• Journal of The Korean Astronomical Society
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• v.51 no.1
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• pp.5-16
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• 2018

We investigate the escape of $Ly{\beta}$ from emission nebulae with a significant population of excited hydrogen atoms in the level n = 2, rendering them optically thick in $H{\alpha}$. The transfer of $Ly{\beta}$ line photons in these optically thick regions is complicated by the presence of another scattering channel leading to re-emission of $H{\alpha}$, alternating their identities between $Ly{\beta}$ and $H{\alpha}$. In this work, we develop a Monte Carlo code to simulate the transfer of $Ly{\beta}$ line photons incorporating the scattering channel into $H{\alpha}$. Both $H{\alpha}$ and $Ly{\beta}$ lines are formed through diffusion in frequency space, where a line photon enters the wing regime after a fairly large number of resonance scatterings with hydrogen atoms. Various line profiles of $H{\alpha}$ and $Ly{\beta}$ emergent from our model nebulae are presented. It is argued that the electron temperature is a critical parameter which controls the flux ratio of emergent $Ly{\beta}$ and $H{\alpha}$. Specifically for $T\;=\;3{\times}10^4\;K$ and $H{\alpha}$ line center optical depth $\tau{\alpha}\;=\;10$, the number flux ratio of emergent $Ly{\beta}$ and $H{\alpha}$ is ~ 49 percent, which is quite significant. We propose that the leaking $Ly{\beta}$ can be an interesting source for the formation of $H{\alpha}$ wings observed in many symbiotic stars and active galactic nuclei. Similar broad $H{\alpha}$ wings are also expected in $Ly{\alpha}$ emitting halos found in the early universe, which can be potentially probed by the James Webb Telescope in the future.

• Progress in Medical Physics
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• v.16 no.2
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• pp.97-103
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• 2005

The energy spectra and dose calculations were performed for secondary neutrons from a 24 MV LINAC using MCNPX code (V2, 4, 0). The energy spectra for neutrons and photons emitted from the LINAC head, and absorbed dose to water were calculated in water phantom. The absorbed doses calculated with Monte Carlo were $0.66\~0.35$ mGy/photon Gy at the surface to d=5 cm, and calculated with interaction data was 0.52 mGy/photon Gy at the depth of electron equilibrium in water. We have shown that this work can be applied to dose estimation of neutrons from high energy LINAC through the comparison of our results with other results.

• Proceedings of the Korean Vacuum Society Conference
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• 1998.02a
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• pp.20-20
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• 1998

I Ion beam technology has recently attracted much interest because it has exciting t technological p아:ential for surface analysis, ion beam mixing, surface cleaning and etching i in thin film growth and semiconductor fabrication processes, etc. Es야~cially, ion beam s sputtering has been widely used for sputter depth profiling with x-photoelectron S spectroscopy (XPS) , Auger electron s$\pi$~troscopy(AES), and secondary-ion mass S야i따oscopy(SIMS). However, The problem of surface compositional ch없1ge due to ion b bombardment remains to be understo여 없ld solved. So far sputtering processes have been s studied by s따face an외ysis tools such as XPS, AES, and SIMS which use the sputtering p process again. It would be improbable to measure the modified surface composition profiles a accurately due to ion beam bombardment with surface analysis techniques based on sputter d depth profiling. However, recently Medium energy ion scattering spectroscopy(MEIS) has b been applied to study the sputtering of solid surface at ion bombardment and has been p proved that it has been extremely valuable in probing the surface composition 뻐d s structure nondestructively and quantita디vely with less than 1.0 nm depth resolution. To u understand the sputtering processes of solid surface at ion bombardment, The Molecular D Dynamics(MD) and Monte Carlo(MC) simulation has been used and give an intimate i insight into the sputtering processes of solid surfaces. In this presentation, the sputtering processes of alloys and compound samples at ion b bombardment will be reviewed and the MEIS results for the Ar+ sputter induced altered l layer of the TazOs thin film 뻐dd없nage profiling of Ar+ ion sputt얹"ed Si(100) surface will b be discussed with the results of MD and MC simulation.tion.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.12a
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• pp.96-100
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• 2006

A pulsed laser ablation deposition (PLAD) technique is an excellent method for the fabrication of amorphous carbon (a-C) films. This paper was focused on the understanding and analysis of the motion of carbon atom (C) and carbon ion ($C^+$) particles in laser ablation assisted by Ar plasmas. The simulation has carried out under the pressure P=10~100 mTorr of Ar plasmas. Two-dimensional hybrid model consisting of fluid and Monte-Carlo models was developed and three kinds of the ablated particles which are C, $C^+$ and electron were considered in the calculation of particle method. The motions of energetic $C^+$ and C deposited upon the substrate were investigated and compared.

• Nuclear Engineering and Technology
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• v.43 no.6
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• pp.567-572
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• 2011

A sensitivity analysis of the methods used to evaluate the transport properties of a CdZnTe detector was performed using two different radiations (${\alpha}$ particle and gamma-ray) emitted from an $^{241}Am$ source. The mobility-lifetime products of the electron-hole pair in a planar CZT detector ($5{\times}5{\times}2\;mm^3$) were determined by fitting the peak position as a function of biased voltage data to the Hecht equation. To verify the accuracy of these products derived from ${\alpha}$ particles and low-energy gamma-rays, an energy spectrum considering the transport property of the CZT detector was simulated through a combination of the deposited energy and the charge collection efficiency at a specific position. It was found that the shaping time of the amplifier module significantly affects the determination of the (${\mu}{\tau}$) products; the ${\alpha}$ particle method was stabilized with an increase in the shaping time and was less sensitive to this change compared to when the gamma-ray method was used. In the case of the simulated energy spectrum with transport properties evaluated by the ${\alpha}$ particle method, the peak position and tail were slightly different from the measured result, whereas the energy spectrum derived from the low-energy gamma-ray was in good agreement with the experimental results. From these results, it was confirmed that low-energy gamma-rays are more useful when seeking to obtain the transport properties of carriers than ${\alpha}$ particles because the methods that use gamma-rays are less influenced by the surface condition of the CZT detector. Furthermore, the analysis system employed in this study, which was configured by a combination of Monte Carlo simulation and the Hecht model, is expected to be highly applicable to the study of the characteristics of CZT detectors.

• Nuclear Engineering and Technology
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• v.53 no.1
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• pp.282-293
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• 2021

This paper examines gamma-ray shielding properties of SBC-Bx glass system with the chemical composition of 40SiO₂-10B₂O₃-xBaO-(45-x)CaO- yZnO- zMgO (where x = 0, 10, 20, 30, and 35 mol% and y = z = 6 mol%). Mass attenuation coefficient (µ/ρ) which is an essential parameter to study gamma-ray shielding properties was obtained in the photon energy range of 0.015-15 MeV using PHITS Monte Carlo code for the proposed glasses. The obtained results were compared with those calculated by WinXCOM program. Both the values of PHITS code and WinXCOM program were observed in very good agreement. The (µ/ρ values were then used to derive mean free path (MFP), electron density (N_eff), effective atomic number (Z_eff), and half value layer (HVL) for all the glasses involved. Additionally, G-P method was employed to estimate exposure buildup factor (EBF) for each glass in the energy range of 0.015-15 MeV up to penetration depths of 40 mfp. The results reveal that gamma-ray shielding effectiveness of the SBC-Bx glasses evolves with increasing BaO content in the glass sample. Such that SBC-B35 glass has superior shielding capacity against gamma-rays among the studied glasses. Gamma-ray shielding properties of SBC-B35 glass were compared with different conventional shielding materials, commercial glasses, and newly developed HMO glasse. Therefore, the investigated glasses have potential uses in gamma shielding applications.

• Journal of Powder Materials
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• v.30 no.5
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• pp.431-435
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• 2023

An irradiation hardening of Inconel 718 produced by selective laser melting (SLM) was studied based on the microstructural observation and mechanical behavior. Ion irradiation for emulating neutron irradiation has been proposed owing to advantages such as low radiation emission and short experimental periods. To prevent softening caused by the dissolution of γ' and γ" precipitates due to irradiation, only solution annealing (SA) was performed. SLM SA Inconel 718 specimen was ion irradiated to demonstrate the difference in microstructure and mechanical properties between the irradiated and non-irradiated specimens. After exposing specimens to Fe³⁺ ions irradiation up to 100 dpa (displacement per atom) at an ambient temperature, the hardness of irradiated specimens was measured by nano-indentation as a function of depth. The depth distribution profile of Fe³⁺ and dpa were calculated by the Monte Carlo SRIM (Stopping and Range of Ions in Matter)-2013 code under the assumption of the displacement threshold energy of 40 eV. A transmission electron microscope was utilized to observe the formation of irradiation defects such as dislocation loops. This study reveals that the Frank partial dislocation loops induce irradiation hardening of SLM SA Inconel 718 specimens.

• Journal of Radiation Protection and Research
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• v.48 no.3
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• pp.117-123
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• 2023

Background: We investigated the impact of 0.35 T magnetic field on dose calculation for non-small cell lung cancer (NSCLC) stereotactic ablative radiotherapy (SABR) in the ViewRay system (ViewRay Inc.), which features a simultaneous use of magnetic resonance imaging (MRI) to guide radiotherapy for an improved targeting of tumors. Materials and Methods: Here, we present a comprehensive analysis of the effects induced by the 0.35 T magnetic field on various characteristics of SABR plans including the plan qualities and dose calculation for the planning target volume, organs at risk, and outer/inner shells. Therefore, two SABR plans were set up, one with a 0.35 T magnetic field applied during radiotherapy and another in the absence of the field. The dosimetric parameters were calculated in both cases, and the plan quality indices were evaluated using a Monte Carlo algorithm based on a treatment planning system. Results and Discussion: Our findings showed no significant impact on dose calculation under the 0.35 T magnetic field for all analyzed parameters. Nonetheless, a significant enhancement in the dose was calculated on the skin surrounding the tumor when the 0.35 T magnetic field was applied during the radiotherapy. This was attributed to the electron return effect, which results from the deviation of the electrons ejected from tissues upon radiation due to Lorentz forces. These returned electrons re-enter the tissues, causing a local dose increase in the calculated dose. Conclusion: The present study highlights the impact of the 0.35 T magnetic field used for MRI in the ViewRay system for NSCLC SABR treatment, especially on the skin surrounding the tumors.

• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2740-2747
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• 2024

The sintering process acquired ferromagnetic copper ferrite ceramic material with a small concentration of Ni ion at 1100 ℃ for 1 h. Previously, copper ferrite with Ni proportions powder was acquired by the wet chemical process according to the relation CuFe_2-xNi_xO₄ where x takes values 0.0, 0.015, 0.03, 0.04, and 0.05. The role of Ni ion in the copper ferrite structure was investigated by X-ray analysis, Scanning electron microscope, EDX analysis, and density measurements. The gamma-ray shielding properties for the fabricated CuFeNiO ceramics samples were evaluated using the Monte Carlo simulation method. The obtained results show an enhancement in the linear attenuation coefficient for the fabricated ceramics with increasing the insertions of Ni ions within the fabricated samples, where increasing the Ni ions concentration between 0 and 1.19 wt% increases the linear attenuation by between 1.581 and 1.771 cm^-1 (at 0.103 MeV), 0.304-0.338 cm^-1 (at 0.662 MeV), and 0.160-0.178 cm^-1 (at 2.506 MeV), respectively. Simultaneously, the radiation protection efficiency for a 1 cm thickness of the fabricated samples increased between 14.8 and 16.3% with increasing the Ni ions between 0 and 1.19 wt%. Although the Ni doping concentration does not exceed 1.5 wt% of the total composition of the fabricated ceramics, the shielding capacity of the fabricated ceramics was enhanced by more than 11%, along the studied energy interval. Therefore, the fabricated samples can be used in gamma-ray shielding applications.

• Nuclear Engineering and Technology
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• v.56 no.6
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• pp.2195-2207
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• 2024

To enhance skeletal dosimetry in conjunction with the adult mesh-type reference Korean phantoms (MRKPs), Korean/Asian photon fluence-to-skeletal dose response functions (DRFs) were established utilizing an updated version of micro-CT-based detailed bone models from Tsinghua University. These bone models were incorporated into the MRKPs using the parallel geometry feature of Geant4. We calculated bone-site-specific electron absorbed fractions and used them to generate DRFs, following a similar methodology employed for ICRP-116 DRFs that have been used with the ICRP reference phantoms for skeletal dosimetry. To assess dosimetric implications of the Korean/Asian DRFs, we calculated RBM and BE doses for the MRKPs exposed to photon beams in the antero-posterior direction using the Korean/Asian and ICRP-116 DRFs. For energies ≥200 keV, the Korean/Asian DRFs-based skeletal doses exhibited excellent agreement with the ICRP-116 DRFs-based skeletal doses, attributed to the existence of charged particle equilibrium across the bone site. Conversely, significant differences of up to ~2.3 times were observed at lower energies, due to differences in the skeletal tissue distributions of bone models used to derive the Korean/Asian and ICRP-116 DRFs. The DRFs established in this study are expected to yield more accurate skeletal doses for Korean and Asian populations compared to the ICRP-116 DRFs.