Recent research in the field of phosphor and scintillator materials and related detectors is reviewed. After a historical introduction the fundamental issues are explained regarding the interaction of x-ray radiation with a solid state. Crucial parameters and characteristics important for the performance of these materials in applications, including the employed measurement methods, are described. Extended description of the materials currently in use or under intense study is given. Scintillation detector configurations are further briefly overviewed and selected applications are mentioned in more detail to provide an illustration.

/pdf/scintillation-detectors-for-x-rays-3rmwfxzjvh.pdf

Scintillation detectors for x-rays

Charge-coupled device (CCD) area x-ray detector technology is reviewed. CCD detectors consist of a serial chain of signal components, such as phosphors, fiber optics or lenses, image intensifiers and the CCD which serve to convert the x-ray energy to light or electron-hole pairs and to record the spatially resolved image. The various combinations of components that have been used to make CCD detectors are described and the properties of each of the critical components are discussed. Calibration and correction procedures required for accurate data collection are described. The review closes with a brief description of future directions for solid-state area x-ray detectors.

Charge-coupled device area x-ray detectors

This paper describes a new system for quantitative measurement of multiphase flow. It is based on the use of high speed (50 frames per second) X-ray tomographic imaging. This requires a new X-ray tube concept to be implemented, together with an annular detector array and data acquisition system. A pressurised krypton microgap detector is being developed to give 90% quantum efficiency for detection of K/sub /spl alpha// radiation from the silver anode X-ray tube. Results from simulation work are presented to justify the overall design strategy selected.

Development of a high speed X-ray tomography system for multiphase flow imaging

A robust fuzzy logic gain scheduler (robust FLGS) is designed, based on the synthesis of fuzzy logic inference and the technique. The robust FLGS has a set of robust control gains in a gain pool. The fuzzy inference engine chooses one of the most desirable control gains considering the steam generator (S/G) operating condition. The robust gains in the gain pool are obtained by the time-domain -control technique such that both of the weighted norms of two transfer functions are minimized: the transfer functions between the steam flow disturbance and the mass capacity portion of S/G level, and the reverse dynamics of S/G. The FLGS rules are automatically generated using a genetic algorithm (GA). The GA gives a set of the gain scheduling rules that reflect given performance design specifications well. Computer simulation confirms that the proposed controller shows both guaranteed stability and good performance in terms of small overshoot and fast settling time in spite of S/G parameter variations and steam flow disturbances.

http://ieeexplore.ieee.org/iel1/23/12840/00588589.pdf

Design of Stability and Performance Robust Fuzzy Logic Gain Scheduler for Nuclear Steam Generators Byung Hak Cho and Hee Cheon No

In this work, ZnO nanowires in anodized aluminum oxide nanoporous template are proposed as an architecture for development of new generation of scintillator based X-ray imagers. The optical response of crystalline ordered ZnO nanowire arrays in porous anodized aluminum oxide template under 20 keV X-ray illumination is simulated using the Geant4 Monte Carlo code. The results show that anodized aluminum oxide template has a special impact as a light guide to conduct the optical photons induced by X-ray toward the detector thickness and to decrease the light scattering in detector volume. This inexpensive and effective method can significantly improve the spatial resolution in scintillator based X-ray imagers, especially in medical applications.

Geant4 simulation of zinc oxide nanowires in anodized aluminum oxide template as a low energy X-ray scintillator detector

Hydrogenated amorphous silicon carbide (a-Si:C:H) has been used as an insulating support pedestal for the anode strip in microgap gas chambers (MGCs) in an attempt to make a thicker high quality insulating layer. MGCs having 2.3 or 4.6 /spl mu/m thick a-Si:C:H and 2.0 /spl mu/m thick SiO/sub 2/ insulating layers have been built and tested. In this paper, the results of gas gains, strip damage by discharges, and preliminary aging studies are presented.

Microgap gas chamber studies

A new method is proposed to improve the spatial and time resolutions, and the detection efficiency with respect to the angle of the incident particles, for gas avalanche micro detectors. The new technique uses a thin (/spl sim/200 /spl mu/m) columnar CsI layer at the drift plane that acts as an efficient source of electrons produced by secondary emission due to the incident particles, and as an electron multiplier. In this paper, we present the measurements of the electron multiplication factor and detection efficiency of this layer, using a /sup 90/Sr /spl beta/-source.

A columnar cesium iodide (CsI) drift plane layer for gas avalanche microdetectors

We describe the structure and avalanche gain of gaseous pixel detectors. Each anode is a square 20 /spl mu/m/spl times/20 /spl mu/m in size connected to an individual pad through a plated center section. The cathodes are plated squares interconnected to a common lead. The anode squares have a pitch of 200 /spl mu/m in both x- and y-directions. The anodes and cathodes are aluminum layers deposited on amorphous silicon alloyed with carbon (a-Si:C:H) to produce a bulk resistivity of /spl sim/10/sup 13/ item. Measurements on signals from a group of anodes shows an avalanche gas gain close to 10/sup 4/ at a cathode-anode potential of 640 volts using a gas mixture of 50/50 argon-ethane. The avalanche gain is about a factor of 3 higher than that of microstrip devices we have tested, having the same pitch. For our initial measurements, 16 anodes were connected together to a charge sensitive preamplifier. In a final chamber each anode would be connected to an a-Si:H p-i-n readout diode with signals read out sequentially as in flat screen devices.

Gas avalanche pixel detectors

Since the effects of spark damage by discharges and aging are very sensitive to metal used for anode strips, several microgap gas chambers (MGCs) have been fabricated with various anode strip metals: aluminum, gold, chromium, nickel, and titanium-tungsten, and a systematic study of spark damage effects has been made to compare their relative sensitivity to failure, over a range of electrical discharge energies. The results of aging studies are being presented separately.

Spark damage studies of microgap gas chambers with various anode strip metals

The performance of gas avalanche pixel detectors of square and circular geometry, with and without semiconducting surface coating, was characterized in terms of gas gain and active region. Although the electric field profile of the square geometry cannot be radially uniform, a 200 /spl mu/m pitch detector of this type exhibited a maximum gain of /spl sim/12000 which is comparable to that of the circular counterpart. Due to the existence of the anode bus lines passing under the cathodes, there is a defocusing effect of the drift field lines converging to the anodes, resulting in inactive regions where electrons produced from gas ionization are not collected at the anodes. Variation of the count rate with the drift field was measured to probe these defocusing effects. The p-type a-Si:C:H surface coating was effective in reducing these inactive regions.

Gas avalanche pixel detectors with amorphous silicon carbide (a-Si:C:H) overcoating

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