Sangheum Eom

Feasibility study of a plasma display-like radiation detector for X-ray imaging.

In this study we have investigated a 2-dimensional gas type detector based on plasma display technology as a candidate for the flat-panel radiation detector. By using the Garfield code, the dependence of X-ray absorption and multiplication on gas composition, cell gap and electric field were examined. Considering the simulation results, three prototype detectors were designed and fabricated. The performance of these detectors was evaluated by measuring the collected charge density, dark current density and sensitivity. The collected charge had the highest value at a condition when Xe 100% and 2.8 mm gap was 108.8 nC/cm² at 1000 V. The dark current of the same detector was varied from 0.0095 to 0.10 nA/cm² and about a fourth of the dark current density of a-Se based detector was at the bias range of 100-1000 V. The sensitivity of Xe 100% and 2.8 mm detector was 0.20 nC/mR·cm² at 0.36 V/um. It is about a tenth lower than that of a-Se based detector at 10 V/um.

Characteristic of a PDP-based radiation detector in Xe-He mixture gas

In this study, we have investigated a 2-dimensional gas detector based on plasma display technology as a candidate for the flat-panel radiation detector. Using the Geant4 and Garfield codes, that simulate the passage of particles through matter, we examined the dependence of X-ray absorption and multiplication factors on the Xe-He gas mixture. Prototype detectors, with four different gas mixtures, were designed and fabricated based on the results from the simulations. The performance of four detectors was evaluated by measuring the collected charge density, dark current density and sensitivity. The maximum collected charge occurred when the Xe 80%-He 20% gas mixture was 1.216 μC/cm2 at -1800 V. The dark current of this detector varied between 0.124 and 0.321 nA/cm2 in the bias range of -300 to -1800 V, which is approximately one-third of the dark current density of an a-Se based detector, in this range. The sensitivity of Xe 80%-He 20% detector was 0.246 nC/mRcm2 at 0.61 V/μm. It is about a tenth lower than that of an a-Se based detector at 10 V/μm.

Simulation Study of Plasma Display Panel-Based Flat Panel X-Ray Detector

Screen-film-based radiography is being rapidly replaced by digital radiography (DR). Thin-film-transistors (TFT) with amorphous silicon (a-Si) or amorphous selenium (a-Se) are usually used in DR X-ray imaging systems. Another flat panel display, plasma display panel (PDP), has a structure that is similar to that of the conventional gas type radiation detectors, and can be manufactured with lower costs than the TFT-based detector panels. The motivation of this study was to develop a cost-effective DR detector using the PDP. In order to apply the PDP technologies in gaseous detectors for X-ray imaging, we modified the pixels structure and optimized the materials inside the PDP panel. To maximize the signals intensity, we re-designed the panels structure based on the gas microstrip detector (GMD), and estimated the performance of the proposed detector using the Monte Carlo simulation method. Signal intensity of gaseous detector is determined by the amount of ionization as well as by the avalanche effect. The ionization and avalanche processes were simulated using the Geant4 and Garfield, respectively. Four types of gas mixtures and various values of electric fields have been explored. The results show that a higher proportion of Xe helps to generate more ionization electrons. The results also suggest that the electric field, which is applied between anode and cathode strips, is a dominant factor for the avalanche effect to occur. In this study, the GMD structure was adopted for the plasma-display-panel-based X-ray detector. A quantitative verification of the effectiveness of the proposed structure was performed as well.

Development of plasma-display-panel-based x-ray detector (PXD)

The plasma display panel (PDP) is popular in the large area flat panel display market due to its relatively simple cell structure, low cost materials, and uncomplicated manufacturing process. The cell structure of PDP, which consists of electrodes and gas mixture, could be utilized in the manufacture of radiation detectors. In this study, we developed a plasma display panel based x-ray detector (PXD) based on Monte-Carlo simulation. This prototype detector panel has row and column strips, and it can thus be utilized as an imaging detector. To achieve the 2D x-ray image from the developed panel, a PXD dedicated driving and data acquisition circuit has been developed. Now we integrate the individual modules into a system. We hope to further study signal processing to achieve the first x-ray image of PXD.

Development of a DAQ circuit for a plasma-display-panel-based X-ray detector

The plasma display panel (PDP) is one of the most widely used display components in flat panel displays. It is popular in the TV market because of its relatively simple cell structure, low-cost materials, and uncomplicated manufacturing process. Recently, several research groups have shown that the cell structure of a PDP, which consists of electrodes and a gas mixture, can be used in the manufacture of radiation detectors. In the previous study, we developed a PDP-based X-ray detector (PXD). This prototype detector panel has row and column strips, and hence, it can be used as an imaging detector. To obtain the 2D X-ray image from the developed panel, a PXD dedicated driving and data acquisition (DAQ) circuit was developed. The proposed DAQ system consists of a multichannel high-voltage switching board, a multichannel DAQ board, and an FPGA-based control board. The prototype system has a compact design that can be easily used for various object imaging experiments. Each of the developed module boards of the DAQ system was tested, and the integrated system was verified as well. We hope to further study the signal processing in the system to obtain a clear image from the detector.

Simulation study of plasma display panel with GMD structure for x-ray imaging detector

Screen-film based radiography has been rapidly substituted by digital radiography(DR), recently. Generally, thin-film-transistor(TFT) with amorphous silicon(a-Si) or amorphous selenium(a-Se) have been used for DR x-ray imaging systems. Another flat panel display method, plasma display panel (PDP) has a similar structure to conventional gas type radiation detectors and can be manufactured with lower cost than TFT-based detector panels. The motivation of this study is to develop cost effective DR detector using PDP. In order to apply PDP technologies into gaseous detector for x-ray imaging, we modified the pixel structure and optimized the materials inside of the PDP panel. To maximize the signal intensity, we re-designed the panel structure based on gas microstrip detector(GMD) and estimated the performance of proposed detector using Monte-Carlo simulation method. Signal intensity of gaseous detector is determined by the amount of ionization and avalanche effect. Each process has been simulated by Geant4 and Garfield, respectively. Four types of gas mixtures and various electric fields have been explored. The results show that more Xe portion helps to create more ionization electrons and electric field which has been applied between anode and cathode strips was dominant factor for avalanche. In this study, we adopted the GMD structure into plasma display panel based x-ray detector. Also, we verified the effectiveness of proposed structure, quantitatively.

Characteristics of a PDP-Based Radiation Detector Dependent on Different Electrode Structures

In this study, a flat-panel detector based on plasma display technology was investigated as a candidate for a flat-panel radiation detector. We studied the dependence of multiplication factors on various electrode structures using the 3-D Garfield code that calculates the passage of particles through the gas-filled gap. Prototype detectors having three different electrode structures were designed and fabricated based on the simulation results. The performances of these detectors were examined by measuring the collected charge density, dark current density, and sensitivity. The collected charge density had the highest value at the condition when the ridged electrode structure was 1.57 μC/cm2 at -1500 V. The dark current of the same detector was varied between 4.8 and 6.17 nA/cm2 at the bias range of -500 to -1500 V. The sensitivity of the ridged electrode detector was 0.363 nC/mR · cm2 at 0.54 V/μm, and it is approaching to 18% of the sensitivity reported for the commercially available amorphous selenium (a-Se) detector at 10 V/μm.

Study on High-Luminance Sustain Pulses Using Consecutive Second Emission in AC-PDP

In this paper, four different sustaining pulses are examined and their electrical and emissive characteristics are compared with those of the conventional pulse. For a comparative study, an infrared emission, luminance, and discharge current during the sustaining period are measured. A distinguishable second emission is observed after the ignition of sustaining discharge and during infrared measurements with the photometer and an intensified charge-coupled device. This is the main reason for enhancing the luminance during the sustaining period. One of the proposed pulses shows a stronger second emission than the other pulses. Its luminance is 25% and its efficiency is 47.3% higher than those of the conventional pulse.

P‐95: A Study of Jitter Characteristics Depending on Wall Charge Status on an Emissive Layer via IR Measurement

We investigated the jitter characteristics depending on wall charge amount and polarity on different emissive layers, such as MgO and CEL MgO. IR emission from Xe discharge was measured with IR photometer and iCCD. The accumulation of negative wall charges on pulse-applied electrode and negative applied voltage were important to decrease the operation voltage and time delay.