• 한국의학물리학회지:의학물리
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• 제26권2호
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• pp.99-105
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• 2015

모니터 전리함은 의료용 선형가속기에서 방출되는 방사선의 세기와 출력 제어를 위하여 사용된다. 본 연구에서는 가속기 기반 방사선 발생장치의 제어 시스템 개발에 사용하기 위하여 모니터 전리함 시작품을 개발하였다. 개발한 모니터 전리함은 평행 평판형 전리함 형태로서 독립적 작동이 가능한 두 개의 전리함으로 구성되어 있으며, 전극의 재료는 방사선의 감쇠를 최소화하기 위하여 얇은 연성인쇄회로기판이 사용되었다. 전리함의 시험을 위하여 코발트-60 방사선원을 이용하여 측정된 전하의 포화특성과 선형성과 같은 선량학적 특성을 평가하였다. 결과적으로 개발된 시작품이 기본 성능을 만족하며 추가 연구의 가능성을 확인하였다.

• 한국방사선학회논문지
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• 제15권6호
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• pp.869-875
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• 2021

이 연구의 목적은 CT 모의치료장치에서 발생된 X-선 빔의 유효에너지 계산식을 유도하는데 있다. 90, 120, 140 kVp X-선 빔 하에서, AAPM CT 성능 팬텀의 CT수 교정 삽입부는 CT 모의치료장치로 5번 스캔하였다. 폴리에틸렌, 폴리스틸렌, 물, 나일론, 폴리카보네이트, 그리고 아크릴의 CT수는 각각의 CT 슬라이스 영상에 대하여 측정하였다. 단일 관전압 하에서 측정된 CT수 평균값과 미국표준기술연구소의 자료로부터 계산된 각각의 광자에너지에 대응하는 선감쇠계수들을 선형정합하였다. 얻어진 상관계수들 중 최대값을 갖는 광자에너지를 유효에너지를 결정하였다. 이와 같은 방법으로, 각각의 관전압에서 생성된 X-선 빔의 유효에너지를 결정하였다. 결정된 유효에너지(y)들와 관전압(x)들을 선형정합하여 유효에너지 계산식으로서 y=0.33026x+30.80263을 유도하였다.

• 대한토목학회논문집
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• 제26권5A호
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• pp.917-925
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• 2006

AE기법을 이용하여 PSC보부재에 대한 음파의 전파속도와 음원위치 산정방법의 타당성을 알아보기 위한 실험을 수행하였다. 이를 위해 길이가 5m 인 PSC보 콘크리트 표면에 7개의 AE센서를 부착하였으며, 슈미트 햄머를 이용하여 콘크리트 표면에 인위적인 충격을 가하였다. 음파의 전파속도는 각각의 AE센서로부터 감지한 음파의 도달시간 차이와 음원과 센서와의 거리 차이를 이용하여 산정하였다. 또한 각 AE센서로부터 감지된 음파의 도달시간과 음파의 전파속도를 토대로 최소제곱법을 이용하여 역으로 음원 발생위치를 산정해 보았다. 실험결과 프리스트레스트콘크리트 매질에 대한 음파의 평균전파속도는 대략 4,000 m/sec 정도이며, 음원과 AE 센서 사이의 거리가 길어짐에 따라 음파의 감쇠현상에 의해 속도가 감소되었다. 최소제곱법을 이용한 음원위치 산정결과, 음파의 전파속도를 전체 AE센서의 평균전파속도를 이용하는 경우보다, 각 AE센서로 부터 산정된 음파의 전파속도를 이용하는 경우 오차가 감소되는 것을 확인하였다.

• Imaging Science in Dentistry
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• 제54권3호
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• pp.264-270
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• 2024

Purpose: This study aimed to propose a methodological approach for reducing the radiation dose in pediatric cone-beam computed tomography (CBCT), focusing exclusively on balancing image quality with dose optimization. Materials and Methods: The dose-area product (DAP) for exposure was reduced using copper-plate attenuation of an X-ray source. The thickness of copper (Cu) was increased from 0 to 2.2 mm, and 10 different DAP levels were used. The QUART DVT_AP phantom and pediatric radiologic dentiform were scanned under the respective DAP levels. The contrast-to-noise ratio (CNR), image homogeneity, and modulation transfer function (MTF) were analyzed using the QUART DVT_AP phantom. An expert evaluation (overall image grade, appropriateness of field of view, artifacts, noise, and resolution) was conducted using pediatric dentiform images. The critical DAP level was determined based on phantom and dentiform analysis results. Results: CNR and image homogeneity decreased as the DAP was reduced; however, there was an inflection point of image homogeneity at Cu 1.6 mm (DAP=138.00 mGy·cm²), where the value started increasing. The MTF showed constant values as the DAP decreased. The expert evaluation of overall image grades showed "no diagnostic value" for dentiform images with Cu 1.9-2.2 mm (DAP=78.00-103.33 mGy·cm²). The images with Cu 0-1.6 mm (DAP=138.00-1697.67mGy·cm²) had a "good," "moderate," or "poor but interpretable" grade. Conclusion: Reducing DAP beyond a 1.6-mm Cu thickness degraded CBCT image quality. Image homogeneity and clinical image grades indicated crucial decision points for DAP reduction in pediatric CBCT scans.

• 비파괴검사학회지
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• 제9권1호
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• pp.8-21
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• 1989

This paper presents the ultrasonic characteristics of weldment and detectability of defects of weldment in Austenitic Stainless Steel Type 304 that is composed of mostly coolant piping system in nuclear power plants. The results of this experient show as follows: 1. When the ultrasonic beam detects the defects on the side of base metal and on the opposite side of weldment, the indications which was detected on the screen show different amplitude and different metal path each. 2. The ultrasonically estimated notch depth is generally oversized than actual notch depth. 3. It is easy for the false indication to show up on the screen because of columnar structure of weldment in austenitic stainless steel. 4. The higher frequencies of transducer have more difficulties to detect the defects of the opposite side of weldment because of ultrasonic attenuation in weldment and the longitudinal transmitter-receiver transducer is the most effective in detecting the opposite side defects of weldment.

• 비파괴검사학회지
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• 제26권6호
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• pp.417-426
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• 2006

A Digital X-ray imaging system using Compton backscattering has been developed to obtain a cross-sectional profile and mass loss of corroded lap-splices of aging aircraft from density variation. A slit-type camera was designed to focus on a small scattering volume inside the material, from which the backscattered photons are collected by a collimated scintillator detector for interpretation of material characteristics. The cross section of the lap-joint is scanned by moving the scattering volume through the thickness direction of the specimen. The mass loss of each layer has been estimated from a Compton backscatter A-scan to obtain the thickness of each layer including the aluminum sheet, the corrosion layer and the sealant. Quantitative information such as location and width of planar corrosion in the lap splices of fuselages is obtained by deconvolution using a nonlinear least-square error minimization method(BFGS method): A simple reconstruction model is also introduced to overcome distortion of the Compton backscatter data due to attenuation effects attributed to beam hardening and quantum noise.

• 비파괴검사학회지
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• 제27권3호
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• pp.239-245
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• 2007

A torsional guided wave mode in a tubular structure has many advantages in obtaining a higher sensitivity and lower attenuation for a defect, because it shows no dispersion characteristics and no radial displacement for a tubular structure. Many attempts have been made to excite and receive torsional guided waves by conventional piezoelectric transducers, but only a few examples are used during a practical field inspection. In this study, an array of electromagnetic acoustic transducers (EMATs) were for an excitation and reception of the torsional guided waves in a pipe was designed and fabricated. The signal patterns were analyzed based on various beam path length. The feasibility of detecting the defects was investigated through a series of experiments with artificial notches on a pipe.

• 대한수의학회지
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• 제58권2호
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• pp.99-101
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• 2018

A 5-year-old intact female Persian cat was referred with anorexia and vomiting. Physical examination revealed icterus in the pinna, oral mucosa, and sclera. Ultrasonography revealed several findings including uniformly hyperechoic hepatic parenchyma compared to adjacent falciform fat, increased attenuation of the ultrasound beam, and poor visualization of intrahepatic vessel borders. Computed tomography revealed hypoattenuation of the hepatic parenchyma with a radiodensity value of -60 Hounsfield units. The adjacent intrahepatic vessels appeared hyperattenuated relative to the hepatic parenchyma as if the vessels were contrast-enhanced. Based on ultrasonography and computed tomography results, the cat was tentatively diagnosed as feline hepatic lipidosis.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.206.2-206.2
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• 2014

Recently, particle induced X-ray emission (PIXE) analysis system was installed at the 2MV ion acceleration system in Korea institute science and technology (KIST). This installation is for complement to low atomic resolution of heavy atoms at Rutherford backscattering spectrometry (RBS) system. For quantitative analysis, a mass calibration of the PIXE set-up has been done with thin film standards and. The GUPIX software package has been used to process the PIXE spectra and the results are compared with the values from RBS system. Therefore, the instrumental constant H (solid angle and correction factor) is determined relying completely on the GUPIX data base (cross-sections, fluorescence and Coster-Kronig probabilities, stopping powers and attenuation coefficients) for a large set of elements. These H values can be used in future analysis.

• Bulletin of the Korean Chemical Society
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• 제32권3호
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• pp.905-908
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• 2011

We report fluorescence excitation and emission spectra of the CHBr molecule generated via pyrolysis of $CH_3Br$ in a molecular beam experiment. The 193 nm attenuation cross sections were estimated from the reduction of the CHBr signal as a function of the excimer laser fluence. The derived 193 nm absorption cross section for CHBr [$(3.24{\pm}0.59){\times}10^{-17}\;cm^2$] is slightly higher than the absorption cross section previously determined for CHCl [$(2.6{\pm}0.8){\times}10^{-17}\;cm^2$], but the difference is within the estimated uncertainties in the measured cross section.