• Nuclear Engineering and Technology
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• 제53권12호
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• pp.4072-4079
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• 2021

This article presents a study on the state-of-the-art methods for automated radioactive material detection and identification, using gamma-ray spectra and modern machine learning methods. The recent developments inspired this in deep learning algorithms, and the proposed method provided better performance than the current state-of-the-art models. Machine learning models such as: fully connected, recurrent, convolutional, and gradient boosted decision trees, are applied under a wide variety of testing conditions, and their advantage and disadvantage are discussed. Furthermore, a hybrid model is developed by combining the fully-connected and convolutional neural network, which shows the best performance among the different machine learning models. These improvements are represented by the model's test performance metric (i.e., F1 score) of 93.33% with an improvement of 2%-12% than the state-of-the-art model at various conditions. The experimental results show that fusion of classical neural networks and modern deep learning architecture is a suitable choice for interpreting gamma spectra data where real-time and remote detection is necessary.

• Nuclear Engineering and Technology
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• 제52권11호
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• pp.2572-2580
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• 2020

Emerging gamma ray detection applications that utilize neutron-based interrogation result in the prompt emission of high-energy (>2 MeV) gamma-rays. Rapid imaging is enabled by scintillators that possess high density, high atomic number, and excellent energy resolution. In this paper, we evaluate the bright (50,000 photons/MeV) oxide scintillator, cerium-doped Gd₂Al₂Ga₃O₁₂ (GAGG(Ce)). A silicon photomultiplier (SiPM) array is coupled to a GAGG(Ce) scintillator array (12 × 12 pixels) and integrated into a coded-aperture based gamma-ray imaging system. A resistor-based symmetric charge division circuit was used reduce the multiplicity of the analog outputs from 144 to 4. The developed system exhibits 9.1%, 8.3%, and 8.0% FWHM energy resolutions at 511 keV, 662 keV, and 1173.2 keV, respectively. In addition, a pixel-identification resolution of 602 ㎛ FWHM was obtained from the GAGG(Ce) scintillator array.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2016년도 춘계학술대회
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• pp.780-781
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• 2016

스테레오 감마선 공간 탐지장치는 감마선원을 탐지하고 그 결과를 바탕으로 2차원 영상분포를 측정한 후, 스테레오 카메라 기법을 적용하여 3차원 공간상에서 장치로부터 선원까지의 거리를 측정할 수 있도록 구현되었다. 본 논문에서는 영상처리 알고리즘을 통해 감마선 공간 탐지를 위한 스캔시간을 줄이고, 방사광 및 가시광 영상을 중첩한 후 스테레오 보정을 통해 3차원 가시화를 통한 감마선 분포 탐지 효율 개선을 위한 연구를 수행하였다. 탐지시험 결과 고속 탐지를 위한 알고리즘을 적용한다면 단일선원을 탐지할 때 약 30%이상의 탐지효율 개선하였으며, 3D 모니터를 통한 3차원 시각화 영상을 통해 공간상의 선원에 대한 분포를 확인하였다.

• Nuclear Engineering and Technology
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• 제54권5호
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• pp.1754-1759
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• 2022

The activity of gamma-ray emitting nuclides is calculated assuming that each gamma-ray is detected individually; thus, the magnitude of the coincidence summing signal must be considered during activity calculations. Here, the correction factor for the coincidence summing effect was calculated, and the detection efficiencies of two HPGe detectors were compared. The CANBERRA Inc. GC4018 high-purity Ge detector provided an estimate for the peak-to-total ratio using a point source to determine the coincidence summing correction factor. The ORTEC Inc. GEM60 high-purity Ge detector uses EFFTRAN in LVis to obtain the parameters of the detector and source model and the gamma-gamma and gamma-X match estimates, in order to determine the coincidence summing correction factor. Nuclide analyses, radioactivity comparisons, and analyses of reference material samples were performed utilizing certified reference materials to accurately determine the detection efficiencies. For both Co-60 and Y-88, the detection efficiency for a point source increased by an average of at least 12-13%, whereas the detection efficiency determined using LVis increased by an average of at least 13-15%. The calculated radioactivity values of the certified reference material and reference material samples were accurate to within 3% and 6% of the measured values, respectively.

• 천문학회지
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• 제38권2호
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• pp.125-128
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• 2005

In this paper, we argue that the gigahertz peaked spectrum (GPS) quasars are special blazars, blazars in dense and dusty gas enviornment. The ROSAT detection rate of GPS quasars is similar to that of flat spectrum radio quasars (FSRQs), suggesting that the relativistic jets in GPS quasars are oriented at small angle to the line of sight. Due to strong inverse Compton scattering off infrared photons from dense and dusty nuclear interstellar media in GPS quasars, most of them may have significant soft gamma-ray and X-ray emission, which is consistent with ASCA X-ray observations. Because Compton cooling in GPS quasars is stronger than that in FSRQs, synchrotron emission in GPS quasars may less dominate over thermal emission of the accretion disk and hot dust, hence most GPS quasars show low optical polarization and small variability, consistent with observations. We suggest that it is the significant radio emission of electron/positron pairs produced by the interaction of gamma-rays with the dense gas and dust grains in GPS quasars that makes GPS quasars show steep radio spectra, low radio polarization, and relatively faint VLBI/VLBA cores. Whether GPS quasars are special blazars can be tested by gamma-ray observations with GLAST in the near future, with the detection rate of GPS quasars being similar to that of FSRQs.

• Journal of Astronomy and Space Sciences
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• 제33권1호
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• pp.1-11
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• 2016

Over the last few years, the data obtained using the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope has provided new insights on high-energy processes in globular clusters, particularly those involving compact objects such as MilliSecond Pulsars (MSPs). Gamma-ray emission in the 100 MeV to 10 GeV range has been detected from more than a dozen globular clusters in our galaxy, including 47 Tucanae and Terzan 5. Based on a sample of known gammaray globular clusters, the empirical relations between gamma-ray luminosity and properties of globular clusters such as their stellar encounter rate, metallicity, and possible optical and infrared photon energy densities, have been derived. The measured gamma-ray spectra are generally described by a power law with a cut-off at a few gigaelectronvolts. Together with the detection of pulsed γ-rays from two MSPs in two different globular clusters, such spectral signature lends support to the hypothesis that γ-rays from globular clusters represent collective curvature emission from magnetospheres of MSPs in the clusters. Alternative models, involving Inverse-Compton (IC) emission of relativistic electrons that are accelerated close to MSPs or pulsar wind nebula shocks, have also been suggested. Observations at >100 GeV by using Fermi/LAT and atmospheric Cherenkov telescopes such as H.E.S.S.-II, MAGIC-II, VERITAS, and CTA will help to settle some questions unanswered by current data.

• Journal of Radiation Protection and Research
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• 제47권4호
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• pp.214-225
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• 2022

Background: The conventional cerium-doped Gd₂Al₂Ga₃O₁₂ (GAGG(Ce)) scintillator-based gamma-ray imager has a bulky detector, which can lead to incorrect positioning of the gammaray source if the shielding against background radiation is not appropriately designed. In addition, portability is important in complex environments such as inside nuclear power plants, yet existing gamma-ray imager based on a tungsten mask tends to be weighty and therefore difficult to handle. Motivated by the need to develop a system that is not sensitive to background radiation and is portable, we changed the material of the scintillator and the coded aperture. Materials and Methods: The existing GAGG(Ce) was replaced with Bi₄Ge₃O₁₂ (BGO), a scintillator with high gamma-ray detection efficiency but low energy resolution, and replaced the tungsten (W) used in the existing coded aperture with lead (Pb). Each BGO scintillator is pixelated with 144 elements (12 × 12), and each pixel has an area of 4 mm × 4 mm and the scintillator thickness ranges from 5 to 20 mm (5, 10, and 20 mm). A coded aperture consisting of Pb with a thickness of 20 mm was applied to the BGO scintillators of all thicknesses. Results and Discussion: Spectroscopic characterization, imaging performance, and image quality evaluation revealed the 10 mm-thick BGO scintillators enabled the portable gamma-ray imager to deliver optimal performance. Although its performance is slightly inferior to that of existing GAGG(Ce)-based gamma-ray imager, the results confirmed that the manufacturing cost and the system's overall weight can be reduced. Conclusion: Despite the spectral characteristics, imaging system performance, and image quality is slightly lower than that of GAGG(Ce), the results show that BGO scintillators are preferable for gamma-ray imaging systems in terms of cost and ease of deployment, and the proposed design is well worth applying to systems intended for use in areas that do not require high precision.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2008년도 High Temperature Superconductivity Vol.XVIII
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• pp.10-10
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• 2008

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2016년도 추계학술대회
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• pp.944-945
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• 2016

감마선 영상화 장치에서 감마선을 탐지하는 검출부는 선원을 바라보는 Collimator와 Collimator 이외의 방향에서 입사되는 감마선을 차폐하기 위한 차폐체로 구성되며 검출센서는 해당 차폐체 내부에 위치하게 된다. 감마선에 대한 분포는 Collimator의 입사구를 통해 들어오는 신호와 검출부가 바라보는 방향에 대한 정보를 통해 분포를 나타낼 수 있다. 때문에 입사구에서 들어오는 신호 외에는 잡음으로 처리해야 하므로 차폐체의 역할이 중요하다. 본 논문에서는 상용 감마선 탐지장치의 보다 축소된 납 기반의 콜리메이터 및 차폐체에 대하여 구조와 물성을 변경하여 소형, 경량화 된 Collimator 및 차폐체를 제작하였다. 또한 감마선 조사시험시설을 이용하여 감마선 입사구의 측정된 신호값을 기준으로 차폐 효율을 분석하였다. 분석결과 제작된 Collimator 및 차폐체가 영상화 장치구현를 구현하는데 보다 효율적임을 확인하였다.

• 한국방사선학회논문지
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• 제14권7호
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• pp.849-856
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• 2020

감마선 에너지 스펙트럼 연구에서 에너지 분석을 통한 핵종 분석은 매우 중요하다. 감마선 에너지 측정에 일반적으로 사용되는 고순도 Ge 검출기는 높은 에너지 분해능과 상대적으로 높은 검출 효율 때문에 일반적으로 사용된다. 그러나 반도체 검출기는 높은 에너지 분해능을 유지하기 위해 주변 환경에서 발생하는 노이즈를 효과적으로 차단하지 않으면 원래의 성능을 유지하기 어렵고 고가의 장치의 효과를 얻지 못하는 문제점이 있. 따라서 본 연구에서는 검출기에서 발생하는 전기적 노이즈를 제거하기 위해 접지 루프 아이솔레이터 (NEXT-001HDGL)를 사용했다. 에너지 분해능 향상 효과를 테스트하기 위해 양성자 가속기 KOMAC에 새로 설치된 HPGe 검출 장치를 사용했다. 감마선 에너지 2614 keV의 경우 에너지 분해능이 (0.16 ± 0.02) %에서 (0.11 ± 0.01) %로 개선되었고, 감마선 에너지 662 keV의 경우 에너지 분해능이 (0.72 ± 0.07) %에서 0.27 ± 0.03 %로 향상되었다. 이 결과는 KOMAC (Korea Multi-Purpose Accelerator Complex)의 HPGe 검출 장비를 이용한 감마선 스펙트럼 연구에 매우 유용한 것으로 판단된다.