• Proceedings of the Korean Nuclear Society Conference
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• 1999.10a
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• pp.334-334
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• 1999

• Journal of Radiation Protection and Research
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• v.28 no.4
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• pp.343-348
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• 2003

We have investigated in detail the operating properties of Gas Electron Multiplier (GEM) detectors with a double conical and a cylindrical structure in a wide range of external fields and GEM voltages. With the double conical GEM, the gain gradually increased with time by 10%; whereas this surface charging was eliminated with the cylindrical GEM. Effective gains above 1000 were easily observed over a wide range of collection field strengths in a gas mixture of $Ar/CO_2(70/30)$. The transparency and electron collection efficiency were found to depend on the ratio of external field and the applied GEM voltage; the mutual influence of both drift and collection fields was found to be trivial.

• Progress in Medical Physics
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• v.25 no.2
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• pp.95-99
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• 2014

Radiation monitoring is one of the most important process in all places where radioactive material is used including hospital. In this preliminary study, we made GAS electron multiplier (GEM) detector and acquired relative efficiencies in order to see if GEM detector can be useful in radiation monitoring system. The relative efficiency was acquired by using the ratio of GEM detector efficiency to CdTe detector efficiency. The relative efficiency of 72% and 4% was acquired for beta-ray and gamma-ray respectively.

• Journal of Radiation Protection and Research
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• v.30 no.2
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• pp.69-75
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• 2005

Gas avalanche microdetectors, such as micro-strip gas chamber (MSGC), micro-gap chamber (MGC), micro-dot chamber (MDOT), etc., are operated under high voltage to induce large electron avalanche signal around micro-size anodes. Therefore, the anodes are highly exposed to electrical damage, for example, sparking because of the interaction between high electric field strength and charge multiplication around the anodes. Gas electron multiplier (GEM) is a charge preamplifying device in which charge multiplication can be confined, so that it makes that the charge multiplication region can be separate from the readout micro-anodes in 9as avalanche microdetectors possible. Primary electron collection efficiency is an important measure for the GEM performance. We have defined that the primary electron collection efficiency is the fractional number of electron trajectories reaching to the collection plane from the drift plane through the GEM holes. The electron trajectories were estimated based on 3-dimensional (3D) finite element method (FEM). In this paper, we present the primary electron collection efficiency with respect to various GEM operation parameters. This simulation work will be very useful for the better design of the GEM.

• Journal of Biomedical Engineering Research
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• v.24 no.2
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• pp.83-89
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• 2003

The gas electron multiplier placed in the drift volume of conventional gas detectors, is a conceptually simple device for producing a large gas gain by concentrating the drift electric field over a very short distance to the point that electron avalanching occurs(〉 10$^4$ V/cm), greatly increasing the number of drifting electrons. This device consists of a thin insulating foil of several tens of urn in thickness. covered on each side with a thin metal layer(Cu), with tiny holes, usually 100 ${\mu}{\textrm}{m}$ or less in diameter. and with a spacing of 100-200 ${\mu}{\textrm}{m}$ through the entire foil. perforated by using chemical etching or high-powered laser beam technique In this study, we have investigated its operating properties with various experimental conditions, and demonstrated the possibility of using this device as a digital X-ray imaging sensor, by acquiring X-ray images based on the scintillation properties of the gas electron multiplier with standard CCD camera.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.34 no.7
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• pp.289-296
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• 1985

The Townsend primary ionization coefficient a was measured by the luminous-flux method using the fact that the intensity of radiant light is proportional to electron density in the townsend discharge domain. The ranges of measurements were 15for He gas and 10

• Journal of Radiation Protection and Research
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• v.26 no.3
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• pp.177-181
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• 2001

The conversion efficiency of a cesium iodine coated micro-channel plate is studied. We use the EGS4 code to transport photons and generated electrons until their energies become less than 1keV and 10keV respectively. Among the generated electrons, the emission from the secondary electrons located within the escape depth of 56nm from the photo-converter boundary is estimated by integrating the product of the secondary electrons with a probability depending only on their geometric locations. The secondary electron emission from the generated electrons of energy higher than 100eV is estimated by the 'universal yield curve'. The sum of these provides an estimate for the secondary electron yield and we show that results of applying this algorithm agree with known experimental results. Using this algorithm, we computed secondary electron emissions from a micro-channel plate used in a gas electron multiplier detector that is currently being developed at Korea Atomic Energy Research Institute.

• Nuclear Engineering and Technology
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• v.52 no.6
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• pp.1277-1281
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• 2020

A novel ceramic Gas Electron Multiplier (GEM) has been developed to meet the demand of high counting rate for the neutron detection which is an alternative to ³He-based detector at China Spallation Neutron Source (CSNS). An experiment was performed to measure the neutron transmittance of ceramic-GEM and FR4-GEM at the small angle neutron scattering (SANS) instrument. The result showed the ceramic-GEM has higher transmittance and less self-scattering especially for cold neutrons. One single ceramic GEM could give a gain of 10²-10⁴ in the mixture gas of Ar and CO₂ (90%:10%) and its energy resolution was about 27.7% by using ⁵⁵Fe X ray of 5.9 keV. A prototype has been developed in order to investigate the performances of the ceramic GEM-based neutron detector. Several neutron beam tests, including detection efficiency, spatial resolution, two-dimensional imaging, and wavelength spectrum, were carried out at CSNS and China Mianyang Research Reactor (CMRR). The results show that the ceramic GEM-based neutron detector is a good candidate to measure the high intensity neutrons.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.4 no.2
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• pp.155-160
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• 2004

In this paper, we describe the results of a study on the edge enhancement of X-ray images by using their fuzzy system representation. A set of gray scale X-ray images was generated using the EGS4 computer code. An aluminum plate or a lead plate with three parallel strips taken out has been used as the object with the thickness and the width of the plate, and the gap between the two strips varied. We started with a comparative study on a set of the fuzzy sets for their applicability as the input fuzzy sets for the fuzzy system representation of the gray scale images. Then we describe how the fuzzy system is used to sharpen the edges. Our algorithm is based on adding the magnitude of the gradient not to the pixel value of concern but rather to the nearest neighboring pixel in the direction of the gradient. We show that this algorithm is better in maintaining the spatial resolution of the original image after the edge enhancement.

• Journal of Radiation Protection and Research
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• v.30 no.1
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• pp.35-37
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• 2005

The radiation detector research group at KAERI has developed a high efficiency neutron detector using a Gas Electron Multiplier (GEM). The double GEM was fabricated and operated in an Ar/Isobutane mixture. For an application to a high efficiency neutron detector, $^6Li\;or\;^{10}B$ neutron converters coated on each surface of the multi GEM foils were considered. The optimized thickness of the thin film for a neutron detection was calculated with the MCNP and SRIM. The neutron efficiency was calculated by changing the chemical components of the thin film, and the thickness of the thin film. The thermalized neutrons were measured by a GEM detector with a thin neutron converter on the drift plate.