• Journal of the Optical Society of Korea
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• 제13권1호
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• pp.22-27
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• 2009

Target design study to improve the quality of an accelerated proton beam from the interaction of a high-intensity short pulse laser with an overdense plasma slab has been accomplished by using a two-dimensional, fully electromagnetic and relativistic particle-in-cell (PIC) simulation. The target consists of a thin core part and a thick peripheral part of equivalent plasma densities, while the ratio of the radius of the core part to the laser spot size, and the position of the peripheral part relative to the fixed core part were varied. The positive effects of this core-peripheral target structure could be expected from the knowledge of the typical target normal sheath acceleration (TNSA) mechanism in a laser-plasma interaction, and were apparently evidenced from the comparison with the case of a conventional simple planar target and the case of the transversal size reduction of the simple planar target. Improvements of the beam qualities including the collimation, the forward directionality, and the beam divergence were verified by detailed analysis of relativistic momentum, angular directionality, and the spatial density map of the accelerated protons.

• International Journal of Precision Engineering and Manufacturing
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• 제8권2호
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• pp.14-19
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• 2007

Angle sensors based on the principle of autocollimation, which are usually called autocollimators, can accurately measure small tilt angles of a light-reflecting flat surface. This paper describes a prototype micro-angle sensor that is based on the laser autocollimation technique. The new angle sensor is compact and consists of a laser diode as the light source and a quadrant photodiode as a position-sensing device. Because of its concise design, the microangle sensor facilitates dynamic measurements of the angular error motions of a precision stage without influencing the original dynamic properties of the stage. This is because the sensor only requires a small extra target mirror to be mounted on the stage. The sensitivity of the angle detection is independent of the focal length of the objective lens; therefore, an objective lens with a relatively short focal length is employed to reduce the size of the device. The micro-angle sensor uses a single lens for the both the laser collimation and focusing, which distinguishes it from the conventional laser autocollimation method that has separate collimate and objective lenses. The new micro-angle sensor has dimensions of $15.1\times22.0\times14.0mm$ and its resolution is better than 0.1 arc-second The optical design and performance of this micro-angle sensor were verified by experimental results.

• Journal of Astronomy and Space Sciences
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• 제33권4호
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• pp.247-256
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• 2016

An analysis of light curves and spectra of observed gamma-ray bursts in gamma-ray ranges is frequently demanded because the prompt emission contains immediate details regarding the central engine of gamma-ray bursts (GRBs). We have revisited the relationship between the collimation-corrected peak luminosity and the spectral lag, investigating the lag-luminosity relationships in great detail by focusing on spectral lags resulting from all possible combinations of channels. Firstly, we compiled the opening angle data and demonstrated that the distribution of opening angles of 205 long GRBs is represented by a double Gaussian function having maxima at ~ 0.1 and ~ 0.3 radians. We confirmed that the peak luminosity and the spectral lag are anti-correlated, both in the observer frame and in the source frame. We found that, in agreement with our previous conclusion, the correlation coefficient improves significantly in the source frame. It should be noted that spectral lags involving channel 2 (25-50 keV) yield high correlation coefficients, where Swift/Burst Alert Telescope (BAT) has four energy channels (channel 1: 15-25 keV, channel 2: 25-50 keV, channel 3: 50-100 keV, channel 4: 100-200 keV). We also found that peak luminosity is positively correlated with peak energy.

• 한국항공우주학회지
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• 제48권12호
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• pp.987-995
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• 2020

고성능 탑재체들과 자세제어 센서들 간의 정밀정렬은 인공위성의 정확한 자세지향 및 높은 지향 안정성을 위해 필수적이다. 위성 개발사들은 조립 및 시험기간 동안 위성 정렬을 위해 데오드라이트 측정 시스템을 주로 사용한다. 데오드라이트 측정 시 시선 방향 오차, 수평축의 오차, 수직방향 인덱스 오차 그리고 수직축 오차로 인해 측정오차가 발생할 수 있다. 이러한 오차들 뿐 아니라 다수의 데오드라이트를 사용한 측정 시 발생할 수 있는 오차들을 정렬큐브 측정실험을 통해 분석하였다. 정렬큐브 측정실험을 기반으로 정렬측정 정확도를 향상시킬 수 있는 방법이 제안되었고, 측정 결과 위성의 설계 요구조건도 만족시킬 수 있었다.

• Current Optics and Photonics
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• 제7권4호
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• pp.419-427
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• 2023

The structural design of an optical-telescope assembly (OTA) for satellite laser ranging (SLR) is conducted in two steps. First, the results of a parametric study of the major design variables (e.g. dimension and shape) of the OTA part are explained, and the detailed structural design of the OTA is derived, considering the design requirements. Among the structural-shape concepts of various OTAs, the Serrurier truss concept is selected in this study, and the collimation of the telescope according to the design variables is extensively discussed. After generating finite-element models for different structural shapes, self-gravity analyses are performed. To minimize the deflection and tilt of the mirror and frame for the OTA under the limited design requirements, a parametric study is conducted according to design variables such as the shapes of the upper and lower struts and the spider vane. The structural features found in the parametric study are described. Finally, the OTA structure is designed in detail to maintain the optical alignment by balancing the gravity deflections of the upper and lower trusses using the optimal combination of the parameters. Additionally, thermal analysis of the optical telescope design is evaluated.

• Radiation Oncology Journal
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• 제1권1호
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• pp.29-36
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• 1983

The treatment of tumors along curved surfaces with stationary electron beams using cone collimation may lead to non-uniform dose distributions due to a varying air gap between the cone surface and patient. For large tumors, more than one port may have to be used in irradiation of the chest wall, often leading to regions of high or low dose at the junction of the adjacent ports. Electron-beam arc therapy may elimination many of these fixed port problems. When treating breast tumors with electrons, the energy of the internal mammary port is usually higher than that of the chest wall port. Bolus is used to increase the skin dose or limit the range of the electrons. We invertiaged the effect of various arc beam parameters in the isodose distributions, and combined into a single arc port for adjacent fixed ports of different electron beam eneries. The higher fixed port energy would be used as the arc beam energy while the beam penetration in the lower energy region would be controlled by a proper thickness of bolus. We obtained the results of following: 1. It is more uniform dose distribution of electron to use rotation than stationary irradiation. 2. Increasing isocenter depth on arc irradiation, increased depth of maximum dose, reduction in surface dose and an increasing penetration of the linear portion of the curve. 3. The deeper penetration of the depth dose curve and higher X-ray background for the smaller field sized. 4. If the isocenter depth increase, the field effect is small. 5. The decreasing arc beam penetration with decreasing isocenter depth and the isocenter depth effect appears at a greater depth as the energy increases. 6. The addition of bolus produces a shift in the penetration that is the same for all depths leaving the shape of the curves unchanged. 7. Lead strips 5 mm thick were placed at both ends of the arc to produce a rapid dose drop-off.

• Imaging Science in Dentistry
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• 제43권3호
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• pp.179-184
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• 2013

Purpose: X-ray exposure should be clinically justified and each exposure should be expected to give patients benefits. Since dental radiographic examination is one of the most frequent radiological procedures, radiation hazard becomes an important public health concern. The purpose of this study was to investigate the attitude of Korean dentists about radiation safety and use of criteria for selecting the frequency and type of radiographic examinations. Materials and Methods: The study included 267 Korean dentists. Five questions related to radiation safety were asked of each of them. These questions were about factors associated with radiation protection of patients and operators including the use of radiographic selection criteria for intraoral radiographic procedures. Results: The frequency of prescription of routine radiographic examination (an example is a panoramic radiograph for screening process for occult disease) was 34.1%, while that of selective radiography was 64.0%. Dentists' discussion of radiation risk and benefit with patients was infrequent. More than half of the operators held the image receptor by themselves during intraoral radiographic examinations. Lead apron/thyroid collars for patient protection were used by fewer than 22% of dental offices. Rectangular collimation was utilized by fewer than 15% of dental offices. Conclusion: The majority of Korean dentists in the study did not practice radiation protection procedures which would be required to minimize exposure to unnecessary radiation for patients and dental professionals. Mandatory continuing professional education in radiation safety and development of Korean radiographic selection criteria is recommended.

• 한국의학물리학회지:의학물리
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• 제11권2호
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• pp.147-155
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• 2000

Patient dose verification is one of the most important parts in quality assurance of the treatment delivery for radiation therapy. The dose distributions may be meaningfully improved by modulating two dimensional intensity profile of the individual high energy radiation beams In this study, a new method is presented for the pre-treatment dosimetric verification of these two dimensional distributions of beam intensity by means of a charge coupled device video camera-based fluoroscopic device (henceforth called as CCD-VCFD) as a radiation detecter with a custom-made software for dose calculation from fluorescence signals. This system of dosimeter (CCD-VCFD) could reproduce three dimensional (3D) relative dose distribution from the digitized fluoroscopic signals for small (1.0$\times$1.0 cm$^2$ square, ø 1.0 cm circular ) and large (30$\times$30cm$^2$) field sizes used in intensity modulated radiation therapy (IMRT). For the small beam sizes of photon and electron, the calculations are performed In absolute beam fluence profiles which are usually used for calculation of the patient dose distribution. The good linearity with respect to the absorbed dose, independence of dose rate, and three dimensional profiles of small beams using the CCD-VCFD were demonstrated by relative measurements in high energy Photon (15 MV) and electron (9 MeV) beams. These measurements of beam profiles with CCD-VCFD show good agreement with those with other dosimeters such as utramicro-cylindrical (UC) ionization chamber and radiographic film. The study of the radiation dosimetric technique using CCD-VCFD may provide a fast and accurate pre-treatment verification tool for the small beam used in stereotactic radiosurgery (SRS) and can be used for verification of dose distribution from dynamic multi-leaf collimation system (DMLC).

• Radiation Oncology Journal
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• 제20권1호
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• pp.68-72
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• 2002

최근 들어 새로운 방사선치료법인 강도변조방사선치료가 많은 종류의 종양치료에 적용되어 치료에 따른 부작용을 줄이고 치료율을 향상시키려는 노력들이 이루어지고 있다. 특히 전립선암에서 강도변조방사선치료법을 적용하여 삼차원입체조형치료에 비해 향상된 선량분포와 이로 인한 주위 정상조직의 방사선량을 줄임으로써 더욱 많은 양의 방사선을 전립선에 투여할 수 있고 이로 인하여 치료율의 상승을 기대할 수 있게 되었다. 저자들은 강도변조방사선치료를 전립선암에 적용하였기에 이에 대한 문헌고찰과 함께 치료과정을 보고하고자 한다.

• 대한디지털의료영상학회논문지
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• 제11권1호
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• pp.15-20
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• 2009

Far reducing medical radiation exposure and managing patient doses, Entrance surface doses(ESDs) were measured at Diagnostic Radiology Department in ASAN medical center, also we determined and compared with the Diagnostic Reference Level(DRL) of some other countries. ESDs were measured far the most common types of X-ray procedures, such as chest PA, lumbar spine AP, lumbar spine lateral, Pelvis AP, Skull PA. ESDs were measured by Glass dosimeter and Unfors Xi meter. Those were applied collimation center of phantom's entrance skin surface. The results of ESDs were compared Glass dosimeter with Unfors Xi meter. Those were measured within 5% statistical difference. It seemed well agreement at two devices. In most cases ESDs measured far the different types of X ray procedures were found to be lower than the DRL of IAEA, but ESDs on chest PA, lumbar spine AP, lumbar spine lateral, Pelvis AP, Skull PA were proximity ar excesses at DRL of advanced country. Through this study, we need an investigation and improvement at present diagnostic radiology exam system. Also, radiologists make an effort to reduce patient dose and having a technical skill.