Energy Absorption Cross Section Research Articles

Spectroscopic properties of Ho3+ doped Sc2O3 transparent ceramic for laser materials

Systematic high resolution spectral investigations of trivalent holmium doped in Sc2O3 polycrystalline transparent ceramic were performed. The spectral characteristics (Stark energy levels, absorption, and emission cross sections) as well as the Judd–Ofelt (JO) intensity parameters Ωt(t=2,4,6) for the f-f transitions of the C2-symmetry center of Ho3+ in Sc2O3 transparent ceramics were determined. The JO intensity parameters are used to estimate the emission probabilities, radiative lifetimes, and branching ratios of the different Ho3+ transitions. The emission gain cross section for the I57→I58 and I56→I58 transitions of special interest for laser application were determined.

Electric-field energy absorption by a bimetallic cylindrical particle

The electric-field energy absorption cross section of a bimetallic cylindrical particle is calculated for an external ac electric field directed along the axis of the particle. The calculations are performed for arbitrary values of the ratio of the particle core radius to the particle radius. The reflection of electrons from the inner and outer surfaces of the metallic shell of the particle is assumed to be diffuse. The limiting cases are considered, and the results obtained are discussed.

On universality of stress-energy tensor correlation functions in supergravity

Using the Minkowski space AdS/CFT prescription we explicitly compute in the low-energy limit the two-point correlation function of the boundary stress-energy tensor in a large class of type IIB supergravity backgrounds with a regular translationally invariant horizon. The relevant set of supergravity backgrounds includes all geometries which can be interpreted via gauge theory/string theory correspondence as being holographically dual to finite temperature gauge theories in Minkowski space–times. The fluctuation–dissipation theorem relates this correlation function computation to the previously established universality of the shear viscosity from supergravity duals, and to the universality of the low energy absorption cross section for minimally coupled massless scalars into a general spherically symmetric black hole. It further generalizes the latter results for the supergravity black brane geometries with non-spherical horizons.

Erratum: “Doppler Broadening and its Contribution to Compton Energy-Absorption Cross Sections: An Analysis of the Compton Component in Terms of Mass-Energy Absorption Coefficient” [J. Phys. Chem. Ref. Data 31, 769 (2002)

First Page

Compton energy-absorption scattering cross-sections for H, C, N, O, P, Ca and assessment of Doppler broadening

Total Compton, individual shell and Compton energy-absorption scattering cross-sections are evaluated in the energy region 0.005 to 10 MeV for H, C, N, O, P and Ca. Compton energy absorption cross-sections deviate numerically with available values. The cause of the numerical discrepancies are not fully understood but can be attributed to Doppler broadening of the Compton scattered photons through a given angle.

Doppler Broadening and its Contribution to Compton Energy-Absorption Cross Sections: An Analysis of the Compton Component in Terms of Mass-Energy Absorption Coefficient

Compton energy absorption cross sections are calculated using the formulas based on a relativistic impulse approximation to assess the contribution of Doppler broadening and to examine the Compton profile literature and explore what, if any, effect our knowledge of this line broadening has on the Compton component in terms of mass–energy absorption coefficient. Compton energy-absorption cross sections are evaluated for all elements, Z=1–100, and for photon energies 1 keV–100 MeV. Using these cross sections, the Compton component of the mass–energy absorption coefficient is derived in the energy region from 1 keV to 1 MeV for all the elements Z=1–100. The electron momentum prior to the scattering event should cause a Doppler broadening of the Compton line. The momentum resolution function is evaluated in terms of incident and scattered photon energy and scattering angle. The overall momentum resolution of each contribution is estimated for x-ray and γ-ray energies of experimental interest in the angular region 1°–180°. Also estimated is the Compton broadening using nonrelativistic formula in the angular region 1°–180°, for 17.44, 22.1, 58.83, and 60 keV photons for a few elements (H, C, N, O, P, S, K, and Ca) of biological importance.

Absorption of scalars by extended objects

We derive the low energy absorption cross section of minimal scalars for a very generic class of geometries, that includes, among others, black holes, strings, p-branes, as well as intersecting brane configurations. The scalar field can be absorbed across a regular surface (a horizon) of finite area, or across a zero area throat, which may be singular or regular. Then we focus on some particular cases and compare with the results obtained using microscopic models at weak coupling. Exact agreement is found for the absorption by the non-degenerate ground state of effective strings. For geometries where the throat is singular, we show that absorption through the stretched horizon yields correct results for degenerate states. For non-degenerate (ground) states we introduce a stretched throat, and show that it accounts for the correct dependence on frequency, charges, and moduli for the absorption by ground states of BPS fundamental strings. It is also shown to lead to the correct dependence on frequency for extremal D-branes.

Hollow sphere as a detector of gravitational radiation

The most important features of the proposed spherical gravitational wave detectors are closely linked with their symmetry. Hollow spheres share this property with solid ones, considered in the literature so far, and constitute an interesting alternative for the realization of an omnidirectional gravitational wave detector. In this paper we address the problem of how a hollow elastic sphere interacts with an incoming gravitational wave and find an analytical solution for its normal mode spectrum and response, as well as for its energy absorption cross sections. It appears that this shape can be designed having relatively low resonance frequencies (about 200 Hz) yet keeping a large cross section, so its frequency range overlaps with the projected large interferometers. We also apply the obtained results to discuss the performance of a hollow sphere as a detector for a variety of gravitational wave signals.

Universality of Low Energy Absorption Cross Sections for Black Holes

In this paper we compute the low energy absorption cross-section for minimally coupled massles scalars and spin-$1/2$ particles, into a general spherically symmetric black hole in arbitrary dimensions. The scalars have a cross section equal to the area of the black hole, while the spin-$1/2$ particles give the area measured in a flat spatial metric conformally related to the true metric.

A computer program to calculate the total energy absorption cross-section for the photodissociation of a diatomic molecule arising from a bound state → repulsive state transition using time dependent quantum dynamical methods

A program is presented for calculating the total energy absorption cross-section for the photodissociation of a diatomic molecule. The mechanism is assumed to involve the absorption of a photon of ultraviolet radiation which causes an electronic transition in the diatomic molecule from a bound to a repulsive electronic state. The two atoms then fly apart under the influence of the forces on the repulsive electronic state causing the molecule to break up into its atomic fragments. Time dependent quantum dynamical methods are used in the calculation. These methods yield the complete absorption spectrum from a single solution of the dynamics of the system. The computer program permits the calculation of cross-sections for molecules in different initial vibrational states. The program is self-contained.

Elastodynamic Scattering From Penny-Shaped and Nonplanar Cracklike Flaws With Dissipation and Restoring Forces

Scattering from penny-shaped and nonplanar cracklike flaws, with a type of boundary condition which incorporates dissipation and restoring forces, is studied. Scattering cross-sections and energy absorption cross-sections are computed, and comparisons with open cracks are performed. A partially debonded inclusion, with the debonding in the form of a cracklike flaw, is also discussed. The method employed is a modified null field approach, incorporating some ideas previously used for treating scattering from nonplanar open or fluid-filled cracks. In the present context, the boundary conditions lead to great simplifications in the implementation of the method, in that part of the relevant matrices can be computed analytically.

Compton Component of the Mass-Energy Absorption Coefficient: Corrections Due to the Energy Broadening of Compton-Scattered Photons

The velocity distribution of atomic electrons causes an energy broadening of photons Compton scattered through a given angle. The energy distribution of the photons is peaked at the Compton energy (that of photons scattered against free electrons at rest). Doubly differential incoherent scattering cross sections calculated in the relativistic impulse approximation show that the broadening is asymmetric around the Compton energy, particularly for photon energies <200 keV and when energy transfers are in the neighborhood of an absorption edge in the atom. Here, doubly differential cross sections are used in calculations of the incoherent energy absorption cross section $\sigma _{{\rm en}}$. The values derived deviate considerably from those in standard tabulations. Neglect of the energy broadening leads to an underestimate of the true energy transferred to Compton electrons and hence to too low values of $\sigma _{{\rm en}}$. Since photoelectric absorption predominates in cases when the energy broadening su...

Erratum: X-ray incoherent scattering total cross sections and energy-absorption cross sections by means of simple calculation routines

Erratum: X-ray incoherent scattering total cross sections and energy-absorption cross sections by means of simple calculation routines

X-ray incoherent scattering total cross sections and energy-absorption cross sections by means of simple calculation routines

Simple but accurate expressions for the total cross sections and energy-absorption cross sections for inelastic scattering of x rays from atomic, molecular, and condensed matter are developed. The starting point is the relativistic impulse approximation for Compton scattering of x rays. This gives the inelastic-scattering cross-section differential with respect to energy and solid-angle interval. Integration over energy of this expression up to all the shells $K$, $L$, $M$,... for the orbitals gives a simple result in the "linear" approximation [R. Ribberfors and K.-F. Berggren, Phys. Rev. A 26, 3325 (1982)]. The result is a cross-section differential with respect to solid angle. Numerical results for Al, Ag, and Pb are in good agreement with available experimental values and with the Waller-Hartree theory. It is shown that a further integration of the differential cross section with respect to the solid angle results in a simple formula for calculating the total cross section for inelastic scattering of x rays. A comparison with integrated values of the incoherent scattering function (Waller-Hartree theory) is carried out. Calculations of the (electron) energy-absorption cross-section result in a compact formula. In this case also, we make comparisons with the double-differential cross section integrated twice and with the Walter-Hartree theory.

Energy Absorption Coefficients and Photon Kerma for LiF

Accurate knowledge of energy absorption coefficients is needed to calculate the absorbed dose in any material. The photon kerma for LiF relative to air and soft tissue is computed using energy absorption coefficient values for Li, F, air, and tissue. Values of energy absorption coefficients for air are already available in J. H. Hubbell's (Photon Cross-Sections, Attenuation Coefficients and Energy Absorption Coefficients from 10 KeV to 100 GeV. National Standard Reference Data System-National Bureau of Standards Report No. 29, Washington, D. C., 1969) tables. Those for tissue are obtained by adding the weighted average of the energy absorption coefficients to the different elements constituting the tissue. For fluorine, they are computed from the values given by F. H. Attix and W. C. Roesche (Eds, Radiation Dosimetry, Vol. I, Fundamentals. Academic Press, New York/London, 1968) for CaF/sub 2/ and Ca. The values for lithium have been computed taking into consideration the photoelectric effect, Compton process, and pair production. Corrections for radiative energy losses, fluorescence yields, screening of electrons, etc., are appropriately applied. The energy absorption coefficients due to photoeffect, Compton scattering, and pair production are added to get the total. The energy absorption cross-section data for photon energies from 0.01 tomore » 10 MeV are tabulated for each interaction.« less

Photon Mass Attenuation and Mass Energy-Absorption Coefficients for H, C, N, O, Ar, and Seven Mixtures from 0.1 keV to 20 MeV

coherent and incoherent scattering, atomic photoeffect, and positron-electron pair and triplet production; the energy-absorption cross sections for these interactions are also listed. From this cross-section data base, mass energy-absorption coefficients pen/p, taking into account bremsstrahlung losses and positron annihilation in flight, Compton-scattered and fluorescence photons, and mass-attenuation coefficients p/p, are tabulated for the above elements and for the mixtures: air, water, polystyrene, methyl methacrylate (Lucite, Perspex, Plexiglass, etc.), polyethylene, bakelite, and amber over the range from 0.1 keV to 20 MeV. For application to cavity ionization detector metrology the ratio pen/p in air to that in carbon and to that in the above six remaining mixtures is tabulated over the same energy range. The air and carbon p,/p values and air/carbon ratios are compared with those in ICRU Report 17 and other earlier compilations.

An analysis of the Z-dependence of photon and electron interactions

The analysis of the dependence upon atomic number was specifically biased towards the application of the data to biological tissues and their substitutes. The photon interactions considered included all the partial attenuation and energy absorption cross-sections. The electron interactions analysed were collision and radiation stopping powers and angular scattering powers. The derived Z-exponents are tabulated for different energies and elemental groupings and indicate the inadequacy of existing Z-exponents. In particular, the continued use of the single exponent 3.94 for photoelectric attenuation (per atom) is put in question.

Optical Spectra and Intensities of Nd3+ in YAlO3

The optical absorption and emission spectra, fluorescence kinetics, and radiative and nonradiative transition probabilities of Nd3+ ions in YAlO3 are investigated. Measurements are presented of the energy levels, absorption and emission cross sections, linewidths as a function of temperature and Nd concentration, thermal line shifts, and fluorescence branching ratios. Judd-Ofelt intensity parameters for electric-dipole transition probabilities are derived from measurements of the absorption spectrum. Stimulated emission cross sections, absorption-band intensities, fluorescence quantum efficiency, possible excited-state absorption, and other properties of importance for YAlO3:Nd3+ laser action are discussed.

The scattering of gamma-rays in extended media I. Perpendicular incidence on a plane slab

As the simplest problem involving the multiple scattering of gamma-rays, the case of perpendicular incidence on a plane slab has been studied by various simple theoretical methods. No exact solution is available as a test of these methods, but approximations of increasing accuracy, known to give too small a dose under the slab, have been combined with a theoretical upper limit for the dose, forming a zone in which the exact solution must lie. Most of the methods tested could be used even if pair-creation or the photoelectric effect gave an appreciable absorption, though for simplicity the computations have been carried out for pure Compton scattering and for quantum energies of a few MeV. Polarization by the Compton effect has been neglected. The best of the simple methods is a modification of the upper limit solution; in problems where this is too difficult to formulate, a good alternative is to calculate the dose from unscattered and once-scattered quanta, giving the latter the penetrating power of the incident quanta and the maximum possible energy-absorption cross-section.