Distribution Of Radiation Field Research Articles

Two-dimensional dose distribution measurement based on rotational optical fiber array: A Monte Carlo simulation study

Quality assurance is particularly important for modulated radiotherapies which improve dose conformity and involve complex processes of dose delivery. This work proposes a dose measurement method based on a rotational optical fiber array and the Cherenkov effect as an alternative pretreatment quality assurance method. Monte Carlo simulation toolkit Geant4 is used to study the accuracy and influencing factors of this method. Four different shapes of radiation field are designed to explore the influence of different reconstruction algorithms, fiber spacing, rotation angles, and radiation types on the accuracy of dose field measurement. The results show that the difference between the reconstructed dose field and the reference dose field is within 8% under the irradiation of uniform radiation field. To obtain high-precision reconstructed images, the fiber spacing should be within 2 mm, and at least 60 angles of projection data should be acquired when the fiber array is rotated 180°. In conclusion, the proposed new method using a rotating fiber array can reconstruct the radiation field distribution rapidly, and provides accurate information on the shape and intensity distribution of the radiation field. Further studies are needed to improve the accuracy and feasibility in real clinical practice.

Minimum collective dose based optimal evacuation path-planning method under nuclear accidents

The effectiveness of the path plan is the main factor of the evacuation affecting the amount of exposure to personnel, however, the effect of the radiation field distribution has not been fully considered in current studies. In this paper, a Minimizing Collective dose based Path-Planning method (MCPP) was proposed. Among which, the accumulative dose based Dijkstra algorithm was proposed to find the optimal evacuation routes, and then the equilibrium model considering road resistance was used to formulate the optimal evacuation path plan under nuclear accidents, in which the obtained routes were reasonably arranged to evacuate all people with minimize collective dose. This paper used the Daya Bay Nuclear Power Station as an application scenario for evacuation simulation to verify the effectiveness of the method. The results showed that the path plan formulated by MCPP method could reasonably reduce personnel radiation exposure during the evacuation process.

A radiation hydrodynamics scheme on adaptive meshes using the Variable Eddington Tensor (VET) closure

AbstractWe present a new algorithm to solve the equations of radiation hydrodynamics (RHD) in a frequency-integrated, two-moment formulation. Novel features of the algorithm include i) the adoption of a non-local Variable Eddington Tensor (VET) closure for the radiation moment equations, computed with a ray-tracing method, ii) support for adaptive mesh refinement (AMR), iii) use of a time-implicit Godunov method for the hyperbolic transport of radiation, and iv) a fixed-point Picard iteration scheme to accurately handle the stiff nonlinear gas-radiation energy exchange. Tests demonstrate that our scheme works correctly, yields accurate rates of energy and momentum transfer between gas and radiation, and obtains the correct radiation field distribution even in situations where more commonly used – but less accurate – closure relations like the Flux-limited Diffusion and Moment-1 approximations fail. Our scheme presents an important step towards performing RHD simulations with increasing spatial and directional accuracy, effectively improving their predictive capabilities.

Space-based full chain multi-spectral imaging features accurate prediction and analysis for aircraft plume under sea/cloud background.

Building a wide-area, high-efficiency, and accurate detection technology for air targets has become a new challenge for the construction of space situational awareness. Firstly, based on the space-based optical detection requirements for aircraft plume, the method of integrated modeling for sea/cloud background radiation characteristics based on coupling of remote sensing data and physical model is proposed, which can effectively deduce the background radiation field distribution under any environmental conditions. Specifically, combined with meteorological satellite sensor data, such as cloud top temperature, cloud type and cloud top height, three-dimensional atmospheric transmittance and atmospheric path thermal radiation texture are generated for different cloud heights and cloud phase conditions. Then, a coupled sea/cloud bidirectional reflectance model matched to the sampling of space-based detectors is established. Further, the accurate prediction model for multi-spectral imaging features of aircraft plume is built by considering the space-based full imaging chains including the complex coupling of aircraft plume, sea/cloud background, environmental atmosphere, optical system, and imaging detector. Finally, combined with the diffraction effect of the optical system, the multi-spectral imaging features of the aircraft plume are simulated under various spectral bands, flying heights, sea/cloud backgrounds, and detection angles, and the detection performances are analyzed and discussed by using the signal-to-clutter ratio (SCR). Research results show that the detection capability in the narrow band of 2.65-2.90µm and 4.25-4.50µm is better than the wide band of 3-5µm. When the aircraft flying height is greater than 5km, the aircraft plume can be detected in both narrow bands. It is more reliable to use the multispectral joint-band to detect aircraft plume in different backgrounds.

Terahertz radiation field distribution manipulation by metasurface with graphene substrate

Abstract Terahertz radiation field distribution manipulation gains increasing attention from both science and technology, but available mechanisms are hard to implement it. We design two asymmetric double-split ring resonators (DSRRs) based on theoretical analysis to realize terahertz radiation field distribution manipulation by metasurface with graphene substrate. Here we show that in principle the dynamic intensity regulation of left-handed circularly polarization (LHCP) and right-handed circularly polarization (RHCP) components can be realized by satisfying certain condition, which is derived from electro-optical effect of graphene in terahertz region. Furthermore, we show that the spatial angle control of LHCP and RHCP components can be realized by designing the arrangement and combination of meta-atoms based on Pancharatnam-Berry (PB) phase. Terahertz radiation field distribution manipulation not only promotes the sensing of terahertz micro-devices, but also facilitates the multifunctional control of holographic projection.

Optimal microwave imaging with random field illuminations

In the recent years, the theory and technologies of electromagnetic computational imaging have been well developed and several novel imaging methods have been proposed, one of which is known as the microwave imaging under random field illumination. In order to solve the matrix equation of imaging model, the key of such an imaging system is to generate the random electromagnetic radiation field distribution, implementing the independent measurements under random field illuminations. In this work, an optimal microwave imaging system for the desired imaging region and resolution is theoretically analyzed and experimentally implemented. In the randomness analysis, the correlation between different measurements is evaluated by the singular value decomposition, which is also adopted as a criterion for choosing the optimal parameters of the imaging system. Based on random field illuminations generated by the least number of antenna elements, a full-rank matrix equation can be used to reconstruct the object by direct matrix inversion, which can be completed in nearly real-time once the system calibration is implemented in advance. The numerical simulation and experimental investigation are performed, and the results prove the effectiveness of the proposed optimal imaging system. By using the traditional array theory, it is found that for an <i>N</i>-element phase array, <i>N</i> illuminations with each element excited by a single frequency, equal amplitude and randomized 0 or <inline-formula><tex-math id="M5000">\begin{document}${\text{π}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20182122_M5000.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20182122_M5000.png"/></alternatives></inline-formula> phase signal will result in <i>N</i> independent measurements. Theoretically, any additional measurement under random illumination will be correlated with the previous <i>N</i> measurements. Since the random field illumination is obtained by array antennas with 1-bit random phase modulation, the power radiated by each transmitting element is not sacrificed, resulting in an optimal power efficiency of the imaging system compared with those of earlier metasurface-based imaging systems. Besides, a single frequency signal source is used in the system, which also realizes the optimal spectrum efficiency. In conclusion, there are two major innovations of the proposed imaging system: 1) the completely random field illuminations based on 1-bit phase modulation; 2) the approach to optimizing the system on desired demand. The compact and low-cost imaging system promises to have various imaging applications, such as public security and indoor localization.

Proficiency of Leaky Coaxial Cable-Based MIMO System Using Radiated Field Distribution

This paper presents channel propagation characteristics of different multiple-input multiple-output (MIMO) systems using ray tracing approach in a confined area at 1.8 GHz according to the LTE-M standards. Leaky coaxial cables were exploited at different transmitted locations to visualize the fluctuated radiated field under different polarization combinations. In order to encounter this vision, the reflected and line-of-sight paths are under consideration for both vertically and horizontally polarized waves emitting from the leaky coaxial cables (LCXs). Emphasis is given to understand the effect of LCX configuration on the channel correlation coefficient and capacity (C) in the confined area. The exploration of experimental results reveals that the MIMO channel using LCXs has significant performance, specifically in the case of horizontal polarization. Furthermore, it is inferred that for the longer distance between transmitter and receiver, the correlation coefficients have higher magnitude.

Fast Near-Field Multifocusing of Antenna Arrays Including Element Coupling Using Neural Networks

A novel near-field focusing approach based on the use of artificial neural networks (NNs) is proposed. It is able to provide the set of weights or feeding values that must be applied to the elements of an array so that the global radiation/reception pattern is focused on one or more predefined positions in the near environment. Due to the use of a properly trained NN, it is able to work fast enough for real-time applications, such as wireless energy and information transfer where moving devices may require quick adaptation of the radiated field distribution and, hence, of the weights applied to the array. Moreover, the training procedure using examples generated with a convenient electromagnetic analysis tool allows taking into account both the radiation pattern of the elements of the array and the coupling effects between them.

Constraints on the Distribution of Gas and Young Stars in the Galactic Centre in the Context of Interpreting Gamma Ray Emission Features

Gamma ray observations have found evidence of an extremely energetic outflow emanating from the Galactic Centre, and an ‘excess’ of emission at GeV energies towards the Galactic Centre over that expected from current models. Determining whether the outflow is AGN- or star formation-driven, and whether the ‘excess’ is astrophysical in origin or requires new physics (e.g., self-annihilation of dark matter), requires the accurate modelling of the expected energy injection from astrophysical sources and the subsequent interaction with the surrounding environment. We briefly summarise current constraints on the distribution of gas and young stars in the inner few hundred parsecs of the Galaxy that can be included in future 2D and 3D modelling of the astrophysical gamma ray emission. The key points to highlight with respect to predominantly axisymmetric models currently in use are: (i) the distribution of dense gas, young stars and interstellar radiation field is highly asymmetric around the Galactic Centre; (ii) star formation is almost exclusively constrained to a Galactocentric radius of ∼100 pc; and (iii) the star formation rate in this region has been constant at ≲0.1 M ⊙ yr − 1 to within a factor of 2 over the last ∼5 Myr.

Numerical investigation of air-staged combustion to reduce NOX emissions from biodiesel combustion in industrial furnaces

In this paper, the combustion model of industrial furnace was established using numerical simulations. The application of air-staged combustion technology was used to solve the problem of high NOX emissions produced from the combustion of biodiesel in industrial furnaces. The simulation results were verified through experiments. The effects of secondary air distribution position (Zsec), secondary air distribution ratio (fsec) and the excess air coefficient (α) on the temperature field, incident radiation field and NOX concentration field distribution in the furnace were also studied. It was found that the simulated temperature and NOX concentration at the outlet of furnace were in good agreement with the experimentally determined results. When the staged combustion was not adopted, the NOX production in the furnace was at a high level. The average NOx concentration at the exit of the furnace was 0.000538 kg/m3. With the introduction of the staged ventilation technology, the lowest NOX production was 0.000276 kg/m3, the best reduction effect was 48.7%. The optimal two-air-staged combustion test conditions were included Zsec of 50%, fsec of 30%, and α of 1.15.

Modeling of Plane Arrays Using a Variational Approach

The variational statement of synthesis problem is generalized in order to account the additional requirements to the synthesized radiation pattern (RP) and field distribution in the specified points of near zone. For this aim, the minimizing functional is supplemented by term providing the possibility to minimize the values of field in these points; creating the deep zeros in the RP for the certain angular coordinates is realized too. The approach foresees reduction of an explicit formula for field values in a near zone. The results of computational modeling testify the possibility to create zeros in the given RP and to minimize the values of field in a near zone of plane arrays in a great extent.

Improving the efficiency and directivity of THz photoconductive antennas by using a defective photonic crystal substrate

One of the shortcomings of photoconductive (PC) antennas in terahertz (THz) generation is low effective radiated power in the desirable direction. In this paper, we propose a defective photonic crystal (DPC) substrate consisting of a customized 2D array of air holes drilled into a solid substrate in order to improve the radiation characteristics of THz PC antennas. The effect of the proposed structure on the performance of a conventional THz PC antenna has been examined from several aspects including radiation efficiency, directivity, and field distribution. By comparing the radiation performance of the THz antenna on the proposed DPC substrate to that of the conventional solid substrate, it is shown that the proposed technique can significantly improve the efficiency and directivity of the THz PC antenna over a wide frequency range. It is achieved by reducing the amount of power coupled to the substrate surface waves and limiting the radiation in undesirable directions. In addition, it is found that the sensitivity of directivity to the substrate thickness is considerably decreased and the adverse Fabry–Perot effects of the thick substrate are reduced by the application of the proposed DPC substrate.

Flavor-dependent Neutrino Angular Distribution in Core-collapse Supernovae

Abstract According to recent studies, the collective flavor evolution of neutrinos in core-collapse supernovae depends strongly on the flavor-dependent angular distribution of the local neutrino radiation field, notably on the angular intensity of the electron lepton number carried by neutrinos. To facilitate further investigations of this subject, we study the energy and angle distributions of the neutrino radiation field computed with the Vertex neutrino-transport code for several spherically symmetric (1D) supernova simulations (of progenitor masses 11.2, 15, and 25 M ⊙) and explain how to extract this information from additional models of the Garching group. Beginning in the decoupling region (“neutrino sphere”), the distributions are more and more forward peaked in the radial direction with an angular spread that is largest for ν e , smaller for , and smallest for ν x , where x = μ or τ. While the energy-integrated ν e minus angle distribution has a dip in the forward direction, it does not turn negative in any of our investigated cases.

Measurement of Spatial Dose Distribution of High Radiation Field by Radiophotoluminescence Photography

Measurement of Spatial Dose Distribution of High Radiation Field by Radiophotoluminescence Photography

Radiation dose and radiation field distribution in 128-slice CT scanning:a pilot study

Radiation dose and radiation field distribution in 128-slice CT scanning:a pilot study

Simulation of the response functions of an extended range neutron multisphere spectrometer using FLUKA

In this paper, the distribution of radiation field in the CSNS spectrometer hall at Dongguan, China, was simulated by the FLUKA program. The results show that the radiation field of the high energy proton accelerator is dominated by neutron radiation, with a broad range of neutron energies, spanning about eleven orders of magnitude. Simulation and calculation of the response functions of four Bonner spheres with a simplified model is done with FLUKA and MCNPX codes respectively, proving the feasibility of the FLUKA program for this application and the correctness of the calculation method. Using the actual model, we simulate and calculate the energy response functions of Bonner sphere detectors with polyethylene layers of different diameters, including detectors with lead layers, using the FLUKA code. Based on the simulation results, we select eleven detectors as the basic structure for an Extended Range Neutron Multisphere Spectrometer (ERNMS).

Brightness of synchrotron radiation from undulators and bending magnets.

The maximum of the Wigner distribution (WD) of synchrotron radiation (SR) fields is considered as a possible definition of SR source brightness. Such a figure of merit was originally introduced in the SR community by Kim [(1986), Nucl. Instrum. Methods Phys. Res. A, 246, 71-76]. The brightness defined in this way is always positive and, in the geometrical optics limit, can be interpreted as the maximum density of photon flux in phase space. For undulator and bending magnet radiation from a single electron, the WD function can be explicitly calculated. In the case of an electron beam with a finite emittance the brightness is given by the maximum of the convolution of a single electron WD function and the probability distribution of the electrons in phase space. In the particular case when both electron beam size and electron beam divergence dominate over the diffraction size and the diffraction angle, one can use a geometrical optics approach. However, there are intermediate regimes when only the electron beam size or the electron beam divergence dominate. In these asymptotic cases the geometrical optics approach is still applicable, and the brightness definition used here yields back once more to the maximum photon flux density in phase space. In these intermediate regimes a significant numerical disagreement is found between exact calculations and the approximation for undulator brightness currently used in the literature. The WD formalism is extended to a satisfactory theory for the brightness of a bending magnet. It is found that in the intermediate regimes the usually accepted approximation for bending magnet brightness turns out to be inconsistent even parametrically.

Seasonal distribution of ozone and radiation field at the stratosphere

利用美国NCAR化学气候耦合模式WACCM3对平流层温度场、风场、臭氧及辐射场进行了模拟.结果表明,在适宜飞艇长期驻留的准零风层高度20～22km(对应大气压强范围为50～30hPa,以下均采用气压值表征对应大气高度),7-8月风速小于5m·s^-1的风带可长期稳定在40°N以北.臭氧空间分布显示,在30hPa气压高度处中国地区臭氧浓度出现了带状分布,30hPa高度以下低纬度地区臭氧浓度低于中纬度地区.平流层太阳加热率的时空变化表明,在平流层上层,太阳加热率可达100×10^-6K·s^-1,而在平流层下层,只有10×10^-6K·s^-1.6-8月中国区域的太阳加热率大于9月;在100～30hPa高度内,中纬度地区太阳加热率高于低纬度地区,在30hPa高度以上,低纬度地区太阳加热率高于中纬度地区;8-9月30～40hPa高度处,太阳加热率的空间变化较小.在30hPa高度上,太阳加热率在40°N昼夜变化最大;50hPa高度处,太阳加热率的昼夜变化小于30hPa高度处,而且白天太阳加热率出现极大值的纬度明显靠北.平流层低纬度地区的长波加热率小于中纬度地区.青藏高原由于地形特殊,其6-7月的臭氧浓度、太阳加热率和长波加热率均小于同纬度其他地区.

WATER VAPOR DISTRIBUTION IN PROTOPLANETARY DISKS

Water vapor has been detected in protoplanetary disks. In this work we model the distribution of water vapor in protoplanetary disks with a thermo-chemical code. For a set of parameterized disk models, we calculate the distribution of dust temperature and radiation field of the disk with a Monte Carlo method, and then solve the gas temperature distribution and chemical composition. The radiative transfer includes detailed treatment of scattering by atomic hydrogen and absorption by water of Lyman alpha photons, since the Lyman alpha line dominates the UV spectrum of accreting young stars. In a fiducial model, we find that warm water vapor with temperature around 300 K is mainly distributed in a small and well-confined region in the inner disk. The inner boundary of the warm water region is where the shielding of UV field due to dust and water itself become significant. The outer boundary is where the dust temperature drops below the water condensation temperature. A more luminous central star leads to a more extended distribution of warm water vapor, while dust growth and settling tends to reduce the amount of warm water vapor. Based on typical assumptions regarding the elemental oxygen abundance and the water chemistry, the column density of warm water vapor can be as high as 1E22 cm^{-2}. A small amount of hot water vapor with temperature higher than ~300 K exists in a more extended region in the upper atmosphere of the disk. Cold water vapor with temperature lower than 100 K is distributed over the entire disk, produced by photodesorption of the water ice.

A Tale of Cosmic Rays Narrated in γ Rays by Fermi

Because cosmic rays are charged particles scrambled by magnetic fields, combining direct measurements with other observations is crucial to understanding their origin and propagation. As energetic particles traverse matter and electromagnetic fields, they leave marks in the form of neutral interaction products. Among those, γ rays trace interactions of nuclei that inelastically collide with interstellar gas, as well as of leptons that undergo Bremsstrahlung and inverse-Compton scattering. Data collected by the Fermi large area telescope (LAT) are therefore telling us the story of cosmic rays along their journey from sources through their home galaxies. Supernova remnants emerge as a notable γ-ray source population, and older remnants interacting with interstellar matter finally show strong evidence of the presence of accelerated nuclei. Yet the maximum energy attained by shock accelerators is poorly constrained by observations. Cygnus X, a massive star-forming region established by the LAT as housing cosmic-ray sources, provides a test case to study the impact of wind-driven turbulence on the early propagation. Interstellar emission resulting from the large-scale propagation of cosmic rays in the Milky Way is revealed in unprecedented detail that challenges some of the simple assumptions used for the modeling. Moreover, the cosmic-ray induced γ-ray luminosities of galaxies-scale quasi-linearly with their massive-star formation rates: the overall normalization of that relation below the calorimetric limit suggests that for most systems, a substantial fraction of energy in cosmic rays escapes into the intergalactic medium. The nuclear production models and the distribution of target gas and radiation fields, not determined precisely enough yet, are key to exploiting the full potential of γ-ray data. Nevertheless, data being collected by Fermi and complementary multiwavelength/multimessenger observations are bringing us ever closer to solving the cosmic-ray mystery.