Point Source Of Radiation Research Articles

The Frequency Spectrum of Rectilinearly Moving Point Sources in a Translation-Invariant Environment Applied to Edge Diffraction

In a translation-invariant environment, the three-dimensional sound field can be determined through spatial Fourier transform by superimposing two-dimensional sound fields. This technique is commonly referred to as the 2.5D method, due to the dimensional reduction that takes place. If the sound source is not stationary but moves along the axis of invariance, the calculation of the sound field generally becomes more complex. However, if a harmonically radiating point source moves uniformly at a constant speed along the invariance axis, the opposite is true, and the calculation is significantly simplified. Motivated by the form of the Green’s function in the free field, the so-called separation of variables, or product approach, reduces the problem to a purely two-dimensional one, the general solution of which is referred to in this work as the Product-Doppler formula. Constructing a Fourier integral over the wavenumber domain along the invariance axis is no longer necessary. It is shown that the Product-Doppler formula can be used to solve both interior and exterior problems. The sound field generated by a moving source inside a cylindrical tunnel, and the sound generated by an exterior moving source and scattered from an absorbing cylinder are analyzed. The complex problem of sound diffraction caused by a source moving along the edge of a wedge or a screen is studied in detail. A comparison with results from the literature shows strong agreement.

Dual-stream gas targets for a point source of vacuum and extreme ultraviolet radiation supported by focused electromagnetic radiation

The article presents the results of visualization of two-stream gas targets for a point source of vacuum ultraviolet and extreme ultraviolet radiation. Measurements of the gas concentration spatial distribution were carried out using a Michelson interferometer. It is shown that adding a light gas to the peripheral channel significantly moves the region of breakdown concentration of injected gas through the central channel away from the nozzle, while maintaining the overall gas flow and background pressure.

P-wave propagation in attenuative elliptical VTI media

Elliptical anisotropy is convenient to use as the reference medium in perturbation methods designed to study P-wave propagation for transverse isotropy (TI). We make the elliptically anisotropic TI model attenuative and discuss the corresponding P-wave dispersion relation and the wave equation. Our analysis leads to two conditions in terms of the Thomsen-type parameters, which guarantee that the P-wave slowness surface and the dispersion relation satisfy elliptical equations. We also obtain the viscoacoustic wave equation for such elliptically anisotropic media and solve it for point-source radiation using the correspondence principle. For the constant- Q TI model, we use the weighting function method to derive the viscoacoustic wave equation in differential form. Numerical examples validate the proposed elliptical conditions and illustrate the behavior of the P wavefield in attenuative elliptical TI models.

Internal stress transfer characteristics of coal–rock medium under concentrated force based on particle flow method

To solve the problem that the macroscopic deformation and failure of coal–rock medium under external loads are easy to be observed while the internal stress transfer mode and path are unclear. Based on the discrete element idea, the numerical models for pure coal or rock samples and coal–rock combination samples with different lithologies and combination methods under concentrated force are established by PFC2D software. Then the influence of coal or rock strength and combination methods on the internal stress transfer law and distribution evolution characteristics of coal–rock medium are discussed from the perspectives of macroscopic stress and mesoscopic force chain, respectively. The results showed that under concentrated load, the macroscopic stress transfer paths within pure coal or rock samples and coal–rock combination samples are primarily in the form of ‘point source radiation’. However, when transferring between coal–rock interfaces, there is a certain interface effect. For pure coal or rock samples, differences in lithology does not change the transfer rules and macro distribution patterns of internal stress, but it can cause changes in internal unit transfer stress value and local area transfer direction. For coal–rock combination samples, the greater the difference in lithology between the two sides of the interface, the more likely the interface effect will occur. In addition, the internal stress transfer is also influenced by the relative stratigraphic relationships of coal and rock. When the stress is transferred from a higher-strength rock to a lower-strength coal mass, the interface effect will be more significant. However, regardless of the combination pattern, the locations where significant stress surges occur are always within the higher strength rock mass near the interface. The findings are helpful to understand the mechanical properties and failure mechanism of mining coal and rock mass, and provide a theoretical basis for the study of the mining-induced mechanical behavior of the floor under the action of the coal pillar.

Characterization of a Germanium Detector by Means of Experimental Measurements and GEANT4 Monte Carlo Simulations

A HPGe detector was modelled and characterized by means of experimental measurements and Monte Carlo simulations. The simulation based on Monte Carlo GEANT4 was used to characterize the potential dead layer/inactive materials and Full Energy Peak Efficiency (FEPE). The calibration of FEPE for the HPGe detector was conducted in the γ-ray energy range from 88 keV to 1332 keV, using eight standard point sources of gamma radiation: 137Cs, 133Ba, 109Cd, 65Zn, 60Co, 57Co, 54Mn, and 22Na. The efficiency dependence curves were obtained by changing the source to detector distance from 8 cm to 12 cm. a remarkable similarity in FEPE for low energy measurements ranging from 88 keV to 122 keV was obtained between the simulation results and the experimental measurements.

Comparison of Dosimetric Methods in Nuclear Medicine

Historically, dosimetry has been conducted with varying degrees of sophistication. A broad and general approach involves computing organ-specific time-integrated activity multiplied by S-factors, as defined by the Medical Internal Radiation Dose (MIRD) Committee. This method uses a standard human body phantom as a reference for mass density distribution. More advanced methods, such as the voxel dose approach, estimate absorbed dose by linearly superimposing contributions from each voxel in the spatial activity distribution, treating each voxel as a radiation point source. The energy dose from a radiation point source with isotropic unit activity in an infinite homogeneous medium is known as a dose point kernel (DPK). Previously, DPKs were calculated using Monte Carlo techniques for tissues like bone, lung, soft tissue, and water, primarily for isotopes such as Iodine-131 and Yttrium-90. Later, continuous DPKs were discretized into dose voxel kernels (DVKs) that can be arbitrarily scaled. The absorbed dose distribution is then derived by convolving the time-integrated spatial activity distribution with the Monte Carlo-based DVK, based on the patient's anatomy. Due to the computational expense of this process, various methods have been explored to estimate approximate DVKs. The highest level of sophistication is achieved with full Monte Carlo simulations of radiation transport inside the patient's body, providing reference results for benchmarking other approaches. The network is trained with DVKs obtained from dedicated Monte Carlo simulations using equally sized kernels of specified tissue density and a specified radioisotope. This method is intermediate between the canonical MIRD protocol and deep neural network approaches that predict whole-body absorbed dose distributions from individual mass density and activity distributions. In this paper, we have discussed and compared all the commonly employed dosimetric method along with new approaches using artificial intelligence.

Application of spherical harmonic filtering to 4π gamma imaging

Abstract 4π gamma imaging with sensitivity in all directions is useful for determining the incident direction of the gamma-ray to the detector. In this study, a spatial filter with a spherical harmonic function was proposed for 4π gamma imaging to reduce statistical noise in lower-event data. The application of the filtered 4π imaging for finding a point radiation source was investigated. In the filtered 4π images, the linearity and root mean squared error of the image improved with a small number of events. Furthermore, the finding of a 137Cs point source based on the filtered gamma imaging was demonstrated, and the accuracy of the estimated source location and activity was improved using lower-event data.

Further development of the LNMRI/IRD's TNF2 thermal system for flexible dose rate irradiation.

The 'Inverse Square Law' (ISL)( 1) requires the existence of a point radiation source to be validated, but in some cases where there is more than one source, its use is possible as long as a point is determined where a virtual source can be positioned and from this point the points correspond to the ISL. Ambient dose equivalent rate values were obtained by simulation and measurements at various points along the LNMRI Thermal Neutron Flux 2 (TNF2) central axis front face, determining a function corresponding to the inverse square of the distance and the font position at the virtual point 'y0', so that the ISL is respected. This function will help in the neutron monitors calibration, previously estimating the ambient dose equivalent at a certain distance from the face.

Method of correlation reception of radio light with spatial resolution and its implementation

A method for receiving ultra-wideband noise-like microwave radiation -- radio light is considered, based on the correlation reception of signals coming from spaced apart space of receiving antennas, for the purpose of further effective image formation radio-illuminated environment. A mathematical model has been developed to study the formation possible response of the receiving system and assessing the influence of signal accumulation time on its dynamicrange. One-dimensional responses of the correlation receiving system to point sources of radiation were obtained, for which radio light sources were used. An experimental model of a correlation radio light receiver was developed and physical experiments were carried out with it, confirming the results obtained during modeling, as well as the overall performance of the proposed approach.

Gas Discharge Point Source of UV Radiation Based on Argon–Copper Gas–Vapor Mixture

Gas Discharge Point Source of UV Radiation Based on Argon–Copper Gas–Vapor Mixture

On a paradox" in the scattering theory

The solution of the "paradox" in scattering theory is considered, according to which the extinction cross section is expressed in terms of the forward scattering amplitude (the so-called "optical theorem"), whereas for a point source, and as a consequence, for any emitter located at a finite distance from the scatterer, a similar ratio is often written through a scattered field near the emitter, i.e. determined by "backscattering". A clear picture of the formation of radiation losses during the transition of energy from the source to the scatterer is presented. It is shown that although the field backscattered to the source determines the change in its radiation characteristics (the Purcell effect), the optical theorem includes an extinction factor which is generally related to the work of the incident wave on the currents induced in the scatterer. This factor passes into the forward scattering amplitude in the limiting case of a plane incident wave. Keywords: optical theorem, energy conservation, radiation losses, Purcell effect, point source of radiation.

МОДЕЛИРОВАНИЕ ВОЗБУЖДЕНИЯ ПОВЕРХНОСТНЫХ ПЛАЗМОН-ПОЛЯРИТОНОВ В ПРЯМОУГОЛЬНОМ НАНОРЕЗОНАТОРЕ НА ОСНОВЕ ЗОЛОТА

This paper considers the modeling of surface plasmon polaritons excitation in a limited nanostructure on the basis of a two-dimensional area discrete model, the area interacts with the oscillator. The nanostructure is a rectangle defined on the metal surface at the interface of the gold–silicon oxide, the surface plasmon–polaritons are excited by an electromagnetic radiation point source located above the metal surface. The dynamics of radiation point source is described by a discrete version of the Van der Pol equation with a small nonlinearity of the source parameters. The parameters of the goldsilicon oxide structure (the wave phase speed, the radiation source frequency, the characteristic time in the system, etc.) will be received from the dispersion relation for surface plasmon–polaritons at a single metal–dielectric interface. The distributions of the wave field in the structure will be analyzed at different positions of the point oscillator and different coupling coefficients of the wave field with the oscillators. The resonant wave field mode composition at different positions of the point oscillator and different coupling coefficients will be found using the two-dimensional Fourier transform of the wave field, the time evolution of excited modes of the wave field amplitudes will be also analyzed. In conclusion, the paper gives applicability limits of the considered model for studying the surface plasmon polaritons excitation in a limited nanostructure.

Gas-Discharge Point Source of UV Radiation Based on a Gas-Vapor Mixture of Argon and Copper

The characteristics of a pulse periodic source of a long-range UV radiation with overvoltage pumping by a bipolar discharge of nanosecond duration between copper electrodes in argon at atmospheric pressure are investigated. Copper vapors were introduced into the discharge due to the ectonic mechanism, in which a sufficient amount of the electrode material vapors is introduced into the discharge gap due to microexplosions of inhomogeneities of the surface of metal electrodes in a strong electric field of an overvoltage high-current nanosecond discharge. The characteristics of an overvoltage nanosecond discharge at a distance between the electrodes of 2 mm are studied. The emission spectra of the discharge were analysed, and the intensity of the UV radiation of a point emitter was optimized depending on the supply voltage of the high-voltage modulator and the repeti-tion rate of discharge pulses. The identification of the emission spectra of plasma made it possible to establish the main excited plasma products that form the spectrum of the UV radiation of the plas-ma. The study of the spectral characteristics of plasma based on gas-vapor mixtures "copper – ar-gon" showed that the most intense were the spectral resonance spectral lines of the copper atom and ion. It was found that a space-uniform overvoltage nanosecond discharge was ignited between copper electrodes at an inter-electrode distance of 2 mm. It was found that the maximum value of the average UV power at p(Ar) = 101 kPa was observed for the UV-A range.

Corrigendum: Particle Filter Based Range Search Approach for Localization of Radioactive Materials

In the original article, there was an error. In equation (1) small "i" is typed instead of capital I, subscript of symbols and italic, use of ";" instead of "," missing of B(x, y), reference (Chin et al., 2008) instead of (Rao et al., 2008).The localization of a point radiation source of unknown strength Au expressed in a unit of micro-Curie (Ci) called the source rate will be considered. The source is located at an unknown location (xu, yu). The source gives a radiation intensity of ( ) = ( , ) = × ×2.22×10 6 ( − ) 2 +( − ) 2(1) Last Name author1 et al.Pc 2 (Expressed in counts per minute or CPM) when measured by a sensor at point p = (x, y), where E is an efficiency constant unique to the sensor. The radiation count induced by the source and observed at the sensor per unit time is a Poisson random variable with parameter λ = I(xi, yi), not accounting for the background radiation B(x, y) (Rao et al., 2008) denote the background radiation strength at (x, y) expressed in CPM, called the background rate. The radiation count measurement (due to the background radiation) at a sensor i located at (xi, yi) is given by the Poisson random variable with parameter B (xi, yi). For comparison purposes, the radiation model, actual measurements, and calibration process (Rao et al., 2008) are followed.

Метод розрахунку функції розсіювання точки оптичної системи

The article presents a mathematical apparatus for precise calculation of the three-dimensional point spread function (PSF) of a high-aperture optical system. The proposed method is based on the Huygens-Fresnel principle: a spherical wave on the three-dimensional surface of the exit pupil is considered as result of the superposition of elementary secondary point radiation sources. These point sources emit coherent electromagnetic waves with a spherical wave front. They form a certain distribution of generalized complex amplitudes in three-dimensional space near the focus point. This distribution is used to calculate the intensity distribution in the focus area of ​​the optical system, which is the PSF. The article presents the results of PSFcalculations and their comparative.

Propagation of Cosmic Rays in Plasmoids of AGN Jets-Implications for Multimessenger Predictions

After the successful detection of cosmic high-energy neutrinos, the field of multiwavelength photon studies of active galactic nuclei (AGN) is entering an exciting new phase. The first hint of a possible neutrino signal from the blazar TXS 0506+056 leads to the anticipation that AGN could soon be identified as point sources of high-energy neutrino radiation, representing another messenger signature besides the established photon signature. To understand the complex flaring behavior at multiwavelengths, a genuine theoretical understanding needs to be developed. These observations of the electromagnetic spectrum and neutrinos can only be interpreted fully when the charged, relativistic particles responsible for the different emissions are modeled properly. The description of the propagation of cosmic rays in a magnetized plasma is a complex question that can only be answered when analyzing the transport regimes of cosmic rays in a quantitative way. In this paper, therefore, a quantitative analysis of the propagation regimes of cosmic rays is presented in the approach that is most commonly used to model non-thermal emission signatures from blazars, i.e., the existence of a high-energy cosmic-ray population in a relativistic plasmoid traveling along the jet axis. It is shown that in the considered energy range of high-energy photon and neutrino emission, the transition between diffusive and ballistic propagation takes place, significantly influencing not only the spectral energy distribution, but also the lightcurve of blazar flares.

Estimation of the contribution of scattered ionising radiation to the dosimeter readings during measurements inside a low-background chamber

The article evaluates the contribution of ionising gamma radiation scattered by structural materials when measuring the dose rate in a low-background chamber. The contribution of scattered radiation to the total dose rate was estimated using Monte Carlo simulations. A model of a low-background camera and a BDKG-05K dosimeter was created in the computer program Fluka. In addition, a model of a point source of 137Cs gamma radiation was placed in the low-background chamber. The fraction of scattered radiation was calculated by comparing the dosimeter readings when measuring the dose rate inside the low-background chamber with the reference model (the dosimeter model is placed together with the source in a vacuum, as a result, scattered radiation is completely absent). The calculation was carried out for two positions of the dosimeter relative to the source (30 and 100 cm). It was found that the contribution of scattered radiation to the dose rate reaches 38 % (distance from the source to the detector is 100 cm). To minimise the contribution of scattered radiation to the readings of the dosimeter, a design in the form of a collimator, inside which the source is located, was considered. Additionally, the work investigated the dependence of the dose rate formed by the scattered radiation on the design features of the collimator. It was found that the use of a collimator makes it possible to reduce the contribution of scattered radiation to 3 %. The aim of the work was to calculate the optimal design of the collimator, in which the contribution of scattered radiation to the total dose rate will be minimal. The results of the work will be used to create a prototype of a low-background camera and an optimised collimator.

Silicon cuboid nanoantenna with simultaneous large Purcell factor for electric dipole, magnetic dipole and electric quadrupole emission

The Purcell effect is commonly used to increase the spontaneous emission rate by modifying the local environment of a light emitter. Here, we propose a silicon dielectric cuboid nanoantenna for simultaneously enhancing electric dipole (ED), magnetic dipole (MD) and electric quadrupole (EQ) emission. We study the scattering cross section, polarization charge distribution, and electromagnetic field distribution for electromagnetic plane wave illuminating the silicon dielectric cuboid nanoantenna, from which we have identified simultaneous existence of ED, MD and EQ resonance modes in this nanoantenna. We have calculated the Purcell factor of ED, MD and EQ emitters with different moment orientations as a function of radiation wavelength by placing these point radiation source within the nanoantenna, respectively. We find that the resonances wavelengths of the Purcell factor spectrum are matching with the resonance modes in the nanoantenna. Moreover, the maximum Purcell factor of these ED, MD and EQ emitters is 18, 150 and 118 respectively, occurring at the resonance wavelength of 475, 750, and 562 nm, respectively, all within the visible range. The polarization charge distribution features allow us to clarify the excitation and radiation of these resonance modes as the physical origin of large Purcell factor simultaneously occurring in this silicon cuboid nanoantenna. Our theoretical results might help to deeply explore and design the dielectric nanoantenna as an ideal candidate to enhance ED, MD and EQ emission simultaneously with very small loss in the visible range, which is superior than the more popular scheme of plasmonic nanoantenna.

Calculation of the Effective Energy Release Centerʼs Position of Inorganic Scintillation Detectors for Calibration at Small “Source–Detector” Distances

Inorganic scintillation detectors are widely used to measure of dose rate in the environment due to their high sensitivity to photon radiation. A distinctive feature when using such detectors is the need to take into account of the position of the effective energy release center. This peculiarity is actual when using measuring instruments with inorganic scintillation detectors as working standards during calibration at short “source–detector” distances in conditions of low-background shield or using a facility with protection from external gamma radiation background in the dose rate range from 0.03 to 0.3 μSv/h (μGy/h). The purpose of this work was to calculate the position of the effective energy release center of NaI(Tl) scintillation detectors and to take it into account when working at short “source–detector” distances.An original method of determining the position of the effective energy release center when irradiating the side and end surfaces of inorganic scintillation detector with parallel gamma radiation flux and point gamma radiation sources at small “source–detector” distances using Monte Carlo methods is proposed. The results of calculations of the position of the effective energy release center of NaI(Tl) based detectors of “popular” sizes for the cases of parallel gamma radiation flux and point sources of gamma radiation at small “source–detector” distances are presented. The functional dependences of the position of the effective energy release center of NaI(Tl) based detectors on the distance to the point gamma radiation sources and the energy of gamma radiation sources are presented.As a result of the study it was found that for scintillation NaI(Tl) detectors of medium size (for example, Ø25×40 mm or Ø40×40 mm) the point gamma radiation source located at a distance of 1 m or more, creates a radiation field which does not differ in characteristics from the radiation field created by a parallel flux of gamma radiation. It is shown that approaching the point gamma radiation source to the surface of scintillation detector leads to displacement of the position of the effective energy release center to the surface of the detector.

Equivalent Analysis of Thermo-Dynamic Blow-Off Impulse under X-ray Irradiation

X-ray thermodynamic effect is an important damage mode for spacecraft. Blow-off impulse as the main thermodynamic damage parameter has been widely studied by combining laboratory and numerical simulations. In this paper, most calculations and analyses have been carried out by using the self-developed software RAMA, including the equivalent calculation of blow-off impulse of monoenergetic and blackbody X-ray, and soft/hard blackbody X-ray irradiated at different incidence angles of LY-12 aluminium target. The results show that the characteristic mono-energetic X-ray can be exploited to simulate the blow-off impulse of the blackbody X-ray under certain conditions as a feasible equivalent method for the equal-flux and equal-impulse relations between mono-energetic and intense pulse blackbody of blow-off impulse. Moreover, the equivalent thermodynamic effect can be achieved between the point source radiation and parallel X-ray of X-ray. Furthermore, the cosine distribution of blow-off impulse is conducive to designing and calculating X-ray radiation load of hard aluminium corresponding to 1–5 keV blackbody spectrum. The mentioned results can be referenced for pulse X-ray simulation source and enhance the fidelity of the thermal-mechanical effect by electron beam. It is noteworthy that the study on the thermodynamic effects of intense pulsed X-ray is of high significance.