• Progress in Medical Physics
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• v.27 no.1
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• pp.31-36
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• 2016

The paper discusses radiation dose of dual energy CT on which copper modulation layer, is mounted in order to improve diagnostic performance of the dual energy CT. The radiation dose is estimated using MCNPX and its results are compared with that of the conventional dual energy CT system. CT X-ray spectra of 80 and 120 kVp, which are usually used for thorax, abdominal, head, and neck CT scans, were generated by the SPEC78 code and were used for the source specification 'SDEF' card for MCNPX dose modeling. The copper modulation layer was located 20 cm away from a source covering half of the X-ray window. The radiation dose was measured as changing its thickness from 0.5 to 2.0 mm at intervals of 0.5 mm. Since the MCNPX tally provides only normalized values to a single particle, the dose conversion coefficients of F6 tally for the modulation layer-based dual energy CBCT should be calculated for matching the modeling results into the actual dose. The dose conversion coefficient is $7.2*10^4cGy/output$ that is obtained from dose calibration curve between F6 tally and experimental results in which GAFCHORMIC EBT3 films were exposed by an already known source. Consequently, the dose of the modulation layer-based dual energy cone beam CT is 33~40% less than that of the single energy CT system. On the basis of the results, it is considered that scattered dose produced by the copper modulation layer is very small. It shows that the modulation layer-based dual energy CBCT system can effectively reduce radiation dose, which is the major disadvantage of established dual energy CT.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.37 no.2
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• pp.106-116
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• 2001

A serious of studies on the fishing gear and system of the East Sea trawl fishery was carried out to improve the fishing efficiency and the working conditions. As the first step of these studies, the fishing gear and system of the traditional East Sea trawl were checked in order to solve the some problems, such as the poor sheering efficiency of net mouth, the inconvenient fishing system of the side trawl and etc. And then the fishing system was reorganized from the side trawl into the stern trawl by setting up the net drum system on the stern deck, and introduction of two types of new designed nets, one for mainly the midwater trawl and the other for the bottom trawl. The results of the field experiment on the modified system and nets can be summarized as follows : 1. the modified system was well worked and could save the man-labour by about 80%. 2. The sheering efficiency of the improved net, A type was improved to 20 m height and 30 m width in the net mouth, and that of B type net, to 10 m height and 33 m width, compared with 1.5 m height and 15 m width in the traditional net. 3. Catch efficiency of pink shrimp in A or B type net was better about 3 or 5 times than that of traditional net, and in B net, for herring and other bottom fishes is better about 2 times than that of the traditional net.

• Journal of Navigation and Port Research
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• v.38 no.4
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• pp.367-371
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• 2014

When the crew or passengers fall into the water due to marine accident of vessel, it is very important to rescue them quickly. In the case of marine accidents, most people in distress have been wearing a lifejacket, so if the GPS and Cospas-Sarsat communication module will be integrated within the lifejacket, it is easy to rescue them. In this paper, development of the dual band lifejacket-integrated antenna for GPS and Cospas-Sarsat communication is discussed. The antenna with the FR-4 substrate of 0.2mm thickness for flexibility was designed that it can be fitted close to the shoulder of the life jacket and operate at 1.575GHz and 406MHz. The GPS communication antenna was implemented with a ring-slot antenna having a circular polarized characteristic and a meander type linear polarized antenna is used as Cospas-Sarsat communication. The two antennas are fed by a single microstrip line and an open stub is used to minimize the mutual interference between the two antennas. The performance of the fabricated antenna attached to the life vest is confirmed by the measurement of the return loss at GPS and Cospas-Sarsat frequency bands.

• Nuclear Engineering and Technology
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• v.26 no.3
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• pp.381-388
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• 1994

Recently, the American National Standards Institute (ANSI) had made some changes in the radiation sources specified from those in the original performance test criteria ANSI N13. 11-1983. In case or beta category, in addition to the high-energy $^{90}$ Sr/$^{90}$ Y beta source, the $^{204}$ Tl source was added because many workplaces have significant levels of lower energy betas. In this study, the performance or the Teledyne PB-3 personnel dosimetry system in the fields of $^{204}$ Tl and $^{90}$ Sr/ $^{90}$ Y beta was investigated using the PTB beta secondary standard sources. The new beta correction function of PB-3 personnel dosimetry system for $^{204}$ Tl beta was also developed in this response experiment. The results show that the Teledyne PB-3 personnel dosimetry system is very effective for $^{90}$ Sr/ $^{90}$ Y beta dose assessment. In case of $^{204}$ Tl beta radiation, however, the results of simple performance test indicated that the use of beta correction factor(=2.088) which was recommanded by manufacturer may result in unexpectable overestimation of delivered dose by about 60%, while the use of developed beta correction function could measure the delivered doses in errors of 15%.

• Journal of Radiation Protection and Research
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• v.28 no.4
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• pp.263-270
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• 2003

Monte Carlo simulation has been peformed to induce optimized parameters of the detector head of gamma camera for the diagnosis of breast cancer and to evaluate it under the diagnosis condition of the breast cancer. For the simulation, we used Tungsten collimator, having a lattice structured array with holes of $3mm{\times}3mm$ and septal thickness of 0.25 mm, which are corresponding to the pixellated photosensor. For driving optimum parameters we used Trade-Offs procedure between the geometric efficiency and the spatial resolution, varying the detector head components. In order to pre-evaluate the performance of the optimized detector head, we assumed diagnosis condition that the breast tumor is located in the middle of phantom with various sizes and its location is 25 mm from the collimator surface, considering background count caused by radiation sources from other organs. It was shown that the performance of the optimized detector head can be degraded according to the breast cancer size and the background count under real diagnosis conditions of breast cancer. Therefore, it is concluded that the spatial resolution, which is used as an indicator to distinguish the various sizes of breast cancer and is dependent on the characteristic of the detector head, appears to be meaningless in early diagnosis of the breast cancer.

• Journal of Radiation Protection and Research
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• v.24 no.4
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• pp.205-213
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• 1999

Effective dose conversion coefficients from unit activity radionuclides contaminated on the ground surface were calculated by using MCNP4A rode and male/female anthropomorphic phantoms. The simulation calculations were made for 19 energy points in the range of 40 keV to 10 MeV. The effective doses E resulting from unit source intensity for different energy were compared to the effective dose equivalent $H_E$ of previous studies. Our E values are lower by 30% at low energy than the $H_E$ values given in the Federal Guidance Report of USEPA. The effective dose response functions derived by polynomial fitting of the energy-effective dose relationship are as follows: $f({\varepsilon})[fSv\;m^2]=\;0.0634\;+\;0.727{\varepsilon}-0.0520{\varepsilon}^2+0.00247{\varepsilon}^3,\;where\;{\varepsilon}$ is the gamma energy in MeV. Using the response function and the radionuclide decay data given in ICRP 38, the effective dose conversion coefficients for unit activity contamination on the ground surface were calculated with addition of the skin dose contribution of beta particles determined by use of the DOSEFACTOR code. The conversion coefficients for 90 important radionuclides were evaluated and tabulated. Comparison with the existing data showed that a significant underestimates could be resulted when the old conversion coefficients were used, especially for the nuclides emitting low energy photons or high energy beta particles.

• Journal of the Korean Geographical Society
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• v.41 no.5 s.116
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• pp.527-544
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• 2006

This study provides a definition of heat waves, which indicate the conditions of strong sultriness in summer, appropriate to Korea and intends to clarify long term(1973-2006) averaged spatial and temporal patterns of annual frequency of heat waves with respect to their intensity. Based on examination of the Korean mortality rate changes due to increase of apparent temperature under hot and humid summer conditions, three consecutive days with at least $32.5^{\circ}C,\;35.5^{\circ}C,\;38.5^{\circ}C,\;and\;41.5^{\circ}C$ of daily maximum Heat Index are defined as the Hot Spell(HS), the Heat Wave(HW), the Strong Heat Wave(SHW), and the Extreme Heat Wave(EHW), respectively. The annual frequency of all categories of heat waves is relatively low in high-elevated regions or on islands adjacent to seas. In contrast, the maximum annual frequency of heat waves during the study period as well as annual average frequency are highest in interior, low-elevated regions along major rivers in South Korea, particularly during the Changma Break period(between late July and mid-August). There is no obvious increasing or decreasing trend in the annual total frequency of all categories of heat waves for the study period However, the maximum annual frequencies of HS days at each weather station were recorded mainly in the 1970s, while most of maximum frequency records of both the HW and the SHW at individual weather stations were observed in the 1990s. It is also revealed that when heat waves occur in South Korea high humidity as well as high temperature contributes to increasing the heat wave intensity by $4.3-9.5^{\circ}C$. These results provide a useful basis to help develop a heat wave warning system appropriate to Korea.

• Progress in Medical Physics
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• v.24 no.3
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• pp.162-170
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• 2013

Dedicated single-photon emission computed tomography (SPECT) systems based on pixelated semiconductors are being developed for studying small animal models of human disease. To clarify the possibility of using a SPECT system with CdTe for a high resolution low-dose small animal imaging, we compared the quality of reconstructed images from pixelated CdTe detector to those from a small SPECT system with NaI(Tl). The CdTe detector was $44.8{\times}44.8$ mm and the pixels were $0.35{\times}0.35{\times}5$ mm. The intrinsic resolution of the detector was 0.35 mm, which is equal to the pixel size. GATE simulations were performed to assess the image quality of both SPECT systems. The spatial resolutions and sensitivities for both systems were evaluated using a 10 MBq $^{99m}Tc$ point source. The quantitative comparison with different injected dose was performed using a voxelized MOBY phantom, and the absorbed doses for each organ were evaluated. The spatial resolution of the SPECT with NaI(Tl) was about 1.54 mm FWHM, while that of the SPECT with a CdTe detector was about 1.32 mm FWHM at 30 mm. The sensitivity of NaI(Tl) based SPECT was 83 cps/MBq, while that of the CdTe detector based SPECT was 116 cps/MBq at 30 mm. The image statistics were evaluated by calculating the CNR of the image from both systems. When the injected activity for the striatum in the mouse brain was 160 Bq/voxel, the CNR of CdTe based SPECT was 2.30 while that of NaI(Tl) based SPECT was 1.85. The CNR of SPECT with CdTe was overall higher than that of the NaI(Tl) based SPECT. In addition, the absorbed dose was higher from SPECT with CdTe than those from NaI(Tl) based SPECT to acquire the same quantitative values. Our simulation results indicated that the SPECT with CdTe detector showed overall high performance compared to the SPECT with NaI(Tl). Even though the validation study is needed, the SPECT system with CdTe detector appeared to be feasible for high resolution low-dose small animal imaging.

• Journal of radiological science and technology
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• v.31 no.3
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• pp.287-292
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• 2008

Position information of radiation interactions in detection material is essential to reconstruct a radiation source image. With most position sensing techniques, the position information of a single interaction inside the detectors can be precisely obtained. Each interaction position of multi-scattering inside scintillators, however, can not be individually measured and only the average of the scattering positions can be obtained, which causes the uncertainty in the measured interaction position. In this paper, the position uncertainties due to the multi-scattering were calculated by Monte Carlo simulation. The simulation model was a 50 by 50 by 5 mm $LaCl_3$(Ce) scintillator(pixel size is 2 by 2 by 5mm) which was utilized for the dual collimation camera. The dual collimation camera uses the information from both photoelectric effect and Compton scattering, and therefore, position uncertainties for both partial and full energy deposition of radiation interactions are calculated. In the case of partial energy deposition(PED), the standard deviations of positions are less than $1{\sim}2mm$, which means the uncertainty caused by multi-scattering is not significant. Because the effect of the multi-scattering with PED is insignificant, the multi-scattering has little effect on the performance of Compton imaging of dual collimation camera. In the case of full energy deposition(FED), however, the standard deviation of the positions is about twice that of the pixel size of the 1stdetector, except for 122keV incident radiations. Therefore, the standard deviations caused by multi-scatterings should be considered in the design of the coded mask of the dual collimation camera to avoid artifact on the reconstructed image. The position uncertainties of the FEDs are much larger than those of the PEDs for all radiation energies and the ratio of PEDs to FEDs increases when the incident radiation energy increases. The position uncertainties of both PEDs and FEDs are dependent on the incident radiation energy.

• Journal of Environmental Policy
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• v.7 no.3
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• pp.89-120
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• 2008

With petroleum being a major source of energy in Korea, the quantity of petroleum transported via ocean routes is on its way up due to increased consumption. Due to the increase, more than 300 cases of pollution caused by petroleum occur annually. Moreover, the number of oil-spill accidents is also on the rise. Causes of such accidents, not including the disposal of waste oil on purpose, turn out to be human error during navigation or defects in the vessels, showing that most accidents are caused by humans. Therefore, to prevent future oil spills, it is imperative that navigation efficiency be enhanced by improving the quality of navigators and replacing old vessels with newer ones. Nevertheless, such improvements cannot occur overnight, so long- and mid-term efforts should be made to achieve it institutionally. As large-scale oil-spill accidents can happen at anytime along the coastal waters of Korea, it is necessary to set-up institutional devices which go beyond the compensation limit of 92FC. The current special law regarding this issue has its limits in that it prescribes compensation be supplemented solely by national taxes. Therefore, the setting-up of a new 'national fund' is recommended for consideration rather than to subscribe to the '2003 Convention for the Supplementary Fund'. It is strongly suggested that a National fund be created from fees collected from oil companies based on the risks involved in oil transportation and according to the profiteers pay principle. In addition, a public fund should be created to handle general environmental damage, such as the large-scale destruction of the ecosystem, which is distinct from the economic damage that harms the local people. The posterior responses to the large-scale oil spill have always been unsatisfactory because of the symbolic nature of the disasters included in such accidents. Oil-spills can be prevented in advance, because they are caused by human beings. But once they occur, they inflict long-term damage to both human life and the natural ecosystem. Therefore, the best response to future oil-spills is to work to prevent them.