• Journal of Radiation Protection and Research
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• v.27 no.1
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• pp.1-10
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• 2002

High energy photon beams from medical linear accelerators produce large scattered radiation by various components of the treatment head, collimator and walls or objects in the treatment room including the patient. These scattered radiation do not provide therapeutic dose and are considered a hazard from the radiation safety perspective. Scattered dose of therapeutic high energy radiation beams are contributed significant unwanted dose to the patient. ICRP take the position that a dose of 500mGy may cause abortion at any stage of pregnancy and that radiation detriment to the fetus includes risk of mental retardation with a possible threshold in the dose response relationship around 100 mGy for the gestational period. The ICRP principle of as low as reasonably achievable (ALARA) was recommended for protection of occupation upon the linear no-threshold dose response hypothesis for cancer induction. We suggest this ALARA principle be applied to the fetus and testicle in therapeutic treatment. Radiation dose outside a photon treatment filed is mostly due to scattered photons. This scattered dose is a function of the distance from the beam edge, treatment geometry, primary photon energy, and depth in the patient. The need for effective shielding of the fetus and testicle is reinforced when young patients ate treated with external beam radiation therapy and then shielding designed to reduce the scattered photon dose to normal organs have to considered. Irradiation was performed in phantom using high energy photon beams produced by a Varian 2100C/D medical linear accelerator (Varian Oncology Systems, Palo Alto, CA) located at the Yonsei Cancer Center. The composite phantom used was comprised of a commercially available anthropomorphic Rando phantom (Phantom Laboratory Inc., Salem, YN) and a rectangular solid polystyrene phantom of dimensions $30cm{\times}30cm{\times}20cm$. the anthropomorphic Rando phantom represents an average man made from tissue equivalent materials that is transected into transverse 36 slices of 2.5cm thickness. Photon dose was measured using a Capintec PR-06C ionization chamber with Capintec 192 electrometer (Capintec Inc., Ramsey, NJ), TLD( VICTOREEN 5000. LiF) and film dosimetry V-Omat, Kodak). In case of fetus, the dosimeter was placed at a depth of loom in this phantom at 100cm source to axis distance and located centrally 15cm from the inferior edge of the $30cm{\times}30cm^2$ x-ray beam irradiating the Rando phantom chest wall. A acryl bridge of size $40cm{\times}40cm^2$ and a clear space of about 20 cm was fabricated and placed on top of the rectangular polystyrene phantom representing the abdomen of the patient. The leaf pot for testicle shielding was made as various shape, sizes, thickness and supporting stand. The scattered photon with and without shielding were measured at the representative position of the fetus and testicle. Measurement of radiation scattered dose outside fields and critical organs, like fetus position and testicle region, from chest or pelvic irradiation by large fie]d of high energy radiation beam was performed using an ionization chamber and film dosimetry. The scattered doses outside field were measured 5 - 10% of maximum doses in fields and exponentially decrease from field margins. The scattered photon dose received the fetus and testicle from thorax field irradiation was measured about 1 mGy/Gy of photon treatment dose. Shielding construction to reduce this scattered dose was investigated using lead sheet and blocks. Lead pot shield for testicle reduced the scatter dose under 10 mGy when photon beam of 60 Gy was irradiated in abdomen region. The scattered photon dose is reduced when the lead shield was used while the no significant reduction of scattered photon dose was observed and 2-3 mm lead sheets refuted the skin dose under 80% and almost electron contamination. The results indicate that it was possible to improve shielding to reduce scattered photon for fetus and testicle when a young patients were treated with a high energy photon beam.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.9 no.3
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• pp.169-179
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• 2011

There are two types of nuclear reactors in Korea and they are PWR type and CANDU type. The safe management of the spent fuels from these reactors is very important factor to maintain the sustainable energy supply with nuclear power plant. In Korea, a reference disposal system for the spent fuels has been developed through a study on the direct disposal of the PWR and CANDU spent fuel. Recently, the research on the demonstration and the efficiency analyses of the disposal system has been performed to make the disposal system safer and more economic. PWR spent fuels which include a lot of reusable material can be considered being recycled and a study on the disposal of HLW from this recycling process is being performed. CANDU spent fuels are considered being disposed of directly in deep geological formation, since they have little reusable material. In this study, based on the Korean Reference spent fuel disposal System (KRS) which was to dispose of both PWR type and CANDU type, the more effective CANDU spent fuel disposal systems were developed. To do this, the disposal canister for CANDU spent fuels was modified to hold the storage basket for 60 bundles which is used in nuclear power plant. With these modified disposal canister concepts, the disposal concepts to meet the thermal requirement that the temperature of the buffer materials should not be over $100^{\circ}C$ were developed. These disposal concepts were reviewed and analyzed in terms of disposal effective factors which were thermal effectiveness, U-density, disposal area, excavation volume, material volume etc. and the most effective concept was proposed. The results of this study will be used in the development of various wastes disposal system together with the HLW wastes from the PWR spent fuel recycling process.

• Journal of the Korean Vacuum Society
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• v.6 no.2
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• pp.129-135
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• 1997

Undoped and Co-doped $ZnIn_2Se_4$ single crystals crystallized in the tetragonal space group 142m, with lattice constants a=5.748 $\AA$ and c=11.475 $\AA$, and a=5.567 $\AA$ and c=11.401 $\AA$. The optical absorption measured near the fundamental band edge showed that the optical energy band structure of these compounds had an indirect band gap, the direct and the indirect energy gaps of these compounds decreased as temperature changed from 10 to 300 K. The temperature coefficients of the direct energy gaps were found to be $\alpha=3.71\times10^{-4}$eV/K and $\beta$=519 K for $\alpha=3.71\times10^{-4}$eV/K and $\beta$=421K for $ZnIn_2Se_4$: Co. The temperature coefficients of the indirect energy gaps were also found to be $\alpha=2.31\times10^{-4}$ eV/K and $\beta$=285 K for $ZnIn_2Se_4$, and $\alpha=3.71\times10^{-4}$eV/K and $\beta$=609 K for $ZnIn_2Se_4$:Co, respectively. Six impurity optical absorption peaks due to cobalt are observed in $ZnIn_2Se_4$:Co single crystal. These impurity optical absorption peaks can be attibuted to the electronic transitions between the split energy levels of$CO^{2+}$ ions located at Td symmetry site of $ZnIn_2Se_4$ host lattice. The 1st order spin-orbit coupling constant ($\lambda$), Racah parameter (B), and crystal field parameter (Dq) ARE GIVEN AS -$243\textrm{cm}^{-1}, 587\textrm{cm}^{-1}, \;and\;327\textrm{cm}^{-1}$, respectively.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2004.06a
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• pp.223-224
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• 2004

고준위폐기물 혹은 사용후 핵연료의 처분용기 재질은 각 국의 처분개념과 처분공의 주위 환경에 따라 달라질 수 있다. 용기의 후보재질로는 탄소강, 스텐레스 강, 구리, 니켈, 티탄 혹은 이들의 합금이 주로 고려되고 있으나, 국내에서는 아직 선정되지 않았다. 국내 처분환경에서 이들 재질의 부식특성을 조사하고자 모의 화강암 지하수를 가해 만든 겔 상태의 경주 벤토나이트에 탄소강, 스텐레스 강, 구리 시편을 넣고, $70^{\circ}C$, 아르곤 분위기에서 530일 경과한 후 시편의 표면 변화 (그림 1) 및 무게 감소를 측정하였다. 철 부식시편은 검정색의 철 화합물 층으로 덮여 있었으며, 구리표면에는 노란색의 부식층이 형성되었는데, 이를 XRD로 분석한 결과 $Cu_2O$로 판명되었다. 그러나 $700^{\circ}C$에서 각각 0, 24, 96시간동안 예민화시킨 스텐레스 강 시편들은 모두 초기상태 그대로 광택을 유지하고 있었으며, XRD에서 다른 화합물의 형성을 발견할 수 없었다 (그림 2). 시편의 무게 감소가 균일부식에 기인한 것으로 가정하여 환산한 결과, 구리와 스텐레스 강 모두 0.3~0.4 $\mu\textrm{m}/yr$의 부식속도를 나타내었다. 그러나 구리는 부식생성물이 표면에 부착되어 있기 때문에 실제 부식두께는 이 값보다 더 클 것으로 생각된다. 용기가 초기 530일간과 같은 속도로 처분용기의 부식이 진행된다면 한국에서 기준처분 개념으로 삼고 있는 50mm 두께의 내부식성 외벽 금속용기는 적어도 만년이상 견딜 수 있을 것으로 추정된다. 한편, 검정색 부식층을 제거한 무게감소로부터 계산한 철의 부식속도는 구리의 약 30배에 해당하였다. 금속 재질의 정확한 부식 거동을 파악하기 위해서는 보다 장기간의 실험이 요구된다. 시험법 선정에 각계(규제기관, 학계, 발전소 현장 및 산업계 등) 전문가로부터 기술자문회의를 통하여 자문 의견을 받기로 하였다. 특히 현재 폐기물 인수 기술기준치가 설정된 국가의 시험법을 심층 있게 검토하기로 하였다.검토하기로 하였다. 혹은 수성주변 환경이 지배하는 산악이나 구릉지에서 흔히 나타나는 침엽수-낙엽활엽수의 혼합림 식생상태를 잘 대변해 주고 있는 것으로 판단된다. 끝으로, 의림지 호저 퇴적층 중에서 인위적인 교란흔적이 없는 암회색 유기질 니층에 대한 탄소연대측정 결과, 제1호공 12번 시료에서 950$\pm$40 years B.P을 얻었으며, 제3-1호공에서도 아래로 내려가면서 8, 10, 11번 시료에 대하여 500$\pm$30 years B.P, 650$\pm$30 years B.P, 800$\pm$40 years B.P의 연대측정 결과를 획득하였다. 이상과 같은 의림지 호저 퇴적층의 형성환경과 형성시기 연구를 통하여 의림지의 제방축조의 최초시기를 해석해 보면, 의림지의 제방은 적어도 과거 약 827년 전에서 866년 전에는 이미 축조되어 있었음을 알 수 있다. 과거 제천 일대에 살았던 옛사람들이 의림지 하류의 곡지중앙과 고기 충적선상지에 대한 관계용 용수조달의 필요성에 부응하여 상류부 곡지하천의 자연입지 환경을 최대한 이용하여 축조한 것으로 판단된다..준비하였다.전류를 구성하는 주요 입자의 에너지 영역(75~l13keV)에서 가장 높은(0.80) 상관계수를 기록했다. 넷째, 회복기 중에 일어나는 입자들의 유입은 자기폭풍의 지속시간을 연장시키는 경향을 보이며 큰 자기폭풍일수록 현저했다. 주상에서 관측된 이러한 특성은 서브스톰 확장기 활동이 자기폭풍의 발달과 밀접한 관계가 있음을 시사한다.se that were all low

• Journal of the Korean Chemical Society
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• v.43 no.2
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• pp.206-212
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• 1999

The main objective of the present investigation is to improve the photoluminescent performance of existing $Zn_2SiO_4:Mn$ phosphors by introducing a new co-dopant. The co-doping effect of Mg and/or Cr upon emission intensity and decay time was studied in the present investigation. The co-dopants incorporated into the $Zn_2SiO_4:Mn$ phosphors are believed to alter the internal energy state so that the change in emission intensity and decay time can be expected. Both Mg and Cr ions have a favourable influence on photoluminescence prpperties, for example, the Mg ion enhances the intensity of manganese green emission and the Cr ion shortens the decay time. The enhancement in emission intensity of $Zn_2SiO_4:Mn,\;Mg$ phosphors was interpreted by taking into account the result from the DV-X${\alpha}$ embedded cluster calculation. On the other hand, the energy transfer between Mn and Cr ions was found to be responsible for the shortening of decay time in$Zn_2SiO_4:Mn,\;Cr$ phosphors.

• Journal of KIISE:Information Networking
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• v.35 no.4
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• pp.251-267
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• 2008

In this paper, we present a distributed topology control algorithm for constructing an optimized topology having a minimal search-time in unstructured peer-to-peer network. According to the proposed algorithm, each node selects the best nodes having higher hit-ratio than other nodes as many as the number being exponentially proportional to the hit-ratio of the node itself, and then it connects to them. The ensemble behavior of the proposed algorithm is very similar to the recrystrallizing phenomenon that is observed in nature. There is a partial order relationship among the hit-ratios of most nodes of constructed topology. Therefore once query message visits a node, it has a higher hit-ratio than the node that was visited last by the message. The query message even sent from freeloader can escape to the node having high hit-ratio by one hop forwarding, and it never revisits any freeloader again. Thus the search can be completed within a limited search time. We also propose the Chain-reactive search scheme using the constructed topology. Such a controlled multicasting reduces the query messages by 43 percent compared to that of the naive Gnutella using broadcasting, while it saves the search time by 94 percent. The search success rate of the proposed scheme is 99 percent.

• Tunnel and Underground Space
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• v.12 no.1
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• pp.52-69
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• 2002

The WIPP (Waste Isolation Pilot Plant), located 42km east of Carlsbad, New Mexico (NM), in bedded salt 655m below the surface, is a mined repository constructed by the US DOE for the permanent disposal of transuranic (TRU) wastes generated by activities related to defence of the US since 1970. Its historical disposal operation began in March 1999 following receipt of a final permit from the State of NM after a positive certification decision for the WIPP was issued by the EPA in 1998, as the first licensed facility in the US for the deep geologic disposal of radioactive wastes. The CCA (Compliance Certification Application) for the WIPP that the DOE submitted to the EPA in 1966 was supported by an extensive performance assessment (PA) carried out by Sandia National Laboratories (SNL), with so-called 1996 PA. Even though such PA methodologies could be greatly different from the way we consider for HLW disposal in Korea largely due to quite different geologic formations in which repository are likely to be located, a review on lots of works done through the WIPP PA studies could be the most important lessons that we can learn from in view of current situation in Korea where an initial phase of conceptual studies on HLW disposal has been just started. The objective of this art report is an overview of the methodology used in the recent WIPP PA to support the US DOE WIPP CCA and some relevant results completed by SNL.

• Analytical Science and Technology
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• v.18 no.1
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• pp.59-65
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• 2005

When the low level radioactivity sample is measured, it is required to have many samples. For increase of the sample volume, a scattering and absorbing probability of the emitted gamma-ray in the sample are to be increased. In order to correct the self-absorption effect, the counting efficiency must be calibrated according to a geometrical condition and sample density. But, it is impossible to determine efficiency for counting sample using standard source with the same geometrical condition and density. In this study, the measuring efficiencies were determined with various counting containers and densities. In order to compare the self-absorption effect with the sample density in the various sample container, the variation of the counting efficiency with the densities was investigated by adding NaI, which has high solubility and density. Also, they were compared with Monte Carlo simulation. The self-absorption effect was found to be significant in the low energy region below 0.5 MeV.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.3 no.1
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• pp.18-25
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• 1978

The 1/f noise spectrum of short-circuited output drain current due to the Shockley-Read-Hal] recombination centers with a single lifetime in homogeneous nondegenerate MOS-field effcte transtors with n-type channel is calculated under the assumptions that the quasi-Fermi level for the carriers in each energy band can not be defined if we include the fluctuation for time varying quantities. and so 1/f noise is a majority carrier effect. Under these assumptions the derived 1/f noise in this paper show some essential features of the 1/f noise in MOS-field effect transistors. That is, it has no lowfrequency plateau and is proportionnal to the channel cross area A and to the driain bias voltage Vd and inversely proportional to the channel length L3 in MOS field effect transistors. This model can explain the discrepancy between the transition frequency of the noise spectrum from 1/f- response to 1/f2 and the frequency corresponding to the relaxation time related to the surface centers in p-n junction diodes. In this paper the results show that the functional form of noise spectrum is greatly influenced by the functional forms of the electron capture probability cn (E) and the relaxation time r (E) for scattering and the case of lattice scattering show to be responsible for the 4 noise in MOS fold effect transistors. So we canconclude that the source of 1/f noise is due to lattice scattering.

• Journal of Radiation Protection and Research
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• v.20 no.4
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• pp.275-283
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• 1995

PERALS(Photon Electron Rejecting Alpha Liquid Scintillation) spectrometry coupled with solvent extraction method has been set up for the analysis of $^{222}Rn\;and\;^{226}Ra$ in the groundwater. This analytical method offers low background, better energy resolution and lower quenching problem than the other techniques. By the analysis of NIST SRM 4966 $^{226}Ra$ standard, the analytical accuracy and precision were found to be 3% and 1%, respectively, and the relative standard deviation of the recovery of Rn extraction between pH2 and pH10 was 7%. Detection limits of $^{222}Rn$ and $^{226}Ra$ for 10 hours counting were counted to be $0.42 pCi/{\iota}\;and\;0.016 pCi/{\iota}$, respectively. For the test analysis of $^{222}Rn\;and\;^{226}Ra$ in the graundwater, hot spring water samples of 17 regions were analyzed. The concentration of $^{222}Rn$ were in the range of $90{\sim}5200pCi/{\iota}$ and average value was $1470pCi/{\iota}\;^{226}Ra$ concentration showed a peak value of $97.9pCi/{\iota}$ in a Kangwon region, but the average value was $1.14pCi/{\iota}$ except that region.