This work presents the Monte Carlo simulation emphasizing that the ionization distribution influenced by the implementation of a 3D multicellular model irradiated with 50 keV gamma. We recorded the ...spatial number of ionizations in cytoplasm after irradiation to the voxelated whole cell model. The biological response of the cytoplasm affected by ionization of the nucleus due to scattering was calculated. In the case of a cell model with a voxels of 21 × 21 × 21, the gamma source induces ten times the number of ionizations in the cytoplasm associated with the nucleus when compared to alpha particles. The gamma source shows that the secondary particles can reach the cytoplasm when the primary particles stay in the nucleus. This demonstrates that in the case of photons, the non-negligible scattering can cause additional damage in the cytoplasm during neighbor irradiation. Realistic simulations on a microscopic scale allow us to prove the important role into the potentially lethal cell damage processes.
In the design of a W/C multilayer mirror, we applied a trilayer model to consider the interdiffusion of tungsten and carbon on the W-on-C interface and investigated the first Bragg angle and its ...reflectivity. As the interdiffusion thickness of a W/C multilayer mirror increased, the first Bragg angle and the reflected X-ray energy increased. However, as the period thickness of the W/C multilayer mirror increased, the effects of the interdiffusion became less pronounced. The criteria for the use of either the bilayer or the trilayer models for the design of W/C multilayer mirrors were presented for various period thicknesses. The trilayer model would be useful for the design of multilayer mirrors with a small period thickness of less than approximately 4.0 nm at an interdiffusion of 0.28 nm.
X-ray computed tomography is a very useful tool for nondestructively imaging a cross section of a sample. By using a computed tomography beamline system of synchrotron radiation, we directly measured ...the radius of the inner reflection surface of a mono-capillary optic with an accuracy of 1.30
μ
m. The inner-surface deformation of a mono-capillary optic approximately 100
μ
m in diameter was first shown by combining radial profiles. The precise determination of the radius will contribute to an increase in fabrication precision for the mono-capillary optic.
This work presents simulations of the concentration of clustered DNA damage of various complexities induced by monoenergetic electrons, protons, and alpha particles within the range of linear energy ...transfer (LET). Using Geant4-DNA tool, we measured the LET in liquid water and calculated the frequency of base damage around single strand breaks, double strand breaks, and complex strand breaks. The protons and the alpha particles depended greatly on LET, which affected the concentration of base damage. For alpha particles, at 206.40 keV/μm, a high LET region was irradiated, the number of cases with more than 6 base damages was increased by about 70 times compared to the low LET region. The data indicate that high-LET radiation is likely to be much more effective in producing concentrated clusters of damage, and that having a quantitative estimate of the extent of this type of damage is important. These lesions are responsible for most of the significant cellular effects associated with ionizing radiation.
Monte Carlo simulations can classify DNA damage into different types and predict the amount of energy deposited. Geant4-DNA was used to predict simple and complex DNA damage induced by irradiation of ...low-energy electrons at 0.1-50 keV. The number of molecules generated at different energy levels of radiation was analyzed after observing the gradual changes in the level of water radiolysis. A DNA model was used to categorize direct damage according to the location of strand breaks at the atomic level. The parameters of energy threshold (minimum amount of energy needed to break DNA strands) and 10 base pairs (maximum distance that separates two strand breaks) were set. All instances of water radiolysis including the main OH radical occurred most frequently at 1 keV followed by at 1.5 and 0.5 keV. Direct strand breaks most commonly occurred at 0.5 keV followed by at 0.3 keV. Finally, most of strand breaks occurred more frequently at 0.5 keV than at 0.3 keV. The computational measurement results for indirect and direct effects of irradiation depend on the type of simulation code and the DNA model used. Values used in Geant4 (physics list, chemical interaction time and energy threshold) may also influence the results.
양성자 치료는 브래그 피크로 인해 우수한 치료 기법으로 알려져 있다. 양성자의 치료 효과를 높이기 위해 금 나노입자를 종양에 분포시켜 흡수선량을 높이는 방법이 연구되고 있다. 마이크로미터와 나노미터 범위에서 금 나노입자를 다루었던 것을 밀리미터 범위에서 금 나노입자를 전산모사 할 수 있는 방법을 제시하였다. 전산모사를 위해 Geant4 툴킷을 사용하였다. ...인체와 유사한 물과 금 나노입자가 균일하게 분포되어 있다는 것을 가정하고 밀도비를 통해 금 나노입자의 개수 또는 농도를 조절하였다. 브래그 피크 위치에서 밀도비가 5%일 때 금 나노입자로 인해 순수 물 팬텀에 비해 흡수 에너지의 이득이 거의 2배로 나타났다. 밀도비가 증가할수록 흡수 에너지의 이득은 선형적으로 증가하였다. 브래그 피크 위치에서 금 나노입자가 하나의 복셀에만 분포하고 있을 때 양성자의 에너지는 자신 주변의 복셀에만 영향을 미치지만, 넓은 영역에 금 나노입자가 분포하는 경우 순수 물 팬텀에서 최고 흡수 에너지 (9.95 keV)의 95% 흡수 에너지(9.46 keV)를 나타내는 부피는 16배 큰 영역에서 흡수 에너지의 이득이 나타났다. 그리고 이 영역은 밀도비가 증가할수록 증가하였다. 밀리미터 범위에서 금 나노입자의 밀도비와 RBE의 관계를 정량화하는 등 추가적인 연구가 필요하다.
Proton therapy is known for its superior treatment method due to Bragg peak. To enhance the therapeutic effects of protons, research has been conducted on distributing gold nanoparticles within tumors to increase the absorbed dose. While previous studies focused on handling gold nanoparticles at micrometer and nonometer scale, this study proposes a method to computationally estimate the effect of gold nanoparticles at the millimeter scale. The Geant4 toolkit was applied to computational modeling. Assuming a uniform distribution of water, similar to the human body, and gold nanoparticles, the concentration of gold nanoparticles was adjusted using density ratios. When the density ratio was 5%, the gain in absorbed energy due to gold nanoparticles was nearly twice that of the pure water phantom at the Bragg peak. As the density ratio increased, the gain in absorbed energy linearly increased. When gold nanoparticles were distributed in only one voxel at the Bragg peak, the energy of the protons affected only the neighboring voxels. However, in cases where gold nanoparticles were distributed over a wide area, the volume showing 95% of the maximum absorbed energy (9.46 keV) for the pure water phantom (9.95 keV) exhibited an improvement in absorbed energy over a region 16 times larger, and this region increased as the density ratio increased. Further research is needed to quantify the relationship between the density ratio of gold nanoparticles and the relative biological effect (RBE) in the millimeter scale.
엑스선형광분석은 비파괴적으로 시료에 포함된 원소와 농도를 분석할 수 있는 기법으로 과학 및 산업분야에 광범위하게 사용되고 있다. 다양한 물질을 포함한 혼합물 또는 화합물 분석의 정밀도 향상을 위해 10 keV 근방의 저에너지와 20 keV 근방의 에너지 영역에 높은 강도 분포를 갖는 엑스선관이 요구된다. 두 에너지 영역에서 높은 강도 분포를 갖는 ...스펙트럼을 얻기 위하여 9.65 keV의 특성엑스선을 가지는 텅스텐과 17.48 keV의 몰리브덴 두 물질을 적층한 구조의 표적을 가지는 투과형 엑스선관을 몬테카를로 전산모사를 통해 스펙트럼을 분석하였다. W-Mo 구조의 표적을 통해 10 keV와 20 keV 근방의 강한 강도를 갖는 특성엑스선을 얻었다. 또한 4 μm 두께의 Mo-W multilayers 구조의 표적을 통해 최적의 강도 분포를 갖는 스펙트럼을 얻을 수 있음을 확인하였다. 다양한 표적 물질을 선택 조합하고 두께 최적화를 통해 원하는 에너지 대역에서 높은 강도 분포를 갖는 스펙트럼을 얻는 것이 가능하다.
X-ray fluorescence analysis has been widely used in the field of science and industry because it gives information about elements and their concentrations without destruction of samples. To increase analysis accuracy of fluorescence generated by photons of the transmission-type X-ray tube for mixture and compound samples would be recommend to have strong energy near 10 keV and 20 keV simultaneously. Tungsten of 9.65 keV and molybdenum of 17.48 keV were considered as targets with dual deposition structure for obtaining two strong characteristic X-rays, and the transmission-type X-ray tube was analyzed using Geant4 Monte Carlo simulation. The W-Mo structure resulted in strong characteristic X-ray near 10 keV and 20 keV simultaneously. A structure with Mo-W multilayers of 5 μm thick also gave optimal spectrum. Various material combination and thickness optimization for the dual-structured target can give X-ray spectrum with strong characteristic X-ray of specific energies.
We examined the occurrence patterns of insect pests in paddy fields using a self-organizing map (SOM) and the influence of meteorological factors on these patterns. Data for nine insect pests and ...three meteorological factors were collected on the Korean nationwide scale from 1992 to 2008. The SOM analysis was based on annual mean densities of each pest species in eight regions. We classified the samples into five clusters (I–V) to display the spatial and temporal changes in the insect pests' occurrences. Clusters I and II included samples collected before 2000; clusters III and IV included samples collected after 2000. The density of Scotinophara lurida was in the lowest range in clusters I and II, and Lissorhoptrus oryzophilus exhibited higher densities in clusters III and IV. Seasonal temperature, humidity, and precipitation were significantly different among clusters, indicating that these factors play a key role in population dynamics and the occurrence of insect pests. The occurrence area of the insect pests was expected to increase with elevated air temperature influenced by global warming based on the IPCC (Intergovernmental Panel on Climate Change) A1B scenario. This study suggests that gathering data on temporal and spatial variations in pest populations and changes in occurrence rate under the effects of global warming can provide insight into the factors governing the population-environment relationships, as well as the information needed for future pest management.
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► SOM identified five occurrence patterns of nine pest insects in the paddy fields. ► The occurrence patterns showed spatial and temporal changes of nine pest insects. ► Meteorological factors were significantly different among patterns. ► The occurrence area of the pests was expected to increase with the global warming.
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