In dual energy imaging systems, two radiation sensitive detectors are superimposed one behind the other. The front detector records and absorbs the low-energy photons, while transmitting the higher energy photons for detection to the thicker back detector. The two data sets are acquired simultaneously and provide information to image the density as in a normal radiograph and the atomic number of the target object which is a considerable advantage.
Luminex and Rapidex screens, which can be precision-cut in strips according to the customers’ requirements, are the ideal scintillator choice for low energy detectors, due to their low costs, high uniformity between batches and possibility to match the screen resolution to the pixel pitch of the detector. Luminex is generally preferred for low frame rate applications when light output and resolution are the main priorities. Rapidex is used in high frame rate application for end-of-line inspection up to speeds of a few metres per second.
Scintacor offers three types of Gadox scintillator screens (sometimes referred to as luminescent screens or intensifying screens):
Luminex – Terbium-doped gadolinium oxysulphide (Gadox:Tb). This phosphor is also known as P43.
Rapidex – Praseodymium-doped gadolinium oxysulphide (Gadox:Pr) for hard X-ray applications (50-300 keV).
MeVex – A very high coating weight screen made of terbium-doped gadolinium oxysulphide (Gadox:Tb) for use at high-energy energy levels (>450 keV – 25 MeV).
The properties of these screens are listed in Table 1.
Light Output (1) | MTF % @ 2lp/mm (2) | MTF % @ 5lp/mm (2) | Attenuation % (2) | Decay to 10% μs | Afterglow @ 20ms % | |
Ultrabright | 205% | 18 | 4 | 92 | 1,500 | <0.1% |
Bright | 175% | 21 | 7 | 92 | 1,500 | <0.1% |
Medium | 170% | 23 | 5 | 91 | 1,500 | <0.1% |
Fine | 129% | 42 | 15 | 86 | 1,500 | <0.1% |
UltraFine | 70% | 65 | 29 | 83 | 1,500 | <0.1% |
UltraFine+ | 50% | 76 | 45 | 76 | 1,500 | <0.1% |
Light Output (1) | MTF % @ 2lp/mm (2) | MTF % @ 5lp/mm (2) | Attenuation % (2) | Decay to 10% μs | Afterglow @ 20ms % | |
Bright | 92% | 16 | 4 | 97 | 7 | <0.1% |
Medium | 91% | 19 | 5 | 94 | 7 | <0.1% |
Fine | 81% | 32 | 9 | 89 | 7 | <0.1% |
Light Output (1) | MTF % @ 1lp/mm (2) | MTF % @ 2lp/mm (2) | Attenuation % (2) | Decay to 10% μs | Afterglow @ 20ms % | |
Medium | 242% | 16 | <10 | 98 | 1,500 | <0.1% |
(1)Relative to Lanex Regular benchmark screen. X-ray source: 150kV unfiltered
(2)X-ray source 70kV
Size & geometry.
Unlike other commercially available products, Scintacor X-ray screens can be ordered in single units and custom-cut to any shape and size, to match the specific requirements of each application.
Large sheets are available with linear dimensions up to 1,000×1,750mm. On request, the screens can also be supplied in precision-cut strips as thin as 3-4mm for coupling to linear diode arrays. They can be mounted on a variety of substrates for easier handling and deployment.
Levy and West, the founders of the renowned laboratories which later became Applied Scintillation Technologies and then Scintacor, were among the pioneers who explored the use of zinc sulphide phosphors for fluoroscopic X-ray imaging. Since then, many additional phosphor systems have been developed and today we find gadolinium oxysulphide (Gd2O2S or simply Gadox / GOS) phosphor is one of the most widely adopted for several reasons. The material morphology is well known and well controlled; the luminescent efficiency is relatively high (approximately 15%) and the emitted light matches well with the spectral response of silicon light detection devices such as charge-coupled detectors (CCD) and complementary metal oxide semiconductors (CMOS).
Gadox scintillator screens were originally developed and commercialized by companies which supplied photographic film and were often described as ‘fine’, ‘regular’ or ‘fast’ depending upon the film speed and spatial resolution of the film with which they were paired. These screens are still widely available up to a maximum size of 14’’x 17’’ but they do not always provide the optimal solution for digital X-ray imaging. Conversely, Scintacor phosphor screens have been specifically designed around digital X-ray imaging systems to provide differentiated performance over standard scintillator screens, in both lens-coupled systems, and direct-coupling to solid-state light detectors, such as CMOS and CCD.
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