• Nuclear Engineering and Technology
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• 제37권4호
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• pp.395-400
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• 2005

An environmental radon monitoring system, comprising a radon-cup, an etching system, and a track counting system, was constructed. The radon cup is a cylindrical chamber with a radius of 2.2 cm and a height of 3.2 cm in combination with a CR-39 detector. Carbon is impregnated in the bodies of the detector chamber to avoid problem of an electrostatic charge. The optimized etching condition for the CR-39 exposed to a radon environment turned out to be a 6 N NaOH solution at 70^{\circ}$ over a 7hour period. The bulk etch rate under the optimized condition was $1.14{\pm}0.03\;{\mu}m\;h^{-1}$. The diameter of the tracks caused by radon and its progeny were found to be in the range of $10\~25\;{\mu}m$ under the optimized condition. The track images were observed with a track counting system, which consisted of an optical microscope, a color charged couple device (CCD) camera, and an image processor. The calibration factor of this system is obtained to be $0.105{\pm}0.006$ tracks $cm^2$ per Bq $m^{-3}$ d.

• Transactions on Electrical and Electronic Materials
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• 제18권6호
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• pp.330-333
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• 2017

$Co_xMn_{3-x}O_4$ ($1.48{\leq}x{\leq}1.63$) ceramics were fabricated using the solid-state reaction method. Structural and electrical properties of specimens based on the composition ratio of Co were observed in order to investigate their applicability in NTC thermistors. All specimens showed a single spinel phase with a homogeneous tetragonal structure. The $Co_{1.57}Mn_{1.43}O_4$ specimen showed a maximum average grain size of approximately $6.47{\mu}m$. In all specimens, TCR properties displayed excellent characteristics of over $-4.2%/^{\circ}C$. The resistivity at 298 K and B-value of the $Co_{1.57}Mn_{1.43}O_4$ specimen were approximately $418{\Omega}-cm$ and 4300, respectively.

• Transactions on Electrical and Electronic Materials
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• 제17권4호
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• pp.227-230
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• 2016

Zn_xMn_3-xO₄ (0.95≤x≤1.20) specimens were prepared using a conventional solid state reaction method. All specimens were sintered in air at 1,200℃ for 12 h, cooled at a rate of 2℃/min to 800℃, and subsequently quenched to room temperature. We investigated the electrical properties of Zn_xMn_3-xO₄ specimens with various amounts of ZnO for use as IR detectors. At a composition of x≥1.15, the ZnO phase precipitates beside the spinel structure. The electrical resistivity at room temperature, activation energy, responsivity, and detectivity of a Zn_1.10Mn_1.90O₄ specimen are 653.2 kΩ-cm, 0.392 eV, 0.016 V/W, and 7.52×10³ cmHz^1/2/W, respectively.

• Journal of Astronomy and Space Sciences
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• 제35권3호
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• pp.195-200
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• 2018

The present paper describes the design of a Solid State Telescope (SST) on board the Korea Astronomy and Space Science Institute satellite-1 (KASISat-1) consisting of four [TBD] nanosatellites. The SST will measure these radiation belt electrons from a low-Earth polar orbit satellite to study mechanisms related to the spatial resolution of electron precipitation, such as electron microbursts, and those related to the measurement of energy dispersion with a high temporal resolution in the sub-auroral regions. We performed a simulation to determine the sensor design of the SST using GEometry ANd Tracking 4 (GEANT4) simulations and the Bethe formula. The simulation was performed in the range of 100 ~ 400 keV considering that the electron, which is to be detected in the space environment. The SST is based on a silicon barrier detector and consists of two telescopes mounted on a satellite to observe the electrons moving along the geomagnetic field (pitch angle $0^{\circ}$) and the quasi-trapped electrons (pitch angle $90^{\circ}$) during observations. We determined the telescope design of the SST in view of previous measurements and the geometrical factor in the cylindrical geometry of Sullivan (1971). With a high spectral resolution of 16 channels over the 100 keV ~ 400 keV energy range, together with the pitch angle information, the designed SST will answer questions regarding the occurrence of microbursts and the interaction with energetic particles. The KASISat-1 is expected to be launched in the latter half of 2020.

• Nuclear Engineering and Technology
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• 제50권3호
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• pp.432-438
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• 2018

The occurrence of saturation in the CR-39 detector reduces and limits its detection dynamic range; nevertheless, this range could be extended using spectroscopic techniques and by measuring the net bulk rate of the saturated CR-39 detector surface. CR-39 detectors were irradiated by 1.5 MeV high alpha-particle fluence varying from $0.06{\times}10^8$ to $7.36{\times}10^8\;alphas/cm^2$ from Am-241 source; thereafter, they were etched in a 6.25N NaOH solution at a temperature of $70^{\circ}C$ for different durations. Net bulk etch rate measurement of the 1.5 MeV alpha-irradiated CR-39 detector surface revealed that rate increases with increasing etching time and reaches its maximum value at the end of the alpha-particle range. It is also correlated with the alpha-particle fluence. The measurements of UV-Visible (UV-Vis) absorbance at 500 and 600 nm reveal that the absorbance is linearly correlated with the fluence of alpha particles at the etching times of 2 and 4 hour. For extended etching times of 6, 10, and 14.5 hour, the absorbance is saturated for fluence values of $4.05{\times}10^8$, $5.30{\times}10^8$, and $7.36{\times}10^8\;alphas/cm^2$. These new methods pave the way to extend the dynamic range of polymer-based solid state nuclear track detectors (SSNTDs) in measurement of high fluence of heavy ions as well as in radiation dosimetry.

• 센서학회지
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• 제24권1호
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• pp.6-9
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• 2015

Conventional leak detectors are widely based on helium gas sensors. However, the usage of hydrogen sensors in leak detectors has increased because of the high prices of helium leak detectors and the dearth in the supply of helium gas. In this study, a hydrogen leak detector was developed using solid-state hydrogen sensors. The hydrogen sensors are based on Park-Rapp probes with heterojunctions made by oxygen-ion conducting Yttria-stabilized zirconia and proton-conducting In-doped $CaZrO_3$. The hydrogen sensors were used for determining the potential difference between air and air balanced 5 ppm of $H_2$. Even though the Park-Rapp probe shows an excellent selectivity for hydrogen, the sensitivity of the sensor was low because of the low concentration of hydrogen, and the oxygen on the surface of the sensor. In order to increase the sensitivity of the sensor, the sensors were connected in series by Pt wires to increase the potential difference. The sensors were tested at temperatures ranging from $500-600^{\circ}C$.

• 한국방사선학회논문지
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• 제11권4호
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• pp.183-188
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• 2017

최근, 감마선 조사기의 자동 원격 조사 제어기가 오동작하여 방사선작업종사자가 방사선 피폭 사고가 지속적으로 보고되고 있다. 이에 NDT 분야에서는 방사선에 대한 잠재적 사고를 미연에 방지하기 위한 방사선원 모니터링 시스템 구축에 많은 시간과 재원을 투자하고 있다. 이에 본 연구에서는 다양한 비파괴검사장비에 범용적으로 적용할 수 있는 방사선원 위치 모니터링 시스템의 개발을 위한 선행연구로써 몬테카를로 시뮬레이션을 통해 산화납 기반 방사선 검출기에 대한 감마선 응답 특성을 모의 추정하였다. 연구 결과, 방사선 검출기의 최적화 두께는 방사선원에서 방사되는 감마선 에너지에 따라 상이하며 에너지가 증가함에 따라 최적화 두께가 점차 증가하는 것으로 나타났다. 결론적으로 PbO 기반 방사선 검출기의 최적화 두께는 Ir-192에 대하여 $200{\mu}m$, Se-75 $150{\mu}m$, Co-60 $300{\mu}m$로 분석되었다. 이러한 연구 결과를 바탕으로 범용적으로 적용하기 위하여 2차 전자 평형을 고려한 PbO 기반 방사선 검출기의 적절한 두께는 $300{\mu}m$로 평가되었다. 이러한 결과는 차후 다양한 NDT 장비에 범용적으로 적용하기 위한 방사선원 위치 모니터링 시스템을 개발 시 방사선 검출기에서 요구되는 적절한 두께를 결정하는데 있어 기초자료로 활용될 수 있을 것으로 사료된다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집B
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• pp.176-180
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• 2001

In this paper, we have studies the images have been reconstructed by using combination of images which has been acquired by the variation of operating frequency. When inner images has been reconstructed, inner image has been superposition by surface state effect. In this case, image enhancement the phase object and enhance the contrast of inner image. In the result of the specimen for the round defect with 2mm diameter, for the types of the depth are 1.5mm, 2mm, 2.5mm, and 3mm, it has been show that the shape of defect has better than before this processing and phase contrast grow large twice. And we have constructed the acoustic microscope by using quadrature detector that is able simultaneously to acquired the amplitude and phase of the reflected signal. Father more we have studied the reconstruction method of the amplitude and phase images and the enhancement method of the defect images' contrast.

• 대한방사선기술학회지:방사선기술과학
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• 제26권4호
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• pp.39-46
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• 2003

의료영상 분야에서의 디지털화가 시도되면서부터 평판형 디지털 영상검출기가 일반촬영 및 투시영상을 비롯한 다양한 영상 획득 장치에의 적용을 위해 꾸준히 연구, 개발되어져 왔다. 본 연구는 비정질 셀레늄을 이용한 디지털 방사선 검출기를 통해 획득된 영상의 평가를 통해 순수 국내 기술로 개발중인 디지털 방사선 검출기의 임상 사용여부를 확인하고, 영상평가의 주요인자인 modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) 이용하여 정량적인 값을 도출함으로써 의료영상평가에 필요한 측정 방법 및 그 기초 자료의 제공을 그 목적으로 한다. 비정질 셀레늄을 이용한 디지털 방사선 검출기는 pixel pitch가 $139\;{\mu}m$이며, 전체 active area은 $14{\times}8.5\;inch^2$, 전체 pixel의 수는 3.9백만개이다. 디지털 X-선 검출기에서 광도전체로서 비정질 셀레늄은 TFT 평판 패널 위에 진공 증착된다. 비정질 셀레늄의 두께는 $500\;{\mu}m$이다. 디지털 방사선 검출기의 성능을 평가하기 위해 민감도, 선형성, MTF, NPS, 그리고 DQE가 측정되었다. 선형성 평가에서는 뛰어난 선형성[($r^2$)=0.9693]을 보였다. 측정된 민감도는 인가전압 $10\;V/{\mu}m$에서 $4.16{\times}10^6\;ehp/pixel{\cdot}mR$이며, MTF는 2.5\;lp/mm에서 52%이다. 그리고 DQE는 1.5\;lp/mm에서 75%이다. 본 연구를 통해 영상평가 측정 기술의 기본적 토대를 마련하고, 측정된 값은 국내 기술로 개발중인 비정질 셀레늄을 이용한 직접방식의 디지털 방사선 검출기의 임상적 사용가치가 충분함을 뒷받침할 수 있는 기초 자료로서 제공될 수 있을 것으로 판단된다.

• 한국군사과학기술학회지
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• 제1권1호
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• pp.227-237
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• 1998

HgCdTe Is the most versatile material for the developing infrared devices. Not like III-V compound semiconductors or silicon-based photo-detecting materials, HgCdTe has unique characteristics such as adjustable bandgap, very high electron mobility, and large difference between electron and hole mobilities. Many research groups have been interested in this material since early 70's, but mainly due to its thermodynamic difficulties for preparing materials, no single growth technique is appreciated as a standard growth technique in this research field. Solid state recrystallization(SSR), travelling heater method(THM), and Bridgman growth are major techniques used to grow bulk HgCdTe material. Materials with high quality and purity can be grown using these bulk growth techniques, however, due to the large separation between solidus and liquidus line on the phase diagram, it is very difficult to grow large materials with minimun defects. Various epitaxial growth techniques were adopted to get large area HgCdTe and among them liquid phase epitaxy(LPE), metal organic chemical vapor deposition(MOCVD), and molecular beam epitaxy(MBE) are most frequently used techniques. There are also various types of photo-detectors utilizing HgCdTe materials, and photovoltaic and photoconductive devices are most interested types of detectors up to these days. For the larger may detectors, photovoltaic devices have some advantages over power-requiring photoconductive devices. In this paper we reported the main results on the HgCdTe growing and characterization including LPE and MOCVD, device fabrication and its characteristics such as single element and linear array($8{\times}1$ PC, $128{\times}1$ PV and 4120{\times}1$ PC). Also we included the results of the dewar manufacturing, assembling, and optical and environmental test of the detectors.