Three-dimensional Radiation Field Research Articles

Genetic algorithm optimized BP neural network for fast reconstruction of three-dimensional radiation field.

The three-dimensional radiation field is an important database reflecting the radioactivity distribution in a nuclear facility. It is of great significance to accurately and quickly grasp the radiation dose field distribution to implement radiation protection. Presently, majority of radiation field reconstruction algorithms concentrate on two-dimensional reconstruction and can only measure on a regular grid. With the progress of artificial intelligence technology, neural networks have great potential in radiation field reconstruction. In this work, an improved Genetic Algorithm Optimized Backpropagation (GA-BP) neural network was proposed, which can efficiently reconstruct the radiation dose rate at any given position within the three-dimensional space, even under the condition of a low sampling rate. The proposed method achieves a remarkable speed, capable of reconstructing nearly 500 spots in 0.01s. Two Monte Carlo simulations corresponding to the shielded and unshielded cases verified the effectiveness of the proposed method. The method was further tested on datasets with equally spaced and randomly distributed data points. In both simulation scenarios, the proposed method demonstrated the ability to reconstruct the three-dimensional dose rate field using less than 6% of the data for the simulation cases with a low error level of 3% (unshielded) to 8% (shielded). In the real experimental validation, the error is at 15%, and the point error is less than 30% in most areas.

Research on a three-dimensional radiation field reconstruction algorithm based on an improved 3D CNN

This article investigates the application of an improved three-dimensional convolutional neural network (3D CNN) for sparse data-based reconstruction of radiation fields. Sparse radiation data points are consolidated into structured three-dimensional matrices and fed into a self-attention integrated CNN, enabling the network to interpolate and produce complete radiation distribution grids. The model’s validity is assessed through experiments with randomly sourced radiation in scenarios both with and without shielding, as well as in refined grid configurations. Results indicate that in unshielded environments, a mere 5%(15 points) sampling yields an average relative error of 4%, while in shielded settings, a 7% (21 points) sampling maintains the error around 11%. In refined grid contexts, a 2% sampling rate suffices to limit the error to 6.58%. Thus, the improved 3D CNN is demonstrated to be highly effective for precise three-dimensional radiation field reconstruction in sparse data scenarios.

Fast three-dimensional radiation field characterization in large-scale nuclear installations

The requirement of the fast three-dimensional radiation field calculation is raised during the decommissioning of large-scale nuclear installations. The most often used methods, such as the Monte Carlo and the discrete ordinates methods, have shortcomings in their simulations of such problems. The coupled Monte Carlo–point kernel computational scheme is developed to meet the requirement. The facility is separated into the source region and the bulk shielding region, with a common interface. The transport within the source region is simulated using the Monte Carlo method, which is by nature good at treating complex geometries. The radiation field in the bulk shielding region is treated by the point kernel approach to avoid the extremely expensive computation for deep penetration problems. The flow rate through the interface, which is given by the Monte Carlo simulation, is considered as the equivalent surface source for the point kernel calculation. Test calculations from simplified typical waste storage facilities have been performed to validate the coupled scheme by comparing them with the results conducted by the Monte Carlo method directly. The good agreement of the results, as well as the significant saving in computing time, indicates that the coupled method is suitable for the fast three-dimensional radiation field calculation.

Spatial variability of photosynthetically active radiation in European beech and Norway spruce

The vertical and horizontal variability of solar radiation within a mature European beech ( Fagus sylvatica L.)–Norway spruce ( Picea abies [L.] Karst) mixed stand in Southern Germany is investigated. A large dataset with more than one million spectral measurements of photon fluence rates at six vertical levels within the stand is analyzed with respect to tree species, meteorological sky conditions, and the influence of solar elevation angle on canopy penetration. Irradiance probability density functions of the photosynthetically active waveband are used to describe the three-dimensional radiation field. For a quantification of umbra, penumbra, and sunfleck frequencies, in-canopy fractions of photon fluence rates within the photosynthetically active waveband are investigated. Different phenological stages of beech and their effects on the in-canopy light climate are compared. The results show that during overcast conditions (OVC) fractions of photosynthetically active radiation (PAR) are higher at all canopy levels than during clear sky (CS) conditions due to their exclusively diffuse character. The lowest median PAR level of less than 1% of above-canopy PAR can be observed in the shade crown of beech and at ground level. More PAR can penetrate the canopy at a higher solar elevation under CS conditions. This effect is more pronounced for spruce than for beech due to the conical crown shape of the conifers that allows photons from higher angles to enter the gaps inbetween trees in contrast to the more homogeneously closed beech canopy. Solar elevation is not an important factor at uniformly overcast conditions. Differences in the vertical distribution of umbra and penumbra can be detected when comparing species or different sky conditions. The frequency of sunflecks differs more by species and by the vertical position within the canopy than by sky condition.

Influence of clouds on the spectral actinic flux density in the lower troposphere (INSPECTRO): overview of the field campaigns

Abstract. Ultraviolet radiation is the key factor driving tropospheric photochemistry. It is strongly modulated by clouds and aerosols. A quantitative understanding of the radiation field and its effect on photochemistry is thus only possible with a detailed knowledge of the interaction between clouds and radiation. The overall objective of the project INSPECTRO was the characterization of the three-dimensional actinic radiation field under cloudy conditions. This was achieved during two measurement campaigns in Norfolk (East Anglia, UK) and Lower Bavaria (Germany) combining space-based, aircraft and ground-based measurements as well as simulations with the one-dimensional radiation transfer model UVSPEC and the three-dimensional radiation transfer model MYSTIC. During both campaigns the spectral actinic flux density was measured at several locations at ground level and in the air by up to four different aircraft. This allows the comparison of measured and simulated actinic radiation profiles. In addition satellite data were used to complete the information of the three dimensional input data set for the simulation. A three-dimensional simulation of actinic flux density data under cloudy sky conditions requires a realistic simulation of the cloud field to be used as an input for the 3-D radiation transfer model calculations. Two different approaches were applied, to derive high- and low-resolution data sets, with a grid resolution of about 100 m and 1 km, respectively. The results of the measured and simulated radiation profiles as well as the results of the ground based measurements are presented in terms of photolysis rate profiles for ozone and nitrogen dioxide. During both campaigns all spectroradiometer systems agreed within ±10% if mandatory corrections e.g. stray light correction were applied. Stability changes of the systems were below 5% over the 4 week campaign periods and negligible over a few days. The J(O1D) data of the single monochromator systems can be evaluated for zenith angles less than 70°, which was satisfied by nearly all airborne measurements during both campaigns. The comparison of the airborne measurements with corresponding simulations is presented for the total, downward and upward flux during selected clear sky periods of both campaigns. The compliance between the measured (from three aircraft) and simulated downward and total flux profiles lies in the range of ±15%.

2‐Dust: A Dust Radiative Transfer Code for an Axisymmetric System

We have developed a general purpose dust radiative transfer code for an axisymmetric system, 2-DUST, motivated by the recent increasing availability of high-resolution images of circumstellar dust shells at various wavelengths. This code solves the equation of radiative transfer following the principle of long characteristic in a two-dimensional polar grid while considering a three-dimensional radiation field at each grid point. A solution is sought through an iterative scheme in which self-consistency of the solution is achieved by requiring a global luminosity constancy throughout the shell. The dust opacities are calculated through Mie theory from the given size distribution and optical properties of the dust grains. The main focus of the code is to obtain insights on (1) the global energetics of dust grains in the shell and (2) the two-dimensional projected morphologies that are strongly dependent on the mixed effects of the axisymmetric dust distribution and inclination angle of the shell. Here test models are presented with discussion of the results. The code can be supplied with a user-defined density distribution function and, thus, is applicable to a variety of dusty astronomical objects possessing the axisymmetric geometry.

An automated system for gamma radiation field mapping

Remote radiation survey equipment was sorely needed at Chernobyl but adequate systems did not exist. The current state of the art still consists of a survey meter mounted on a robotic carriage, which scans an area at many points on a grid. This process is both time consuming and somewhat inaccurate. The system we have developed will overcome these limitations, and would provide significant savings in man-hours and man-rem over manual survey techniques. The system we have developed consists of a collimated ionization chamber mounted in a scanning head. The measurement process is similar to that used in medical computed tomography (CT) imaging and consists of a series of collimator rotations and translations. The key to this work is the use of a collimator to provide position information with a position insensitive detector. In addition, an inverse filter image reconstruction technique has been used to reduce the distortion effects due to the scanner and scanning process in the resulting maps. This technique models the distortion as a linear, space invariant degrading function which is removed in a deconvolution process. We have constructed first- and second-generation prototype scanners, and developed software to produce three-dimensional radiation field “iso-dose” maps. The iso-dose maps will be superimposed on three-dimensional computer-aided design and drafting (CADD) drawings of the radiation area, aiding in the characterization of the source of radiation.

A new method for the resolution of the radiative transfer equation in three-dimensional geometry. I - Theory

A method for solving the three-dimensional equation of transfer for an inhomogeneous static medium is described. The resolution of the three-dimensional transfer equation is important for studying the planetary atmosphere where an accurate model of the radiation field near the terminator region and in the nightside is necessary. The procedure involves: the reduction of the three-dimensional equation to a one-dimensional equation system; the resolution of this system by the discrete ordinate method, and reconstruction of the three-dimensional radiation field. This method considers variations in atmospheric parameters and reflectance at the bottom of the atmosphere relative to spatial and frequency parameters. 22 refs.

Radiation focusing in the cyclotron autoresonance maser

In the cyclotron autoresonance maser, an electromagnetic wave is amplified by interaction with an electron beam. Because of the copropagating electron beam, the refractive index seen by the wave is modified from the vacuum index and the dielectric properties of the electron beam can alter the propagation of the radiation beam. This phenomenon is studied through the use of a source-dependent modal expansion of the fully three-dimensional radiation field. In the exponential gain regime, the natural tendency of the radiation beam to spread diffractively is overcome and the beam is focused. The nature of the focusing is found to depend on the relative magnitude of the Doppler-shifted wave frequency and the gyrofrequency.

Image of a radiation field by a directional detector with a flat directivity diagram

The work deals with a composite directional scintillation detector of a slab form. The detector, exhibiting an axially asymmetric directivity diagram, enables one to scan the radiation field with two variously sharp diagrams of the directional efficiency. Mathematical expressions describing the image of the scanned field are derived and an example of a three-dimensional radiation field image is presented for illustration.

Analysis of radiation focusing and steering in the free-electron laser by use of a source-dependent expansion technique.

In the free-electron laser the resonant interaction between the radiation field and electron beam can result in radiation focusing (optical guiding). If the centroid of the electron beam is transversely displaced off axis, the radiation field, under certain conditions, will follow and be steered by the electron beam. The effect of a spatial modulation on the electron-beam envelope can also modify the propagation characteristics of the radiation. These and other phenomena are analytically and numerically studied using a novel source-dependent Laguerre-Gaussian modal representation of the fully three-dimensional radiation field. Unlike the vacuum Laguerre-Gaussian modal expansion, the longitudinal spatial dependence of the radiation waist and curvature are determined and characterized by the source term in the wave equation. Among the advantages of this general source-dependent expansion approach is that few modes are needed to accurately describe the radiation. Hence, fast and accurate numerical solutions of the fully three-dimensional free-electron laser problem can be obtained over distances of many Rayleigh lengths. Furthermore, this expansion enables us to drive an envelope equation for the radiation beam as well as an expression for the centroid of the beam.

Radiation focusing and guiding with application to the free electron laser.

In the free-electron laser the interaction between the radiation and electrons can result in radiation focusing. The radiation tends to follow the electron beam when the centroid of the electron beam is laterally displaced. Spatial modulation of the electron-beam envelope induces a similar modulation in the radiation-beam envelope. These and other phenomena are studied by use of a novel source-dependent modal representation of the fully three-dimensional radiation field. Among the merits of this approach is that few modes are needed to describe the radiation accurately.

Extended Jaynes–Cummings model in a damped cavity

By using a new technique, developed recently by the author, analytic and numerical solutions are obtained for the spontaneous emission from a single two-level atom interacting with a three-dimensional multimode radiation field with a narrow frequency range in a damped cavity.

Three-dimensional numerical simulations of FEL's by the transverse mode spectral method

We present a numerical method for solving a three-dimensional radiation field by decomposing the radiation field into transverse modes that satisfy the free space wave equation and the boundary conditions. The formalism includes betatron oscillations in a realizable wiggler, finite emittance, and energy spread in an amplifier or oscillator configuration. This formalism can be generalized to calculate sidebands resulting from the synchrotron oscillations. The transverse mode spectral method is compared to the finite difference method, spectral method, and transform spectral method. Examples from a computer code using Gaussian-Hermite expansion are given. We show self-focusing of the radiation beam due to gain and refraction of the FEL.

Extended Jaynes–Cummings model

By using a new technique, we solve the Jaynes–Cummings model for spontaneous emission in the case of a three-dimensional multimode radiation field with frequencies lying in a narrow range about some given frequency.

Numerical investigation of the three-dimensional radiation field in hypersonic flow over segmented bodies

The authors have made a numerical study of three-dimensional radiation field in the shock layer on segmented bodies washed by a hypersonic inviscid, selectively radiating and absorbing gas.

A formula for efficient computation of radiation from a current source in proximity to cylindrical scatterers

A systematic and efficient two-dimensional method is presented for calculation of the three-dimensional radiation field from current sources which are located in proximity to long cylindrical scatterers. The method is applied to the calculation of the isolated-element pattern of a linear array of crossed dipoles (i.e., current sources) mounted above a long and narrow ground plane. Computed and measured results are given. The results are subsequently applied to the problem of prediction of the radiation characteristics of a cylindrical reflector antenna fed by such a linear array.

Analysis of the three-dimensional selective radiation field in a combustion chamber using mathematical modeling

Using the zonal method, the spectral structure of radiation fluxes over the height of furnace baffles in the BKZ-320-140 PT steam generator, appearing with the combustion of lignite in the combustion chamber, is investigated.

Comparative Study of Spontaneous Emission and Spin-Lattice Relaxation atT=0

In this paper we present a comparative study of spontaneous emission and spin-lattice relaxation at zero temperature. In particular, we study the time evolution of the density matrix for two simple models as determined from an analysis of the Prigogine-R\'esibois master equation. The first model treated is that of the Wigner-Weisskopf atom in a three-dimensional radiation field; the second model is that of a single, effective spin in interaction with the phonon modes of a three-dimensional lattice. The divergence which arises in the solution of the master equation for the first model is avoided using a frequency cutoff. A frequency cutoff in the second model is imposed by the upper bound of the spectrum of modes in the crystal, and this fact manifests itself when one integrates over the first Brillouin zone only. From a detailed numerical study of the analytic results obtained in solving the master equation, we find that for both models the relaxation to equilibrium is characterized, in part, by a sequence of slowly damped oscillations. This result seems to be in agreement with the observation made by Zwanzig, namely, that exponential decay in time seems not to be universal, and may, in fact, be hidden behind some other kind of time dependence. The numerical study also reveals, however, that the nonexponential modes of decay can be quantitatively different in magnitude and qualitatively different in structure for atomic versus spin systems. Finally, based on the solution obtained for the spin problem, an estimate is made of the relaxation time for cerium ethyl sulfate, and this estimate is found to be consistent with experiment.