Uniform Radiation Field Research Articles

Fermi-bubble Bulk and Edge Analysis Reveals Dust, Cooling Breaks, and Cosmic-Ray Diffusion, Facilitating a Self-consistent Model

The full, radio to γ-ray spectrum of the Fermi bubbles is shown to be consistent with standard strong-shock electron acceleration at the bubble edge, without the unnatural energy cutoffs and unrealistic electron cooling of previous studies, if the ambient interstellar radiation is strong; the γ-ray cooling break should then have a microwave counterpart, undetected until now. Indeed, a broadband bubble-edge analysis uncovers a pronounced downstream dust component, which masked the anticipated ∼35 GHz spectral break, and the same overall radio softening consistent with Kraichnan diffusion previously reported in γ-rays. A self-consistent bulk and edge model implies a few Myr old bubbles, with fairly uniform radiation fields and enhanced magnetization near the edge.

A New Photoionization Model of the Narrow-line Region in Active Galactic Nuclei

The photoionization model of narrow-line regions in active galactic nuclei (AGNs) has been investigated for decades. Many published models are restricted to simple linear scaling abundance relations, dust-free assumption, uniform AGN radiation field, and using one specific photoionization code, which restricts them from providing a satisfactory prediction on a broad range of AGN observations. Through a comprehensive investigation, here we present how the choice of abundance scaling relations, dust inclusion, AGN radiation fields, and different photoionization codes CLOUDY and MAPPINGS affect the predictions on the strength of strong UV, optical, and infrared emission lines. We find the dust-depleted radiation-pressure-dominated AGN model built with the latest nonlinear abundance sets and photoionization code MAPPINGS V are consistent with AGN observations across a broad range of wavelengths. We also assess new potential H ii-AGN separation diagrams in the optical and UV wavelengths.

A simple method to import CAD mesh format models in FLUKA.

Monte Carlo (MC) code FLUKA possesses widespread usage and accuracy in the simulation of particle beam radiotherapy. However, the conversion from computer-aided design (CAD) mesh format models to FLUKA readable geometries could not be implemented directly and conveniently. A simple method was required to be developed. The present study proposed a simple method to voxelize CAD mesh format files by using a Python-based script and establishing geometric models in FLUKA. Five geometric models including cube, sphere, cone, ridge filter (RGF), and 1D-Ripple Filter (1D-RiFi) were created and exported as CAD mesh format files (.stl). An open-source Python-based script was used to convert them into voxels by endowing X, Y, and Z (following the Cartesian coordinates system) of solid materials in the three-dimensional (3D) grid. A FLUKA (4-2.2, CERN) predefined routine was used to establish the voxelized geometry model (VGM), while Flair (3.2-1, CERN) was used to build the direct geometry model (DGM) in FLUKA for comparison purposes. Uniform carbon ion radiation fields 8×8cm3 and 4×4cm3 were generated to transport through the five pairs of models, 2D and 3D dose distributions were compared. The integral depth dose (IDD) in water of three different energy levels of carbon ion beams transported through 1D-RiFis were also simulated and compared. Moreover, the volume between CAD mesh and VGMs, as well as the computing speed between FLUKA DGMs and VGMs were simultaneously recorded. The volume differences between VGMs and CAD mesh models were not more than 0.6%. The maximum mean point-to-point deviation of IDD distribution was 0.7%±0.51% (mean±standard deviation). The 3D dose Gamma-index passing rates were never lower than 97% with criteria of 1%-1mm. The difference in computing CPU time was 2.89%±0.22 on average. The present study proposed and verified a Python-based method for converting CAD mesh format files into VGMs and establishing them in FLUKA simply as well as accurately.

The effects of local stellar radiation and dust depletion on non-equilibrium interstellar chemistry

ABSTRACT Interstellar chemistry is important for galaxy formation, as it determines the rate at which gas can cool, and enables us to make predictions for observable spectroscopic lines from ions and molecules. We explore two central aspects of modelling the chemistry of the interstellar medium (ISM): (1) the effects of local stellar radiation, which ionizes and heats the gas, and (2) the depletion of metals on to dust grains, which reduces the abundance of metals in the gas phase. We run high-resolution (400 M⊙ per baryonic particle) simulations of isolated disc galaxies, from dwarfs to Milky Way-mass, using the fire galaxy formation models together with the chimes non-equilibrium chemistry and cooling module. In our fiducial model, we couple the chemistry to the stellar fluxes calculated from star particles using an approximate radiative transfer scheme; and we implement an empirical density-dependent prescription for metal depletion. For comparison, we also run simulations with a spatially uniform radiation field, and without metal depletion. Our fiducial model broadly reproduces observed trends in H i and H2 mass with stellar mass, and in line luminosity versus star formation rate for [C ii]$_{158 \rm {\mu m}}$, [O i]$_{63 \rm {\mu m}}$, [O iii]$_{88 \rm {\mu m}}$, [N ii]$_{122 \rm {\mu m}}$, and H α6563Å. Our simulations with a uniform radiation field predict fainter luminosities, by up to an order of magnitude for [O iii]$_{88 \rm {\mu m}}$ and H α6563Å, while ignoring metal depletion increases the luminosity of carbon and oxygen lines by a factor ≈ 2. However, the overall evolution of the galaxy is not strongly affected by local stellar fluxes or metal depletion, except in dwarf galaxies where the inclusion of local fluxes leads to weaker outflows and hence higher gas fractions.

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.

Linearity and rate capability measurements of RPC with semi-insulating crystalline electrodes operating in avalanche mode

The intrinsic rate capability and the ageing properties of the Resistive Plate Chambers are closely related to the electrodes material and to the front-end electronics threshold. The development of a low noise pre-amplifier led us to improve the intrinsic rate capability of High Pressure Laminate (bakelite) RPCs up to ∼10 kHz/cm2, nevertheless the effective rate is significantly limited by electrodes ageing. To further improve the effective rate capability new materials are investigated. A Resistive Plate Chamber with crystalline semi-insulating Gallium Arsenide electrodes has been characterized with high energy electrons beam at the Beam Test Facility (BTF), (INFN National Laboratory of Frascati, Italy). The response of the Resistive Plate Chamber to multiple bunched electrons was measured operating the detector in avalanche mode. The intrinsic rate capability has been also measured operating the detector in a uniform high energy gamma radiation field at the GIF++ facility (EHN1 of SPS, CERN).

Research on Energy-Saving Design of Rural Building Wall in Qinba Mountains Based on Uniform Radiation Field

How to create a healthy and comfortable indoor environment without causing a substantial increase in energy consumption has become a strategic problem that the development of all countries must face and solve. According to the climatic conditions of Qinba Mountains in China, combined with the characteristics of local rural residential buildings and residents’ living habits, the field survey and theoretical analysis were used to study the thermal environment status and the heating energy consumption condition of local rural residential buildings. The thermal design method of walls for the local rural energy-saving buildings based on the indoor uniform radiation field was explored by using the outdoor comprehensive temperature function expressed by the fourth-order harmonic Fourier series as the boundary condition of the wall thermal analysis. ANSYS CFX was adopted to study the suitability of the energy-saving wall structure designed by the above method. The results show that the indoor thermal environment of local rural residential buildings in winter is not ideal and the heating energy consumption is high, but this area has the geographical advantage to develop solar energy buildings. It is proposed that the indoor thermal comfort temperature of local rural residential buildings in winter should not be lower than 14°C. When the internal surface temperature of the external walls in different orientations are equally based on the design principle of uniform radiation field, the heat transfer coefficient of the east wall, the west wall, and the north wall of the local rural residential buildings is 1.13 times, 1.06 times, and 1.14 times of the south wall heat transfer coefficient, respectively. The energy-saving structural wall with KPI porous brick as the main material and the south wall heat transfer coefficient of 0.9 W/(m2·K) is the most suitable energy-saving wall for local rural residential buildings.

Writing arbitrary distributions of radiant exposure by scanning a single illuminated spatially random screen

Arbitrary distributions of radiant exposure may be written by transversely scanning a single known spatially-random screen that is normally illuminated by spatially but not necessarily temporally uniform radiation or matter wave fields. The arbitrariness, of the written pattern of radiant exposure, holds up to both (i) a spatial resolution that is dictated by the characteristic transverse length scale of the illuminated spatially random screen, and (ii) a background term that grows linearly with the number of random-illumination patterns. Two classes of the method are developed. The former assumes the distance between the illuminated random mask and the target plane to be sufficiently small that the effects of diffraction may be neglected. The latter accounts for the effects of Fresnel diffraction in the regime of large Fresnel number. Numerical simulations are provided for both variants of the method. Contrast and signal-to-noise ratio are also considered. The method may be parallelized, and is suited to both magnifying and de-magnifying geometries. Possible applications include spatial light modulators and intensity projectors for those matter and radiation wave fields for which such devices do not exist, printing or micro-fabrication in both two and three spatial dimensions, and lithography.

Increasing the precision in the estimates of noise power spectrum in digital x-ray imaging systems

The noise power spectrum (NPS) of a digital x-ray imaging device is usually estimated from the average of periodograms of ROIs in images obtained with uniform radiation fields. The purpose of this work was developing a new estimator for calculating the NPS and comparing its uncertainties with those of the smoothed periodogram.The new estimator is built by removing those addends in the summation of the periodogram that do not contain information on stochastic noise. This was carried out by applying a short-length lag window to the autocorrelation function of noise. The length of the window was obtained from the support of this function. It has to be large enough not to eliminate information on noise autocorrelation and it has be as short as possible to minimize uncertainty. In this work, this length was set to three times the support of the autocorrelation function of noise.The new truncated sum (TS) estimator is shown to be unbiased and to have a much higher precision than that of the periodogram. The combined process of applying lag windows to the autocorrelation function of noise and removing addends with null expected values from the periodogram summation has a double effect on NPS curves. On the one hand, the curves are smoothed and, on the other hand, the uncertainties in the calculated values are highly reduced.

An injectable dosimeter for small animal irradiations

Accuracy and precision in dosimetry is crucial in studies involving animal models. Small animal dosimetry, in particular for protracted exposures to non uniform radiation fields is particularly challanging. We have developed a novel in vivo dosimeter based on glass encapsulated TLD rods. These encapsulated rods can be injected into mice and used for validating doses to an individual mouse in a protracted irradiation scenario where the mouse is free to move in an inhomogenous radiation field. Data from 30 irradiated mice shows a reliable dose reconstruction within 10% of the nominal delivered dose.

Comparison of two vibro-acoustic inverse methods to radiate a uniform sound field from a plate

The radiated sound from a conventional panel speaker, often excited by an actuator, is usually distorted due to the multi-modal response of the regular panel. To avoid such an acoustically disadvantageous feature of the conventional panel speakers, an array of actuators can be used for controlling the panel vibration to obtain the desired acoustic response. In this paper, two different control methods by using the actuator array are compared in the viewpoint of the solution stability, the input efficiency, and the acoustic performance, in particular at low frequencies rendered in a hemispherical uniform radiation. The indirect inverse rendering method is to create a vibration pattern composed of a virtual speaker and baffle, and the direct inverse rendering method controls the array actuators to form a spatial distribution of panel vibration to directly produce the uniform radiation field. The actuator positions are confined at the periphery of the plate, which are advantageous in exciting the multiple modes and saving the central zone covered by the plate for other purposes. Numerical simulations are conducted for a thin rectangular plate with simply supported boundary condition in the frequency range below 300 Hz. It is found that both rendering methods can produce the uniform hemispherical sound radiation field, but the rendering error is −20 dB for indirect method and −50 dB for direct method. The singularity problem due to the ill-conditioning of the system appears in the direct method. Effect of applying the regularization technique to obtain a stable solution is studied for the system contaminated with a large amount of noise. It is observed that the result of using the direct method becomes dramatically stable with a reduction of condition number from O (1017) to O (104). Also, the input gains of the actuator are reduced as much as 35 dB for both rendering methods.

Efficient detrending of uniform images for accurate determination of the noise power spectrum at low frequencies

The noise power spectrum (NPS) of a digital x-ray imaging device is usually estimated from the average of periodograms of regions of interest (ROIs) in images obtained with uniform radiation fields. In order to mitigate low frequency trends, present in the images and not arising from stochastic processes, detrending methods are applied to the images before being Fourier transformed. The most common of these methods subtracts a second-order polynomial fit from the image.In this work, it is shown that the characteristics of low frequency trends can deviate from the quadratic dependence on spatial coordinates. This results in large residual trends that give rise to important correlations in the detrended images and produce an inaccurate rise of the NPS calculations at low frequencies.A new detrending method of uniform images is presented. The method operates in the subbands of a wavelet transform, removing the low frequency contents of the uniform image. To do this, the approximation subband of the highest level of the wavelet transform is cancelled.The effect on the NPS calculations for three digital detectors is shown and the importance of the parameters of the wavelet transform is discussed. The main result states that the performance of the new method improves those of two polynomial detrending methods commonly used and is close to the performance of the subtraction of uniform exposure images method.Finally, guidelines for the implementation of the procedure, like the number of levels in the wavelet decomposition, are provided. As the number of levels in the wavelet transform increases, the removal of trends is restricted to lower frequencies. The selection of the number of levels should be guided by the shape of the autocorrelation function of the detrended image, which has to resemble the shape expected from the propagation of noise through the imaging chain.

Irradiation of astrophysical objects – SED and flux effects on thermally driven winds

We develop a general method for the self consistent calculation of the hydrodynamics of an astrophysical object irradiated by a radiation field with an arbitrary strength and spectral energy distribution (SED). Using the XSTAR photoionization code, we calculate heating and cooling rates as a function of gas photoionization parameter and temperature for several examples of SEDs: bremsstrahlung, blackbody, hard and soft state XRBs, Type 1 and Type 2 AGN. As an application of our method we study the hydrodynamics of 1-dimensional spherical winds heated by a uniform radiation field using the code Athena++. We find that in all cases explored a wind settles into a transonic, steady state. The wind evolves along the radiative heating equilibrium curve until adiabatic cooling effects become important and the flow departs from radiative equilibrium. If the flow is heated very rapidly, for example as in a thermally unstable regime, the corresponding column density of gas is low. Perhaps one of the most intriguing results of our work is the two stage acceleration of the wind that happens when there are two thermally unstable regions and the flux is relatively high. The efficiency with which the radiation field transfers energy to the wind is dependent on the SED of the external source, particularly the relative flux of soft X-rays. These results suggest that detailed photoionization calculations are essential not only to predict spectra but also to properly capture the flow dynamics.

Two-dimensional thermoluminescence method for checking LiF crystals homogeneity

Thermoluminescence (TL), being one of the common luminescence methods, is very sensitive to the presence of any impurities in the material structure and can be used for the detection of impurity distribution in the bulk of the crystal. If in a TL reader a CCD camera is used, a measurement of TL signal would give us an unique two-dimensional (2-D) imaging of TL signal distribution, and thereby the distribution of dopants. The possibility of the application of 2-D TL method for the control of uniformity of the crystal related to dopant distribution in the volume of the bulk crystal was tested on the large area samples of LiF doped and un-doped crystals grown by Czochralski method at the IFJ PAN in Kraków. The special TL reader with a CCD camera was used for analyzing of luminescence emitting during the heating of the irradiated in uniform radiation field slices of crystals cut longitudinal and perpendicular to the growth axis and for analyzing of the shape of TL glow curves for selected crystal areas. Non-uniform distribution of the dopants was demonstrated for doped crystal grown with relatively slow growth rate.

Application of an adapted Fano cavity test for Monte Carlo simulations in the presence of B-fields

With the advent of MR guided radiotherapy the relevance of Monte Carlo radiation transport simulations in the presence of strong magnetic fields (B-fields) is increasing. While new tests are available to benchmark these simulation algorithms for internal consistency, their application to known codes such as EGSnrc, PENELOPE, and GEANT4 is yet to be provided. In this paper a method is provided to apply the Fano cavity test as a benchmark for a generic implementation of B-field effects in PENELOPE. In addition, it is investigated whether violation of the conditions for the Fano test can partially explain the change in the response of ionization chambers in the presence of strong B-fields.In the present paper it is shown that the condition of isotropy of the secondary particle field (Charged Particle Isotropy, CPI) is an essential requirement to apply the Fano test in the presence of B-fields. Simulations in PENELOPE are performed with (B = 0.0 T) and (B = 1.5 T) for cylindrical cavity geometry. The secondary particle field consists of electrons generated from a mono-energetic source (E = 0.5–4.0 MeV) with a uniform source density and different angular distributions; isotropic, mono-directional, and Compton. In realistic photon fields the secondary radiation field has a non-isotropic angular distribution due to the Compton process. Based on the simulations for the Compton angular distribution (non-CPI), the response change of the cavity model in a uniform radiation field in the presence of B-fields is investigated.For the angular distributions that violate the CPI condition and B = 1.5 T, the deviations from 1 are considerable, which emphasizes the requirement of CPI. For the isotropic angular distributions obeying this requirement, both the results for B = 0.0 T and B = 1.5 T shows deviations from the predictions for E ⩾ 1.5 MeV with values up to 1.0% for E = 4.0 MeV. Nevertheless, due to the high correlation in the deviation for B = 0.0 T and B = 1.5 T, the accuracy of the PENELOPE code for the simulation of the change in detector response in the presence of B-fields is within 0.3%. The effect of the B-field on the detector response for non-isotropic angular distributions suggests that violation of CPI is a major contribution to the response change of ionization chambers in the presence of B-fields.

Experimental set up for the irradiation of biological samples and nuclear track detectors with UV C

AimIn this work we present a methodology to produce an “imprint” of cells cultivated on a polycarbonate detector by exposure of the detector to UV C radiation. BackgroundThe distribution and concentration of 10B atoms in tissue samples coming from BNCT (Boron Neutron Capture Therapy) protocols can be determined through the quantification and analysis of the tracks forming its autoradiography image on a nuclear track detector. The location of boron atoms in the cell structure could be known more accurately by the simultaneous observation of the nuclear tracks and the sample image on the detector. Materials and MethodsA UV C irradiator was constructed. The irradiance was measured along the lamp direction and at different distances. Melanoma cells were cultured on polycarbonate foils, incubated with borophenylalanine, irradiated with thermal neutrons and exposed to UV C radiation. The samples were chemically attacked with a KOH solution. ResultsA uniform irradiation field was established to expose the detector foils to UV C light. Cells could be seeded on the polycarbonate surface. Both imprints from cells and nuclear tracks were obtained after chemical etching. ConclusionsIt is possible to yield cellular imprints in polycarbonate. The nuclear tracks were mostly present inside the cells, indicating a preferential boron uptake.

A model of the radiation-induced bystander effect based on an analogy with ferromagnets. Application to modelling tissue response in a uniform field

We propose a model of the radiation-induced bystander effect based on an analogy with magnetic systems. The main benefit of this approach is that it allowed us to apply powerful methods of statistical mechanics. The model exploits the similarity between how spin–spin interactions result in correlations of spin states in ferromagnets, and how signalling from a damaged cell reduces chances of survival of neighbour cells, resulting in correlated cell states. At the root of the model is a classical Hamiltonian, similar to that of an Ising ferromagnet with long-range interactions. The formalism is developed in the framework of the Mean Field Theory. It is applied to modelling tissue response in a uniform radiation field. In this case the results are remarkably simple and at the same time nontrivial. They include cell survival curves, expressions for the tumour control probability and effects of fractionation. The model extends beyond of what is normally considered as bystander effects. It offers an insight into low-dose hypersensitivity and into mechanisms behind threshold doses for deterministic effects.

Investigation of OSL signal of resistors from mobile phones for accidental dosimetry

Resistors from mobile phones, usually located near the human body, are considered as individual dosimeters of ionizing radiation in emergency situations. The resistors contain Al2O3, which is optically stimulated luminescence (OSL) material sensitive to ionizing radiation. This work is focused on determination of dose homogeneity within mobile phones which was carried out by OSL measurements of resistors placed in different parts inside the mobile phone. Separate, commercially available resistors, similar in the shape and size to the resistors from circuit board of the studied mobile phone, were situated in different locations inside it. The irradiations were performed in uniform 60Co and 137Cs radiation fields, with the mobile phones connected and not connected to the cellular network. The dose decrease of 9% was measured for original resistors situated between circuit board and battery, in comparison to the dose at the front of the phone. The resistors showed the lower signal when the mobile phone was connected to the cellular network, due to higher temperature inside the housing. The profile of fading was investigated within 3 month period for resistors irradiated with 1 Gy of gamma rays to estimate of the fading coefficient.

Basic characteristics of kinetic energy transfer in the dynamic hohlraums of Z-pinch

The applications of Z-pinch are realized through dynamic hohlraum driven by Z-pinch, in which a uniform and symmetrical radiation field may be produced for ablating implosion of the inertial confinement fusion (ICF) capsule, and the radiation sources may also be created for heating and backlighting the samples in opacity measurement experiments. The radiation field is essentially related to driven current, hohlraum configuration and material. In physics it is determined by energy transfer in the hohlraum. For rapidly obtaining the knowledge about the primary energy transfer chracteristics in the hohlraum, and its trends of variation in the configuration, linear mass of the load, and the driven current, the simplified model is used to simulate the dynamic hohlraum implosion. The obtained implosion kinetic energy of the cylindrical foam accords well with the kinetic energy obtained from a one-dimensional magneto radiation hydrodynamics simulation of Z-pinch-driven dynamic hohlraum. In the dynamic hohlraum for ICF the kinetic energy loss is important for the radiation field formation when the imploding wire-array plasma collides with the cylindrical foam, while ones for radiation source the kinetic energy loss and for the final implosion kinetic energy of the foam are both important. The maximum implosion kinetic energy of cylindrical foam is directly proportional to the square of the peak current, while the kinetic energy loss increases with the mass of cylindrical foam increasing. The mass energy density in the foam tends to increase, and in turn the radiation power is enhanced when the rise time of the current turns longer.

The effect of fluctuations on the helium-ionizing background

Interpretation of He II Ly{\alpha} absorption spectra after the epoch of He II reionization requires knowledge of the He II ionizing background. While past work has modelled the evolution of the average background, the standard cosmological radiative transfer technique assumes a uniform radiation field despite the discrete nature of the (rare) bright quasars that dominate the background. We implement a cosmological radiative transfer model that includes the most recent constraints on the ionizing spectra and luminosity function of quasars and the distribution of IGM absorbers. We also estimate, for the first time, the effects of fluctuations on the evolving continuum opacity in two ways: by incorporating the complete distribution of ionizing background amplitudes into the standard approach, and by explicitly treating the quasars as discrete -- but isolated -- sources. Our model results in a He II ionization rate that evolves steeply with redshift, increasing by a factor ~2 from z=3.0 to z=2.5. This causes rapid evolution in the mean He II Ly{\alpha} optical depth -- as recently observed -- without appealing to the reionization of He II. The observed behaviour could instead result from rapid evolution in the mean free path of ionizing photons as the helium in higher H I column density absorbers becomes fully ionized.