• Progress in Medical Physics
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• v.25 no.3
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• pp.123-127
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• 2014

The Cs-137 irradiator is widely used to irradiate biological samples for radiobiological research. To obtain the accurate outcomes, correct measurements of the delivered absorbed dose to a sample is important. The IAEA protocols such as TRS-277 and TRS-398 were recommended for the Cs-137 reference dosimetry. However in TRS-398 protocol, currently known as the most practical dosimetry protocol, the quality factor ($k_{Q,Q_0}$) for Cs-137 gamma rays is not suggested. Therefore, the use of TRS-398 protocol is currently unavailable for the Cs-137 dosimetry directly. The calculation method previously introduced for high energy photon beams in radiotherapy was used for deriving the Cs-137 beam qualities ($k_{Q,Q_0}$) for the 15 commercially available farmer type ionization chambers in this study. In conclusion, $k_{Q,Q_0}$ values were ranged from 0.998 to 1.002 for Cs-137 gamma rays. These results can be used as the reference and dosimeter calibrations for Cs-137 gamma rays in the future radiobiological researches.

• Radiation Oncology Journal
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• v.10 no.2
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• pp.147-153
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• 1992

It is ideal thing to compensate tissue deficit without skin contamination in curvatured irradiation field of high energy photon beam. The 3-dimensional compensating technique utilizing tissue equivalent materials to ensure an adequate dose distribution and skin sparing effect was described. This compensator was made of paraffin ($70\%$) and stearin wax ($30\%$) compound. The parameters for evaluation of the effect on skin dose in application of compensator were considered in the size of the field, the thickness of the compensator and the source-to-axis distance. The results are as follows; the skin doses were not changed even though application of the compensator, but depended on the field size and the source-to-axis distance, and the skin doses were only slightly changed within $1\%$ relative errors as increasing the thickness of the compensator in these experiments.

• 한국신재생에너지학회:학술대회논문집
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• 2005.11a
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• pp.561-566
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• 2005

Polycrystalline silicon films were deposited using hot wire CVD (HWCVD). The deposition of silicon thin films was approached by the theory of charged clusters (TCC). The TCC states that thin films grow by self-assembly of charged clusters or nanoparticles that have nucleated in the gas phase during the normal thin film process. Negatively charged clusters of a few nanometer in size were captured on a transmission electron microscopy (TEM) grid and observed by TEM. The negatively charged clusters are believed to have been generated by ion-induced nucleation on negative ions, which are produced by negative surface ionization on a tungsten hot wire. The electric current on the substrate carried by the negatively charged clusters during deposition was measured to be approximately $-2{\mu}A/cm^2$. Silicon thin films were deposited at different $SiH_4$ and $H_2$ gas mixtures and filament temperatures. The crystalline volume fraction, grain size and the growth rate of the films were measured by Raman spectroscopy, X-ray diffraction and scanning electron microscopy. The deposit ion behavior of the si1icon thin films was related to properties of the charged clusters, which were in turn controlled by the process conditions. In order to verify the effect of the charged clusters on the growth behavior, three different electric biases of -200 V, 0 V and +25 V were applied to the substrate during the process, The deposition rate at an applied bias of +25 V was greater than that at 0 V and -200 V, which means that the si1icon film deposition was the result of the deposit ion of charged clusters generated in the gas phase. The working pressures had a large effect on the growth rate dependency on the bias appled to the substrate, which indicates that pressure affects the charging ratio of neutral to negatively charged clusters. These results suggest that polycrystalline silicon thin films with high crystalline volume fraction and large grain size can be produced by control1ing the behavior of the charged clusters generated in the gas phase of a normal HWCVD reactor.

• Resources Recycling
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• v.15 no.5 s.73
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• pp.17-25
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• 2006

Al-MCM-48 was used as a catalyst to decompose high density polyethylene(HDPE). Catalytic activity of Al-MCM-48 was compared with those of Al-MCM-41, Beta, and ZSM-5. Catalytic decomposition rate over Al-MCM-48 was much higher than at of non-catalytic pyrolysis only. Compared to other catalysts, Al-MCM-48 revealed the little higher activation energy value. The progressive deactivation behavior of the catalysts has also studied. ZSM-5 and Al-MCM-48 showed slower deactivation rates than Al-MCM-41 and Beta. Pyrolysis coupled with gas chromatographic separation and flame ionization detection (Py-GC/ FID) was also performed to assess the characteristics of pyrolysis products. ZSM-5 gave a higher fraction of gaseous products ($C_1-C_4$). Al-MCM-41 and Beta produced mainly $C_5-C_{12}$ products. The selectivity to oil product ($C_5-C_{22}$) obtained with Al- MCM-48 is higher an that with the other catalysts employed in this study.

• Applied Chemistry for Engineering
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• v.21 no.3
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• pp.311-316
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• 2010

This study aimed to prepare antimony-doped tin oxide (ATO) dispersion with high stability. The methods to achieve this goal were sought by investigating the changes of ATO particle size, size distribution, dispersion property as wet ball milling treatment time increased. And the changes of wet ball milled ATO dispersion property were also investigated, as pH increased. The changes of ATO particle size and size distribution, according to wet ball milling treatment time were evaluated with laser diffraction particle size analyzer and scanning electron microscope (SEM). The changes of ATO dispersion property, as wet ball milling treatment time and pH increased, were evaluated with zeta potential analysis and Turbiscan. By 60 min wet ball milling treatment time, ATO particle size decreased and size distribution became narrower, as the treatment time increased. After 60 min milling, the ATO particle size decreased to less than 30% of the initial size and the size distribution was narrowed to $0.1{\sim}5{\mu}m$ from $1{\sim}35{\mu}m$. However, more than 60 min milling, ATO particles aggregated and the particle size increased. ATO dispersion stability also increased as the treatment time and pH increased because the reduced particle size increased particle surface energy and repulsion between particles and the increased pH enhanced particle surface ionization. Hence, after proper length of wet ball milling treatment, highly stable ATO dispersion can be prepared, as increasing pH of the dispersion.

• Journal of the Korean Chemical Society
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• v.46 no.4
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• pp.363-377
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• 2002

The purpose of this study was to improve the problems of the voltaic cell described in the science textbooks of secondary schools. For this purpose, the contents of science textbooks which are related to the voltaic cell were analyzed and the problems which were not explained clearly by theorems were tried to be explained by experiments, and lastly sug-gestions were made toward the improvements regarding the voltaic cell in the science textbooks. The findings are that there are problems on the ways of ensuring whether the voltaic cell operates properly as a chemical battery, on the explanation of why the hydrogen bubbles form at the zinc electrode, on the cell potential, on the unification of the electrode terminology used, and on the mention of the current. Solutions to the problems except the cell potential were suggested. According to the experiment, the theoretical potential was calculated by considering the potentials of redox reactions at the two electrodes of the cell and by taking into account the characteristics of the electrodes such as the work function, ionization energy, stan-dard reduction potential, and electronegativity.The cell potential of the voltaic cell is explained by several factors. In the improved version of the textbook's introduction section to the voltaic cell, it is necessary to describe the voltaic cell his-torically.For the conceptual section, it should be explained in terms of the Daniel cell.

• Progress in Medical Physics
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• v.20 no.4
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• pp.290-297
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• 2009

In case of radiation treatment using small field high-energy photon beams, an accurate dosimetry is a challenging task because of dosimetrically unfavorable phenomena such as dramatic changes of the dose at the field boundaries, dis-equilibrium of the electrons, and non-uniformity between the detector and the phantom materials. In this study, the absorbed dose in the phantom was measured by using an ion chamber and a diode detector widely used in clinics. $GAFCHROMIC^{(R)}$ EBT films composed of water equivalent materials was also evaluated as a small field detector and compared with ionchamber and diode detectors. The output factors at 10 cm depth of a solid phantom located 100 cm from the 6 MV linear accelerator (Varian, 6 EX) source were measured for 6 field sizes ($5{\times}5\;cm^2$, $2{\times}2\;cm^2$, $1.5{\times}1.5\;cm^2$, $1{\times}1\;cm^2$, $0.7{\times}0.7\;cm^2$ and $0.5{\times}0.5\;cm^2$). As a result, from $5{\times}5\;cm^2$ to $1.5{\times}1.5\;cm^2$ field sizes, absorbed doses from three detectors were accurately identified within 1%. Wheres, the ion chamber underestimated dose compared to other detectors in the field sizes less than $1{\times}1\;cm^2$. In order to correct the observed underestimation, a convolution method was employed to eliminate the volume averaging effect of an ion chamber. Finally, in $1{\times}1\;cm^2$ field the absorbed dose with a diode detector was about 3% higher than that with the EBT film while the dose with the ion chamber after volume correction was 1% lower. For $0.5{\times}0.5\;cm^2$ field, the dose with the diode detector was 1% larger than that with the EBT film while dose with volume corrected ionization chamber was 7% lower. In conclusion, the possibility of $GAFCHROMIC^{(R)}$ EBT film as an small field dosimeter was tested and further investigation will be proceed using Monte Calro simulation.