• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2002년도 제3회 최신 분말제품 응용기술 Workshop
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• pp.25-37
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• 2002

The most important industrial application of gamma radiation in characterizing green compacts is the determination of the density. Examples are given where this method is applied in manufacturing technical components in powder metallurgy. The requirements imposed by modern quality management systems and operation by the workforce in industrial production are described. The accuracy of measurement achieved with this method is demonstrated and a comparison is given with other test methods to measure the density. The advantages and limitations of gamma ray densitometry are outlined. The gamma ray densitometer measures the attenuation of gamma radiation penetrating the test parts (Fig. 1). As the capability of compacts to absorb this type of radiation depends on their density, the attenuation of gamma radiation can serve as a measure of the density. The volume of the part being tested is defined by the size of the aperture screeniing out the radiation. It is a channel with the cross section of the aperture whose length is the height of the test part. The intensity of the radiation identified by the detector is the quantity used to determine the material density. Gamma ray densitometry can equally be performed on green compacts as well as on sintered components. Neither special preparation of test parts nor skilled personnel is required to perform the measurement; neither liquids nor other harmful substances are involved. When parts are exhibiting local density variations, which is normally the case in powder compaction, sectional densities can be determined in different parts of the sample without cutting it into pieces. The test is non-destructive, i.e. the parts can still be used after the measurement and do not have to be scrapped. The measurement is controlled by a special PC based software. All results are available for further processing by in-house quality documentation and supervision of measurements. Tool setting for multi-level components can be much improved by using this test method. When a densitometer is installed on the press shop floor, it can be operated by the tool setter himself. Then he can return to the press and immediately implement the corrections. Transfer of sample parts to the lab for density testing can be eliminated and results for the correction of tool settings are more readily available. This helps to reduce the time required for tool setting and clearly improves the productivity of powder presses. The range of materials where this method can be successfully applied covers almost the entire periodic system of the elements. It reaches from the light elements such as graphite via light metals (AI, Mg, Li, Ti) and their alloys, ceramics ($AI_20_3$, SiC, Si_3N_4, $Zr0_2$, ...), magnetic materials (hard and soft ferrites, AlNiCo, Nd-Fe-B, ...), metals including iron and alloy steels, Cu, Ni and Co based alloys to refractory and heavy metals (W, Mo, ...) as well as hardmetals. The gamma radiation required for the measurement is generated by radioactive sources which are produced by nuclear technology. These nuclear materials are safely encapsulated in stainless steel capsules so that no radioactive material can escape from the protective shielding container. The gamma ray densitometer is subject to the strict regulations for the use of radioactive materials. The radiation shield is so effective that there is no elevation of the natural radiation level outside the instrument. Personal dosimetry by the operating personnel is not required. Even in case of malfunction, loss of power and incorrect operation, the escape of gamma radiation from the instrument is positively prevented.

• 치과방사선
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• 제18권1호
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• pp.53-66
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• 1988

Irradiation is widely used for the treatment of malignant diseases, and possibly cause the osteoporosis. The bone densitometry and bone scintigraphy are valuable when used to monitor the patients longitudinally to access the progression of osteoporosis and risk of osteoradionecrosis. To evaluate the osteoporosis after irradiation of cobalt-60 gamma ray on the lumbar spines of New Zealand white rabbits, bone densitometry by dual photon absortiometry and bone scintigraphy were performed weekly. The decrease of bone density began at the first week after irradiation, and were in the nadir at 4-6th week. The osteoblastic activity measured by bone scintigraphy decreased in the first week, and was in the nadir at 4-6th week. The severity of these changes were related to the radiation dose. In conclusion, the osteoporosis before presentation of the osteoradionecrosis can be developed at low dose irradiation and confirmed by bone densitometry, bone scanning, and histopathology.

• 대한핵의학회지
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• 제24권2호
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• pp.307-316
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• 1990

Irradiation is widely used for the treatment of malignant diseases, and possibly cause the osteoporosis. The densitometry and bone scintigraphy are valuable when used to monitor the patients longitudinally to access the progression of osteoporosis and risk of osteoradionecrosis. To evaluate the osteoporosis after irradiation of Cobalt-60 gamma ray on the lumbar spines of New Zealand white rabbits, bone densitometry by dual photon absorptiometry and bone scintigraphy were performed weekly. The decrease of bone density began at the first week after irradiation, and were in the nadir at 4-6th week. The osteoblastic activity measured by bone scintigraphy decreased in the first week, and was in the nadir at 4-6th week. The severity of these changes were related to the radiation dose. In conclusion, the osteoporosis before the presentation of the osteoradionecrosis can be diagnosed early with the dual photon absorptionmetry and bone scintigraphy.

• Journal of Radiation Protection and Research
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• 제34권1호
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• pp.9-14
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• 2009

High density polyethylene (HDPE) is degraded due to a radiation-induced oxidation when it is used as a neutron moderator in a neutron counter for a nuclear material accounting of spent fuels. The HDPE exposed to the gamma-ray emitted from the fission products in a spent nuclear fuel results in a radiation-induced degradation which changes its original molecular structure to others. So a neutron moderating power variation of HDPE, irradiated by a gamma radiation, was investigated in this work. Five HDPE moderator structures were exposed to the gamma radiation emitted from a $^{60}Co$ source to a level of $10^5-10^9$ rad to compare their post-irradiation properties. As a result of the neutron measurement test with 5 irradiated HDPE structures and a neutron measuring system, it was confirmed that the neutron moderating power for the $10^5$ rad irradiated HDPE moderator revealed the largest decrease when the un-irradiated pure one was used as a reference. It implies that a neutron moderating power variation of HDPE is not directly proportional to the integrated gamma dose rate. To clarify the cause of these changes, some techniques such as a FTIR, an element analysis and a densitometry were employed. As a result of these analyses, it was confirmed that the molecular structure of the gamma irradiated HDPEs had partially changed to others, and the contents of hydrogen and oxygen had varied during the process of a radiation-induced degradation. The mechanism of these changes cannot be explained in detail at present, and thus need further study.

• 대한본초학회지
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• 제26권2호
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• pp.1-10
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• 2011

Objective ： Lonicera japonica contains anti complementary polysaccharides and polyphenolic compound. Among these polyphenolic substances, chlorogenic acid is the major active component of this plant. However, the immunological mechanisms for these activities, have not been elucidated, nor the active components. To clarify immunomodulatory effects of those we examined the relationship between the activity of CD8+ T cell-mediated lysis and the frequency of cytokine profiles in spleen, thymus (especially IFN-${\gamma}$, IL-4, GM-CSF etc.) expressing CD8+ T cells activated by IL-2. Methods : To study immunomodulatory effects ethyl acetate fraction from Lonicera japonica, chlorogenic acid on cytokine gene expression from spleen, thymus cells, RT-PCR was performed after quantitative normalization for each gene by a densitometry using ${\beta}$-actin gene expression. A modified standard $^{51}Cr$-release assay was used to measure cytotoxic activities of cytotoxic T cells. Spleen, thymus cells from NOD mice were stained with CD3, CD4, CD44, CD69 in staining buffer and analyzed by two color flow cytometry. Results : We showed that ethyl acetate fraction from Lonicera japonica in combination with IL-2 resulted in a significant enhancement of PCR products for IFN-${\gamma}$, IL-4, IL-10, GM-CSF, IL-6 and cytotoxtic CD8+ T cell proportion in spleen and thymus T cells in NOD mice. This suggests that IFN-${\gamma}$, IL-6 like IL-4 may be acting as a regulatory rather than proinflammatory cytokine. Conclusions : In conclusion, based on the results of the present study which showed that ethyl acetate fraction from Lonicera japonica and chlorogenic acid upregulating cytokine gene expression in spleen and thymus, we are tempted to speculate that some of the therapeutic efficacies such as anti-diabetic activity of Lonicera japonica are due to the immunomodulatory its ethylacetate fraction and chlorogenic acid.

• Nuclear Engineering and Technology
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• 제53권7호
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• pp.2334-2340
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• 2021

Radioactive particle tracking (RPT) is a minimally invasive nuclear technique that tracks a radioactive particle inside a volume of interest by means of a mathematical location algorithm. During the past decades, many algorithms have been developed including ones based on artificial intelligence techniques. In this study, RPT technique is applied in a simulated test section that employs a simplified mixer filled with concrete, six scintillator detectors and a¹³⁷Cs radioactive particle emitting gamma rays of 662 keV. The test section was developed using MCNPX code, which is a mathematical code based on Monte Carlo simulation, and 3516 different radioactive particle positions (x,y,z) were simulated. Novelty of this paper is the use of a location algorithm based on a deep learning model, more specifically a 6-layers deep rectifier neural network (DRNN), in which hyperparameters were defined using a Bayesian optimization method. DRNN is a type of deep feedforward neural network that substitutes the usual sigmoid based activation functions, traditionally used in vanilla Multilayer Perceptron Networks, for rectified activation functions. Results show the great accuracy of the DRNN in a RPT tracking system. Root mean squared error for x, y and coordinates of the radioactive particle is, respectively, 0.03064, 0.02523 and 0.07653.

• Radiation Oncology Journal
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• 제11권2호
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• pp.439-448
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• 1993

Leksell 감마나이프(B-형)가 1992년 3월 경희대학교 의과대학 병원에 설치되었다. 선택적 빔 Plugging방법을 이용하여 정상 민감 조직에 대한 저선량 분포를 현저히 줄일 수 있으며, 또한 치료 부위에 더 좋은 선량 분포를 얻을 수 있다. 저선량에 대한 여러가지 선량 분포의 변화에 대한 연구를 하였으며, 사용중인 KULA프로그램의 선량 분포 곡선을 평가하기 위해 필름을 이용한 방사선량 계측을 실시하였고, RFA-3자동 밀도 측정기를 이용하여 평가하였다. 1992년 3월부터 1993년 2월까지 1년동안 100명의 환자중 17명의 환자에 선택적 빔 차폐 방법이 적용되었다. 고선량 영역에서는 측정값과 프로그램에서 제공된 선량 분포가 잘 일치하였다. 뇌하수체 선종의 치료시 치료 부위가 클 경우에는 본 연구 방법의 적용이 매우 중요시 되었으며, 반면에 치료 영역이 작을 경우에는 적절한 헬맷의 선택이 중요함을 알 수 있었다. 치료 환자의 중요 민감 장기의 방사선 선량 평가에서는 뇌간에 3~12 Gy, 시신경 교차에 3~11.2 Gy이었다. 중추신경계 영역의 최적화된 치료를 위하여 다양한 Plugging형태를 임상에 적용하는 것이 방사선에 민감한 정상 조직을 보호하기 위해 매우 중요한 인자가 됨을 알았다.

• 대한방사선기술학회지:방사선기술과학
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• 제32권4호
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• pp.411-418
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• 2009

성인들의 생화학적 표식자를 검사해 골밀도에 직접 관여할 수 있는 중요한 유전적 또는 생화학적 인자들을 규명하고 성인들의 골다공증 병태생리에 관련된 정보를 제공하고 골다공증의 위험인자 등과의 관련요인을 분석하였다. 2007년 9월 12일부터 2008년 3월 18일까지 대학병원 건강증진센터에 내원한 남성 568명 여성 430명으로 총 998명 수진자를 대상으로 양 에너지 엑스선 골밀도 측정기를 이용하여 대퇴경부 및 척추의 골밀도를 측정하였다. 골밀도에 직접 관여하는 혈액의 생화학적 표식자는 인, 칼슘, 관절염, 헤모글로빈, 글루코오스, 간 기능검사의 GOT, GPT, $\gamma$-GTP를 측정하여 성인들의 골다공증 병태생리에 관련된 정보를 제공하여, 골다공증의 진단과 치료 및 예방에 생화학적 위험인자를 분석하여 관련요인을 조사하였다. 남성은 대퇴경부 및 척추의 골밀도는 20대에서 가장 높았고, 60대에서 대퇴경부와 척추의 골밀도가 가장 낮았다. 여성은 대퇴경부의 골밀도가 20대에서 가장 높았으나 척추는 40대에서 골밀도가 가장 높았고, 60대에서 대퇴경부와 척추의 골밀도가 가장 낮았다. 여성들 중 폐경 후의 여성들보다 폐경 전의 여성들이 골밀도가 유의하게 높았으며, 남성의 생화학적 표식자 인에서 정상 기준치 이상 군에서 대퇴경부와 척추에서 골밀도가 높았으며 여성은 정상치군일 때가 대퇴경부와 척추에서 골밀도가 높게 나타났다. 나이가 많아짐에 따라 골밀도는 낮아지고 체중이 높아지면 골밀도는 높아졌다.