• Macromolecular Research
• /
• v.12 no.1
• /
• pp.141-143
• /
• 2004

We have investigated the dynamic mechanical behavior of ultra-high molecular weight polyethylene (UHMWPE) irradiated with varying doses of gamma rays. A relaxation peak in the loss factor curve, which has not been reported previously in the literature, is observed at a temperature above the crystal melting temperature. The peak is unique to UHMWPE and appears to be related to the high degree of entanglement. Because the temperature and intensity of the peak are reduced by irradiation-induced chain scission and crosslinking, respectively, we believe that the peak is associated with disentanglement relaxation. The behavior of the storage modulus in the melt state agrees with the classical theory of rubber elasticity.

• Journal of the Korean Magnetic Resonance Society
• /
• v.8 no.1
• /
• pp.37-46
• /
• 2004

When human tooth enamel is exposed to the X-ray or ${\gamma}$-rays, free radicals and defects are created in a small quantity of carbonate enclosed in the tooth enamel. The intensity of the ESR signal of the free radicals is almost proportional to the absorbed radiation dose. However this dosimetric character is affected to some extent with the measurement temperature and thermal treatment of the samples. We found that the shape of the ESR signals of the samples is dependent upon the measurement temperature, the thermal annealing prior to the irradiation and that after the irradiation.

• Proceedings of the Korean Society of Medical Physics Conference
• /
• 2003.09a
• /
• pp.64-64
• /
• 2003

Objectives: Patient dose verification is clinically the most important parts in the treatment delivery of radiation therapy. The three dimensional(3D) reconstruction of dose distribution delivered to target volume helps to verify patient dose and determine the physical characteristics of beams used in intensity modulated radiation therapy(IMRT). We present Beam Intensity Scanner(BInS) system for the pre treatment dosimetric verification of two dimensional photon intensity. The BInS is a radiation detector with a custom made software for relative dose conversion of fluorescence signals from scintillator. Methods: This scintillator is fabricated by phosphor Gadolinium Oxysulphide and is used to produce fluorescence from the irradiation of 6MV photons on a Varian Clinac 21EX. The digitized fluoroscopic signals obtained by digital video camera will be processed by our custom made software to reproduce 3D relative dose distribution. For the intensity modulated beam(IMB), the BInS calculates absorbed dose in absolute beam fluence, which are used for the patient dose distribution. Results: Using BInS, we performed various measurements related to IMRT and found the followings: (1) The 3D dose profiles of the IMBs measured by the BInS demonstrate good agreement with radiographic film, pin type ionization chamber and Monte Carlo simulation. (2) The delivered beam intensity is altered by the mechanical and dosimetric properties of the collimating of dynamic and/or static MLC system. This is mostly due to leaf transmission, leaf penumbra, scattered photons from the round edges of leaves, and geometry of leaf. (3) The delivered dose depends on the operational detail of how to make multileaf opening. Conclusions: These phenomena result in a fluence distribution that can be substantially different from the initial and calculative intensity modulation and therefore, should be taken into account by the treatment planing for accurate dose calculations delivered to the target volume in IMRT.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.44 no.11
• /
• pp.949-956
• /
• 2016

There are a number of effects by solar radiation in many aerospace industrial fields, such as degradation of mechanical properties, sealing effect of sealants or decolorization. Because it takes long time to investigate these effects by using the light of natural state, new methods are developed for accelerating this phenomenon. In this paper, we developed an apparatus to simulate accelerated solar radiation phenomenon selecting irradiation intensity $1,120W/m^2$ as the designed environment. Epoxy polymer as the composite material was chosen and processed by ASTM-D638, a reference for tensile test of polymer and plastic. Total color shift was selected as the test category to evaluate acceleration of the test. We obtained acceleration factors and numerical model from test data and concluded it can shorten test periods by accelerated irradiation intensity of $1,120W/m^2$.

• Korean Journal of Food Science and Technology
• /
• v.32 no.3
• /
• pp.525-530
• /
• 2000

A study was carried out to establish the detection method of irradiated agricultural products cultivated in Korea by Thermoluminscece(TL). Samples were irradiated using Co-60 gamma rays at various doses(0.05, 0.1, 0.2, 0.3 and 0.5 kGy). After irradiation, separated minerals of the samples measured by TL. TL intensity increased with increasing doses and the irradiated samples were higher than the non-irradiated samples. TL first and second glow curves showed maximum TL temperature point at $176.16{\sim}190.08^{\circ}C$ and $143.84{\sim}146.56^{\circ}C$, respectively. All the irradiated samples can be classified correctly by the shape of the glow curve and the glow curve ratio. Correlation coefficients of ginger, carrot, potato and sweet potato were 0.9968, 0.8522, 0.9612 and 0.9071, respectively, that showed very high correlation between irradiation dose and TL intensity. Therefore, these results suggest that TL measurement is an useful detection method for irradiated agricultural products.

• Journal of Conservation Science
• /
• v.32 no.4
• /
• pp.501-510
• /
• 2016

In this study, we investigated the degradation of adhesives when exposed to ultraviolet light irradiation using samples of lacquer (L), treated lacquer (TL), lacquer mixed with glue (LG), and urushiol mixed with glue (UG). Four types of film specimens were collected under the ultraviolet exposure time, and gloss test, tensile shear strength test, scanning electron microscope analysis, and infrared spectroscopic analysis were conducted for the specimens. LG and UG showed lowering rate of gloss is somewhat later than L. Also, it was observed that with increasing exposure time to ultraviolet irradiation, the surface of L began to show spherical pits and cracks when the polysaccharide layers started to be exposed, whereas the surfaces of LG and UG remained smooth. The Infrared spectra of L and TL showed that the intensity of the overall peak decreased with increasing ultraviolet irradiation time. There was no change in the peak intensity of LG, but for UG, the peaks at $3013cm^{-1}$, $1593cm^{-1}$ and so on disappeared and the overall intensity declined. The tensile shear strength of LG and UG was maintained or increased as compared to the initial test, whereas the tensile shear strength of L decreased sharply after 600 h. LG and UG exhibited fewer changes as a result of high temperature and humidity conditions, and they retained their strength under UV exposure. These results indicate that LG and UG are more durable than L when subjected to environmental change.

• Progress in Medical Physics
• /
• v.34 no.4
• /
• pp.41-47
• /
• 2023

Purpose: This study aimed to dosimetrically compare the technique of three-dimensional conformal radiotherapy (3D CRT), which is a traditional prophylactic cranial irradiation method, and the intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) techniques used in the last few decades with the dynamic conformal arc therapy (DCAT) technique. Methods: The 3D CRT, VMAT, IMRT, and DCAT plans were prepared with 25 Gy in 10 fractions in a Monaco planning system. The target volume and the critical organ doses were compared. A comparison of the body V₂, V₅, and V₁₀ doses, monitor unit (MU), and beam on-time values was also performed. Results: In planned target volume of the brain (PTV_Brain), the highest D99 dose value (P<0.001) and the most homogeneous (P=0.049) dose distribution according to the heterogeneity index were obtained using the VMAT technique. In contrast, the lowest values were obtained using the 3D CRT technique in the body V₂, V₅, and V₁₀ doses. The MU values were the lowest when DCAT (P=0.001) was used. These values were 0.34% (P=0.256) lower with the 3D CRT technique, 66% (P=0.001) lower with IMRT, and 72% (P=0.001) lower with VMAT. The beam on-time values were the lowest with the 3D CRT planning (P<0.001), 3.8% (P=0.008) lower than DCAT, 65% (P=0.001) lower than VMAT planning, and 76% (P=0.001) lower than IMRT planning. Conclusions: Without sacrificing the homogeneous dose distribution and the critical organ doses in IMRTs, three to four times less treatment time, less low-dose volume, less leakage radiation, and less radiation scattering could be achieved when the DCAT technique is used similar to conventional methods. In short, DCAT, which is applicable in small target volumes, can also be successfully planned in large target volumes, such as the whole-brain.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.22 no.3
• /
• pp.193-198
• /
• 2009

Recently, characteristic research by the changes in the spectrum, one of the factors that influence analysis of maximum output power of PV module, has been studied. In this paper, a one-day intensity of solar irradiation, change of spectrums with time and electrical output for spectrums are analyzed. As a result, blue-rich wavelength compared with red-rich wavelength has large variation of solar irradiance with time, so we recognized that change of solar irradiance is dominated by variation of blue~rich wavelength. Also in same intensity of solar irradiance, electrical output in blue-rich wavelength was 3-8 % higher than one in red-rich wavelength.

• Journal of Korean Society on Water Environment
• /
• v.20 no.6
• /
• pp.577-582
• /
• 2004

The photocatalytic degradation of atrazine and PCP, a endocrine disruptors, has been investigated over $TiO_2$ photocatalysts under ultraviolet (UV) light irradiation. The effect of operational parameters, i.e., pH, light intensity and persulphate concentration on the degradation rate of aqueous solution of atrazine and PCP has been examined. The results presented in this work demonstrate that, as pH and the light intensity increased, the photocatalytic reaction rates were enhanced. Individual use of $TiO_2$-persulphate was far more effective than using only $TiO_2$ in atrazine and PCP removal. Based on the overall experimental results, the photocatalytic oxidation of atrazine and PCP with the coated $TiO_2$ photocatalyst is found to be very effective under the operational conditions delineated in this study.

• Journal of Life Science
• /
• v.6 no.3
• /
• pp.193-197
• /
• 1996

The action spectrum for mycelial growth and fruitbody primordium formation in Pleurotus ostreatus has been studied by irradiation at various wavelengths. Effective wavelengths. Effective wavelengths were distributed from near ultraviolet to blue region of spectrum. The most effect of light was observed in the region between 340 to 500 nanometers. The light intensity required to obtain of the maximum effect at the most effective wavelengths(430-500nm), was over 6.8 mW/Cm$^{2}$. Up to 6.8 mW/Cm$^{2}$, the primordium formed about 25 hr after the start of illumination. The higher the light intensity, the earlier the formation of the primordium formation : Up to about 6.8 mW/Cm$^{2}$.