• Progress in Medical Physics
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• v.29 no.1
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• pp.16-22
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• 2018

Current dosimetry protocols recommend the use of parallel-plate chambers in electron dosimetry because the electron fluence perturbation can be effectively minimized. However, substitutable methods to calibrate and measure the electron output and energy with the widely used cylindrical chamber should be developed in case a parallel-plate chamber is unavailable. In this study, we measured the correction factors and absolute dose-to-water of electrons with energies of 4, 6, 9, 12, 16, and 20 MeV using Farmer-type and Roos chambers by varying the dose rates according to the AAPM TG-51 protocol. The ion recombination factor and absolute dose were found to be varied across the chamber types, energy, and dose rate, and these phenomena were remarkable at a low energy (4 MeV), which was in good agreement with literature. While the ion recombination factor showed a difference across chamber types of less than 0.4%, the absolute dose differences between them were largest at 4 MeV at approximately 1.5%. We therefore found that the absolute dose with respect to the dose rate was strongly influenced by ion-collection efficiency. Although more rigorous validation with other types of chambers and protocols should be performed, the outcome of the study shows the feasibility of replacing the parallel-plate chamber with the cylindrical chamber in electron dosimetry.

• Journal of the Korean Society of Radiology
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• v.3 no.4
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• pp.23-28
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• 2009

Monochromatic X-ray can make a medical image of high contrast under a low radiation dose and can be easily generated by combining an X-ray tube and a multilayer mirror. A W/C multilayer mirror was optimally designed for a characteristic X-ray generated from a X-ray tube with Mo target. The d-spacing and the thickness ratio in design parameters were determined under the maximum-reflectivity condition. Tolerances for deposition and alignment of the W/C multilayer mirror were calculated. Within a deposition tolerance of 0.2nm and a alignment tolerance of ${\pm}0.01^{\circ}$, 85% of the theoretical peak reflectivity could be achieved. A multilayer mirror can be widely used for making medical images because of generating high fluence monochromatic X-ray.

• Journal of Nutrition and Health
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• v.36 no.5
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• pp.491-499
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• 2003

Selenium is a strong antioxidant trace mineral, scavenging free radicals. The prevalence of chronic degenerative diseases is increasing in Korean adults with increasing age. The increased cell damage from free radicals has been implicated in the etiology of these diseases, and evidence is accumulating that the low selenium status that comes with advanced aged is involved in the prevalence of age-associated diseases. However, little is known about the selenium status of Koreans, its age-related change and its relationship to dietary nutrient intake. In this study, the serum selenium levels of healthy adult females according to life cycle and its association with blood albumin levels and nutrient intake were examined. Serum selenium level was measured with the Huwo research reactor using the neutron activation analysis method (NAA). The overall proportion of women with selenium deficiency, serum selenium concentrations below 7.0 $\mu\textrm{g}$/dl, was 9.4%. The average serum selenium levels were 12.39 $\mu\textrm{g}$/dl, 9.45 $\mu\textrm{g}$/dl and 9.16 $\mu\textrm{g}$/dl in the young adult, middle-aged and elderly groups, respectively, showing a reduction of selenium status with advancing age. Selenium deficiency was seen only in the elderly group. Generally, serum selenium levels positively or negatively correlated with nutrient intake, but these association patterns differed depending on the age. The nutrients that showed positive correlations with selenium levels were proteins and phosphate in the young adult group (p < 0.05, p < 0.05), and total calcium, potassium and vegetable-origin calcium in the middle-aged group. Vitamin C and fiber were the negative correlated nutrients with serum selenium levels in the elderly group (p < 0.05, p < 0.05). Multiple stepwise regression analysis of the determining factors responsible for selenium status showed that age and serum albumin levels were important factors which explained up to 26.9% variances in serum selenium levels. The average selenium concentrations of Korean adult female subjects were above the deficiency levels in all three age groups. There was a tendency toward decreasing selenium levels as the age of the subjects increased. The factors with the strongest in-fluence on selenium status in healthy adult Korean females were age and serum protein status. (Korean J Nutrition 36(5): 491~499, 2003)

• Nuclear Engineering and Technology
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• v.42 no.2
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• pp.203-210
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• 2010

The $\underline{H}igh$ flux $\underline{A}dvanced$ $\underline{N}eutron$ $\underline{A}pplication$ $\underline{R}eact\underline{O}r$ (HANARO), an open-tank-in-pool type reactor, is one of the multi-purpose research reactors in the world. Since the commencement of HANARO's operations in 1995, a significant number of experimental facilities have been developed and installed at HANARO, and continued efforts to develop more facilities are in progress. Owing to the stable operation of the reactor and its frequent utilization, more experimental facilities are being continuously added to satisfy various fields of study and diverse applications. The irradiation testing equipment for nuclear fuels and materials at HANARO can be classified into capsules and the Fuel Test Loop (FTL). Capsules for irradiation tests of nuclear fuels in HANARO have been developed for use under the dry conditions of the coolant and materials at HANARO and are now successfully utilized to perform irradiation tests. The FTL can be used to conduct irradiation testing of a nuclear fuel under the operating conditions of commercial nuclear power plants. During irradiation tests conducted using these capsules in HANARO, instruments such as the thermocouple, Linear Variable Differential Transformer (LVDT), small heater, Fluence Monitor (F/M) and Self-Powered Neutron Detector (SPND) are used to measure various characteristics of the nuclear fuel and irradiated material. This paper describes not only the status of HANARO and the status and perspective of irradiation devices and instrumentation for carrying out nuclear fuel and material tests in HANARO but also some results from instrumentation during irradiation tests.

• Nuclear Engineering and Technology
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• v.52 no.4
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• pp.827-834
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• 2020

Damage of tungsten due to helium ions of a PF device was studied. The tungsten was analyzed by SEM and AFM after irradiation. SEM revealed fine bubbles of helium atoms with diameters of a few nanometers, which join and form larger bubbles and blisters on the surface of tungsten. This observation confirmed the results of molecular dynamics simulation. SEM analysis after etching of the irradiated surface indicated cavities with depth range of 35-85 nm. The average fluence of helium ion of the PF device was calculated about 5.2 × 10¹⁵ cm^-2 per shot, using Lee code. Energy spectrum of helium ions was estimated using a Thomson parabola spectrometer as a function of dN/dE ∝ E^-2.8 in the energy range of 10-200 keV. The characteristics of helium ion beam was imported to SRIM code. SRIM revealed that the maximum DPA and maximum helium concentration occur in the depth range of 20-50 nm. SRIM also showed that at depth of 30 nm, all of the tungsten atoms are displaced after 20 shots, while at depth of higher than 85 nm the destruction is insignificant. There is a close match between SRIM results and the measured depths of cavities in SEM images of tungsten after etching.

• Nuclear Engineering and Technology
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• v.52 no.8
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• pp.1784-1791
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• 2020

The 14 MeV neutron generator facility is being developed by the Institute for Plasma Research India to conduct the lab scale experiments related to Indian breeding blanket system for ITER and DEMO. It will also be utilized for material testing, shielding experiments and development of fusion diagnostics. Occupational radiation exposure control is necessary for the all kind of nuclear facilities to get the operational licensing from governing authorities and nuclear regulatory bodies. In the same way, the radiation exposure for the 14 MeV neutron generator facility at the occupational worker area and accessible zones for general workers should be under the permissible limit of AERB India. The generator is designed for the yield of 10¹² n/s. The shielding assessment has been made to estimate the radiation dose during the operational time of the neutron generator. The facility has many utilities and constraints like ventilation ducts, accessible doors, accessibility of neutron generator components and to conduct the experiments which make the shielding assessment challenging to provide proper safety for occupational workers and the general public. The neutron and gamma dose rates have been estimated using the MCNP radiation transport code and ENDF -VII nuclear data libraries. The ICRP-74 fluence to dose conversion coefficients has been used for the assessment. The annual radiation exposure has been assessed by considering 500 h per year operational time. The provision of local shield near to neutron generator has been also evaluated to reduce the annual radiation doses. The comprehensive results of radiation shielding capability of neutron generator building and local shield design have been presented in the paper along with detailed maps of radiation field.

• Progress in Medical Physics
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• v.23 no.1
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• pp.42-47
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• 2012

In this paper, Acousto-Optical tomography is modeled by a linear integral equation and an inverse problem involving a diffusion equation in n-spatial dimensions. We make two-step mathematical model. First, we solve a linear integral equation. Assuming the optical energy fluence rate has been recovered from the previous equation, the absorption coefficient ${\mu}$ is then reconstructed by solving an inverse problem. Numerical experiments are presented for the case n=2. The traditional gradient descent method is used for the numerical simulations. The result of the gradient descent method produces the blurring effect. To get rid of the blurring effect, we suggest the total variation regularization for the minimization problem.

• Journal of the Korean Ceramic Society
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• v.23 no.6
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• pp.37-44
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• 1986

Yttria-antimonia-stabilized zirconia was investigated with respect to the amount of $Sb_2O_3$ addition in the range of 0.5~5mole% to the base composition of $(ZrO)_{0.92}(Y_2O_3)_{0.08}$ The sinterbility modulus of rupture Vickers hardness evaporation of components phase form-tion and mcicrostructure were evaluated with antimonia content. Also two probe A. C conductivity measurement was subjected to all specimens and the best results are achieved with 1mol% $Sb_2O_3$ as a sinter agent and relative density of~98% obtained at 140$0^{\circ}C$ and this composition has a maximum electrical conductivity due to the possible substition of $Sb^{3+}$ for $Zr^{4+}$ site. The effect of $Sb_2O_3$ on the electrical conductivity of th bulk and the grain boundaries has on investigated using frequency dispersion analysis (5~106 Hz) Antimonia addition has a negative in-fluence on both the bulk and the grain boundary conductivity except for a 1 mon% addition. The additive antimonia has improve a modulus of rupture to 60~MPa due to metastable-tetragonal phase apparence and decrease the hardness with increasing the $Sb_2O_3$ content.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.11
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• pp.25-35
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• 2000

A simple two-terminal cyclic current0voltage(I-V) technique was used to measure the current-transients in metal-oxide-semiconductor capacitors. Distinct charging/discharging currents were measured and analyzed as a function of the hold time, the delay time, the gate polarity during the FNT electron injection, the injection fluence and the annealing time after the injection had stopped. The charge-exchange current was distinguished from total current-transients containing the displacement current components. Charging/discharging current caused by the charge exchange was strongly dependent not only on the density of positive charges in the $SiO_2$, but also on the density of interface traps generated during the FNT electron injection. Several tentative mechanisms were suggested.

• Journal of Radiation Protection and Research
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• v.2 no.1
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• pp.1-8
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• 1977

A base of photographic posi-film which is commecially available has been found to be a possible alpha-particle track detector. Its neutron dosimetric characteristics, i. e., alpha-particle track registrating efficiency and optimum condition of track formation by chemical etching, have been determined experimentally. The range of neutron fluence and dose capable of being measured by a neutron dosimeter consisting of alpha-particle radiator foils $(^{10}B\;and\;^{27}Al)$ and posi-flim solid state track detector, has been estimated on the basis of experimental results and theoryetical background. This detector seems to be useful for neutron dosimetry because of many favorable properties, i. e., simplicity, cheapness and a wide range of sensitivitiy.