• Journal of The Korean Astronomical Society
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• v.37 no.5
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• pp.583-587
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• 2004

With the aim to investigate the statistical properties and the connection between thermal and non-thermal properties of the ICM in galaxy clusters, we have developed a statistical magneto-turbulent model which describes, at the same time, the evolution of the thermal and non-thermal emission from galaxy clusters. In particular, starting from the cosmological evolution of clusters, we follow cluster. mergers, calculate the spectrum of the magnetosonic waves generated in the ICM during these mergers, the evolution of relativistic electrons and the resulting synchrotron and Inverse Compton spectra. We show that the broad band (radio and hard x-ray) non-thermal spectral properties of galaxy clusters can be well accounted for by our model for viable values of the parameters (here we adopt a EdS cosmology).

• Journal of Environmental Impact Assessment
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• v.12 no.4
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• pp.303-313
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• 2003

This study was carried out to survey the high ozone episode of summertime in Busan. The selected day was July 18, 1999 and August 24, 2001 which recorded exceed to 12ppb/hr at 3 station in Busan simultaneously. In case July 18, 1999, thick cloud and variable wind made weak ozone concentration during morning hour. And increase of ozone concentration by revolution of mixed layer for morning hour did not occur in this case study day. Photochemical reaction by strong radiation after 1100LST made sharp increase rate of ozone concentration(50ppb/hr). In case August 24, 2001, the meteorological condition of this day was not general wind with gradient force, very clear day with less cloud amount, high insolation and sunshine. Dongsamdong, Beomcheondong, Daeyeondong, and Sinpyeongdong had double peak which twice maximum concentration in the early afternoon and late afternoon. Ozone concentration of this day was in inverse proportion to Nitrogen oxide strongly. Ozone concentration exceed to 60ppb/hr occurred at 1400LST, continued to 2300LST.

• Progress in Medical Physics
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• v.4 no.2
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• pp.37-47
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• 1993

The quality of radiation for a high energy x-ray beam can be specified by its attenuation curve in a selected material. The inverse Laplace transform of the attenuation curve can be used as an approximate indication of the energy spectrum of the beam. We have made a comparative investigation of the estimated spectrum obtained by the Laplace transform analysis of the transmitted exposure data measured in an absorption study of a 6MV x-ray beam. Two of existing transform pair models have been investicated and discussed.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.222-224
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• 2002

In proton and heavy ion radiotherapy, compensators are required to modify the energy of heavy ion, to compensate the local difference of tumor depth. Conventional compensators have to be created, exchanged, and stored for each patient and for each irradiation directions. A Cylinder Type Liquid Variable Compensator is and is under development. Hexagonal cylinders will be arranged in honeycomb structure. In which air and fluid are divided by hexagonal pistons. The position of each piston will be changed in each cylinder for adjusting the thickness of fluid for variable compensator. The location of each hexagonal piston is determined by each controlling cylinder connected to the hexagonal cylinder by inlet pipes of fluid. Each controlling cylinder includes controlling a piston, which is moved mechanically. Each controlling cylinder is to be moved by a motor driven by a computer.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.83.2-83.2
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• 2010

During the formation of cosmic web, collisionless shock waves are produced around and inside the substructures. In these shock waves electrons and ions are accelerated to such high energies that they can produce gamma rays in several ways. Many authors have studied the contribution of shock-induced radiation to the cosmic gamma-ray background. However not all the important physical processes are included in their calculation. By considering more complete physical process, we re-investigate the problem. In our model, the energy distribution of the cosmic rays (CRs) are calculated by widely accepted diffusive shock acceleration model, both primary and secondary CR electrons are included, both inverse Compton scattering and bremsstrahlung process are considered. The difference of the results are discussed.

• Nuclear Engineering and Technology
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• v.39 no.6
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• pp.717-724
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• 2007

A measurement-based time-domain noise simulation of radiation detector-preamplifier (front-end) noise in nuclear spectroscopy is described. The time-domain noise simulation was performed by generating "noise random numbers" using Monte Carlo's inverse method. The probability of unpredictable noise was derived from the empirical cumulative distribution function via the sampled noise, which was measured from a preamplifier output. Results of the simulated noise were investigated as functions of time, frequency, and statistical domains. Noise behavior was evaluated using the signal wave-shaping function, and was compared with the actual noise. Similarities between the response characteristics of the simulated and the actual preamplifier output noises were found. The simulated noise and the computed nuclear pulse signal were also combined to generate a simulated preamplifier output signal. Such simulated output signals could be used in nuclear spectroscopy to determine energy resolution degradation from front-end noise effect.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.51.2-52
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• 2021

Pulsar Wind Nebula(PWN)는 radio부터 TeV band까지 넓은 파장에 걸쳐 복사를 하며 이 복사는 Spectral Energy Distribution(SED)으로 측정된다. 관측된 SED는 두 개의 주요한 bump를 보이는데 low-energy emission bump는 synchrotron radiation에 의해 만들어지고 high-energy emission bump는 inverse Compton scattering에 의해 만들어진다. 대부분 PWN들의 SED는 단일 전자 분포로 설명이 가능하지만 최근 연구 결과에 의하면 Crab nebula, G21.5-0.9 같은 일부 young pulsar wind nebula의 X-ray SED에서 단차나 기울기의 변화 등 단일 전자 분포로 설명하기 어려운 부분이 관측되기도 한다. 이런 PWN에 대하여 우리는 이중 전자 분포를 이용해서 broadband SED가 잘 설명이 되는지 확인하고 이를 통하여 PWN 입자 가속의 특성을 이해해보고자 한다.

• Nuclear Engineering and Technology
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• v.56 no.3
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• pp.916-921
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• 2024

The control rod worth sensitivity to the neutron detector position in the rod drop experiment is studied by the time-dependent Monte Carlo (TDMC) neutron transport calculations for AGN-201K educational reactor and the Kyoto University Critical Assembly. The TDMC simulations of the rod drop experiments are conducted by the Seoul National University Monte Carlo (MC) code, McCARD, yielding time-dependent neutron densities at detector positions. The detector-position-dependent results of the total control rod worth calculated by the extrapolation, the integral counting, and the inverse methods are compared with the numerical reference using the MC eigenvalue calculations and the experimental results. From these comparisons, it is observed that the total control rod worth can be estimated with a considerable difference depending on the detector position through the rod drop experiment. The proposed TDMC simulation of the rod drop experiment can be applied for searching a better detector position or quantifying a bias for the control rod worth measurement.

• Progress in Medical Physics
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• v.11 no.2
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• pp.91-99
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• 2000

This is a preliminary study for developing the method of the dose reconstruction in the patients, irradiated by mega-voltage photon beams from the linear accelerator, using the transit dose distributions. In this study we present the method of three-dimensional dose reconstruction and evaluate the method by computer simulation. To acquire the dose distributions in the patients (or phantoms) we first calculate the differences between the doses at the arbitrary points in the patients and the doses at the corresponding points where the transit doses are measured. Then, we can get the dose in the patients from the measured transit dose and the calculated value of the difference. The dose differences are calculated by applying the inverse square law and using the linear attenuation coefficient. The scatter to primary dose ratios, which are calculated by the Monte Carlo program using the CT data of the patient (or phantoms), are also used in the calculations. For the evaluation of this method we used various kinds of homogeneous and inhomogeneous phantoms and calculated the transit dose distributions with the Monte Carlo program. From the distributions we reconstructed the dose distributions in the phantom. We used mono-energy Photon beam of 1.5MeV and Monte Carlo program EGS4. The comparison between the dose distributions reconstructed using the method and the distributions calculated by the Monte Carlo program was done. They agreed within errors of -4%∼+2%. This method can be used to predict the dose distributions in the patient

• Journal of the Korean Society of Radiology
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• v.15 no.6
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• pp.789-794
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• 2021

Brachytherapy is a treatment in which radioactive isotopes are placed inside the body to intensively irradiate the tumor with radiation. Because brachytherapy uses a radioisotope source with a high dose rate, it is very important to know the exact location and dose of the source. However, in clinical practice, it is evaluated inaccurately with the naked eye through rulers and autoradiographs. Therefore, in this study, a dosimeter that can be used for brachytherapy was developed using a lead(II) iodide (PbI₂) material, and the applicability was evaluated by analyzing the reproducibility, linearity, and PID items. As a result of reproducibility evaluation, the RSD value was 1.41%, satisfying the evaluation criteria of 1.5%. As a result of the linearity evaluation, the R² value was 0.9993, which satisfies the evaluation criterion of 0.9990. As a result of PID evaluation, it showed only a difference of 0.06 cm compared with the theoretical value of the inverse square law of distance at the 50% dose reduction point. The dosimeter manufactured in this experiment shows results that satisfy the standard in all evaluations, so it is judged that the possibility of applying the dosimeter in the radiation brachytherapy area is sufficient.