Hyung-Won Lee

Effect of Annealing on the X-ray Detection Properties of Nano-sized Polycrystalline Lead Oxide Films

Polycrystalline lead oxide (PbO) film is an excellent candidate material for a direct conversion X-ray detector. However, the thick-bulky film tends to significantly reduce the charge collection efficiency for recombination process, and the effective number of electron-hole pairs is lower than that of thin film, because it is difficult to fabricate high-dense and thick PbO films. In this paper, we first synthesized nano-sized PbO particles that could be used in a novel high-efficiency flat panel X-ray detector using a simple solution/combustion method. Energy dispersive X-ray spectrometry, X-ray diffraction, and field emission scanning electron microscopy were used to analyze the component ratio and morphology of the PbO particles as a function of annealing temperature. Then, 150-µm-thick PbO films were deposited on glass substrates using a particle-in-binder method at room temperature. The influences of annealing before deposition on the X-ray detection characteristics of the PbO films were investigated in detail. The key parameters–the dark current, X-ray sensitivity, signal-to-noise ratio, and signal decay–were measured. The annealing conditions strongly affected the electrical properties of the PbO films. The X-ray sensitivity of films annealed in oxygen gas increased dramatically with increasing annealing temperatures up to 500 °C.

Quantitative evaluation of mercuric iodide and selenium for X-ray imaging device

Analog film/screen systems have been replaced with digital X-ray imaging devices using direct conversion materials. In this paper, mercuric iodide (HgI/sub 2/) and amorphous selenium (a-Se) films were deposited through the particle-in-binder (PIB) and physical vapor deposition (PVD) methods, respectively. Using the MCNP 4C code, the interaction of X-ray photons in HgI/sub 2/ and a-Se bulk, their transport, and transmitted energy spectrum of continuous X-ray, with total absorbed energy were simulated. Using I-V measurements, their electrical properties, such as leakage current, X-ray sensitivity, and signal-to-noise ratio (SNR), were investigated. The results of our study can be useful in the future design and optimization of direct active-matrix flat-panel detectors (AMFPD) for various digital X-ray imaging modalities.

X-ray response characterization of Y/sub 2/O/sub 2/S:Tb-CdS layered semiconductor

Phosphors coupled with photodetectors have been widely used in digital X-ray imaging applications. Some of the advantages of using phosphor films include X-ray conversion efficiency, spatial resolution, and integration with the imaging array. In this paper, the experimental studies of the Y/sub 2/O/sub 2/S:Tb synthesis, deposition, and characterization are reported on. Y/sub 2/O/sub 2/S:Tb powder was characterized in terms of scanning electron microscopy (SEM), X-ray diffraction (XRD), luminescence spectroscopy, and X-ray conversion efficiency. In addition, a Y/sub 2/O/sub 2/S:Tb layer was formed on cadmium sulphide (CdS) for the hybrid X-ray detector structure. The evaluation of the Y/sub 2/O/sub 2/S:Tb-CdS detector was performed by determining the leakage current, X-ray sensitivity, and linearity with respect to X-ray exposure dose. The results of the study made on the two-layered detector are compared with those from a conventional amorphous selenium (a-Se) detector.