• Nuclear Engineering and Technology
• /
• 제56권10호
• /
• pp.3993-4006
• /
• 2024

Compton imaging excels at visualizing gamma rays in the range of several hundred kiloelectronvolts to several megaelectronvolts. However, this technique has limitations in the imaging of low-energy gamma rays. In contrast, collimatorless imaging technique determines the location of a source by analyzing the distribution of interactions. Because the collimatorless imaging technique excels at imaging low-energy gamma rays that are easily shielded by detector components, it can compensate for the shortcomings of the Compton imaging technique. In this study, we propose a dual-mode imaging technique that selects the imaging method depending on the target gamma-ray energy and fuses them during reconstruction. The collimatorless imaging method demonstrated high angular resolution at low energy levels, whereas the Compton image surpasses it starting from 200 keV within its reconstructible range. The angular resolution of the dual-mode image was between those of the two methods. The trend of the positional error of gamma ray energy was similar to that of the angular resolution, and the dual-mode method exhibited the lowest average error of 0.7°. The dual imaging method exhibited higher efficiency, figure of merit, and signal-to-noise ratio by utilizing events from both imaging modalities. In addition, we investigated the geometrical effects of various structures.

• Nuclear Engineering and Technology
• /
• 제53권4호
• /
• pp.1277-1283
• /
• 2021

It is important for operators of poly-pipelines in petroleum industry to continuously monitor characteristics of transferred fluid such as its type and amount. To achieve this aim, in this study a dual energy gamma attenuation technique in combination with artificial neural network (ANN) is proposed to simultaneously determine type and amount of four different petroleum by-products. The detection system is composed of a dual energy gamma source, including americium-241 and barium-133 radioisotopes, and one 2.54 cm × 2.54 cm sodium iodide detector for recording the transmitted photons. Two signals recorded in transmission detector, namely the counts under photo peak of Americium-241 with energy of 59.5 keV and the counts under photo peak of Barium-133 with energy of 356 keV, were applied to the ANN as the two inputs and volume percentages of petroleum by-products were assigned as the outputs.

• 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 Radiation Protection and Research
• /
• 제44권2호
• /
• pp.53-63
• /
• 2019

Background: As neutron fields are always accompanied by gamma rays, it is essential to distinguish neutrons from gamma rays in the detection of neutrons. Neutrons and gamma rays can be separated by pulse shape discrimination (PSD) methods. Recently, we performed characterization of a stilbene scintillator detector and an EJ-301 liquid scintillator detector with a high-speed digitizer DT5730 and investigated optimized PSD variables for both detectors. This study is for providing a basis for developing fast neutron/gamma-ray dual-particle imager. Materials and Methods: We conducted PSD experiments using stilbene scintillator and EJ-301 liquid scintillator and evaluated neutron and gamma ray discriminability of each PSD method with a $^{137}Cs$ gamma source and a $^{252}Cf$ neutron source. We implemented digital signal processing techniques to apply two PSD methods - the charge comparison (CC) method and the constant time discrimination (CTD) method - to distinguish neutrons from gamma rays. We tried to find optimized PSD variables giving the best discriminability in a given experimental condition. Results and Discussion: For the stilbene scintillator detector, the charge comparison method and the constant time discrimination method both delivered the PSD FOM values of 1.7. For the EJ-301 liquid scintillator detector, both PSD methods delivered the PSD FOM values of 1.79. With the same PSD variables, PSD performance was excellent in $300{\pm}100keVee$, $500{\pm}100keVee$, and $700{\pm}100keVee$ energy regions. This result shows that we can achieve an effective discrimination of neutrons from gamma rays using these scintillator detector systems. Conclusion: We applied both PSD methods to a stilbene and a liquid scintillator and optimized the PSD performance represented by FOM values. We observed a good separation performance of both scintillators combined with a high-speed digitizer and digital PSD. These results will provide reference values for the dual-particle imager we are developing, which can image both fast neutrons and gamma rays simultaneously.

• Nuclear Engineering and Technology
• /
• 제55권5호
• /
• pp.1587-1592
• /
• 2023

Time-encoded imagers (TEI) are important class of instruments to search for potential radioactive sources to prevent illicit transportation and trafficking of nuclear materials and other radioactive sources. The energy of the radiation cannot be known in advance due to the type and shielding of source is unknown in practice. However, the response function of the time-encoded imagers is related to the energy of neutrons or gamma-rays. An improved image reconstruction method based on MLEM was proposed to correct for the energy induced response difference. In this method, the count vector versus time was first smoothed. Then, the preset response function was adaptively corrected according to the measured counts. Finally, the smoothed count vector and corrected response were used in MLEM to reconstruct the source distribution. A one-dimensional dual-particle time-encode imager was developed and used to verify the improved method through imaging an Am-Be neutron source. The improvement of this method was demonstrated by the image reconstruction results. For gamma-ray and neutron images, the angular resolution improved by 17.2% and 7.0%; the contrast-to-noise ratio improved by 58.7% and 14.9%; the signal-to-noise ratio improved by 36.3% and 11.7%, respectively.

• 한국의학물리학회지:의학물리
• /
• 제20권4호
• /
• pp.216-224
• /
• 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
• /
• 제53권11호
• /
• pp.3784-3789
• /
• 2021

We report a simple technique for direct neutron spectroscopy using pure LaCl₃ crystals. Pure LaCl₃ crystals exhibit considerably better pulse shape discrimination (PSD) capabilities with relatively good energy resolution as compared with Ce-doped LaCl₃ crystals. Single crystals of pure and Ce-doped LaCl₃ were grown using an inhouse-developed Bridgman furnace. PSD capabilities of these crystals were investigated using ²⁴¹Am and ¹³⁷Cs sources. Fast neutron detection was tested using a²⁵²Cf source and three separate bands corresponding to electron, proton, and alpha were observed. The proton band induced by the ³⁵Cl(n,p)³⁵S reaction can be used for direct neutron spectroscopy because proton energy is proportional to incident neutron energy. Owing to good scintillation performance and excellent PSD capabilities, pure LaCl₃ is a promising candidate for space detectors and other applications that necessitate gamma/fast neutron discrimination capability.

• Nuclear Engineering and Technology
• /
• 제56권11호
• /
• pp.4826-4836
• /
• 2024

The formation of scales in pipes is one element that has a major impact on the efficiency of machinery used in the oil and gas sector. With the help of artificial intelligence, this new, non-invasive device was able to figure out the volume fraction of a two-phase flow by taking into account the thickness of the scale in the tested pipeline. The proposed design uses an isotope pair of barium-133 and cesium-137 as a dual-energy gamma generator. One detector records photons that are transmitted, and another detector records photons that are scattered. The signals from the detectors were simulated using the Monte Carlo N-Particle (MCNP) code, and then ten frequency and wavelet characteristics were extracted. To choose the best inputs from the collected features for computing the volume fraction, an ant colony optimization (ACO)-based method is applied. Six attributes, representing the optimal combination, were developed using this method. In order to forecast the volume percentage of two-phase flows independently of flow regime and scale thickness, we fed the characteristics introduced by ACO into a group method of data handling (GMDH) neural network. Volume fraction calculations had a maximum RMSE of 0.056, which is quite little compared to previous research. By using the ACO to choose the best characteristics, the current work has significantly increased its accuracy in identifying volume fractions.

• Journal of Radiation Protection and Research
• /
• 제37권4호
• /
• pp.191-196
• /
• 2012

한양대학교에서는 핵물질 탐지를 위해 고에너지 감마선원 영상화에 적합한 이중산란형 컴프턴 카메라의 원형을 개발하였다. 이중산란형 컴프턴 카메라는 높은 영상해상도를 제공하지만, 기존의 단일산란형 컴프턴 카메라보다 상대적으로 영상감도가 낮다는 한계가 있다. 이에 본 연구에서는 개발된 이중산란형 컴프턴 카메라에 단일산란형 컴프턴 카메라의 기능을 추가함으로써 하나의 시스템에서 두 가지 모드로 작동하는 이중모드 컴프턴 카메라(고민감도(단일산란형)모드와 고해상도(이중산란형)모드)에 대한 개념설계와 이에 대한 최적화 설계를 수행하였다. 최적화된 시스템에서 고민감도 모드는 고해상도 모드에 비해 전 에너지 영역에서 약 100배 정도 높은 고유영상감도를 제공하는 것으로 평가되었으며, 고해상도 모드에서 영상해상도는 기존의 이중산란형 컴프턴 카메라와 거의 같은 결과를 보여 고해상도 영상을 제공하는 것으로 나타났다.