• Journal of Radiation Protection and Research
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• 제25권2호
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• pp.67-73
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• 2000

자주달개비 식물체에 감마선과 중성자를 중복 조사하였을 패 나타나는 수술털(TSH) 분흥돌연변이율의 변화를 분석하였다. 감마선은 $0{\sim}2$ Gy의 범위에서 선량별 조사를 하였으며 중성자는 $^{252}Cf$ 선원으로부터 일정한 거리에 식물체를 배열하여 조사하였다. 감마선을 선량별로 조사한 후 중성자를 조사한 때의 TSH 분홍돌연변이 감마선량-반응의 증가계수는 6.17로 감마선량-반응식의 5.98에 비해 12%의 방사선효율 증가를 초래했으며 중성자를 먼저 조사한 다음 감마선을 조사한 경우는 증가계수가 7.48로서 25%의 방사선 생물효율 증대가 나타났다. 두 종류의 방사선 중복 조사시 조사방식의 선 후 조합에 따른 방사선생물효율 증대가능성은 멸균 또는 세포사멸 등 방사선을 긍정적으로 이용하는 분야에 있어 매우 중요한 의미가 있다.

• 한국군사과학기술학회지
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• 제20권1호
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• pp.72-80
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• 2017

Gamma-ray has some advantages as a weapon: it has the ability to transmutate matter, high penetrability through materials, and it is very harmful to living things. So it is worth to study the features of gamma-ray weapon in order to utilize it. Such abilities were simulated on the basis of Monte Carlo simulation program GEANT4. For the simulation conceptual design of gamma-ray weapon was conducted. High energy electrons, which were necessary for the high energy gamma-rays, were produced by linear electron accelerator, of which the parameters were derived from the Pohang Light Source(PLS-II). Gamma-rays were get by bremsstrahlung mechanism. The spectra of gamma-rays, that were measured at distances of 500 m, 1000 m, 1500 m and 2000 m, were gained by GEANT4.

• Nuclear Engineering and Technology
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• 제5권4호
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• pp.291-309
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• 1973

TRIGA Mark II와 III 원자로의 여러가지 가동조건에 있어서 노벽으로 부터의 누설 ${\gamma}$선에 의한 조사선양률을 3"$\times$3"원통형 NaI(T1) 섬광계수기와 400 channel파 고분석장치로 측정하였는데 측정된 spectrum으로부터 조사선양률을 산출하는데는 실제적면에서 복잡하기 짝이 없는 response matrix 방법대신 정도가 좋으면서도 비교적 그 과정이 단순한 Moriuchi의 specturm -조사선양률 환산 이론을 적용하였다. 연구결과에 따르면 노심에서 발생된 누설 ${\gamma}$선의 기본적인 spectrum 형태는 원자로의 열출력이나 차장벽에 의한 강도의 감쇠에 별로 영향을 받지 않고 있으며 원자로 누설${\gamma}$선에 의란 전조사선양률의 공기중에서의 감쇠는 폭 넓은 energy분포에도 불구하고 지수함수적 감쇠를 하고 있음이 판명되있다. 이 전조사선양률은 원자로의 열출력에 대체로 비례하고 있으나 TRIGA Mark III과 같은 가동형노심의 경우는 측정된 spectrum이 매우 다양한바, 그로부터 산출된 전조사선양률의 크기에는 관계없이, spectrum 분해방법을 적용하여 노심에서 발생된 누설 ${\gamma}$선과 원자로가동중 발생되는 여지 ${\gamma}$선의 기여를 판별 해석하는데 성공하였다.

• Nuclear Engineering and Technology
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• 제55권3호
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• pp.1031-1035
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• 2023

Neutron is an indirectly ionizing particle without charge, which is normally measured by detecting reaction products. Neutron detection system based on measuring gadolinium-converted gamma-rays is a good way to monitor the neutron because the representative prompt gamma-rays of gadolinium have low energies (79, 89, 182, and 199 keV). Low energy gamma-rays and their high attenuation coefficient on materials allow the simple design of a detector easier to manufacture. Thus, we designed a cadmium zinc telluride detector to investigate feasibility of simultaneous detection of gamma-rays and neutrons by using the Monte-Carlo simulation, which was divided into two parts; first was gamma-detection part and second was gamma- and neutron-simultaneous detection part. Consequently, we confirmed that simultaneous detection of gamma-rays and neutrons could be feasible and valid, although further research is needed for adoption on real detection.

• Journal of Radiation Protection and Research
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• 제43권4호
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• pp.137-142
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• 2018

Background: Gamma-ray detectors having a thin window of a material with low atomic number can increase the true coincidence summing effects for radionuclides emitting X-rays or gamma-rays. This effect can make efficiency calibration or spectrum analysis more complicated. In this study, a Cu shield was tested as an X-ray filter to neglect the true coincidence summing effect by X-rays and gamma-rays in gamma-ray spectrometry, in order to simplify gamma-ray energy spectrum analysis. Materials and Methods: A Cu shield was designed and applied to an n-type high-purity germanium detector having an $X-{\gamma}$ summing effect during efficiency calibration. This was tested using a commercial, certified mixed gamma-ray source. The feasibility of a Cu shield was evaluated by comparing efficiency calibration results with and without the shield. Results and Discussion: In this study, the thickness of a Cu shield needed to avoid true coincidence summing effects due to $X-{\gamma}$ was tested and determined to be 1 mm, considering the detection efficiency desired for higher energy. As a result, the accuracy of the detection efficiency calibration was improved by more than 13% by reducing $X-{\gamma}$ summing. Conclusion: The $X-{\gamma}$ summing effect should be considered, along with ${\gamma}-{\gamma}$ summing, when a detection efficiency calibration is implemented and appropriate shielding material can be useful for simplifying analysis of the gamma-ray energy spectra.

• Journal of Radiation Protection and Research
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• 제42권4호
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• pp.189-196
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• 2017

Background: The effects of radiation on tissues vary depending on the radiation type. In this study, a minipig model was used to compare the effects of ${\beta}$-rays from $^{166}Ho$ and ${\gamma}$-rays from $^{60}Co$ on the skin. Materials and Methods: In this study, the detrimental effects of ${\beta}$- and ${\gamma}$-irradiation on the skin were assessed in minipigs. The histopathological changes in the skin from 1 to 12 weeks after exposure to 50 Gy of either ${\beta}$- (using $^{166}Ho$ patches) or ${\gamma}$- (using $^{60}Co$) irradiation were assessed. Results and Discussion: The skin irradiated by ${\beta}$-rays was shown to exhibit more severe skin injury than that irradiated by ${\gamma}$-rays at 1-3 weeks post-exposure; however, while the skin lesions caused by ${\beta}$-rays recovered after 8 weeks, the ${\gamma}$-irradiated skin lesions were not repaired after this time. The observed histopathological changes corresponded with gross appearance scores. Seven days post-irradiation, apoptotic cells in the basal layer were detected more frequently in ${\beta}$-irradiated skin than in ${\gamma}$-irradiated skin. The basal cell density and skin thickness gradually decreased until 4 weeks after ${\gamma}$- and ${\beta}$- irradiation. In ${\beta}$-irradiated skin lesions, and the density and thickness increased sharply back to control levels by 6-9 weeks. However, this was not the case in ${\gamma}$-irradiated skin lesions. In ${\gamma}$-irradiated skin, cyclooxygenase-2 (COX-2) was shown to be expressed in the epidermis, endothelial cells of vessels, and fibroblasts, while ${\beta}$-irradiated lesions exhibited COX-2 expression that was mostly limited to the epidermis. Conclusion: In this study, ${\beta}$-rays were shown to induce more severe skin injury than ${\gamma}$-rays; however, the ${\beta}$-rays-induced injury was largely repaired over time, while the ${\gamma}$-rays-induced injury was not repaired and instead progressed to necrosis. These findings reveal the differential effects of ${\gamma}$- and ${\beta}$-irradiation on skin and demonstrate the use of minipigs as a beneficial experimental model for studying irradiation-induced skin damage.

• 천문학회지
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• 제29권spc1호
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• pp.57-58
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• 1996

There is an excess gamma flux from the general direction of the Galactic North Pole compared with that from the south when allowance is made for the contribution from CR interactions with the HI gas (Osborne et al., 1994). The extent to which it is in accord with the predictions of Wdowczyk and Wolfendale (1990 a,b) for gamma rays secondary to very high energy CR escaping from the VIRGO cluster is examined and it is claimed that the observations may well be of the order of those expected.

• Journal of Radiation Protection and Research
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• 제44권2호
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• pp.53-63
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• 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.

• Journal of Astronomy and Space Sciences
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• 제29권1호
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• pp.51-55
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• 2012

A few high-mass X-ray binaries-consisting of an OB star plus compact companion-have been observed by Fermi and ground-based Cerenkov telescopes like High Energy Stereoscopic System (HESS) to be sources of very high energy (VHE; up to 30 TeV) ${\gamma}$-rays. This paper focuses on the prominent ${\gamma}$-ray source, LS 5039, which consists of a massive O6.5V star in a 3.9-day-period, mildly elliptical ($e{\approx}0.24$) orbit with its companion, assumed here to be an unmagnetized compact object (e.g., black hole). Using three dimensional smoothed particle hydrodynamics simulations of the Bondi-Hoyle accretion of the O-star wind onto the companion, we find that the orbital phase variation of the accretion follows very closely the simple Bondi-Hoyle-Lyttleton (BHL) rate for the local radius and wind speed. Moreover, a simple model, wherein intrinsic emission of ${\gamma}$-rays is assumed to track this accretion rate, reproduces quite well Fermi observations of the phase variation of ${\gamma}$-rays in the energy range 0.1-10 GeV. However for the VHE (0.1-30 TeV) radiation observed by the HESS Cerenkov telescope, it is important to account also for photon-photon interactions between the ${\gamma}$-rays and the stellar optical/UV radiation, which effectively attenuates much of the strong emission near periastron. When this is included, we find that this simple BHL accretion model also quite naturally fits the HESS light curve, thus making it a strong alternative to the pulsar-wind-shock models commonly invoked to explain such VHE ${\gamma}$-ray emission in massive-star binaries.

• 천문학회지
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• 제37권5호
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• pp.447-454
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• 2004

During the hierarchical formation of large scale structure in the universe, the progressive collapse and merging of dark matter should inevitably drive shocks into the gas, with nonthermal particle acceleration as a natural consequence. Two topics in this regard are discussed, emphasizing what important things nonthermal phenomena may tell us about the structure formation (SF) process itself. 1. Inverse Compton gamma-rays from large scale SF shocks and non-gravitational effects, and the implications for probing the warm-hot intergalactic medium. We utilize a semi-analytic approach based on Monte Carlo merger trees that treats both merger and accretion shocks self-consistently. 2. Production of $^6Li$ by cosmic rays from SF shocks in the early Galaxy, and the implications for probing Galaxy formation and uncertain physics on sub-Galactic scales. Our new observations of metal-poor halo stars with the Subaru High Dispersion Spectrograph are highlighted.