Introduction
In indirect-detection cameras, incoming x-rays are absorbed in a polycrystalline or crystalline phosphor. The visible light emitted from this phosphor is channeled through a coherent fiberoptic bundle and subsequently detected by a camera, typically a back-illuminated or front-illuminated CCD camera.
Teledyne Princeton Instruments has developed two types of phosphors for x-ray imaging applications in the energy range between 5 keV and 50 keV. The Gd2O2S:Tb is recommended for x-ray energies <33 keV due to its higher absorption efficiency, while the CsI:Tl is recommended where higher resolution is required.
Polycrystalline Gadolinium Oxysulphide with Terbium
Teledyne Princeton Instruments has developed three distinct phosphors for 8, 12, and 17 keV x-ray energies based on Gd2O2S:Tb polycrystalline powder. To provide the best possible resolution and sensitivity, small-grain powder is used on special Mylar®. These phosphors are recommended when large image area, high efficiency, and lower cost are primary considerations.
![](https://www.princetoninstruments.com/wp-content/uploads/2022/01/gdos-polycrystalline-phosphor.png)
Type of Extramural Absorber (EMA)
![](https://www.princetoninstruments.com/wp-content/uploads/2022/01/csl-tl-needle-phosphor.png)
Teledyne Princeton Instruments has developed phosphors based on crystalline (needle structure) CsI:Tl for 8 and 24 keV x-ray energies, recommended when high resolution is the primary consideration. Although it has lower absorption at x-ray energies < 33 keV, CsI:Tl holds a number of advantages over GdOS:Tb powder phosphors, providing higher resolution, needles acting as a light guide, and more uniform light output due to special coatings.