Point Source Of Radiation Research Articles

Parameters of plasma of high-current nanosecond discharge in air with small admixtures of copper vapor

Introduction . The use of a discharge in air of atmospheric pressure opens the possibility of developing windowless UV lamps that are promising for applications with significant mechanical overloads under various extreme conditions, since they do not contain any quartz elements (windows or bulbs). The output characteristics of such point lamps strongly depend on the plasma parameters of the nanosecond discharge with small admixtures of the vapor metal from which the electrodes are made. At present, there are no data on the parameters of air plasma with small admixtures of copper vapor under the operating conditions of a point lamp, which inhibits the establishment of mechanisms for populating the excited levels of atoms and copper ions in such a plasma. This in turn inhibits the long-range optimization of the output characteristics of such point sources of UV radiation. Purpose . The purpose of the study was to determine the emission characteristics in the spectral range of 200-250 nm of the plasma of high-current nanosecond discharge, between copper electrodes in air at atmospheric pressure under conditions of strong overstress of the discharge gap and to carry out a numerical simulation of the parameters of the plasma of air with small copper impurities under conditions close to those realized in the experiment. Methods . The nanosecond discharge in air of atmospheric pressure between copper electrodes was ignited. The distance between the copper electrodes was 1 mm, which led to the ignition at atmospheric pressure air of a point diffuse discharge of a spherical shape with a diameter of 1 mm. The standard program was used to solve the Boltzmann kinetic equation for the electron energy distribution function (EEDF) for modeling air plasma atmospheric pressure parameters with small copper vapor admixtures, since under the experimental conditions the maximum value of the E/P parameter reached about 530 V cm -1 torr -1 , which is less than the critical value of E/P for nitrogen according to the local electron runaway criterion – 590 V cm -1 torr -1 . Results . Numerical simulation of the plasma parameters established that for the range of reduced electric field strength 610 Td-810 Td, at which experimental studies of the characteristics of a point nanosecond discharge were carried out, mean electron energies varied within the range of 12.2 -15.6 eV; the value of the electron concentration was 10.7·10 21 m -3 – 8.7 ·10 21 m -3 at a current density of 765 · 10 6 A / m 2 on the surface of the copper electrode. The excitation constants of the 2 P 3/2, 1/2 , 2 D 3/2 , 2 D 5/2 , 4 F 7/2 , - states of the copper atom and its ionization were in the range (7.3 – 8.5) 10 -13 m 3 /c, ( 0.29 - 0.28) 10 -13 m 3 /c, ( 0.22 - 0.22) 10 -13 m 3 /c, (0.19 – 0.22) 10 -15 m 3 /c and (0.33 -0.45) 10 -13 m 3 /c,, respectively. The maximum excitation rate constant for nitrogen molecules was for the sum of the singlet states: they were (1.4 10 -14 ) m 3 / s for an electric field strength of 810 Td. The specific losses of the discharge power in the plasma on inelastic collisions of electrons with the components of the gas mixture were maximal for nitrogen molecules and reached 32% for excitation of the sum of singlet nitrogen states. Conclusion . Radiation of the plasma is concentrated in a narrow spectral interval of 200-250 nm, is promising for use as a point UV lamp; the spectral lines 248.9 and 254.4 nm Cu II are promising for estimating the electron temperature in a plasma. Mean electron energy, electron mobility, specific electric power losses and the rate constants of elastic and inelastic scattering of electrons by copper, argon and carbon dioxide, oxygen and nitrogen molecules, the ratio of which was 3: 7.098: 0.266: 159.157: 593.438, depending on the magnitude of the reduced electric field (ratio of the electric field strength (E) to the total concentration of atoms and gas molecules (N)). The range of changes in the parameter E / N = 1-1300 Td (1 ∙10 -17 - 1 ∙ 10 -15 V ∙ cm 2 ) and included the values of the parameter E / N, which were realized in the experiment (610-810) Td.

Physico-mathematical model for determining the direction in space to point sources of gamma radiation using spherical absorber.

Physico-mathematical model for determining the direction in space to point sources of gamma radiation using spherical absorber.

Comparison of two spectrum-dose conversion methods based on NaI(Tl) scintillation detectors

In order to measure the gamma dose more accurately than before, methods of spectrum-dose conversion have been in practice more often instead of count-dose conversion. There are two common methods that have been developed and published. They are the method of G(E) function and the method of unfolding spectrum. The method of G(E) function has been applied in the instrument, because it is easier to implement with limited resources of embedded computers. It is reported that the method of unfolding spectrum cannot only obtain the gamma dose, but also identify nuclides. In this paper these two methods were compared with each other using same initial data. The data was acquired by NaI(Tl) scintillation detectors and other relevant nuclear electronic instruments with three gamma radiation point sources 137Cs, 60Co and 152Eu. The simulation software Geant4 has been used in both methods to calculate the response function and matrix. Results were presented and compared with each other, and all relative deviations were better than 15%.

Background reduction by Cu/Pb shielding and efficiency study of NaI(TI) detector

Abstract The background spectrum of a 3″ × 3″ NaI(Tl) well-type scintillation SILENA detector was measured without shielding, in 6 cm thick lead shielding, and with 2 mm thick electrolytic copper covering the detector inside the lead shielding. The relative remaining background of the lead shield lined with copper was found to be ideal for low-level environmental radioactive spectroscopy. The background total count rate in the (20–2160 KeV) was reduced 28.7 times by the lead and 29 times by the Cu + Pb shielding. The effective reduction of background (1.04) by the copper mainly appeared in the energy range from X-ray up to 500 KeV, while for the total energy range the ratio is 1.01 relative to the lead only. In addition, a strong relation between the full-energy peak absolute efficiency and the detector well height was found using gamma-ray isotropic radiation point sources placed inside the detector well. The full-energy peak efficiency at a midpoint of the well (at 2.5 cm) is three times greater than that on the detector surface. The energy calibrations and the resolution of any single energy line are independent of the locations of the gamma source inside or outside of the well.

Near-field multiple traps of paraxial acoustic vortices with strengthened gradient force generated by sector transducer array

In order to improve the capability of particle trapping close to the source plane, theoretical and experimental studies on near-field multiple traps of paraxial acoustic vortices (AVs) with a strengthened acoustic gradient force (AGF) generated by a sector transducer array were conducted. By applying the integration of point source radiation, numerical simulations for the acoustic fields generated by the sector transducer array were conducted and compared with those produced by the circular transducer array. It was proved that strengthened AGFs of near-field multiple AVs with higher peak pressures and smaller vortex radii could be produced by the sector transducer array with a small topological charge. The axial distributions of the equivalent potential gradient indicated that the AGFs of paraxial AVs in the near field were much higher than those in the far field, and the distances at the near-field vortex antinodes were also proved to be the ideal trapping positions with relatively higher AGFs. With the established 8-channel AV generation system, theoretical studies were also verified by the experimental measurements of pressure and phase for AVs with various topological charges. The formation of near-field multiple paraxial AVs was verified by the cross-sectional circular pressure distributions with perfect phase spirals around central pressure nulls, and was also proved by the vortex nodes and antinodes along the center axis. The favorable results demonstrated the feasibility of generating near-field multiple traps of paraxial AVs with strengthened AGF using the sector transducer array, and suggested the potential applications of close-range particle trapping in biomedical engineering.

Application of Time-Difference-of-Arrival Localization Method in Impulse System Radar and the Prospect of Application of Impulse System Radar in the Internet of Things

The impulse system radar is based on the generation, transmission, radiation, receiving, data collection, data processing, and imaging of impulse signals. It identifies the position or shape of the target object by accurately measuring the time difference and the waveform parameter difference of the electromagnetic signals reflected by the target object. It is a typical impulse-system-based ultra-wideband radar. Based on the existing studies on transmission characteristics of impulse signals and radiation characteristics of elementary time-domain antennas, a “point source approximation” analytical model, which considers an elementary antenna as the radiation point source and can reflect the radiation characteristics of specific elementary antennas, is proposed. On this basis, a time-difference-of-arrival (TDOA) method, whereby targets are localized by testing the TDOA of non-collinear multi-antenna (three or more) for target echo signaling, is proposed. Meanwhile, a detailed analytical analysis and numerical calculation programming are performed. Experimental test results show that the present method enables fairly accurate localization of targets. The application of time-difference localization in an impulse radar can also be extended to the Internet of Things. Positioning and tracking targets by an impulse radar is exactly a key technology in the application of Internet of Things. The research work done in this paper has excellent application values in Internet of Things.

Single freeform surface design for prescribed input wavefront and target irradiance.

In beam shaping applications, the minimization of the number of necessary optical elements for the beam shaping process can benefit the compactness of the optical system and reduce its cost. The single freeform surface design for input wavefronts, which are neither planar nor spherical, is therefore of interest. In this work, the design of single freeform surfaces for a given zero-étendue source and complex target irradiances is investigated. Hence, not only collimated input beams or point sources are assumed. Instead, a predefined input ray direction vector field and irradiance distribution on a source plane, which has to be redistributed by a single freeform surface to give the predefined target irradiance, is considered. To solve this design problem, a partial differential equation (PDE) or PDE system, respectively, for the unknown surface and its corresponding ray mapping is derived from energy conservation and the ray-tracing equations. In contrast to former PDE formulations of the single freeform design problem, the derived PDE of Monge-Ampère type is formulated for general zero-étendue sources in Cartesian coordinates. The PDE system is discretized with finite differences, and the resulting nonlinear equation system is solved by a root-finding algorithm. The basis of the efficient solution of the PDE system builds the introduction of an initial iterate construction approach for a given input direction vector field, which uses optimal mass transport with a quadratic cost function. After a detailed description of the numerical algorithm, the efficiency of the design method is demonstrated by applying it to several design examples. This includes the redistribution of a collimated input beam beyond the paraxial approximation, the shaping of point source radiation, and the shaping of an astigmatic input wavefront into a complex target irradiance distribution.

Radiative heat transfer from multiple discrete fires

The behavior of multiple discrete fires is often different from that of a single fire. Because of the interaction among these fires, their burning rates and flame lengths can increase. Also, the increasing radiative heat transfer from multiple flames is partially responsible for the remote ignition and accelerated flame spread in large-scale urban and wildland fires. To understand the distribution of radiant heat fluxes from multiple discrete fires, experiments have been performed with an array of individual pool fires of variable spacing and size. Results show that a point-source radiation model can be extended from a single pool fire to the array of discrete pool fires. The analysis shows that the radiative heat flux from the fire array was proportional to the fuel–area ratio (or the fuel surface density) and was inversely proportional to the square of the distance to fire array. This work quantifies the role of radiative heat transfer from large-scale discrete fires, thus helps understand the extreme fire behaviors in large-scale urban and wildland fires.

Computational study of optical force between two nanodistant plasmonic submicrowires

In this paper, the optical force between two circular plasmonic wires of submicrometer diameter (0.3μm) with nanometer surface-to-surface distances (3-30nm) interacting with radiation of a complex point source (λ≈0.2 μm) is numerically studied. Calculations (which are based on the Müller integral equations and the Maxwell stress tensor) show that an attractive optical force with a number of distinct peaks is created in distances 3-10nm. However, for plasmonic-dielectric and plasmonic-reflector double-wires, the optical force has no such peaks. Comparisons reveal that the peaks are originated from the excitation of coupled surface plasmon polaritons in the gap region between the plasmonic wires.

Upgrade of the tangential gamma-ray spectrometer beam-line for JET DT experiments

The JET tangential gamma-ray spectrometer is undergoing an extensive upgrade in order to make it compatible with the forthcoming deuterium-tritium (DT) experiments. The paper presents the results of the design for the main components for the upgrade of the spectrometer beam-line: tandem collimators, gamma-ray shields, and neutron attenuators. The existing tandem collimators will be upgraded by installing two additional collimator modules. Two gamma-ray shields will define the gamma-ray field-of-view at the detector end of the spectrometer line-of-sight. A set of three lithium hydride neutron attenuators will be used to control the level of the fast neutron flux on the gamma-ray detector. The design of the upgraded spectrometer beam-line has been supported by extensive radiation (neutron and photon) transport calculations using both large volume and point radiation sources.

Theoretical Modeling of Average Force Acted on Nano Plasma Spheres in Presence of Radiation of Long Wavelength Point Source

Using the solutions of field equation, due to the electromagnetic wave scattering phenomena from a nano plasma sphere(NPS), the inserted force on nano plasma sphere is simulated. For this purpose, with using suitable Green’s function, the scattering phenomena of long wavelength electromagnetic waves from a nano plasma sphere will be investigated. A point electromagnetic source is considered in finite distance from the NPS. The computations will be generalized to two monopole point sources with the same strength but with opposite sign in two sides of sphere to simulating a NPS in presence of a plane electromagnetic wave. The resonance frequency and pattern scattering for these problems will be presented. The graphs of variations of inserted force with respect to wave frequency and geometrical dimension variations are presented.

Primary Beam Air Kerma Dependence on Distance from Cargo and People Scanners.

The distance dependence of air kerma or dose rate of the primary radiation beam is not obvious for security scanners of cargo and people in which there is relative motion between a collimated source and the person or object being imaged. To study this problem, one fixed line source and three moving-source scan-geometry cases are considered, each characterized by radiation emanating perpendicular to an axis. The cases are 1) a stationary line source of radioactive material, e.g., contaminated solution in a pipe; 2) a moving, uncollimated point source of radiation that is shuttered or off when it is stationary; 3) a moving, collimated point source of radiation that is shuttered or off when it is stationary; and 4) a translating, narrow "pencil" beam emanating in a flying-spot, raster pattern. Each case is considered for short and long distances compared to the line source length or path traversed by a moving source. The short distance model pertains mostly to dose to objects being scanned and personnel associated with the screening operation. The long distance model pertains mostly to potential dose to bystanders. For radionuclide sources, the number of nuclear transitions that occur a) per unit length of a line source or b) during the traversal of a point source is a unifying concept. The "universal source strength" of air kerma rate at 1 m from the source can be used to describe x-ray machine or radionuclide sources. For many cargo and people scanners with highly collimated fan or pencil beams, dose varies as the inverse of the distance from the source in the near field and with the inverse square of the distance beyond a critical radius. Ignoring the inverse square dependence and using inverse distance dependence is conservative in the sense of tending to overestimate dose.

The double copy: Bremsstrahlung and accelerating black holes

Advances in our understanding of perturbation theory suggest the existence of a correspondence between classical general relativity and Yang-Mills theory. A concrete example of this correspondence, which is known as the double copy, was recently introduced for the case of stationary Kerr-Schild spacetimes. Building on this foundation, we examine the simple time-dependent case of an accelerating, radiating point source. The gravitational solution, which generalises the Schwarzschild solution, includes a non-trivial stress-energy tensor. This stress-energy tensor corresponds to a gauge theoretic current in the double copy. We interpret both of these sources as representing the radiative part of the field. Furthermore, in the simple example of Bremsstrahlung, we determine a scattering amplitude describing the radiation, maintaining the double copy throughout. Our results provide the strongest evidence yet that the classical double copy is directly related to the BCJ double copy for scattering amplitudes.

Sparse Approximation-Based Maximum Likelihood Approach for Estimation of Radiological Source Terms

A computationally efficient and accurate method is presented for identifying the number, intensity and location of stationary multiple radiological sources. The proposed method uniformly grids the region of interest resulting in a finite set of solutions for the source locations. The resulting problem is a sparse convex optimization problem based on ${{\cal L}_1}$ -norm minimization. The solution of this convex optimization encapsulates all information needed for the estimation of source terms; the values of the nonzero elements of the solution vector approximates the source intensity, the grid points corresponding to the nonzero elements approximates the source locations, and the number of nonzero elements is the number of sources. The accuracy limited by the resolution of the grid is further improved by making use of the maximum likelihood estimation approach. The performance of sparse approximation based maximum likelihood estimation is verified using real experimental data acquired from radiological field trials in the presence of up to three point sources of gamma radiation. The numerical results show that the proposed approach efficiently and accurately identifies the source terms simultaneously, and it outperforms existing methods which have been used for stationary multiple radiological source terms estimation.

IMITATION OF STANDARD VOLUMETRIC ACTIVITY METAL SAMPLES

Due to the specific character of problems in the field of ionizing radiation spectroscopy, the R&D and making process of standard volumetric activity metal samples (standard samples) for calibration and verification of spectrometric equipment is not only expensive, but also requires the use of highly qualified experts and a unique specific equipment. Theoretical and experimental studies performed have shown the possibility to use imitators as a set of alternating point sources of gamma radiation and metal plates and their use along with standard volumetric activity metal samples for calibration of scintillation-based detectors used in radiation control in metallurgy. Response functions or instrumental spectra of such spectrometer to radionuclides like 137 Cs, 134 Cs, 152 Eu, 154 Eu, 60 Co, 54 Mn, 232 Th, 226 Ra, 65 Zn, 125 Sb+ 125m Te, 106 Ru+ 106 Rh, 94 Nb, 110m Ag, 233 U, 234 U, 235 U and 238 U are required for calibration in a given measurement geometry. Standard samples in the form of a probe made of melt metal of a certain diameter and height are used in such measurements. However, the production of reference materials is costly and even problematic for such radionuclides as 94 Nb, 125 Sb+ 125m Te, 234 U, 235 U etc. A recognized solution to solve this problem is to use the Monte-Carlo simulation method. Instrumental experimental and theoretical spectra obtained by using standard samples and their imitators show a high compliance between experimental spectra of real samples and the theoretical ones of their Monte-Carlo models, between spectra of real samples and the ones of their imitators and finally, between experimental spectra of real sample imitators and the theoretical ones of their Monte-Carlo models. They also have shown the adequacy and consistency of the approach in using a combination of metal scattering layers and reference point gamma-ray sources instead of standard volumetric activity metal samples. As for using several reference point gamma-ray sources with radionuclide like 152 Eu, 232 Th, 226 Ra etc, they allow, in a combination of metal scattering layers, to compensate for the absorption of low energy gamma rays in the metal and to generate the desired response in the backscatter peak range, and finally to get the correct amplitude distribution that is equivalent to interaction effects that occur in the volumetric standard sample with radionuclide uniformly distributed in it.

Direct Analytical Method to Calculate Photopeak Efficiency and Photopeak Attenuation Coefficient of NaI(Tl) Well-Type Detector

In this paper full-energy peak (photopeak) efficiency and photopeak attenuation coefficient of 3'' × 3'' NaI(Tl) well-type scintillation detector were calculated using gamma-rayisotropic radiating point sources (with photon energy: 0.245, 0.344, 0.662, 0.779, 0.964, 1.1732, 1.333 and 1.408 MeV) placed outside the detector well. These energies were obtained from 152Eu, 137Cs and 60Co. The relations between the full energy peak efficiency and photopeak attenuation coefficients, were plotted vs. photon energy at different sources to detector distance, and it found that the full energy peak efficiency decreased by increasing the distance between the source and the detector.

Distribution of solar irradiance on inclined surfaces caused by moving clouds

The distribution of solar irradiance in shadows of discrete (broken) clouds differs from the distribution calculated for inclined surfaces on the basis of traditional transposition models and changes fast. This phenomenon is studied in this paper. For calculations of dynamic distributions of irradiance on inclined surfaces, a formal point source of direct radiation near the real position of the sun is defined as the source of the “imaginable radiation.” This notion is used to create a one-dimensional (1D) simulation model, which allows the fast-changing distribution of irradiance to be calculated. In general, the coincidence of calculated and measured irradiance on inclined surfaces is good. The paper also shows how the current value of the diffuse component of solar radiation can be derived from measurements of total radiation in four differently tilted planes.

Polarization and mutual coupling effects in aluminum nanoantenna arrays

This paper uses finite-difference time-domain modeling to study the impact of varying the polarization of the point source(s) on both a single aluminum dipole nanoantenna and a 2×2 array. Starting with the single dipole nanoantenna, this paper demonstrates the strong dependence of power enhancement and resonance on the polarization of the source by alternating between orthogonal polarization states. With each element of the array excited by a single point source, the resonance, power enhancement, and far-field radiation patterns are observed as the polarization of each source is rotated, in varying combinations. The results demonstrate that a unique far-field radiation pattern is produced for each polarization combination, which may lead to applications in subdiffraction limit imaging and quantum optics.

Specific features of two diffraction schemes for a widely divergent X-ray beam

We investigated the specific features of two diffraction schemes for a widely divergent X-ray beam that use a circular diaphragm 30–50 μm in diameter as a point source of characteristic radiation. In one of the schemes, the diaphragm was set in front of the crystal (the diaphragm-crystal (d-c) scheme); in the other, it was installed behind the crystal (the crystal-diaphragm (c-d) scheme). It was established that the diffraction image in the c-d scheme is a topographic map of the investigated crystal area. In the d-c scheme at L = 2l (l and L are the distances between the crystal and the diaphragm and between the photographic plate and the diaphragm, respectively), the branches of hyperbolas formed in this family of planes (hkl) by the characteristic Kα and Kβ radiations, including higher order reflections, converge into one straight line. It is experimentally demonstrated that this convergence is very sensitive to structural inhomogeneities in the crystal under study.

Research of the system response of neutron double scatter imaging for MLEM reconstruction

A Maximum Likelihood image reconstruction technique has been applied to neutron scatter imaging. The response function of the imaging system can be obtained by Monte Carlo simulation, which is very time-consuming if the number of image pixels and particles is large. In this work, to improve time efficiency, an analytical approach based on the probability of neutron interaction and transport in the detector is developed to calculate the system response function. The response function was applied to calculate the relative efficiency of the neutron scatter imaging system as a function of the incident neutron energy. The calculated results agreed with simulations by the MCNP5 software. Then the maximum likelihood expectation maximization (MLEM) reconstruction method with the system response function was used to reconstruct data simulated by Monte Carlo method. The results showed that there was good consistency between the reconstruction position and true position. Compared with back-projection reconstruction, the improvement in image quality was obvious, and the locations could be discerned easily for multiple radiation point sources.