• Journal of Radiation Protection and Research
• /
• 제40권1호
• /
• pp.25-35
• /
• 2015

We analyzed the differential effects of histopathology, apoptosis and expression of radiation response genes after chronic low dose rate (LDR) and acute high dose rate (HDR) radiation exposure in spleen, lung and liver of rats. Female 6-week-old Sprague-Dawley rats were used. For chronic low-dose whole body irradiation, rats were maintained for 14 days in a $^{60}Co$ gamma ray irradiated room and received a cumulative dose of 2 Gy or 5 Gy. Rats in the acute whole body exposure group were exposed to an equal dose of radiation delivered as a single pulse ($^{137}Cs$-gamma). At 24 hours after exposure, spleen, lung and liver tissues were extracted for histopathologic examination, western blotting and RT-PCR analysis. 1. The spleen showed the most dramatic differential response to acute and chronic exposure, with the induction of substantial tissue damage by HDR but not by LDR radiation. Effects of LDR radiation on the lung were only apparent at the higher dose (5 Gy), but not at lower dose (2 Gy). In the liver, HDR and LDR exposure induced a similar damage response at both doses. RT-PCR analysis identified cyclin G1 as a LDR-responsive gene in the spleen of rats exposed to 2 Gy and 5 Gy gamma radiation and in the lung of animals irradiated with 5 Gy. 2. The effects of LDR radiation differed among lung, liver, and spleen tissues. The spleen showed the greatest differential effect between HDR and LDR. The response to LDR radiation may involve expression of cyclin G1.

• 한국정보통신학회:학술대회논문집
• /
• 한국정보통신학회 2012년도 춘계학술대회
• /
• pp.719-721
• /
• 2012

본 시험은 군전자장비의 전원제어부품으로 사용되는 TPS54315소자에 대하여 과도방사선에 따른 과도응답특성인 Upset/Latch-up특성을 평가하기 시험으로 포항가속기 연구소내의 Test LINAC 조사시설을 이용하여 $1.43{\times}10^7$rad(si)/sec~$1.25{\times}10^8$rad(si)/sec 선량률 조건에서의 실측시험을 수행하였다. 시험결과 $1.0{\times}10^8$rad(si)/sec 이후 Latch-up 현상이 확인되었으며 연속펄스 인가 시 Latch-up상태에서 정상상태로 복귀하는 결과를 확인하였다. 또한 이러한 현상은 과도방사선에 의한 광전류가 내부전원 Reset로직을 트리거 시킴으로써 Latch-up상태에서의 전원바이어스를 일시적으로 차단함에 따라 발생된 것으로 본 실험을 통하여 Reset회로가 내장된 소자의 경우 일부 Latch-up현상과 동시에 Reset회로가 트리거 되는 경우 Latch-up상태에서 정상상태로 복귀되는 결과를 확인하였다.

• Journal of Radiation Protection and Research
• /
• 제42권1호
• /
• pp.48-55
• /
• 2017

Background: Simultaneous detection of neutrons and gamma rays have become much more practicable, by taking advantage of good gamma-ray discrimination properties using pulse shape discrimination (PSD) technique. Recently, we introduced a commercial CLYC system in Korea, and performed an initial characterization and simulation studies for the CLYC detector system to provide references for the future implementation of the dual-mode scintillator system in various studies and applications. Materials and Methods: We evaluated a CLYC detector with 95% $^6Li$ enrichment using various gamma-ray sources and a $^{252}Cf$ neutron source, with validation of our Monte Carlo simulation results via measurement experiments. Absolute full-energy peak efficiency values were calculated for gamma-ray sources and neutron source using MCNP6 and compared with measurement experiments of the calibration sources. In addition, behavioral characteristics of neutrons were validated by comparing simulations and experiments on neutron moderation with various polyethylene (PE) moderator thicknesses. Results and Discussion: Both results showed good agreements in overall characteristics of the gamma and neutron detection efficiencies, with consistent ~20% discrepancy. Furthermore, moderation of neutrons emitted from $^{252}Cf$ showed similarities between the simulation and the experiment, in terms of their relative ratios depending on the thickness of the PE moderator. Conclusion: A CLYC detector system was characterized for its energy resolution and detection efficiency, and Monte Carlo simulations on the detector system was validated experimentally. Validation of the simulation results in overall trend of the CLYC detector behavior will provide the fundamental basis and validity of follow-up Monte Carlo simulation studies for the development of our dual-particle imager using a rotational modulation collimator.

• Journal of KIEE
• /
• 제11권1호
• /
• pp.32-40
• /
• 2001

This paper presents the detailed statistics on radiation field signatures associated with multiple-intracloud lightning discharges. A transient signal recording system was used to measure the electric and magnetic fields produced by lightning flashes. The measurements were made in th summers of 1995 through 1999, and the location of the observation station was in Inchon on the coast of the Yellow Sea in Korea(37$^{\circ}$25'N, 126$^{\circ}$ 39'E). Most of lightning flashes typically contains between two and five strokes. The individual intracloud stork radiation fields were the bipolar pulse. On the average, the ratio of the peak of the second stroke to the first stroke peak was 75.1$\pm$40.1% for the negative, and a fraction of the subsequent stroke peaks were higher than the first stroke peak. The greater the number of the subsequent stroke order, less time separations between strokes were produced. The mean of the depth of the dip was 81.2$\pm$27.9% for the positive polarity and 75.9$\pm$24.4% for the negative. The depth of the dip increased for the positive bipolar pulses and decreased for the negative as the number of the stroke order increased.

• 대한전기학회논문지
• /
• 제41권9호
• /
• pp.1013-1020
• /
• 1992

The conductivity variation of a high resistivity bulk silicon semiconductor, whose electrodes were deposited with aluminum vapor, was studied experimentally by measuring the X-ray intensity and current flow, which was developed by X-ray radiation while applying a pulse voltage to the silicon, in a load resistor connected to the semiconductor. The current flow observed immediately as the X-ray radiated, and when the X-ray decreased. It was found from the observation of switching current for the X-ray intensity and the voltage applied in the semiconductor that the switching current of the semiconductor increased as the intensity of the X-ray and the applied voltage increased. In case of lower applied voltage, the switching current for higher applied voltage depended on the intensity of the X-ray radiated due to the saturation of electron and hole.

• 한국의학물리학회지:의학물리
• /
• 제31권4호
• /
• pp.145-152
• /
• 2020

Purpose: In ionization-chamber dosimetry for high-dose-rate electron beams-above 20 mGy/pulse-the ion-recombination correction methods recommended by the International Atomic Energy Agency (IAEA) and the American Association of Physicists in Medicine (AAPM) are not appropriate, because they overestimate the correction factor. In this study, we suggest a practical ion-recombination correction method, based on Boag's improved model, and apply it to reference dosimetry for electron beams of about 100 mGy/pulse generated from an electron linear accelerator (LINAC). Methods: This study employed a theoretical model of the ion-collection efficiency developed by Boag and physical parameters used by Laitano et al. We recalculated the ion-recombination correction factors using two-voltage analysis and obtained an empirical fitting formula to represent the results. Next, we compared the calculated correction factors with published results for the same calculation conditions. Additionally, we performed dosimetry for electron beams from a 6 MeV electron LINAC using an Advanced Markus^® ionization chamber to determine the reference dose in water at the source-to-surface distance (SSD)=100 cm, using the correction factors obtained in this study. Results: The values of the correction factors obtained in this work are in good agreement with the published data. The measured dose-per-pulse for electron beams at the depth of maximum dose for SSD=100 cm was 115 mGy/pulse, with a standard uncertainty of 2.4%. In contrast, the k_s values determined using the IAEA and AAPM methods are, respectively, 8.9% and 8.2% higher than our results. Conclusions: The new method based on Boag's improved model provides a practical method of determining the ion-recombination correction factors for high dose-per-pulse radiation beams up to about 120 mGy/pulse. This method can be applied to electron beams with even higher dose-per-pulse, subject to independent verification.

• 한국정보통신학회:학술대회논문집
• /
• 한국정보통신학회 2012년도 춘계학술대회
• /
• pp.778-781
• /
• 2012

전자소자는 방사선 피폭으로 손상이 발생하므로 인공위성이나 우주선에 적용하기 위해서는 방사선 내성을 가진 내방사선 전자소자의 사용이 필수적이다. 국내에서 처음 수행한 과도방사선 시험평가 자료를 데이터베이스(DB)로 구축하였다. 이 DB는 웹기반으로 자료검색과 갱신이 가능하도록 설계되었고, 기존 외국 (NASA, ESA)의 공개 자료를 포함하여 총 695종의 데이터가 입력되어 있다. 기존 외국의 DB보다 검색이 효율적이고 실용적인 DB이다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
• /
• 제54권6호
• /
• pp.286-292
• /
• 2005

Terahertz wave is a kind of electromagnetic radiation whose frequency lies in 0.1THz $\~$10THz range. In this paper, generation and detection characteristics of terahertz (THz) radiation by photoconductive antenna (PCA) method has been described. Using modern integrated circuit techniques, micron-sized dipole antenna has been fabricated on a low-temperature grown GaAs (LT-GaAs) wafer. A mode-locked Ti:Sapphire femtosecond laser beam is guided and focused onto photoconductive antennas (emitter and detector) to generate and measure THz pulses. Ultra-wide band THz radiation with frequencies between 0.1 THz and 3 THz was observed. Terahertz field amplitude variation with antenna bias voltage, pump laser power, pump laser wavelength and probe laser power was investigated. As a primary application example. a live clover leaf was imaged with the terahertz radiation.

• 한국정보통신학회:학술대회논문집
• /
• 한국정보통신학회 2013년도 춘계학술대회
• /
• pp.791-794
• /
• 2013

본 연구에서는 초기 핵 방사선 조건에서 반도체소자의 과도응답특성을 분석하기 위한 선행연구의 일환으로 반도체 소자의 과도방사선에 의한 영향에 대한 주요원인과 반도체의 물성, 설계구조, 공정방식의 조건에 따라 소자내부에 생성되는 광전류 거동특성에 대한 정략적인 분석을 위한 시뮬레이션 분석을 수행하였으며 결과적으로 반도체소자의 설계조건과 입력되는 과도방사선의 선량율에 따른 비선형 특성을 확인하였다.

• 한국방사선학회논문지
• /
• 제7권1호
• /
• pp.81-84
• /
• 2013

고 에너지 방사선의 이용과 치료 계획의 발전이 이루어지면서 치료방사선에서 선량 측정의 중요성은 더욱 부각되고 있다. 이러한 선량 측정을 위한 검출기에는 이온 전리함, 필름, 열형광선량계, 다이오드 등이 있다. 이중, 다이오드 검출기는 입사되는 방사선에 의하여 전기적인 신호를 생성하는 광도전체 물질을 사용하는데, 이러한 광도전체 물질에 대해서 최근 많은 연구 그룹들이 관심을 가지고 있다. 하지만, 방사선 치료 영역에서만은 실리콘(Si) 이외에 물질에 대한 연구 결과가 활발히 도출되고 있지 않은 실정이다. 본 논문에서는 광도전체 물질의 고 에너지 방사선에 대한 반응 특성을 확인함으로써 선량계로의 적용 가능성을 검증하고자 하였다. 요오드화수은($HgI_2$)과 요오드화납($PbI_2$)을 기반으로 하는 검출기를 제작하여, 선형가속기에서 입사되는 고 에너지 방사선에 대하여 재현성, 선형성, Pulse rate response를 평가하였다. 이러한 항목들은 치료방사선의 선량계로써의 역할을 평가할 수 있는 필수 요소들이다. 실험결과, 제작된 요오드화수은($HgI_2$)은 약 7% 내외의 재현성과 선형성 오차를 나타내었으며, 요오드화납($PbI_2$)은 1.7%의 선형성 오차와 12.2%의 재현성 오차를 가지는 것으로 확인되었다.