• Nuclear Engineering and Technology
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• 제54권5호
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• pp.1760-1768
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• 2022

When gamma-camera sensor modules, which are key components of radiation imagers, are derived from the coupling between scintillators and photosensors, the light collection efficiency is an important factor in determining the effectiveness with which the instrument can identify nuclides via their derived gamma-ray spectra. If the pixel area of the scintillator is larger than the pixel area of the photosensor, light loss and cross-talk between pixels of the photosensor can result in information loss, thereby degrading the precision of the energy estimate and the accuracy of the position-of-interaction determination derived from each active pixel in a coded-aperture based gamma camera. Here we present two methods to overcome the information loss associated with the loss of photons created by scintillation pixels that are coupled to an associated silicon photomultiplier pixel. Specifically, we detail the use of either: (1) light guides, or (2) scintillation pixel areas that match the area of the SiPM pixel. Compared with scintillator/SiPM couplings that have slightly mismatched intercept areas, the experimental results show that both methods substantially improve both the energy and spatial resolution by increasing light collection efficiency, but in terms of the image sensitivity and image quality, only slight improvements are accrued.

• 천문학회보
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• 제37권2호
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• pp.129.2-129.2
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• 2012

Solar flares and coronal mass ejections (CMEs) are two major solar eruptive phenomena which can cause enormous economic and commercial losses: (1) flares are sudden, rapid, and intense brightenings from radio waves to Gamma-rays in the chromosphere and corona, and (2) CMEs are large-scale transient eruptions of magnetized plasma from the solar corona that propagate outward into interplanetary space. Most flares and CMEs occur in magnetically complicated solar active regions (ARs). Therefore, it is crucial to investigate magnetic fields in ARs and their temporal variations for understanding a precondition and a trigger mechanism related to flare/CME initiation. In this presentation, we will introduce an automated system for empirical forecasting of flares and CMEs in ARs using full-disk photospheric line-of-sight magnetogram data taken by the Helioseismic and Magnetic Imager (HMI) onboard the SDO.

• 한국의학물리학회지:의학물리
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• 제32권4호
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• pp.116-121
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• 2021

Purpose: To investigate the effects of dose rate on intensity-modulated radiation therapy (IMRT) quality assurance (QA). Methods: We performed gamma tests using portal dose image prediction and log files of a multileaf collimator. Thirty treatment plans were randomly selected for the IMRT QA plan, and three verification plans for each treatment plan were generated with different dose rates (200, 400, and 600 monitor units [MU]/min). These verification plans were delivered to an electronic portal imager attached to a Varian medical linear accelerator, which recorded and compared with the planned dose. Root-mean-square (RMS) error values of the log files were also compared. Results: With an increase in dose rate, the 2%/2-mm gamma passing rate decreased from 90.9% to 85.5%, indicating that a higher dose rate was associated with lower radiation delivery accuracy. Accordingly, the average RMS error value increased from 0.0170 to 0.0381 cm as dose rate increased. In contrast, the radiation delivery time reduced from 3.83 to 1.49 minutes as the dose rate increased from 200 to 600 MU/min. Conclusions: Our results indicated that radiation delivery accuracy was lower at higher dose rates; however, the accuracy was still clinically acceptable at dose rates of up to 600 MU/min.

• 천문학회보
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• 제39권2호
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• pp.76.1-76.1
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• 2014

We present near-infrared spectroscopic and photometric observations of the nova V2468 Cyg taken from 2008 March 14 till 2008 November 11 following its outburst on 2008 March 7. The JHK spectra of the nova have been taken from the Mount Abu Infrared Observatory using the Near-Infrared Imager/Spectrometer. The early spectra are dominated by strong H I lines from the Brackett and Paschen series, Fe II, O I and C I lines, typical of Fe II type novae but after 46 days from outburst there is significant reduction in the strength of the C I lines and the spectra are dominated by He I lines. The FWHM of the Pa-beta and Br-gamma lines change from 2200-2300 km s-1 to 1700-1800 km s-1 after 12 days from outburst. Three additional small amplitude outbursts are seen near 110, 185 and 240 days in the V band light curve after the discovery. The upper limit for the ejecta mass for V2468 Cyg is estimated to be $5.2{\times}10-6Msun$.

• 대한방사선치료학회지
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• 제27권2호
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• pp.167-174
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• 2015

목 적 : 복잡하고 정교하게 계획된 용적변조회전 방사선치료(Volumetric Arc Therapy, VMAT)의 Portal Dosimetry를 이용한 치료 전 선량평가가 다양한 인자에 따라 재현성을 유지하는지 분석하고자 하였다. 대상 및 방법 : 실험에는 TrueBeam STx$^{TM}$(Ver.1.5, Varian, USA), Portal dosimetry application(Ver.10, Varian)과 Portal Vision aS1000 Imager(Varian, USA)을 사용하였다. 두경부암 환자 2명, 전립샘암 환자 3명, 폐암 환자 1명, 자궁경부암 환자 1명, 총 7명의 환자에 대하여 Portal Dosimetry용 VMAT 전산화치료계획(Eclipse, Ver.10.0, Varian, USA)을 수립하였다. 오전 치료 전과 후 오후 치료 종료 후 각 4시간 간격을 두고 3회씩 5일에 걸쳐 선량평가를 시행하였다. Gamma pass rate(GPR 3%, 3mm 95%신뢰구간)와 Beam 출력의 상관관계를 확인하기 위하여 선량평가 시행 전 Beam 출력 을 물등가모형과 이온전리함(IBA dosimetry, Germany)을 이용하여 측정하였다. Electronic Portal Imaging Device(EPID) 상태에 따른 GPR 의 변화를 확인하기 위하여 EPID의 영상 교정 (Dark field correction, Flood field correction) 전과 후로 나누어 선량평가를 시행하였다. 또한 다엽콜리메이터(Multi Leaf Collimator) 상태에 따른 GPR의 변화를 확인하기 위해 다엽콜리메이터 Initialize 전과 후로 나누어 선량평가를 시행하였다. 결 과 : Portal Dosimetry를 시행하여 얻은 모든 환자들의 각 시간대 별 GPR의 평균값은 97.11%, 96.09%, 95.37% 였고 최대 차이를 보인 환자의 경우 각 시간대 별 GPR의 평균값은 95.73%, 94.20% 93.23% 였다. 선량평가 시점의 Beam 출력을 측정한 결과 각 시간대별 평균값은 100.45%, 100.46%, 100.59% 였다. EPID의 영상 교정(Dark field correction, Flood field correction)을 시행하기 전과 후의 대상 환자들의 GPR의 평균값은 95.94 %, 96.01% 였다. 또한 다엽콜리메이터 의 Initialize 를 시행하기 전과 후의 대상 환자들의 GPR 의 평균값은 95.83%, 96.40%였다. 결 론 : 치료기 사용시간이 경과됨에 따라 대상 환자들의 GPR 평균값이 0.8% 감소함을 확인할 수 있었다. Beam 출력은 각 측정시점에 0.1% 오차범위 안에서 일정한 상태를 유지하였다. EPID의 영상 교정 전, 후 의 선량평가 결과 GPR은 평균 0.1% 차이를 나타내었다. 다엽콜리메이터의 Initialize 전, 후의 선량평과 결과 Initialize 시행 후 GPR이 평균 0.6% 상승하였고 다엽콜리메이터 상태에 따라 GPR이 변화할 수 있다는 것을 확인할 수 있었다. 복잡하고 정교하게 계획된 VMAT의 치료 전 선량평가 도구로서 재현성을 유지하며 Portal Dosimetry를 이용하기 위해서는 주기적인 장비의 점검뿐만 아니라, 선량평가에 영향을 미칠 수 있는 다양한 인자들에 대한 관리가 이뤄져야 할 것으로 판단된다.

• Nuclear Engineering and Technology
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• 제55권8호
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• pp.2797-2801
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• 2023

CdZnTeSe (CZTS) has attracted attention for applications in X- and gamma-ray detectors owing to its improved properties compared to those of CdZnTe (CZT). In this study, we grew and processed single crystals of CZT and CZTS using the Bridgeman method to confirm the feasibility of using a dosimeter for high-energy X-rays in radiotherapy. We evaluated their linearity and precision using the coefficient of determination (R²) and relative standard deviation (RSD). CZTS showed sufficient RSD values lower than 1.5% of the standard for X-ray dosimetry, whereas CZT's RSD values increased dramatically under some conditions. CZTS exhibited an R² value of 0.9968 at 500 V/cm, whereas CZT has an R² value of 0.9373 under the same conditions. The X-ray response of CZTS maintains its pulse shape at various dose rates, and its properties are improved by adding selenium to the CdTe matrix to lower the defect density and sub-grain boundaries. Thus, we validated that CZTS shows a better response than CZT to high-energy X-rays used for radiotherapy. Further, the applicability of an onboard imager, a high-energy X-ray (>6 MV) image, is presented. The proposed methodology and results can guide future advances in X-ray dose detection.

• Journal of Astronomy and Space Sciences
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• 제21권4호
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• pp.329-342
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• 2004

In this paper, we present preliminary feasibility studies on three types of solar observation payloads for future Korean Science and Technology Satellite (STSAT) programs. The three candidates are (1) an UV imaging telescope, (2) an UV spectrograph, and (3) an X-ray spectrometer. In the case of UV imaging telescope, the most important constraint seems to be the control stability of a satellite in order to obtain a reasonably good spatial resolution. Considering that the current pointing stability estimated from the data of the Far ultraviolet Imaging Spectrograph (FIMS) onboard the Korean STSAT-1, is around 1 arc minutes/sec, we think that it is hard to obtain a spatial resolution sufficient for scientific research by such an UV Imaging Telescope. For solar imaging missions, we realize that an image stabilization system, which is composed of a small guide telescope with limb sensor and a servo controller of secondary mirror, is quite essential for a very good pointing stability of about 0.1 arcsec. An UV spectrograph covering the solar full disk seems to be a good choice in that there is no risk due to poor pointing stability as well as that it can provide us with valuable UV spectral irradiance data valuable for studying their effects on the Earth's atmosphere and satellites. The heritage of the FIMS can be a great advantage of developing the UV spectrograph. Its main disadvantage is that two major missions are in operation or scheduled. Our preliminary investigations show that an X-ray spectrometer for the full disk Sun seems to be the best choice among the three candidates. The reasons are : (1) high temporal and spectral X-ray data are very essential for studying the acceleration process of energetic particles associated with solar flares, (2) we have a good heritage of X-ray detectors including a rocket-borne X-ray detector, (3) in the case of developing countries such as India and Czech, solar X-ray spectrometers were selected as their early stage satellite missions due to their poor pointing stabilities, and (4) there is no planned major mission after currently operating Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) mission. Finally, we present a preliminary design of a solar X-ray spectrometer covering soft X-ray (2 keV) to gamma ray (10 MeV).