• 천문학회지
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• 제43권3호
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• pp.95-104
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• 2010

We outline our GRB afterglow observation program using the 1-m telescope at Mt. Lemmon Optical Astronomy Observatory (LOAO), and report the first observations of the GRB afterglows. During the 2007B semester, we performed follow-up imaging obsrevations of 6 GRBs, and succeeded in detecting four GRB afterglows (GRB 071010B, GRB 071018, GRB 071020, and GRB 071025) while placing useful upper limits on the light curves of the other GRBs. Among the observed events, we find that three events are special and interesting. GRB 071010B has a light curve which has an unusually long jet break time of 11.8 days. For GRB 071025, its red R-I(~2) color suggests that it is likely to be at z~5. GRB 071020 has a light curve which shows a clear brightening at 0.3-1 days after the burst, where our LOAO data play a crucial role by providing an unambiguous evidence for the brightening. These are the first successful detections of GRB afterglows by a facility owned and operated by a Korean institution, demonstrating the usefulness of the 1-m telescope for transient phenomena such as GRBs up to very high redshift.

• Nuclear Engineering and Technology
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• 제54권5호
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• pp.1747-1753
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• 2022

Compton imaging is the main method for locating radioactive hot spots emitting high-energy gamma-ray photons. In particular, this imaging method is crucial when the photon energy is too high for coded-mask aperture imaging methods to be effective or when a large field of view is required. Reconstruction of the photon source requires advanced Compton event processing algorithms to determine the exact position of the source. In this study, we introduce a novel method based on a Deep Learning algorithm with a Convolutional Neural Network (CNN) to perform Compton imaging. This algorithm is trained on simulated data and tested on real data acquired with Caliste, a single planar CdTe pixelated detector. We show that performance in terms of source location accuracy is equivalent to state-of-the-art algorithms, while computation time is significantly reduced and sensitivity is improved by a factor of ~5 in the Caliste configuration.

• 한국의학물리학회지:의학물리
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• 제25권3호
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• pp.151-156
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• 2014

본 연구의 목적은 붕소 중성자 포획 치료 시 집적된 붕소 영역에서 중성자 선속의 변화와 그에 따른 방출된 즉발 감마선의 검출 시뮬레이션을 통하여 치료 영역에 대한 영상화의 가능성을 확인하고자 함이다. 전산 모사를 통하여 (1) 붕소 유무에 따른 중성자의 영향, (2) 내부와 외부에서의 즉발 감마선량 검출, (3) 즉발 감마선에 대한 에너지 스펙트럼 검출을 수행하였다. 모든 전산 모사는 Monte Carlo n-particle extended (MCNPX, Ver.2.6.0, Los Alamos National Laboratory, Los Alamos, NM, USA)를 이용하여 가상의 물 팬텀과 열중성자(thermal neutron) 소스, 붕소 영역을 지정하였다. 열중성자의 에너지는 1 eV 이하의 에너지였으며 선속은 2,000,000 n/sec.로 설정하였다. 이 때, 발생된 즉발 감마선의 검출은 물 팬텀과 수직 방향으로 위치시키고 납으로 둘러싸인 lutetium-yttrium oxyorthosilicate (Lu0,6Y1,4Si0,5:Ce; LYSO) 섬광체 검출기를 이용하였다. 붕소가 존재하는 영역인 5 cm 깊이에서의 28 분할로서 대략 0.18 cm의 bin을 도출하여 붕소 영역의 얕은 깊이에서부터 급격하게 저하되는 것을 확인하였다. 또한 붕소 영역이 시작되는 지점인 9 cm 깊이에서 감마선의 피크 레벨을 확인하였다. 그리고 478 keV 지점에서 정확한 즉발 감마선 피크가 관찰되는 것을 확인하였다. 478 keV의 즉발 감마선 피크는 41 keV의 반치폭으로 에너지 분해능 값은 8.5%로 측정되었다. 결론적으로 붕소 중성자 포획 치료 시 발생되는 즉발 감마선의 계측으로 치료가 행해지는 부위를 감마 카메라 또는 단일 광자 방출 단층 촬영 기기에서 영상화할 수 있는 가능성을 확인하였다.

• Nuclear Engineering and Technology
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• 제55권10호
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• pp.3822-3830
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• 2023

The large-area Compton camera (LACC), featuring significantly high detection sensitivity, was developed for high-speed localization of gamma-ray sources. Due to the high gamma-ray interaction event rate induced by the high sensitivity, however, the multiplexer-based data acquisition system (DAQ) rapidly saturated, leading to deteriorated energy and imaging resolution at event rates higher than 4.7 × 10³ s^-1. In the present study, a new simultaneous multi-channel DAQ was developed to improve the energy and imaging resolution of the LACC even under high event rate conditions (10⁴-10⁶ s^-1). The performance of the DAQ was evaluated with several point sources under different event rate conditions. The results indicated that the new DAQ offers significantly better performance than the existing DAQ over the entire energy and event rate ranges. Especially, the new DAQ showed high energy resolution under very high event rate conditions, i.e., 6.9% and 8.6% (for 662 keV) at 1.3 × 10⁵ and 1.2 × 10⁶ s^-1, respectively. Furthermore, the new DAQ successfully acquired Compton images under those event rates, i.e., imaging resolutions of 13.8° and 19.3° at 8.7 × 10⁴ and 10⁶ s^-1, which correspond to 1.8 and 73 μSv/hr or about 18 and 730 times the background level, respectively.

• Journal of Korean Neurosurgical Society
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• 제43권1호
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• pp.26-30
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• 2008

Objective : The authors developed a stereotactic device for irradiation of small animals with Leksell Gamma Knife Model C. Development and verification procedures were described in this article. Methods : The device was designed to satisfy three requirements. The mechanical accuracy in positioning was to be managed within 0.5 mm. The strength of the device and structure were to be compromised to provide enough strength to hold a small animal during irradiation and to interfere the gamma ray beam as little as possible. The device was to be used in combination with the Leksell G-$frame^{(R)}$ and $KOPF^{(R)}$ rat adaptor. The irradiation point was determined by separate imaging sequences such as plain X-ray images. Results : The absolute dose rate with the device in a Leksell Gamma Knife was 3.7% less than the value calculated from Leksell Gamma $Plan^{(R)}$. The dose distributions measured with $GAFCHROMIC^{(R)}$ MD-55 film corresponded to those of Leksell Gamma $Plan^{(R)}$ within acceptable range. The device was used in a series of rat experiments with a 4 mm helmet of Leksell Gamma Knife. Conclusion : A stereotactic device for irradiation of small animals with Leksell Gamma Knife Model C has been developed so that it fulfilled above requirements. Absorbed dose and dose distribution at the center of a Gamma Knife helmet are in acceptable ranges. The device provides enough accuracy for stereotactic irradiation with acceptable practicality.

• Nuclear Engineering and Technology
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• 제56권7호
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• pp.2650-2658
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• 2024

In this paper, we use a Monte Carlo (MC) simulation based on Geant4 to investigate the influence of four parameters on the spatial resolution of the lens-coupled lutetium yttrium orthosilicate (LYSO) scintillator, including the thickness of the LYSO scintillator, the F-number and minification factor of the lens, and the incident position of the gamma-rays. Simulation results show that when the gamma-rays are incident along the lens axis, the smaller the thickness, the larger the F-number, the larger the minification factor, the higher the spatial resolution, with an isotropic point spread function (PSF). As the incident position of the gamma-rays deviates from the lens axis, the spatial resolution decreases, and the PSF becomes anisotropic. In addition, by analyzing the whole physical process of the lens-coupled LYSO scintillator from gamma-rays to secondary electrons to fluorescence photons, we aim to provide a detailed analysis of the influence of each parameter on the spatial resolution. The results show that the PSF of the secondary electrons energy deposition is almost constant in the simulation, which determines the upper limit of the spatial resolution. Meanwhile, the dispersion process of the fluorescence photons can explain the reason why each parameter affects the spatial resolution.

• 연구논문집
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• 통권31호
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• pp.135-147
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• 2001

The wall-thickness of insulated pipelines can be easily evaluated by measuring the gamma-ray transmission intensity because this intensity is inversely proportional to the thickness of insulated pipeline. The main purpose of this study is to develop the nondestructive and filmless on-line inspection system of corrosion by measuring the wall thickness of insulated pipeline. The inspection system is constructed with radioisotope, 64 channel photo diode array detector, crawler system and data taking and operating software. The traditional off-line radiographic method carried out by exposing film cassettes can be replaced by this cost-effective on-line digital imaging method and the application will be greatly expected especially in the chemical and petrochemical industries.

• 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).

• 한국의학물리학회지:의학물리
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• 제20권4호
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• pp.216-224
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• 2009

$^{99m}Tc$은 핵의학 영상 획득 물리적 특성이 우수하지만 유기화 작용이 일어나지 않아 갑상선 호르몬의 합성능력이 없는 결절을 진단하는데 제한을 받는다. 이와는 달리 $^{131}I$은 유기화 작용으로 인하여 갑상선의 기능을 평가하는데 활용됨은 물론 높은 에너지의 베타선과 감마선을 방출함으로써 암의 치료에도 널리 사용되고 있는 방사선 핵종이다. 그러나 $^{131}I$은 단일에너지의 감마선을 방출하는 $^{99m}Tc$ 등과는 달리, 다양한 에너지의 감마선을 방출함으로써 핵의학 영상의 정량화가 어려운 단점이 있으며, 특히 고에너지 영역의 감마선에 의한 격벽투과와 산란선은 핵의학 진단영상에 악영향을 미치게 되는 단점이 있다. 본 연구에서는 팬텀 내에서 선원의 위치 변화에 따른 산란의 영향을 알아보기 위해 GATE (Geant4 Application for Tomographic Emission) 시뮬레이션 도구로 dual-head 감마카메라(ECAM), PMMA 팬텀(RADICAL, USA), 점선원 0.1 mCi를 사용하여 모사하였다. 팬텀 내에서 $^{131}I$ 점선원을 X축, Y축으로 위치를 변화시키며 영상을 획득하였다. 또 산란 매질의 유무에 따른 영향을 확인하기 위해 같은 위치에서 점선원이 팬텀 안에 있을 때와 공기 중에 있을 때를 비교 하였다. 저에너지 선원과 비교를 위해 같은 방법으로 $^{99m}Tc$으로도 시뮬레이션 하였다. 또한 시뮬레이션과 똑같은 환경에서 측정 실험을 통해 시뮬레이션의 타당성을 검증 하였다. 이 연구에서는 한 팬텀 내에서도 위치 변화에 따라 산란의 영향이 달라진다는 것을 시뮬레이션을 통해 확인하였다. 이러한 분포 변화는 시뮬레이션과 측정 실험 모두에서 동일한 경향을 나타내었으므로 시뮬레이션이 타당함을 확인할 수 있었다. 시뮬레이션을 이용하면 X축, Y축 위치 변화만 아닌 다양한 경우에 대해서도 위치 변화에 따른 산란 영향의 예상이 가능할 것이며 나아가 산란 보정 연구의 기초 자료로 사용될 것이라 생각한다.

• Nuclear Engineering and Technology
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• 제54권8호
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• pp.3006-3016
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• 2022

In this study, the images of specific prompt gamma (PG)-rays of 719 keV emitted from proton-boron reactions were analyzed using single-photon emission computed tomography (SPECT). Quantitative evaluation of the images verified the detection of anatomical changes in tumors, one of the important factors in daily adaptive proton therapy (DAPT) and verified the possibility of application of the PG-ray images to DAPT. Six scenarios were considered based on various sizes and locations compared to the reference virtual tumor to observe the anatomical alterations in the virtual tumor. Subsequently, PG-rays SPECT images were acquired using the modified ordered subset expectation-maximization algorithm, and these were evaluated using quantitative analysis methods. The results confirmed that the pixel range and location of the highest value of the normalized pixel in the PG-rays SPECT image profile changed according to the size and location of the virtual tumor. Moreover, the alterations in the virtual tumor size and location in the PG-rays SPECT images were similar to the true size and location alterations set in the phantom. Based on the above results, the tumor anatomical alterations in DAPT could be adequately detected and verified through SPECT imaging using the 719 keV PG-rays acquired during treatment.