• Nuclear Engineering and Technology
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• 제53권1호
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• pp.266-272
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• 2021

In the pulsed electron beam generators, such as plasma focus devices and linear induction accelerators whose electron pulse width is in the range of nanosecond and less, as well as in cases where there is no direct access to electron beam, like runaway electrons in Tokamaks, measurement of the electron energy spectrum is a technical challenge. In such cases, the indirect measurement of the electron spectrum by using the bremsstrahlung radiation spectrum associated with it, is an appropriate solution. The problem with this method is that the matrix equation between the two spectrums is an ill-conditioned equation, which results in errors of the measured X-ray spectrum to be propagated with a large coefficient in the estimated electron spectrum. In this study, a method based on the neural network and the MCNP code is presented and evaluated to recover the electron spectrum from the X-ray generated by collision of the electron beam with a target. Multilayer perceptron network showed good accuracy in electron spectrum recovery, so that for the X-ray spectrum with errors of 3% and 10%, the network estimated the electron spectrum with an average standard error of 8% and 11%, on all of the energy intervals.

• Korean Journal of Radiology
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• 제1권4호
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• pp.198-207
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• 2000

Uterine cervical carcinoma is one of the most common malignant tumors occurring in females. After primary treatment, patients are usually followed up with CT or MRI and the findings of these modalities may be the first sign of recurrent disease. Because earlier additional treatment by chemotherapy or radiation therapy may improve the prognosis, the early detection of recurrent cervical carcinoma is clinically important. In this article, we review the CT and MR imaging findings of recurrent uterine cervical carcinoma, and assign them to one of four groups: a) recurrence at the primary site, involving the intrapelvic organs, b) extension to the pelvic side-wall, c) metastases to pelvic and extrapelvic lymph nodes, or d) metastases to distant organs. A further contribution of CT and MR imaging is the detection of hydronephrosis due to ureteral obstruction. The cases in each group are illustrated and discussed, and since an awareness of the spectrum of imaging findings of recurrent cervical carcinoma is likely to lead to its early detection, radiologists should be familiar with the information presented.

• Journal of Radiation Protection and Research
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• 제42권3호
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• pp.158-165
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• 2017

Background: Nuclear facilities in South Korea have generally adopted pressurized ion chambers to measure ambient gamma ray exposure rates for monitoring the impact of radiation on the surrounding environment. The rates assessed with pressurized ion chambers do not distinguish between natural and man-made radiation, so a further step is needed to identify the cause of abnormal variation. In contrast, using NaI(Tl) scintillation detectors to detect gamma energy rates can allow an immediate assessment of the cause of variation through an analysis of the energy spectra. Against this backdrop, this study was conducted to propose a more effective way to monitor ambient gamma exposure rates. Materials and Methods: The following methods were used to analyze gamma energy spectra measured from January to November 2016 with NaI detectors installed at the Korea Atomic Energy Research Institute (KAERI) dormitory and Hanbat University. 1) Correlations of the variation of rates measured at the two locations were determined. 2) The dates, intervals, duration, and weather conditions were identified when rates increased by $5nSv{\cdot}h^{-1}$ or more. 3) Differences in the NaI spectra on normal days and days where rates spiked by $5nSv{\cdot}h^{-1}$ or more were studied. 4) An algorithm was derived for automatically calculating the net variation of the rates. Results and Discussion: The rates measured at KAERI and Hanbat University, located 12 kilometers apart, did not show a strong correlation (coefficient of determination = 0.577). Time gaps between spikes in the rates and rainfall were factors that affected the correlation. The weather conditions on days where rates went up by $5nSv{\cdot}h^{-1}$ or more featured rainfall, snowfall, or overcast, as well as an increase in peaks of the gamma rays emitted from the radon decay products of $^{214}Pb$ and $^{214}Bi$ in the spectrum. This study assumed that $^{214}Pb$ and $^{214}Bi$ exist at a radioactive equilibrium, since both have relatively short half-lives of under 30 minutes. Provided that this assumption is true and that the gamma peaks of the 352 keV and 1,764 keV gamma rays emitted from the radionuclides have proportional count rates, no man-made radiation should be present between the two energy levels. This study proved that this assumption was true by demonstrating a linear correlation between the count rates of these two gamma peaks. In conclusion, if the count rates of these two peaks detected in the gamma energy spectrum at a certain time maintain the ratio measured at a normal time, such variation can be confirmed to be caused by natural radiation. Conclusion: This study confirmed that both $^{214}Pb$ and $^{214}Bi$ have relatively short half-lives of under 30 minutes, thereby existing in a radioactive equilibrium in the atmosphere. If the gamma peaks of the 352 keV and 1,764 keV gamma rays emitted from these radionuclides have proportional count rates, no man-made radiation should exist between the two energy levels.

• Journal of Radiation Protection and Research
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• 제26권3호
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• pp.249-253
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• 2001

Neutron dose assessment in criticality accidents using Whole Body Counter (WBC) was proved to be an effective method as rapid neutron dose estimation at the JCO criticality accident in Tokai-mura. The 1.36MeV gamma-ray of $^{24}Na$ in a body can be detected easily by a germanium detector. The Minimum Detectable Activity (MDA) of $^{24}Na$ is approximately 50Bq for 10miniute measurement by the germanium-type whole body counter at JNC Tokai Works. Neutron energy spectra at the typical shielding conditions in criticality accidents were calculated and the conversion factor, whole body activity-to-organ mass weighted neutron absorbed dose, corresponding to each condition were determined. The conversion factor for uncollied fission spectrum is 7.7 $[(Bq^{24}Na/g^{23}Na)/mGy]$.

• 한국의학물리학회지:의학물리
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• 제27권1호
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• pp.8-13
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• 2016

이중 에너지 콘빔 CT는 원자번호가 다른 두 물질을 구분해낼 수 있다는 장점을 가진다. 이중 에너지 콘빔 CT를 구현하는 여러 가지 방법 중, 에너지 변조 필터(modulation layer)에 기반한 이중 에너지 콘빔 CT의 원리는 x-선 발생창의 절반을 구리와 같은 에너지 변조 필터로 차단하면, 차단되지 않은 곳에서는 원래의 관전압에 해당하는 x-선 스펙트럼이 발생하고 에너지 변조 필터로 가려진 부분에서는 저에너지 x-선이 감소된 x-선 스펙트럼이 발생하여 한 번의 스캔에서 두 가지 스펙트럼을 획득할 수 있다는 것이다. 우리는 에너지 변조 필터를 이용한 이중 에너지 콘빔 CT 구현의 가능성을 평가하기 위하여 다양한 두께의 에너지 변조 필터에 의해 생성되는 x-선 스펙트럼을 몬테칼로 전산모사를 이용하여 획득하였다. 전산모사 결과를 검증하기 위하여 동일한 콘빔 CT 시스템에서 CdTe 검출기를 이용하여 50~100 kVp에 대하여 스펙트럼을 측정하였고, 80 kVp 관전압에 대하여 실험과 전산모사로 획득한 스펙트럼의 평균 에너지가 유사함을 확인하였다. 또한 에너지 변조 필터의 두께를 2.0 mm로 하였을 때 스펙트럼의 평균 에너지는 80과 120 kVp에 대하여 각각 1.67, 1.52배까지 증가함을 확인하였다. 따라서 에너지 변조 필터를 사용하면 하나의 x-선 발생장치를 이용하여 가상의 이중 에너지 선원을 구현할 수 있음을 확인하였다.

• Nuclear Engineering and Technology
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• 제36권3호
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• pp.229-236
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• 2004

Radiation hardening is a multiscale phenomenon involving various processes over a wide range of time and length. We present a multiscale model for estimating the amount of radiation hardening in pressure vessel steel in the environment of a light water reactor. The model comprises two main parts: molecular dynamics (MD) simulation and a point defect cluster (PDC) model. The MD simulation was used to investigate the primary damage caused by displacement cascades. The PDC model mathematically formulates interactions between point defects and their clusters, which explains the evolution of microstructures. We then used a dislocation barrier model to calculate the hardening due to the PDCs. The key input for this multiscale model is a neutron spectrum at the inner surface of reactor pressure vessel steel of the Younggwang Nuclear Power Plant No.5. A combined calculation from the MD simulation and the PDC model provides a convenient tool for estimating the amount of radiation hardening.

• Nuclear Engineering and Technology
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• 제42권3호
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• pp.313-318
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• 2010

Alnine pellets were installed in a nuclear power plant for one or two operation cycles and measured by electron spin resonance (ESR) spectrometers for dosimetry. Dose and "x/y ratio", i.e., satellite peak over main center peak ratio, were measured for the returned alanine dosimeters from the nuclear power plant and compared to the values of reference alanine dosimeters exposed only to gamma rays. The variation of the x/y ratio change depended on the population of radicals from each radiation component with different LET. The gamma dose in a mixed radiation field was estimated by an additive gamma ray irradiation experiment and the measured dose rate at specified locations in the containment building.

• Journal of Radiation Protection and Research
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• 제20권3호
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• pp.163-168
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• 1995

비전리 방사선의 인체에 대한 작용은 최근 우리 주위에서 많이 사용되는 microwave, radio wave, laser, ultrasoundwave, ultravioletradiation 등의 문제가 될 수 있으며 본고에서는 주로 Radio Frequency Electromagnetic (RFEM) spectrum의 shortwave와 microwave의 생물학적인 작용을 정리 발표하고자 한다. RFEM에 의한 carcinogenesis에 관해서는 아직 RFEM이 인체에서는 발암물질로서 작용한다는 보고는 없으나, cancer promotion에는 작용할 것이라는 보고는 있다. chromosomal effect에 관해서는 체외실험에서 microwave에 의한 chromosome의 stickiness의 증가와 mitotic index의 변화에 관한 보고가 있다. 인체에서는 RFEM에 많이 피폭되었다고 알려진 Moscow의 미 대사관 직원 5000명을 대상으로 한 역학조사에서는 특별한 염색채 이상은 발견되지 않았다. 동구에서의 보고에 의하면 RFEM에 의한 선천성 기형아의 출산이 보고된바 있으나 출산시의 통증을 줄이기 위한 2450 MHz의 microwave를 조사한 산모 2000명 출산아에서 기형은 없었다고 한다. 인간의 행동과 정서적인 측면에서 RFEM에 의한 변화는 1974년 Sadcikoda에 의해 기술된바 있는 µwave sickness&는 irritability, 두통, 전신쇄약, 불면증, 성욕 감퇴 및 발기부전 등을 호소하는 증후군으로 주로 동유럽의 저자들에 의하여 보고되고 있으며 구 소련에서는 microwave sickness 또는 radio wave sickness는 확실한 하나의 임상병명으로 간주되고 있다. cataractogenesis에 관해서는 실험 동물에서 잘 연구되고 있으며, 사람에서도 1952년 레이다 작업종사자 에서 보고된 이후 50여례 이상의 보고가 있으나 백내장 자체가 그 발생 빈도가 높은 질환이고 많은 원인이 있으므로 아직 인간에서의 확실한 cataractogenesis에 관해서는 더욱 연구가 필요한 분야이다. radar wave에 노출된 적이 있는 군인을 대상으로 한 미 해군의 역학조사에 의하여 radar wave에 의한 uveitis, retinitis와 비진행성 백내장등이 보고되고 있으나 딴 연구에서는 입증된바 없다.

• 한국방사선학회논문지
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• 제11권4호
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• pp.189-195
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• 2017

방사선 특히, 엑스선 또는 감마선으로부터 인체를 보호하기 위해 납(Pb)으로 된 보호 장구를 광범위하게 사용해왔다. 최근 납 중독 및 환경오염의 문제로 납을 대신하는 무연 방사선 차폐재의 개발이 활발히 이루어지고 있다. 차폐재의 성능 확보를 위해서는 제작 및 평가의 순환 사이클을 반복하게 된다. 본 연구는 실제 무연 방사선 차폐소재의 제작에 앞서 차폐재의 성능을 몬테카를로 전산모사를 통해 확인함으로써 가능한 차폐소재의 조합을 연구하였다. 방사선 차폐소재의 평가에 사용되는 조건으로 엑스선관을 Geant4를 이용하여 전산모사하고 획득된 광자 스펙트럼을 이용하여 텅스텐과 비스무스의 조합에 따른 차폐소재의 성능을 평가하였다. 차폐소재의 공극에 따른 성능 저하도 평가하였다. 방사선 차폐 소재 개발 시 공극률을 줄이는 것이 중요한 인자라는 것을 알 수 있었다.

• 한국태양에너지학회 논문집
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• 제30권5호
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• pp.25-31
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• 2010

A Precision Spectral Pyranometer (PSP) is mainly used as a reference to calibrate other pyranometers due to its high accuracy and sensitivity in response to the spectrum wavelength range of 0.285 ${\mu}$ to 2.8 ${\mu}$, while the sensitivity of photovoltaic-type Li-Cor pyranometer is limited within a certain spectral range from 0.4 ${\mu}$ to 1.1 ${\mu}$. In this study, two Eppley PSPs($PSP_1$ and $PSP_2$) were first compared to the calibrated Eppley PSPs from National Renewable Energy Laboratory (NREL), resulting in two linear correction factors based on the comparison between the logger output (V) from the test PSP and the solar radiation (W/m2) from the NREL PSP. The Li-Cor pyranometer used in this study was then corrected based on the comparison of measured solar radiation ($W/m^2$) from the corrected $PSP_1$ and the Li-Cor pyranometer. In addition, instrument scale corrections were also performed for the PSPs and the Li-Cor from the transmitter to the data logger. From the comparisons, a linear correction factor (1.0214) with R=0.9998 was developed for the scale correction between$PSP_1$ and $PSP_2$, while the Li-Cor pyranometer has a scale(1.0597) and offset (32.046) with R=0.9998 against$PSP_1$. As a result, it was identified that there were good agreements within ${\pm}$ 10 W/ $m^2$ between Eppley $PSP_1$ vs. $PSP_2$ solar radiation and within ${\pm}$ 20 W/$m^2$ between$PSP_1$ vs Li-Cor solar radiation after the empirical scale corrections developed in this study.