• Journal of Radiation Protection and Research
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• v.38 no.2
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• pp.78-90
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• 2013

Recently, the interest on exposure to radiation is rising. The radiation exposure of mammography is higher in absorbed dose than of X-ray, therefore unnecessary exposure needs to be reduced, and higher image quality is needed. Generally, ray quality of the radiation imaging is an important factor that determines image quality and the amount of ray exposure, and they are affected by tube voltage and added filter. The X-ray energy that is exposed from mammography device is generally a continuous spectrum, which includes low energy that has minute influence on the image quality, and high energy that hinders contrast on image. Currently, molybdenum (Mo) and rhodium (Rh) are the most used added filters for mammography device, and they are used differently according to the energy region of X-ray. This study aims to find out the degree of reduction in exposure dose according to the thickness of aluminum (Al), and to study the changes in image quality and dose when the added filter plates that are made with niobium (Nb) or zirconium (Zr) are used, other than molybdenum (Mo) and rhodium (Rh), the two most used added filters that have similar atomic number and K-absorption regions as Nb and Zr. In this study, single-added filters of molybdenum (Mo), niobium (Nb), and zirconium (Zr) are used, and in some cases, Aluminum (Al) is combined with the single filters. In this case, image quality is considered to be improved depending on the type of added filters, and by using Aluminum (Al) filter together with the others, unnecessary X-ray of low energy would be absorbed, therefore the dose is expected to decrease without any influence when the concentration level becomes identical.

• Progress in Medical Physics
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• v.9 no.4
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• pp.267-276
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• 1998

Any detector inserted into a phantom should have such a geometry that it caused as small as possible perturbation of the electron fluence. Plane parallel chambers meet this requirement better than other chambers of configurations. IAEA protocol recommends the use of plane parallel chambers for this reason. However, the cylindrical chambers are widely used for convenient. The purpose of this study is to evaluate the absorbed dose due to the differences of four different dosimetry protocols such as IAEA protocol using cylindrical chamber, TG 21 protocol using cylindrical chamber, Markus protocol using plane parallel chamber, and TG 39 report for the calibration of plane parallel chamber in electron beams. Depth-ionization measurements for the electron beams of nominal energy 6, 9, 12, 15, and 18 MeV from Siemens accelerator with a 10$\times$10 cm$^2$ field size were made using a radiation field analyser with 0.125 cc ion chamber. Dosimetric measurements by IAEA and TG 21 protocol were made with a farmer type ionization chamber in solid water for each electron energy, respectively. Dosimetric measurements by Markus protocol were made with a plane parallel ionization chamber in solid water for each electron energy, respectively. The cavity-gas calibration factor for the plane parallel chamber was obtained with the use of 18 MeV electron beam as guided by TG 39 report. Dosimetric measurements by TG 39 were performed with a plane parallel ionization chamber in solid water for each electron energy, respectively. For all the energies and protocols, measurements were made along the central axis of the distance of 100 cm (SSD = 100 cm) with 10$\times$10 cm$^2$ field size at the depth of d$_{max}$ for each electron beam, respectively. In the case of 18 MeV, the discrepancy of 0.9 % between IAEA and TG 21 was found and the two protocols were agreed within 0.7 % for other energies. In the case of 18 MeV and 6 MeV, the discrepancies of $\pm$ 0.8 % between Markus and TG 39 was found, respectively and the two protocols were agreed within 0.5 % for other energies. Since the discrepancy of 1.6 % between cylindrical and plane parallel chamber was found for 18 MeV, it is suggested to get the calibration factor using other method as guided. by TG 39.9.

• Journal of the Korean Society of Radiology
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• v.12 no.2
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• pp.123-131
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• 2018

This study compared PENELOPE with measured values from low energy peak to high energy peak to reduce peak to compton ratio and continuum background spectrum using $^{60}Co$, $^{137}Cs$ and mixed volume source. In addition, the change in backscattering and compton edge efficiency was compared with that of PENELOPE through changes in the vicinity of low energy. The results from the mixed volume source are applied to the soil samples to determine how much the minimum detection limits of the soil samples are reduced in the suppression and unsuppressed mode. The compton suppression of the low energy region of $^{60}CO$ (1,173 keV) was considerable, and the Compton edge RF for the $^{137}Cs$ (661 keV) peak was 2.8. In particular, the $^{60}Co$ source emits coincidence gamma rays of 1,173.2 keV and 1,332.5 keV, so compton inhibition was reduced by approximately 21%. RF of compton edges of 1,173 keV and 1,332 keV emitted from a $^{60}Co$ source was 3.2 and 3.4, and the peak to compton edge ratio was improved to 8: 1. And Compared with Penelope, the uncertainty was well within 2%. In compton unsuppressed mode, MDA values of 661 keV, 1,173 keV and 1,332 keV were 0.535, 0.173 and 0.136 Bq/kg, respectively, but decreased in compton suppressed mode to 0.121, 0.00826 and 0.00728 Bq/kg. Thus, Compton suppressed could reduce the background radioactivity and the radioactivity contained in the detector itself.

• Nuclear Engineering and Technology
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• v.54 no.2
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• pp.479-485
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• 2022

At the Korea Institute of Radiological and Medical Sciences, physical human phantoms were developed to evaluate various radiation protection quantities, based on the mesh-type reference computational phantoms of the International Commission on Radiological Protection. The physical human phantoms were fabricated such that a radiophotoluminescent glass dosimeter (RPLGD) with a Tin filter, namely GD-352M, could be inserted into them. A Tin filter is used to eliminate the overestimated signals in low-energy photons below 100 keV. The measurement uncertainty of the RPLGD reader system based on GD-352M should be analyzed for obtaining reliable protection quantities before using it for practical applications. Generally, the measurement uncertainty of RPLGD systems without Tin filters is analyzed for quality assurance of radiotherapy units using a high-energy photon beam. However, in this study, the measurement uncertainty of GD-352M was analyzed for evaluating the protection quantities. The measurement uncertainty factors in the RPLGD include the reference irradiation, regression curve, reproducibility, uniformity, energy dependence, and angular dependence, as described by the International Organization for Standardization (ISO). These factors were calculated using the Guide to the Expression of Uncertainty in Measurement method, applying ISO/ASTM standards 51261(2013), 51707(2015), and SS-ISO 22127(2019). The measurement uncertainties of the RPLGD reader system with a coverage factor of k = 2 were calculated to be 9.26% from 0.005 to 1 Gy and 8.16% from 1 to 10 Gy. A blind test was conducted to validate the RPLGD reader system, which demonstrated that the readout doses included blind doses of 0.1, 1, 2, and 5 Gy. Overall, the E_n values were considered satisfactory.

• Bulletin of the Korean Chemical Society
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• v.30 no.8
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• pp.1719-1723
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• 2009

The LiFeP$O_4$ powder was synthesized by using the solid state reaction method with Fe($C_2O_4){\cdot}2H_2O,\;(NH_4)_2HPO_4,\;Li_2CO_3$, and chitosan as a carbon precursor material for a cathode of a lithium-ion battery. The chitosan added LiFePO4 powder was calcined at 350 ${^{\circ}C}$ for 5 hours and then 800 ${^{\circ}C}$ for 12 hours for the calcination. Then we calcined again at 800 ${^{\circ}C}$ for 12 hours. We characterized the synthesized compounds via the crystallinity, the valence states of iron ions, and their shapes using TGA, XRD, SEM, TEM, and XPS. We found that the synthesized powders were carbon-coated using TEM images and the iron ion is substituted from 3+ to 2+ through XPS measurements. We observed voltage characteristics and initial charge-discharge characteristics according to the C rate in LiFeP$O_4$ batteries. The obtained initial specific capacity of the chitosan added LiFeP$O_4$ powder is 110 mAh/g, which is much larger than that of LiFeP$O_4$ only powder.

• Progress in Medical Physics
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• v.12 no.2
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• pp.103-112
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• 2001

Purpose: The purpose of this study was to investigate the current status of performing nuclear medicine quality control in korea and to test selected protocols of quality control of nuclear medicine counting system and gamma camera. Materials and Methods: Fifty three hospitals were included to investigate the current status of nuclear medicine quality control in korea. The precision of dose calibrator and thyroid uptake system was measured with Tc-99m 35.52 MBq for 2 minuets and Tc-99m 5.14 MBq for 10 sec every one minute, respectively. The sensitivity of CeraSPECT$^{TM}$ with low energy high resolution parallel hole collimator was measured using two cylindrical phantoms with 15 cm in diameter and 12 cm and 30 cm in heights containing Tc-99m. The correction factor for sensitivity of CeraSPECT$^{TM}$ was calculated using phantom data. The system planar sensitivity, uniformity, count rate and spatial resolution were measured for Varicam gamma camera with low energy high resolution parallel hole collimator using 140 keV centered 20% energy window, 256$\times$256 or 512$\times$512 matrix sizes. Results: The quality control of dose calibrator and well counter were showed poor performance status. On the other hand, The quality control of gamma camera and other systems were showed relatively good performance status. The results of precision of dose calibrator and thyroid uptake system was $\pm$1.4%(<$\pm$5%) and chi^2=29.7(>16.92), respectively. It showed that the sensitivity of CeraSPECT$^{TM}$ was higher in center slices compared with the edge slices. After correction of nonuniform sensitivities for patient data, it showed better results compare with prior to correction. System planar sensitivity of Varicam gamma camera was 4.39 CPM/MBq. The observed count rate at 20% loss was 102,407 counts/sec (head 1), 113,427 counts/sec (head 2), when input count rate was 81,926 counts/sec (head 1), 90,741 counts/sec (head 2). The spatial resolution without scatter medium were 8.16 mm of FWHM and 14.85 mm of FWTM. The spatial resolution with scatter medium were 8.87 mm of FWHM and 18.87 mm of FWTM. Conclusion: It is necessary to understand the importance of quality control and to perform quality control of nuclear medicine devices.vices.

• Journal of the Mineralogical Society of Korea
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• v.27 no.1
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• pp.1-15
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• 2014

Probing the electronic structures of crystalline Mg-silicates at high pressure is essential for understanding the various macroscopic properties of mantle materials in Earth's interior. Quantum chemical calculations based on the density functional theory are used to explore the atomic configuration and electronic structures of Earth materials at high pressure. Here, we calculate the partial density of states (PDOS) and O K-edge energy-loss near-edge structure (ELNES) spectra for $MgSiO_3$ perovskite at 25 GPa and 120 GPa using the WIEN2k program based on the full-potential linearized projected augmented wave (FP-LPAW) method. The calculated PDOS and O K-edge ELNES spectra for $MgSiO_3$ Pv show significant pressure-induced changes in their characteristic spectral features and relative peak intensity. These changes in spectral features of $MgSiO_3$ Pv indicate that the pressure-induced changes in local atomic configuration around O atoms such as Si-O, O-O, and Mg-O length can induce the significant changes on the local electronic structures around O atoms. The result also indicates that the significant changes in O K-edge features can results from the topological densification at constant Si coordination number. This study can provide a unique opportunity to understand the atomistic origins of pressure-induced changes in local electronic structures of crystalline and amorphous $MgSiO_3$ at high pressure more systematically.

• Radiation Oncology Journal
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• v.20 no.4
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• pp.381-390
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• 2002

Purpose : To develop a dose calibration program for the IAEA TRS-277 and AAPM TG-21, based on the air kerma calibration factor (or the cavity-gas calibration factor), as well as for the IAEA TRS-398 and the AAPM TG-51, based on the absorbed dose to water calibration factor, so as to avoid the unwanted error associated with these calculation procedures. Materials and Methods : Currently, the most widely used dosimetry Protocols of high energy photon beams are the air kerma calibration factor based on the IAEA TRS-277 and the AAPM TG-21. However, this has somewhat complex formalism and limitations for the improvement of the accuracy due to uncertainties of the physical quantities. Recently, the IAEA and the AAPM published the absorbed dose to water calibration factor based, on the IAEA TRS-398 and the AAPM TG-51. The formalism and physical parameters were strictly applied to these four dose calibration programs. The tables and graphs of physical data and the information for ion chambers were numericalized for their incorporation into a database. These programs were developed user to be friendly, with the Visual $C^{++}$ language for their ease of use in a Windows environment according to the recommendation of each protocols. Results : The dose calibration programs for the high energy photon beams, developed for the four protocols, allow the input of informations about a dosimetry system, the characteristics of the beam quality, the measurement conditions and dosimetry results, to enable the minimization of any inter-user variations and errors, during the calculation procedure. Also, it was possible to compare the absorbed dose to water data of the four different protocols at a single reference points. Conclusion : Since this program expressed information in numerical and data-based forms for the physical parameter tables, graphs and of the ion chambers, the error associated with the procedures and different user could be solved. It was possible to analyze and compare the major difference for each dosimetry protocol, since the program was designed to be user friendly and to accurately calculate the correction factors and absorbed dose. It is expected that accurate dose calculations in high energy photon beams can be made by the users for selecting and performing the appropriate dosimetry protocol.

• Journal of Radiation Protection and Research
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• v.35 no.2
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• pp.85-90
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• 2010

In the present work, peak relative efficiency for the energy was obtained and response function was worked out. This study was carried out using the high resolution high efficiency HPGe detector(diameter 78.7 mm, length 86.5 mm) and NaI(Tl) detector for anti-compton. The anti-coincidence of the signals from the two detectors could be used to lessen the Compton effect signal; thus, the $\gamma$-ray energy resolution could be improved. The $\gamma$-ray spectrum was measured at $55^{\circ}$ to the direction of the incident proton beam. Reaction spectrum was obtained from the $^{23}Na$(p, $\gamma$)$^{24}Mg$ reaction at $E_p$ = 1424 keV and $^{27}Al$(p, $\gamma$)$^{28}Si$ reaction at $E_p$ = 992 keV. To accelerate the incident proton which creates the (p, $\gamma$) capture reaction, the 3 MeV Pelletron accelerator at the Tokyo Institute of Technology was used. Response function was worked out by a noble technique. We worked out a response function from 1.2 to 9.4 MeV at intervals of 0.75 MeV.

• Korean Chemical Engineering Research
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• v.50 no.5
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• pp.929-932
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• 2012

Novel platform technology has been developed to replace the photolithography used currently for manufacturing semiconductors and display devices. As a substrate, plastics, especially polycarbonates, have been considered for future application such as flexible display. Other plastics, i.e. polyimide, polyetheretherketon, and polyethersulfone developed for the substrate at this moment, are available for photolithography due to their high glass transition temperature, instead of high price. After thin polystyrene film was coated on the polycarbonate substrate, microstructure of the film was formed with polydimethylsiloxane template over the glass transition temperature of the polystyrene. The surface of the structure was treated with potassium permanganate and octadecyltrimethoxysilane so that the surface became hydrophobic. After this surface treatment, the nanoparticles dispersed in aqueous solution were aligned in the structure followed by evaporation of the DI water. Without the treatment, the nanoparticles were placed on the undesired region of the structure. Therefore, the interfacial interaction was also utilized for the nanoparticle alignment. The surface was analyzed using X-ray photoelectron spectrometer. The evaporation of the solvent occurred after several drops of the solution where the hydrophilic nanoparticles were dispersed. During the evaporation, the alignment was precisely guided by the physical structure and the interfacial interaction. The alignment was applied to the electric device.