• Title, Summary, Keyword: Backscatter factor

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A New Approach for the Calculation of Neutron Dose Equivalent Conversion Coefficients for PMMA Slab Phantom (PMMA 평판형 팬텀에서의 중성자 선량당량 환산계수의 새로운 계산법)

  • Kim, Jong-Kyung;Kim, Jong-Oh
    • Journal of Radiation Protection and Research
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    • v.21 no.4
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    • pp.297-311
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    • 1996
  • ANSI decided PMMA slab phantom as a calibration phantom and introduced a conversion coefficient calculation method for it. For photon, the conversion coefficient can be obtained by using backscatter factor and conversion coefficient of the ICRU tissue cube and backscatter factor of the PMMA slab. For neutron, however, the ANSI has not introduced any conversion coefficient calculation method for the PMMA slab. In this work, the ANSI method for the photon conversion coefficient calculation was applied to the neutron conversion coefficient calculation of the PMMA slab. Quality weighted tissue kerma of neutron was applied to calculate the backscatter factors on the ICRU cube and the PMMA slab. The dose conversion coefficient of the ICRU cube was also calculated by using MCNP code. Then, the dose conversion coefficient of the PMMA slab was calculated from two backscatter factors and the dose conversion coefficient of the ICRU cube. The discrepancies of the dose conversion coefficients of the PMMA slab and the ICRU cube were less than 10% except 1eV(20%), 1keV(17%), and 4 MeV(16%).

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Retrieval of Lidar Overlap Factor using Raman Lidar System (라만 라이다 시스템을 이용한 라이다 중첩함수 산출)

  • Noh, Young-M.;Muller, Detlef;Shin, Dong-Ho;Lee, Kyung-Hwa
    • Journal of Korean Society for Atmospheric Environment
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    • v.25 no.5
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    • pp.450-458
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    • 2009
  • The range-dependent overlap factor of a lidar system can be determined experimentally if a Raman backscatter signal by molecule is measured in addition to the usually observed elastic backscatter signal, which consists of a molecular component and a particle component. The direct determination of the overlap profile is presented and applied to a lidar measurement according to variation of telescope field-of-view and distance between telescope and transmitting laser. The retrieval of extinction coefficient by Raman method can generate high errors for heights below planetary boundary layer if the overlap effect is ignored. The overlap correction method presented here has been successfully applied to experimental data obtained in Gwangju, Korea.

Investigation on backscatter According to Changed in Components of Linear Accelerator Using Monte Carlo Simulation (몬테카를로 시뮬레이션을 이용한 선형가속기 구성요소 변화에 따른 후방산란에 관한 연구)

  • Kim, Hwein;Chon, Kwonsu
    • Journal of the Korean Society of Radiology
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    • v.9 no.4
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    • pp.239-247
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    • 2015
  • It should be accurate dose calculation to increase the efficiency of radiation therapy, and it is priority to figure out the beam characteristics for this purpose. The target and primary collimator in head components of the linear accelerator have the greatest influence on determining the beam characteristics which is caused by backscatter and it is the factor to consider the shielding structures and equipment management. In this study, we made modeling of the linear accelerator through the Geant4 Monte Carlo simulation and investigated backscatter according to the change of the size and shape in head components. For the scattered electrons, it showed the greatest number of distributions inside of the inner radius at primary collimator. But, for the scattered photons which have the high energy, it was mostly located outside of the inner radius at primary collimator. Scattered positrons showed a small occurrence in about 0.03%. According to the change of the inner radius at primary collimator, it was great changes in the inside of inner radius for all three scattered particles. According to the change of the outer radius at primary collimator, it was shown some considerable effects from more than 60 mm outer radius. It was no significant effect according to the change of target thickness. In this study, we found that backscatter should be considered, and figured out that geometric size and shape of the peripheral components are the factors that influences the backscatter effect.

Topographic Normalization of Satellite Synthetic Aperture Radar(SAR) Imagery (인공위성 레이더(SAR) 영상자료에 있어서 지형효과 저감을 위한 방사보정)

  • 이규성
    • Korean Journal of Remote Sensing
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    • v.13 no.1
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    • pp.57-73
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    • 1997
  • This paper is related to the correction of radiometric distortions induced by topographic relief. RADARSAT SAR image data were obtained over the mountainous area near southern part of Seoul. Initially, the SAR data was geometrically corrected and registered to plane rectangular coordinates so that each pixel of the SAR image has known topographic parameters. The topographic parameters (slope and aspect) at each pixel position were calculated from the digital elevation model (DEM) data having a comparable spatial resolution with the SAR data. Local incidence angle between the incoming microwave and the surface normal to terrain slope was selected as a primary geometric factor to analyze and to correct the radiometric distortions. Using digital maps of forest stands, several fields of rather homogeneous forest stands were delineated over the SAR image. Once the effects of local incidence angle on the radar backscatter were defined, the radiometric correction was performed by an empirical fuction that was derived from the relationship between the geometric parameters and mean radar backscatter. The correction effects were examined by ground truth data.

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The Study of Tissue Dose Perturbation by Air Cavity with 6MV Photon Beam (6MV 광자선에서 공동에 의한 조직 선량변동에 관한 연구)

  • Shin, Byung-Chul;Yoo, Myung-Jin;Moon, Chang-Woo;Jeung, Tae-Sig;Yum, Ha-Yong
    • Radiation Oncology Journal
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    • v.13 no.4
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    • pp.397-402
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    • 1995
  • Purpose : To determine the perturbation effect in the tissue downstream from surface layers of lesions located in the air/tumor-tissue interface of larynx using 6MV photon beam. Materials and Methods : Thermoluminescent dosimeters(TLDs), were embedded at 3 measurement locations in slab no. 7 of a humanoid phantom and exposed to forward and backward direction using various field sizes($4{\times}4cm^2\;-\;15{\times}15cm^2$). Results : At the air/tissue interface, forward dose perturbation factor(FDPF) is about 1.085 with $4{\times}4cm^2,\;1.05\;with\;7{\times}7cm^2,\;1.048\;with\;10{\times}10cm^2$ and $1.041\;with\;15{\times}15cm^2$. Backscatter dose perturbation factor(BDPF) is about 0.99 with $4{\times}4cm^2$, 0.981 with $7{\times}7cm^2$, 0.956 with $10{\times}10cm^2$ and 0.97 with $15{\times}15cm^2$. Conclusion : FDPF is greater as field size is smaller. And FDPF is smaller as the distance is further from the air/tissue interface.

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Thermoelectric and Mechanical Properties of Bi0.4Sb1.6Te3 Prepared by Using Encapsulated Melting and Hot Extrusion

  • Jung, Woo-Jin;Kim, Il-Ho
    • Journal of the Korean Physical Society
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    • v.70 no.5
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    • pp.511-516
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    • 2017
  • $Bi_{0.4}Sb_{1.6}Te_3$ solid solutions were synthesized by using encapsulated melting (EM) and were consolidated by using hot extrusion (HE), and their thermoelectric and mechanical properties were examined and compared with those of specimens prepared by using hot pressing (HP). The relative densities of all hot-extruded specimens were higher than 97%. The basal plane (00l) was preferentially orientated parallel, rather than perpendicular, to the HE direction. The values of the orientation factor (F) were as follows: $F_{max}=0.082$ for specimens hot-extruded at 723 K and $F_{max}=0.115$ for specimens hot-pressed at 723 K. Thus, the crystallographic anisotropy was not high. From the pole figure and the electron backscatter diffraction analyses, the microstructures and the crystallinities of the HE specimens were found to be similar and comparable to those of the HP specimens. A bending strength of 57 MPa and a Vickers hardness of 74 Hv were obtained for $Bi_{0.4}Sb_{1.6}Te_3$ hot-extruded at 698 K, which were superior to the corresponding properties of the HP specimens. However, the mechanical properties degraded with increasing HE temperature owing to the occurrence of grain growth. All specimens exhibited a negative temperature dependence for the electrical conductivity, indicating a degenerate semiconductor behavior. All Seebeck coefficients showed positive signs (p-type conduction); they attained peak values at 373 K and then decreased with increasing temperature owing to intrinsic conduction. The HE specimens exhibited lower values of the power factor than the HP specimens did because of the lower electrical conductivity and Seebeck coefficient of the former. The thermal conductivity was lower than $1.0Wm^{-1}K^{-1}$ at room temperature, and it increased slightly with increasing temperature. The maximum figure of merit, $ZT_{max}=1.04$, and the average figure of merit, $ZT_{ave}=0.87$, were achieved at 323 K for $Bi_{0.4}Sb_{1.6}Te_3$ hot-extruded at 698 K.