Angular Distribution Of Radiation Intensity Research Articles

Local burst model of CMB temperature fluctuations: luminescence in lines of primary para- and orthohelium

We have considered the formation of the luminescent subordinate HeI lines by the absorption of continuum radiation from a source in the lines of the main HeI series in the expanding Universe. It is suggested that at some moment of time, corresponding to the redshift z0, a burst of superequilibrium blackbody radiation with a temperature T + ΔT occurs. This radiation is partially absorbed at different z < z0 in the lines of the main HeI series and then converted into the radiation of subordinate lines. If νij is the laboratory frequency of the transition of some subordinate line originating at some z, then in the present time its frequency will be ν = νij/(1 + z). For different z (and, consequently, for different ν), the quantum yield for the subordinate lines of para- and orthohelium - the number of photons emitted in the subordinate line, per one initial excited atom and line profiles are calculated. Different pumping channels were considered. Spatial and angular distributions of radiation intensity of luminescent lines for the spherically symmetric radiation sources are presented. It is shown that for sufficiently large ΔT/T, the luminescent lines can be very noticeable in the spectrum of blackbody background radiation.

Transition radiation from relativistic electrons crossing a perfectly conducting conical surface: Calculation and experiment

The angular distributions of the transition radiation intensity when a charged particle passes through the vertex of a perfectly conducting conical surface have been calculated. The radiation generated both when the particle exits the conductor and when it falls on the conductor has been considered. The angular distributions of the intensity of the transition radiation generated by a bunch of relativistic electrons have been measured in the millimeter wavelength range. A microtron with a particle energy of 7.4 MeV was the source of electrons. The influence of the particle injection direction and the conical-surface opening angle on the angular distribution of the radiation intensity has been studied. The measurements have shown that the distribution of the radiation generated by a charge when it enters the horn differs significantly in pattern from the distribution when it exits the horn.

Transition radiation emitted by a particle moving along the axis of a perfectly conducting conical surface

The spatial field distribution is determined for the transition radiation emitted by a relativistic particle moving along the axis of a perfectly conducting circular conical surface with a fixed apex. Emission from particles moving away from and towards the apex is examined. Expressions are obtained that can be used to calculate the angular distribution of radiation intensity for various apex angles between 0 and π. Significant differences are demonstrated between the spatial distributions of radiation generated by outgoing and incoming particles.

Propagation of a burst of radiation in an expanding and recombining universe: Thomson scattering

Within the framework of a flat cosmological model a propagation of an instantaneous burst of nonpolarized isotropic radiation is considered from the moment of its beginning at some initial redshift z0 to the moment of its registration now (at z=0). Thomson (Rayleigh) scattering by free electrons is considered as the only source of opacity. Spatial distributions of the mean (over directions) radiation intensity are calculated as well as angular distributions of radiation intensity and polarization at some different distances from the center of the burst. It is shown that for redshifts z0 large enough (z0 > 1400) the profile of the mean intensity normalized to the total number of photons emitted during the burst weakly depends on initial conditions (say the moment z0 of the burst, the width and shape of initial radiation distribution in space). As regards angular distributions of intensity and polarization they turn to be rather narrow (3 - 5 arcmin) while polarization can reach 70%. On the average an expected polarization can be about 15%.

10.1007/s11455-008-3015-1

A model is proposed for theoretical calculations of the angular distribution of radiation intensity at the output of a flat X-ray waveguide representing an air-filled gap between two quartz plates. Good agreement between the theoretical and experimental angular profiles of CuKα fluorescence intensity is obtained for planar waveguides with the gap widths ranging from 40 to 3000 nm. It is concluded that the Kirchhoff method can be applied to calculations of the spatial distribution of radiation intensity at the X-ray waveguide output.

Transition radiation in a dihedral angle formed by perfectly conducting planes

The spatial distribution of the field of transition radiation generated by a relativistic particle flying into a dihedral angle formed by perfectly conducting plane surfaces is determined. The cases when particles are injected from the edge and from a plane of the dihedral angle are considered. The angular distributions of radiation intensity in dihedral angles of different values are calculated.

Experimental study of coherent transition radiation from relativistic electrons in a dihedral angle

Angular intensity distributions for transition radiation excited by a beam of relativistic electrons in the emitter in the form of a dihedral angle are measured in the millimeter range. The angle is formed by the intersection of two conducting planes. The source of radiation is a microtron with an electron energy of 7.4 MeV. We analyze the effect of the magnitude of the dihedral angle of the emitter, the position of the electron transition point on the surface of the angle, and the direction of motion of electrons on the angular distribution of radiation intensity. It is shown that the spectral and angular distributions of radiation intensity in the dihedral angle substantially differ from analogous distributions for a particle intersecting a planar conducting surface. The possibility of using radiation to measure the energy, spatial position, and direction of motion of charges is considered.

Theoretical calculation of the angular distribution of radiation at the output of a flat nanodimensional X-ray waveguide

A model is proposed for theoretical calculations of the angular distribution of radiation intensity at the output of a flat X-ray waveguide representing an air-filled gap between two quartz plates. Good agreement between the theoretical and experimental angular profiles of CuKα fluorescence intensity is obtained for planar waveguides with the gap widths ranging from 40 to 3000 nm. It is concluded that the Kirchhoff method can be applied to calculations of the spatial distribution of radiation intensity at the X-ray waveguide output.

On features of the radiation from an electron moving along a helix inside a cylindrical hole in a homogeneous dielectric

The radiation from a charge moving along a helical trajectory inside a cylindrical hole in homogeneous dielectric medium is investigated. Prompted by availability of materials with large dielectric permittivity ε and small absorption, we discuss the features of this type of radiation for media with ε ≫ 1 . It is shown that there are high peaks in the angular distribution of radiation intensity at well-defined harmonics. The conditions are specified for the cavity-to-helix radii ratio, ρ 1 / ρ 0 , under which the angle-integrated radiation intensity on some harmonics exceeds that in the empty space. Though the amplification of radiation intensity increases with increasing ε , the corresponding “resonant” values of ρ 1 / ρ 0 ratio are practically independent of the dielectric permittivity of surrounding medium. It is shown that an analogous amplification of radiation takes place essentially for the same values of ρ 1 / ρ 0 also for the radiation in a cylindrical waveguide with conducting walls. An explanation of this phenomenon is given.

Radiation transfer due to a point source in an isotropically scattering, inhomogeneous solid sphere

A method of analysis is presented for solving radiation transfer due to a point source in an absorbing, isotropically scattering, inhomogeneous sphere, which is subjected to a diffusely reflecting boundary. The space-dependent single-scattering albedo is represented in the form ω( r) = Σ K k=0 D K r k , where r is the optical variable and D k are the known expansion coefficients. The effects of various functional forms of albedo on the incident radiation, angular distribution of radiation intensity and emissivity are examined.

Radiation transfer in an isotropically scattering homogeneous solid sphere

Radiative heat transfer in an absorbing, emitting, isotropically scattering sphere with a diffusively reflecting and emitting boundary is solved by the Galerkin method. By using the expressions given in this work, the radiation heat flux, the angular distribution of radiation intensity and the divergence of the radiation heat flux anywhere in the sphere can be determined with a high degree of accuracy for all values of the single scattering albedo, from small to moderately large optical radii. Results are presented for representative cases to illustrate the accuracy and the convergence of the method.

The use of the galerkin method for radiation transfer in an anisotropically scattering slab with reflecting boundaries

Radiation transfer in an absorbing, emitting, anisotropically scattering, plane-parallel medium with diffusely reflecting boundaries is solved by application of the Galerkin method. With this approach, the radiation heat flux, angular distribution of radiation intensity, and the divergence of the radiation heat flux anywhere in the medium can be determined highly accurately. For optical thicknesses up to about 10, exact results are also readily obtainable if sufficient number of terms are considered in the expansion. Numerical results are presented for representative cases.

Radiation transfer in infinite atmospheres. II

The connections between four characteristic angular distributions of radiation intensity in plane infinite and semiinfinite media are studied. These distributions correspond to cases when the source and receiver lie in the same plane (at the boundary for a semiinfinite medium) and when they are infinitely far apart. This made it possible, in particular, to obtain from physical considerations previously unknown Fredholm equations for the intensity u(~) at the boundary in the Milne problem and for the Ambartsumyan functions ~iJ) The possibility of dividing an infinite medium into two adjacent half-spaces lies at the basis of the analysis.

Synchrotron radiation from a charged, current-carrying ring

The problem of synchrotron radiation from a charged, current-carrying ring is considered. An expression is found for the spectral and angular distribution of radiation intensity including polarization effects. Some special cases of the general formula are examined: a limiting transition to the generalized Schott formula, a formula for the intensity of synchrotron radiation from a magnetic dipole oriented along the tangent to the trajectory, and a transition to the formulas for the intensity of Vavilov-Cherenkov radiation from a charged, current-carrying, annular cloud by taking sums of Bessel functions.

Radiative transfer in adjacent half‐spaces with specular reflection

Radiative transfer in absorbing, emitting, isotropically scattering, gray adjacent half‐spaces with specular reflection at the interface is solved rigorously by the application of normal‐mode expansion technique. An alternative method based on the superposition of half‐space problems is also presented for the solution of the problem. Once the expansion coefficients for the solutions are evaluated from the given relations, the physical quantities such as the angular distribution of radiation intensity and the net radiative heat flux anywhere in the medium can readily be determined.

Shielding of Radiation from a Plane Circular Source*

The angular distribution of radiation intensity emitted from a plane circular source is altered by an attached cylindrical shield. Under the assumption of cylindrical symmetry, explicit expressions are obtained for the angular intensity distribution of the radiation emerging from the mouth of the shield. The source is characterized by an intensity which is a function of the point of emission and the direction of emission. The shield is characterized by its length-to-diameter ratio and by the reflectivity of its inner surface. The reflectivity is not necessarily uniform. The general result is an infinite series of integrals over subregions of the source area. For certain cases these integrals are evaluated in terms of elementary mathematical functions.