Large area x-ray detectors based on phosphors coupled to flat panel amorphous silicon diode technology offer significant
advances for cargo radiologic imaging. Flat panel area detectors provide large object coverage offering high throughput
inspections to meet the high flow rate of container commerce. These detectors provide excellent spatial resolution when
needed, and enhanced SNR through low noise electronics. If the resolution is reduced through pixel binning, further
advances in SNR are achievable. Extended exposure imaging and frame averaging enables improved x-ray penetration
of ultra-thick objects, or "select-your-own" contrast sensitivity at a rate many times faster than LDAs. The areal
coverage of flat panel technology provides inherent volumetric imaging with the appropriate scanning methods. Flat
panel area detectors have flexible designs in terms of electronic control, scintillator selection, pixel pitch, and frame
rates. Their cost is becoming more competitive as production ramps up for the healthcare, nondestructive testing (NDT),
and homeland protection industries. Typically used medical and industrial polycrystalline phosphor materials such as
Gd2O2S:Tb (GOS) can be applied to megavolt applications if the phosphor layer is sufficiently thick to enhance x-ray
absorption, and if a metal radiator is used to augment the quantum detection efficiency and reduce x-ray scatter.
Phosphor layers ranging from 0.2-mm to 1-mm can be "sandwiched" between amorphous silicon flat panel diode arrays
and metal radiators. Metal plates consisting of W, Pb or Cu, with thicknesses ranging from 0.25-mm to well over 1-mm
can be used by covering the entire area of the phosphor plate. In some combinations of high density metal and phosphor
layers, the metal plate provides an intensification of 25% in signal due to electron emission from the plate and
subsequent excitation within the phosphor material. This further improves the SNR of the system.
The objective of this effort is to improve x-ray absorption and light production while maintaining high spatial resolution in x-ray imaging phosphor screens. Our current target is to improve screen absorption efficiency and screen brightness by factors of 2 or greater over existing screens that have 10-1p/mm resolution. In this program, commercial phosphor screens are combined with highly absorbing, high-resolution scintillating fiber-optic (SFO) face plates to provide a hybrid sensor that exhibits superior spatial resolution, x-ray absorption, and brightness values over the phosphor material alone. These characteristics of hybrid scintillators can be adjusted to meet specific x-ray imaging requirements over a wide range of x-ray energy. This paper discusses the design, fabrication, and testing of a new series of hybrid scintillators.
It is now possible to reduce the costs and time needed to perform radiography of aging aircraft, space vehicles, and aerospace components. Recent advances in high resolution x-ray detectors, high fidelity low light level camera systems, image enhancement techniques, and robotic inspections have made the use of real time techniques more attractive from the standpoint of reducing film costs, reducing waste products from film processing, obtaining more reliable inspections, and gaining computer assisted interpretations. This paper summarizes ongoing efforts in support of the U.S. Air Force Wright Laboratories to develop a semiautomated high resolution digital real-time radiographic (HRRTR) inspection system to detect anomalous conditions on aircraft structures, turbine engine components, and composite materials. Examples of detection of corrosion and cracking in various aircraft structures using this system are reported.
A four CCD, multi-port, fiber-optically coupled mosaic camera system is described. System design issues and a functional overview of the camera are discussed with emphasis placed on the multi-port readout and data recombination aspects. Preliminary performance data are presented.
This report summarizes an investigation of new luminescent glasses for use as x-ray-tolight conversion imaging media for x-ray radiographic applications. Luminescent activators such as T b3+ Eu2+ and Ce3+ were investigated in high density 3 g/cm3) high z fluoroborate fluoride borate and silicate host glasses. Terbium activation in each of these materials has at least a factor of 2 higher luminescent response under x-rays than either of the other two activators. The selection of the host material has a large effect on the luminescence characteristics. Terbium activated silicate glasses have a luminescent response 3 times higher than any of the other terbium activated glass materials investigated. The addition of Gd3 to terbium activated silicate glass has been shown to improve the x-ray-to-light conversion efficiency by as much as a factor of 1. 2 for this glass material. This increase in efficiency most likely occurs because of a Gd3+ Tb3 energy transfer process. 1.