• Journal of the Optical Society of Korea
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• v.3 no.1
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• pp.27-31
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• 1999

The two-photon absorption of a SiC photodiode was utilized to obtain autocorrelation signals of the pulses from a mode-locked Rh6G dye laser. The autocorrelation signals were in good agreement with those obtained by a conventional autocorrelator using a second harmonic crystal and photomultiplier tube. The sensitivity of the autocorrelator with the SiC photodiode was about $4{\times}10^3 {(mW)}^2$ . From these results it was demonstrated that the SiC photodiode is suitable as a nonlinear device for an autocorrelation measurement in the visible range.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.172-172
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• 2000

진공상태에서 diamond stylus로 MgO 표면을 마모시킬 때 발생되는 photon, electron과 마찰력을 시간의 함수로 동시에 측정하였다. 전자 방출(EE)은 Channeltron electron multiplier로 , 광자 에너지는 Photomultiplier tube를 사용하여 측정하였는데 180~600nm 영역의 photon을 검출하였다. 광자 방출(PhE,) 실험은 공기중에서도 할 수 있으나 전자방출은 1$\times$10-4pa 이하의 진공에서 실험하여 얻었다. 본 실험을 통하여 결정과 diamond stylus 사이에서 일어나는 마모 현상은 millisecond로 관찰하여 표면 변화에 대한 상관관계를 조사하였다. 열처리 한것과 열처리 하지 않은 시료를 비교한 결과 3개의 signal(마찰력, PhE, EE)을 시간에 따라 분석하면 stick-slip-like 현상을 볼 수 있었다. 이것으로 보아 stick은 변형에 의해 생기고 ms 후에 벽개 현상이 발생됨을 볼 수 있다. 방출과 마찰력은 표면조건, load, stylus velocity에 따라 변하였다. luminescence는 주로 변형에 의해 생겼으며, 전자 방출은 벽개(fracture)에 의해 발생됨을 알 수 있었다. 시료의 처리과정과 load 속도에 따른 Photon, electron의 방출은 시료의 표면 상태에 따라 좌우되었다. 마찰력, PhE, EE의 시간에 따른 분석에서 PhE는 변형 과정에 민감하며, EE는 stylus velocity에 의존하였다. 이러한 방출 현상은 세라믹의 급격한 벽개 과정을 이해하는데 많은 도움을 주었다.

• Bulletin of the Korean Chemical Society
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• v.8 no.5
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• pp.403-405
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• 1987

A dynamic laser light scattering system has been constructed using a personal computer. The intensity of the scattered light was detected with a photomultiplier tube and a photon counter. The BCD output of the photon counter which is proportional to the intensity of scattered light is fed into a personal computer via an interface card. The personal computer was programmed as an autocorrelator in machine language. The data acquisition rate of the system was about 600 samples/s which is adequate for studies on the molecular dynamics of concentrated polymer solutions, polymer latices with large particle size, and polymer glass systems. The constructed system was tested with polystyrene latex and the measured diameter of the latex particle agrees well with the supplier's value.

• The Korean Journal of Nuclear Medicine
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• v.38 no.5
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• pp.338-343
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• 2004

Purpose: The purpose of this study was to develop a small animal PET using dual layer phoswich detector to minimize parallax error that degrades spatial resolution at the outer part of field-of-view (FOV). Materials and Methods: A simulation tool GATE (Geant4 Application for Tomographic Emission) was used to derive optimal parameters of small PET, and PET was developed employing the parameters. Lutetium Oxyorthosilicate (LSO) and Lutetium-Yttrium Aluminate-Perovskite(LuYAP) was used to construct dual layer phoswitch crystal. $8{\times}8$ arrays of LSO and LuYAP pixels, $2mm{\times}2mm{\times}8mm$ in size, were coupled to a 64-channel position sensitive photomultiplier tube. The system consisted of 16 detector modules arranged to one ring configuration (ring inner diameter 10 cm, FOV of 8 cm). The data from phoswich detector modules were fed into an ADC board in the data acquisition and preprocessing PC via sockets, decoder block, FPGA board, and bus board. These were linked to the master PC that stored the events data on hard disk. Results: In a preliminary test of the system, reconstructed images were obtained by using a pair of detectors and sensitivity and spatial resolution were measured. Spatial resolution was 2.3 mm FWHM and sensitivity was 10.9 $cps/{\mu}Ci$ at the center of FOV. Conclusion: The radioactivity distribution patterns were accurately represented in sinograms and images obtained by PET with a pair of detectors. These preliminary results indicate that it is promising to develop a high performance small animal PET.

• Journal of Korean Ophthalmic Optics Society
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• v.6 no.2
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• pp.71-75
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• 2001

In this paper, a three-dimensional measuring system of thermoluminescence(TL) spectra based on temperature, wavelength and luminescence intensity was introduced. The system was composed of a spectrometer, temperature control unit for thermal stimulation, photon detector and personal computer for control the entire system. Temperature control was achieved by using feedback to ensure a linear-rise in the sample temperature. Digital multimeter(KEITHLEY 195A) measures the electromotive force of Copper-Constantan thermocouple and then transmits the data to the computer through GPIB card. The computer converts this signal to temperature using electromotive force-temperature table in program, and then control the power supply through the D/A converter. The spectrometer(SPEX 1681) is controlled by CD-2A, which is controlled by the computer through RS-232 communication port. For measuring the luminescence intensity during the heating run, the electrometer(KEITHLEY 617) measures the anode current of photomultiplier tube(HAMAMATSU R928) and transmits the data to computer through the A/D converter. And, we measured and analyzed thermoluminescence of $CaSO_4$ : Dy, P using the system. The measuring range of thermoluminescence spectra was 300K-575K and 300~800 nm, $CaSO_4$ : Dy. P was fabricated by the Yamashita's method in Korea Atomic Energy Research Institute(KAERI) for radiation dosimeter. Thermoluminesce spectra of the $CaSO_4$ : Dy, P consist of two main peak at temperature of $205^{\circ}C$, wavelength 476 nm and 572 nm and with minor ones at 658 nm and 749 nm.

• Nuclear Engineering and Technology
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• v.52 no.4
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• pp.835-840
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• 2020

A position-sensitive CsI(Tl) crystal array coupled with the multi-anode position sensitive photomultiplier tube (PS-PMT), Hamamatsu H8500C, has been developed at the Institute of Modern Physics. An effective, fast, and economical readout circuit based on discretized positioning circuit (DPC) bridge was designed for the 64-channel multi-anode flat panel PSPMT. The horizontal and vertical position resolutions are 0.58 mm and 0.63 mm respectively for the 1.0 × 1.0 × 5.0 ㎣ CsI(Tl) array, and the horizontal and vertical position resolutions are 0.86 mm and 0.80 mm respectively for the 2.0 × 2.0 × 10.0 ㎣ CsI(Tl) array. These results show that the CsI(Tl) crystal array with low cost could be applied in the fields of medical imaging and high-resolution gamma camera.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.318-321
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• 2002

As a part of the next generation PET project, we have developed a depth of interaction detector which is consist of three-dimensional arrays of GSO crystal elements sized 2.9mm ${\times}$ 2.9mm ${\times}$ 7.5mm. The basic structure of a detector block is 4-stages in depth, one stage is composed of 2 by 2 array of the crystal elements. The blocks are optically coupled to a position sensitive photomultiplier tube. Each crystal element can be in different conditions; rough or chemical etching for the crystal surface. The effect of the difference of crystal surface condition on the detector performance was analyzed in one-dimensional crystal array as a basic study for the three-dimensional detector by a simple model which is considered only probabilities of transmission, reflect and absorption of photons are in a crystal. As the next step, we investigated the effect of different crystal surface condition in a "U shaped detector" which is an array of stacked crystals bending at the center.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.3
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• pp.51-54
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• 2008

A novel stereolithography method using evanescent light has been proposed as a means to realize 100-nanometer resolution. An in-process measurement system with high accuracy has been introduced to the nanostereolithography apparatus. Specifically, an optical microscopic system was developed to monitor the exposure process and a confocal positioning system was established to improve the longitudinal positioning accuracy in the layer-by-layer process. A high-power objective lens, a tube lens, and a charge coupled device (CCD) were included in the optical microscopic system, whereas a laser, a high-power objective lens, a piezoelectric (PZT) stage, a condenser lens, a pinhole, and a photomultiplier (PMT) made up the confocal microscopic system. Two verification experiments were conducted, and the results indicated that the optical microscopic system had a horizontal resolution of 200 nm and that the confocal positioning system provided a depth resolution of 30.8 nm. These results indicate that nanostereolithography can be successfully performed with this system.

• 한국가시화정보학회:학술대회논문집
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• 2004.12a
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• pp.147-155
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• 2004

Self-excited noise generation from laminar flames in thin annular jets of methane/air premixture has been investigated experimentally. Various flames were observed in this flow configuration, including conical shape flames, ring shape flames, steady crown shape flames, and oscillating crown shape flames. Self-excited noise with the total sound pressure level of about 70dB was generated from the oscillating crown shape flames for the equivalence ratio larger than 0.95. Sound pressure and $CH^*$ chemiluminescence were measured by using a microphone and a photomultiplier tube. The frequency of generated noise was measured as functions of equivalence ratio and premixture velocity. A frequency doubling phenomena have also been observed. The flame shape during flame oscillation was reconfirmed by a synchronized PIV experiment. The velocity and pressure field were obtained from PIV. The minimum pressure was formed near the edge of flame representing circulation. By comparing the results of sound pressure, flame luminosity and PIV, the noise source can be attributed to the flame front fluctuation near the edge of the oscillating crown-shape flames.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.311-316
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• 2010

The ignition and the burning characteristics of aluminum and magnesium particles ($30-110{\mu}m$ in diameter) isolated due to electrodynamic levitation were experimentally investigated. The burning time, the ignition delay time, the flame temperature, and the flame diameter were measured. The thermal radiation intensity was measured using the photomultiplier tube and the combustion history was monitored by high-speed cinematography. Two-wavelength pyrometry measured the temperature of the burning particles. The burning times of aluminum particles were measured approximately 5 to 8 times longer than those of magnesium particles. Exponents of $D^n$-law, for the burning rate of magnesium and aluminum particles of diameters less than $110{\mu}m$, are found to be 0.6 and 1.5, respectively. The instant of aluminum ignition is clearly distinguished with the ignition delay time little less than 10 ms, however the burning history of magnesium particle exhibits no distinct instant of the ignition. The ignition delay time of magnesium particle (less than $110{\mu}m$) were approximately shown in the range from 50 to 200 ns. The flame temperatures of single metal particles are lower than the boiling point of the oxide. The nondimensional flame diameters for magnesium are decreased with increasing of the diameter. The nondimensional flame diameters for aluminum are not changed significantly.