• Progress in Medical Physics
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• v.6 no.2
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• pp.41-50
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• 1995

The absorbed dose and contaminant electron distribution of therapeutic X-ray beam (15MV photon) was studied with a half blocked beams of 30$\times$30$\textrm{cm}^2$ and field size ranging from 5$\times$5 to 30$\times$30$\textrm{cm}^2$. For a 15MV photon beam energy, the value of the depth of dose maximum, d$_{max}$, gradually decrease with increasing field size from 5$\times$5 to 30$\times$30$\textrm{cm}^2$ due to mainly by contaminant electrons which are produced in the flattening filter and scattered by collimator jaws, tray holder〔Lucite〕, blocking block and air. The results suggest that separate dosimetry data should be kept for blocked and unblocked field. The inherence of the contaminant electrons to the open field depth of maximum dose can lead to mistaken results if attenuation measurements are made at that depth. A nurmerous contaminant electrons mainly were distributed as shape of corn in the central photon beam and their path length in the water were shorter than 30mm because of the electrons energy having around 6MeV. These results clearly appears that the substraction of scattered electrons (electrons and positrons) from the total depth dose curve not only lowers the absolute dose in the bulidup region and surface dose, it also causes a shift of d$_{max}$ to a deeper depth. In the terapeutic high energy photon beam, the absorbed dose near the buildup region is the combined result of incident contaminant electrons and phantom generated electronsrons.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.403-408
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• 1999

In this paper, ultrasonic tomography by the Mode-Converted Rayleigh wave (MCRW) in the back-scattered direction is presented. When a beam with a short pulse and narrow beam width enters a reflector with smooth surface, in general, two major arrivals can be observed in the output waveform: the specular reflection and the radiation of the MCRW from the reflector surface. The time-delay between the two waves is relatively large and thus can be measured easily. This large time-delay is due to the fact that the MCRW is slower than incident wave. In our method, this large time- delay is used for ultrasonic image reconstruction. To effectively detect the MCRW, the arrayed-receiving transducers are circularly arranged around the transmitter. In addition, a deconvolution method is employed to remove specular echo signals for reconstructing the MCRW image.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
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• 2001.06a
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• pp.1627-1627
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• 2001

In this study, a newly constructed optical measurement system, whose main components were a parametric tunable laser and a near infrared photoelectric multiplier, was applied to detection of the information for the inside of Satsuma mandarin using time-of-flight near infrared spectroscopy (TOF-NIRS). The combined effects on the time resolved profile of sample diameter, sugar content, the wavelength of the laser beam, and the detection position of transmitted light were investigated in detail. The samples used were Satsuma mandarin (Citrus unshu $M^{ARC}$.) (location: Wakayama, Japan) having the diameters of 50-84 mm. The sugar content measured by a refractometer varied from 9.9 to 16.3 Brix%. Equator of sample was irradiated vertically with the pulsed laser, and transmitted output power was measured on the restricted position of the equator using the optical fiber cable. The sampling time and the number of averaging the output power were 100 ns and 100 times, respectively. The variation of the attenuance of peak maxima At, the time delay of peak maxima t and the variation of full width at half maximum w were strongly dependent on the detection position and the wavelength of the laser beam. At, t and w increased gradually as the sample diameter increased to be much absorbed and vigorously scattered. On the other hand, each optical parameter had a tendency to increase as the sugar content increased. Such behavior was remarkable when the transmitted light was detected at the side face of a sample. When we apply TOF-NIRS to detection of the information for the inside of fruit with high moisture content like Satsuma mandarin, it is very important to give attention to the difference in the scattered light within tissues and the semi-straightly propagated light. Furthermore, we tried to express the resulting phenomena by using a model samples composed of water, sucrose, and milk. The variation of the time resolved profile is strongly governed by the combination of the light absorption component, scattering medium, and refractive index.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
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• 2001.06a
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• pp.1626-1626
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• 2001

In this study, a newly constructed optical measurement system, whose main components were a parametric tunable laser and a near infrared photoelectric multiplier, was applied to detection of the information for the inside of Satsuma mandarin using time-of-flight near infrared spectroscopy (TOF-NIRS). The combined effects on the time resolved profile of sample diameter, sugar content, the wavelength of the laser beam, and the detection position of transmitted light were investigated in detail. The samples used were Satsuma mandarin (Citrus unshu $M_{ARC}$.) (location: Wakayama, Japan) having the diameters of 50-84 mm. The sugar content measured by a refractometer varied from 9.9 to 16.3 Brix%. Equator of sample was irradiated vertically with the pulsed laser, and transmitted output power was measured on the restricted position of the equator using the optical fiber cable. The sampling time and the number of averaging the output power were 100 ns and 100 times, respectively. The variation of the attenuance of peak maxima At, the time delay of peak maxima $\Delta$t and the variation of full width at half maximum Δw were strongly dependent on the detection position and the wavelength of the laser beam. At, $\Delta$t and $\Delta$w increased gradually as the sample diameter increased to be much absorbed and vigorously scattered. On the other hand, each optical parameter had a tendency to increase as the sugar content increased. Such behavior was remarkable when the transmitted light was detected at the side face of a sample. When we apply TOF-NIRS to detection of the information for the inside of fruit with high moisture content like Satsuma mandarin, it is very important to give attention to the difference in the scattered light within tissues and the semi-straightly propagated light. Furthermore, we tried to express the resulting phenomena by using a model samples composed of water, sucrose, and milk. The variation of the time resolved profile is strongly governed by the combination of the light absorption component, scattering medium, and refractive index.

• The Korean Journal of Ceramics
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• v.6 no.2
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• pp.129-133
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• 2000

Boron nitride films were synthesized with $N_2$ion flux of low energy, up to 100 eV, at different substrate temperatures of no heating, 200, 400, 500, and $800^{\circ}C$, respectively. Boron was supplied by e-beam evaporation at the rate of $1.5\AA$/sec. For all the conditions, hexagonal BN (h-BN) phase was mainly synthesized and high resolution transmission electron microscopy (HRTEM) showed that (002) planes of h-BN phase were aligned vertical to the Si substrate. The maximum alignment occurred around $400^{\circ}C$. In addition to major h-BN phase, transmission electron diffraction (TED) rings identified the formation of cubic BN (c-BN) phase. But HRTEM showed no distinct and continuous c-BN layer. These results suggest that c-BN phase may form in a scattered form even when h-BN phase is mainly synthesized under small momentum transfer by bombarding ions, which are not reconciled with the macro compressive stress model for the c-BN formation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.3
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• pp.566-574
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• 1988

A study is described for obtaining real time in situ size and velocity measurements of the spray-droplet using crossed-beam interferometry. The optical arrangement is similar to dual-beam laser Doppler velocimetry(LDV). Droplets passing trough the probe volume scatter light to the collecting lens placed at 90.deg. off-axis angle. The dual-beam light scatter is analyzed by the geometric optics theory to relate the scattered fringe pattern to droplet diameter. The droplet size measurement is based upon the signal visibility. As the system is based on the Doppler effect, a single component of velocity is velocity is extracted concurrent with the size information. The validity of the method is evaluated by comparing its performance to widely accepted but limited technique, the collection method. By using 90.deg. off-axis scatter detection angle, the measurement of the droplet size and velocity distributions, and the local correlations between droplet sizes and velocities in relatively dense spray environments are made possible.

• Progress in Medical Physics
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• v.32 no.4
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• pp.137-144
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• 2021

Purpose: This study aimed to investigate the accuracy of head scatter factor (S_c) by applying a developed multi-leaf collimator (MLC) scatter source model for an unflattened photon beam. Methods: Sets of S_c values were measured for various jaw-defined square and rectangular fields and MLC-defined square fields for developing dual-source model (DSM) and MLC scatter model. A 6 MV unflattened photon beam has been used. Measurements were performed using a 0.125 cm³ cylindrical ionization chamber and a mini phantom. Then, the parameters of both models have been optimized, and S_c has been calculated. The DSM and MLC scatter models have been verified by comparing the calculated values to the three S_c set measurement values of the jaw-defined field and the two S_c set measurement values of MLC-defined fields used in the existing modeling, respectively. Results: For jaw-defined fields, the calculated S_c using the DSM was consistent with the measured S_c value. This demonstrates that the DSM was properly optimized and modeled for the measured values. For the MLC-defined fields, the accuracy between the calculated and measured S_c values with the addition of the MLC scatter source appeared to be high, but the only use of the DSM resulted in a significantly bigger differences. Conclusions: Both the DSM and MLC models could also be applied to an unflattened beam. When considering scattered radiation from the MLC by adding an MLC scatter source model, it showed a higher degree of agreement with the actual measured S_c value than when using only DSM in the same way as in previous studies.

• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.919-926
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• 2023

To analyze the cause of the destruction of thin, carbon-backed lithium fluoride targets during a measurement of the fusion of ⁷Li and ¹⁷O, we estimate theoretically the lifetimes of carbon and LiF films due to sputtering, thermal evaporation, and lattice damage and compare them with the lifetime observed in the experiment. Sputtering yields and thermal evaporation rates in carbon and LiF films are too low to play significant roles in the destruction of the targets. We estimate the lifetime of the target due to lattice damage of the carbon backing and the LiF film using a previously reported model. In the experiment, elastically scattered target and beam ions were detected by surface silicon barrier (SSB) detectors so that the product of the beam flux and the target density could be monitored during the experiment. The areas of the targets exposed to different beam intensities and fluences were degraded and then perforated, forming holes with a diameter around the beam spot size. Overall, the target thickness tends to decrease linearly as a function of the beam fluence. However, the thickness also exhibits an increasing interval after SSB counts per beam ion decreases linearly, extending the target lifetime. The lifetime of thin LiF film as determined by lattice damage is calculated for the first time using a lattice damage model, and the calculated lifetime agrees well with the observed target lifetime during the experiment. In experiments using a thin LiF target to induce nuclear reactions, this study suggests methods to predict the lifetime of the LiF film and arrange the experimental plan for maximum efficiency.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.209-212
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• 2009

It has been widely reported that carbide-free bainitic steels or super-bainite WP (SB-TRIP) steels for the automotive industry are a new family of steels offering a unique combination of high strength and ductility. Hence, it is important to exactly evaluate the volume fraction of RA and to identify the 3-D morphology of constituent phases, because it plays a crucial role in mechanical properties. Recently, as electron back-scattered diffraction (EBSD) equipped with focused ion beam (FIB) has been developed, 3-D EBSD technique for materials science are used to these steels. Moreover, newly developed atom probe tomography (APT) technique can provide the exact distribution and chemical concentration of alloying elements in a sub-nm scale. The APT analysis results indicate exactly the distribution and composition of alloying elements in the austenite and bainite phases of SB-TRIP steels with the atomic-scale resolution. And thus, no partitioning of aluminum and manganese atoms was showed between the austenite containing $7.73{\pm}0.39$ at% C and the bainitic ferrite associated with $0.22{\pm}0.06$ at% C in the SB-TRIP steel.

• Transactions of Materials Processing
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• v.19 no.1
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• pp.44-49
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• 2010

It has been widely reported that carbide-free bainitic steels or super-bainite TRIP (SB-TRIP) steels for the automotive industry are a new family of steels offering a unique combination of high strength and ductility. Hence, it is important to exactly evaluate the volume fraction of RA and to identify the 3-D morphology of constituent phases, because it plays a crucial role in mechanical properties. Recently, as electron back-scattered diffraction (EBSD) equipped with focused ion beam (FIB) has been developed, 3-D EBSD technique for materials science are used to these steels. Moreover, newly developed atom probe tomography (APT) technique can provide the exact distribution and chemical concentration of alloying elements in a sub-nm scale. The APT analysis results indicate exactly the distribution and composition of alloying elements in the austenite and bainite phases of SB-TRIP steels with the atomic-scale resolution. And thus, no partitioning of aluminum and manganese atoms was showed between the austenite containing $7.73{\pm}0.39$ at% C and the bainitic ferrite associated with $0.22{\pm}0.06$ at% C in SB-TRIP steel.