 2.5 mu Gy, 70 kVp, and 0.5 nun Cu filtration for a CsBr:Eu2+ needle screen in a flying-spot scanner. Up to 3 lp/mm, DQE was 2 times higher than for state-of-the-art CR systems and equal to the DQE claimed for flat panel DR systems, based on a-Si photodiodes combined with a CsI:Tl scintillator layer.