• 대한방사선기술학회지:방사선기술과학
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• 제22권2호
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• pp.47-51
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• 1999

We calculated the energy distribution and the percentage depth-dose at 10 cm in a $10{\times}10\;cm^2$ with a photon beam at SSD of 100 cm by using a Monte Carlo Simulation. PDD is used as a beam-quality specifier for radiotherapy beams. It is better than the commonly used values of TPR or nominal accelerating potential. The presence of electron contamination affects the measurement of PDD, but can be removed by the use of a 0.1 cm lead filter. It reduces surface dose from contaminant electrons from the accelerator by more than 90% for radiotherapy beams. The filter performs best when it is placed immediately below the head. An electron-contamination correction factor is introduced to correct for electron contamination from the filter and air. It converts PDD which includes the electron contamination with the filter in place into PDD for the photons in the filtered beam. The correction factor can be used to determine stopping-power ratio. Calculations show that the values of water-to-air slopping power ratio in the unfiltered beam are related to PDD.

• Radiation Oncology Journal
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• 제6권1호
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• pp.109-116
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• 1988

The Alcyon Co-60 gamma rays was studied for electron contamination. The surface dose, attributable almost entirely to contamination electrons, has a linear dependence on field width for square fields and an inverse square dependence on distance from the bottom of the fixed head assembly Build-up and surface dose measurements were taken with and without an acrylic blocking tray in place. Further measurements were made with a copper filter designed to reduce secondary electrons emitted by photon interactions with the acrylic tray. The results are discussed in relation to skin sparing effect for radiation therapy Patients. And to achieve the maximum skin sparing effect, the selection of the optimum SSD and TSD is needed.

• Radiation Oncology Journal
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• 제7권2호
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• pp.293-297
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• 1989

Electron contamination due to the interaction between radiation beam and material was analyzed for the factors such as source-skin distance (SSD), field size, tray characteristics and position of filter, which can affect the surface dose in Cobalt teletherapy. Surface dose in open beam was more influenced by SSD with increasing field size. Relative surface charge (RSC) increased with the use of tray (solid, circular hole, slotted), compared with open beam, which is thought to be due to increased electron contamination of the tray. To reduce the surface dose, 0.4mm thick Lipowitz metal filter was used. Compared with open beam, RSC decreased by 8.8%, 11.3%, 13.3%, 16.6%, 19.3% and 21.7% for the field size of $5{\times}5$, $10{\times}10$, $15{\times}15$, $20{\times}20$, $25{\times}25$ and $30{\times}30cm^2$, respectively. On the contrary, use of Lipowitz metal filter increased RSC at 60cm or less SSD. Surface dose was effectively reduced with Lpowitz metal filter placed right below solid tray in Cobalt teletherapy.

• 전자공학회논문지A
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• 제30A권11호
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• pp.99-104
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• 1993

We analyzed the D.I. water used in wet cleaning process of semiconductor device manufacturing both at the D.I. water plant and at the wafer cleaning bath to detect the impurity source of D.I. water contamination. This shows that the quantity of impurity is related to the resistivity of D.I. water, and we found that the cleanliness of the wafer surface processed in D.I. water bath was affected by the degree of the ionic impurity contamination. So we evaluated the cleaning effect as different method for Fe ion, having the best adsoptivity on wafer surface. Moreover the temperature effect of the D.I. water is investigated in case of anion in order to remove the chemical residue after wet process. In addition to the control of D.I. water resistivity, chemical analysis of impurity control in D.I. water should be included and a suitable cleaning an drinsing method needs to be investigated for a high yielding semiconductor device.

• 한국물환경학회지
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• 제21권4호
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• pp.403-409
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• 2005

Methyl tert-butyl ether (MTBE) contamination in groundwater often coexists with benzene, toluene, ethylbenzene, and xylene (BTEX) near the source of the plume. Then, groundwater contamination problems have been developed in areas where the chemical is used. Common sources of water contamination by BTEX and MTBE include leaking underground gasoline storage tanks and leaks and spills from above ground fuel storage tanks, etc. In oil-contaminated environments, anaerobic biodegradation of BTEX and MTBE depended on the concentration and distribution of terminal electron acceptor. In this study, effect of electron acceptor on the anaerobic biodegradation for BTEX and MTBE-contaminated soil was investigated. This study showed the anaerobic biodegradation of BTEX and MTBE in two different soils by using nitrate reduction, ferric iron reduction and sulfate reduction. The soil samples from the two fields were enriched for 65 days by providing BTEX and MTBE as a sole carbon source and nitrate, sulfate or iron as a terminal electron acceptor. This study clearly shows that degradation rate of BTEX and MTBE with electron acceptors is higher than that without electron acceptors. Degradation rate of Ethylbenzene and Xylene is higher than that of Benxene, Toluene, and MTBE. In case of Benzene, Ethylbenzene, and MTBE, nitrate has more activation. In case of Toluene and Xylene, sulfate has more activation.

• Radiation Oncology Journal
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• 제15권2호
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• pp.159-165
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• 1997

목적 : 광자선과 블록을 얻는 트레이와의 상호작용에 의해 생성된 2차 전자는 피하층에 과도 한 선량증가의 원인이 된다. 이런 전자오염으로 인한 표면선량을 감소시키기 위해 트레이 아래 전자필터를 부착하는 것이 유용하다. 대상 및 방법 :두께가 다른 Cu판, Al판 그리고 Cu/Al 복합판을 사용하여 전자오염에 의한 표면선량을 감소시키는 효과를 측정하였다. 최적의 필터를 찾기 위해서 $10m\times10cm$ 조사야와 SSD 78.5cm의 기하학적 모형으로 표면에서부터 최대선량 지점까지 2mm 간격으로 흡수선량을 측정하였다. 최적필터의 조사야 의존성을 구하기 위해서 $4cm\times4cm$에서부터 $25cm\times25cm$까지 조사면적을 변화시켜가며 흡수선량을 측정하였다 결과 : 표면선량은 조사면적을 증가시키면 서서히 증가하였고 $15cm\times15cm$ 조사면적 이상에 서는 표면선량이 급속히 증가하였다. Al판을 사용했을 경우 표면선량이 최대선량 지점의 선량보다 낮게 유지되지 않으므로 Al판은 전자필터로는 부적합하였으며 0.5mm Cu판과 Cu/Al=0.28mm/1.5mm 복합판이 최적 전자필터로 결정되었다. 두가지 최적필터의 경우 $4cm\times4cm$ 조사면에서는 표면선량을 $5.5\%$(tray 사용할때 표면선량에서 filter 사용할때 표면선량을 뺀 것) 낮출 수 있었고 $10cm\times10cm$에서는 $11.3\%,\;25cm\times25cm$에서는 $21.3\%$로 낮출 수 있었다. 결론 : 전자오염에 기인한 표면선량은 조사면적에 의존하였고 트레이를 설치했을때 표면의 전자오염은 많았고 특히 조사면적이 클 때 표면의 전자오염은 더욱 증가하였다 표면 및 build-up영역의 선량 특성을 측정한 결과 0.5mm Cu판과 Cu/Al=0.28mm/1.5mm 복합판이 최적 필터로 결정되었다. 트레이 밑에 최적 필터를 부착하면 표면선량을 유효하게 감소시킬 수 있었고 필터의 효과는 조사면적이 클 때 더욱 좋았다.

• 천문학회보
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• 제38권2호
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• pp.95.1-95.1
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• 2013

The RBSPICE (Radiation Belt Storm Probes Ion Composition Experiment) is one of five instrument suites onboard the twin Van Allan Probes (or Radiation Belt Storm Probes; RBSP), launched August 30, 2012 by NASA. One of science targets of RBSPICE instrument is to determine "how changes in that ring current affect the creation, acceleration, and loss of radiation belt particles?". For that purpose, it measures ions and electrons simultaneously. Ion's energy range is from ~20 keV to ~1 MeV and electron's energy channel is from ~35 keV to 1 MeV in order to provide supplementary information about the radiation belts. In this paper, we investigate a reliability of the electron flux measured from the RBSPICE by comparing with ECT (The Energetic Particle, Composition and Thermal Plasma Suite) data. We found there is a critical proton contamination problem in the electron channels of ~ 1MeV of RBSPICE observations during one moderate storm event of Sym H ~ -76 nT on March 1, 2013.

• Journal of Periodontal and Implant Science
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• 제26권1호
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• pp.133-142
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• 1996

Ten intrabony defects in 10 patients were treated by flap surgery including root surface debridement and placement of an expanded polytetrafluoroethylene(ePTFE) membrane. The membranes were removed after 4-6 weeks. This study was performed to examine the retrived ePTFE membrane by scanning electron microscopy(SEM) for bacterial contamination and adherent connective tissue elements, and to compare it with clinical conditions. The cervical portion of the membrane, which in most cases had become partially exposed to the oral cavity, had a bacterial deposit. Small bacterial colonies and a scatter of single cells in some instances extended into the apical portion of the membrane. Fibroblast-like cells, erythrocytes and fibrous structures were seen in the apical portion of the membrane. Outer surface of membrane tends to more bacterial contamination than inner surface(p<0.01), and upper portions more than lower portions(P<0.01). Comparison of ultrastructural findings and clinical conditions revealed that extent of bacterial contamination of the membrane correlated with gingival inflammation and extent of membrane exposure, but it was not significant statistically. The results suggested that gingival inflammation and membrane exposure affect periodontal regeneration by the use of ePTFE membrane.

• Journal of Astronomy and Space Sciences
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• 제32권3호
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• pp.167-180
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• 2015

Herein, we discuss the in situ measurement of the electron temperature in the ionosphere/plasmasphere by means of DC Langmuir probes. Major instruments which have been reported are a conventional DC Langmuir probe, whose probe voltage is swept; a pulsed probe, which uses pulsed bias voltage; a rectification probe, which uses sinusoidal signal; and a resonance cone probe, which uses radio wave propagation. The content reviews past observations made with the instruments above. We also discuss technical factors that should be taken into account for reliable measurement, such as problems related to the contamination of electrodes and the satellite surface. Finally, we discuss research topics to be studied in the near future.

• Applied Microscopy
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• 제38권4호
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• pp.383-386
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• 2008

In performing in situ heating transmission electron microscopy (TEM) for materials characterizations, arising concerns such as specimen drifts and unintentional Cu contamination are discussed. In particular, we analysed the thermal and mechanical characteristics of in situ heating holders to estimate thermal drift phenomena. From the experimental results, we suggest an empirical model to describe the thermal drift behavior so that we can design an effective plan for in situ heating experiment. Practical approaches to minimize several hindrances arisen from the experiment are proposed. We believe that our experimental recommendations will be useful for a microscopist fascinated with the powerful potential of in situ heating TEM.