Differential Scattering Cross Sections Research Articles

Neutralization of slow helium ions scattered from single crystalline aluminum and tantalum surfaces and their oxides

We investigated the impact of surface oxygen on the ion yield for He+ ions scattered from different single crystalline surfaces in low-energy ion scattering. Initially clean Al(111) and Ta(111) were exposed to molecular oxygen and ion spectra for different oxidation stages and different primary energies were recorded. A comparison of ion yields normalized to the differential scattering cross section as well as experimental factors allows obtaining information about the influence of oxygen on charge exchange processes. The decrease in the ion yield of both metals with exposure cannot be explained by different surface coverages exclusively, but requires the neutralization efficiency to be dependent on the chemical structure of the surface. For Ta, additionally, a different energy dependency of the ion yield obtained in the metal and oxide occurs. The ion yield for O shows in both surfaces a significantly weaker energy dependency than the investigated metals.

Regge pole description of scattering of gravitational waves by a Schwarzschild black hole

We revisit the problem of plane monochromatic gravitational waves impinging upon a Schwarzschild black hole using complex angular momentum techniques. By extending our previous study concerning scalar and electromagnetic waves [A. Folacci and M. Ould El Hadj, Phys.\, Rev.\, D {\bf 99}, 104079, (2019), arXiv:1901.03965], we provide complex angular momentum representations and Regge pole approximations of the helicity-preserving and helicity-reversing scattering amplitudes and of the total differential scattering cross section. We show, in particular, that for high frequencies (i.e., in the short-wavelength regime), a small number of Regge poles permits us to describe numerically with very good agreement the black hole glory and the orbiting oscillations and we then provide a semiclassical approximation that unifies these two phenomena.

Electron Emission in Ion-Alkali Atoms Collision Process: Three Body Effect

Double differential scattering cross section for emitted electron from ground and excited states when the Ar+18 (75, 85 and 95 Mev/u) scattered off Alkali atom have been calculated within Born approximation following Stolterfoht et al, theoretical model. The emitted electrons from the excited state give large differential cross section comparison with the ground state. Many features of the scattering process are also discussed.

Scattering of twisted light from a crystal

Recent years have seen significant progress in the generation and application of twisted beams carrying orbital angular momentum. Here we study the elastic scattering of twisted Bessel light from a crystal and compare our predictions with the results for incident plane-wave radiation. Based on form-factor approximation our numerical calculations of the differential scattering cross sections have been carried out for a crystal of lithium at x-ray energies. It is shown that the use of twisted light can lead to a measurable change in the scattering cross section for the nanocrystals approaching a few nm in size.

On a measurement approach to support evaluation of thermal scattering law data

Inelastic thermal neutron scattering in materials that act as neutron moderators, reflectors, and filters results in shaping the neutron spectrum at low energies. This phenomenon is described using differential scattering cross sections calculated from three components including the bound atom (i.e., nuclear) scattering cross section of the neutron, the ratio of the outgoing and incoming neutron energy, and the thermal scattering law (TSL), i.e., S(α,β), where α and β represent dimensionless momentum and energy exchange variables, respectively. To date, no TSL libraries are generated using measured data. However, valuable information may be derived from measurements and “targeted” experiments that can validate TSL data and the related inelastic scattering cross sections. As a demonstration, a suite of coordinated measurements and experiments is described that was designed and used to support the evaluation of the TSL for “nuclear” graphite. This experimental suite includes neutron powder diffraction (for structure analysis), positron annihilation (for nano porosity assessment), inelastic neutron scattering measurements using a chopper spectrometer, transmission experiments using neutrons with energy below the Bragg cutoff thereby accessing the total (inelastic) cross section, and a slowing-down-time experiment to observe the developing neutron spectrum in the material. This experimental suite was key to understanding the difference in TSL between “nuclear” and “ideal” graphite and for the inclusion of “nuclear” graphite in the ENDF/B-VIII.0 nuclear data library release.

Validation of ENDF/B-VIII thermal neutron scattering data of heavy water by differential cross section measurements at various temperatures

Temperature-dependent thermal neutron differential scattering cross sections for heavy water (D2O) were measured using a triple-axis spectrometer at the National Research Universal reactor located in Chalk River, Canada. The measurements were performed at temperatures from 22 to 85 °C and at atmospheric pressure, with incident neutron energies from 16 to 44 meV and scattering angles from 10 to 110°. The temperature range in the measurements covered the common D2O moderator conditions (65–70 °C and 1 atm pressure) in pressurized heavy-water reactors. The measured results were compared with the D2O data libraries from the ENDF/B-VII.1 evaluation and the recently released ENDF/B-VIII.0 evaluation. The experimental results indicate significant improvements in the new release compared to the previous ENDF/B-VII.1 release.

Resonant Compton Scattering of Two Photons by a Multiply Charged Atomic Ion

A pronounced K α1,2 X-ray emission spectrum is theoretically predicted for the resonant inelastic scattering of two photons in the energy region near the 1s shell ionization threshold of a free multiply charged atomic ion. The observed double differential scattering cross section is estimated quantitatively. The results for the Fe16+ ion may be important in interpreting the X-ray emission spectra from galactic clusters, active galactic nuclei, and stars.

Toward a better thermal scattering law of (C5O2H8)n: Inelastic neutron scattering and oClimax + NJOY2016

With the advancements in technology (both experimental and computational) the determination of the“true” experimental phonon spectrum became more accessible. In this work a methodology for producing thermal scattering libraries from the experimental data (namely the DFT + oClimax method) for lucite (C5O2H8)n is discussed. Double differential scattering cross section (DDSCS) experiments were performed at the Spallation Neutron Source of Oak Ridge National Laboratory (SNS ORNL). New scattering kernel evaluations, based on the phonon spectrum for (C5O2H8)n,were created using oClimax and NJOY2016 codes. In order to compare and asses the performance of the newly created library, the experimental setup was simulated using MCNP6.1. Compared to the current ENDF/B-VIII.0, the resulting RPI (C5O2H8)n library improved the calculation of both double differential scattering and total scattering cross sections. A set of criticality benchmarks containing (C5O2H8)n from HEU-MET-THERM resulted in an overall improved calculation of Keff. The DFT + oClimax method is shown to be the most comprehensive method for analysis of moderator materials, due to the fact that it can be verified against all data measured at VISION, ARCS and SEQUOIA neutron spectrometers at SNS ORNL, and experimental total scattering cross section measurements. This method also provides a new technique for calculating any phonon spectrum-related quantities such as scattering law kernel, specific heat capacity, thermal conductivity, etc. for any solid state material.

Analytical Expressions for the Differential Elastic Scattering Cross Sections of Nonidentical Nuclear Particles with Channel Spins 3/2 and 5/2

Analytical Expressions for the Differential Elastic Scattering Cross Sections of Nonidentical Nuclear Particles with Channel Spins 3/2 and 5/2

Regge pole description of scattering of scalar and electromagnetic waves by a Schwarzschild black hole

We revisit the problem of scalar and electromagnetic waves impinging upon a Schwarzschild black hole from complex angular momentum techniques. We focus more particularly on the associated differential scattering cross sections. We derive an exact representation of the corresponding scattering amplitudes by replacing the discrete sum over integer values of the angular momentum which defines their partial wave expansions by a background integral in the complex angular momentum plane plus a sum over the Regge poles of the $S$-matrix involving the associated residues. We show that, surprisingly, the background integral is numerically negligible for intermediate and high frequencies and, as a consequence, that the cross sections can be reconstructed in terms of Regge poles with very good agreement. We show in particular that, for large values of the scattering angle, a small number of Regge poles permits us to describe the black hole glory and that, by increasing the number of Regge poles, we can reconstruct very efficiently the differential scattering cross sections for small and intermediate scattering angles and therefore describe the orbiting oscillations. In fact, in the short-wavelength regime, the sum over Regge poles allows us to extract by resummation the information encoded in the partial wave expansion defining a scattering amplitude and, moreover, to overcome the difficulties linked to its lack of convergence due to the long-range nature of the fields propagating on the black hole. As a consequence, from asymptotic expressions for the lowest Regge poles and the associated residues based on the correspondence Regge poles -- ``surface waves'' propagating close to the photon sphere, we can provide an analytical approximation describing both the black hole glory and a large part of the orbiting oscillations. We finally discuss the role of the background integral for low frequencies.

Formulation of Raman scattering revisited

AbstractIn Raman scattering, photons are scattered by electrons in a molecule. Its mechanism was elucidated early after the development of quantum mechanics. If the frequencies of incident and scattered photons are denoted respectively by ν0 and νs, the differential scattering cross section of a Raman band is proportional to . The differential scattering cross section of Rayleigh scattering is proportional to , as is known as the ν4 rule. This article reconfirms these points from a tutorial viewpoint.

X-Ray Quadrupole Emission in the Scattering of Two Photons by a Multicharged Atomic Ion

Pronounced spectrally extended quadrupole X-ray emission has been theoretically predicted in resonant inelastic scattering of two photons near the ionization threshold energy of the 1s shell of a free multielectron atom. The observed double differential scattering cross section is estimated quantitatively. The results predicted for the Ar8+ ion possibly concern the problem of identification of X-ray emission spectra near 3.5 keV from galaxies and clusters of galaxies.

Analysis of the internal electric fields of pristine ice crystals and aggregate snowflakes, and their effect on scattering

The discrete dipole approximation is used to explore the internal electric fields of plane-wave-illuminated ice particles, and analyse their differential scattering cross sections. The results are displayed for monocrystals and aggregates of size parameters x=2 and x=10. We show that the field is relatively uniform for x=2, but for monocrystals of x=10 there is a complex internal structure. For a hexagonal plate, this structure is a combination of two components: a “distorted” plane wave, with wavefronts aligned perpendicular to the incident wave close to the centre of the plate, and curved forward near the particle boundary; and a standing wave, internally reflected around the perimeter. The former is due to the transverse component of the field i.e., the component perpendicular to the incident wave, and the latter is due to the component parallel to the incident direction. Focussing of the field towards the forward side of the particle is observed. As the particle complexity is increased due to aggregation, the field becomes smoother and less focussing is seen. For complex aggregates, the individual monomers act independently of one another, suggesting simplified methods of calculating scattering from such particles. The influence of the internal fields on far-field scattering is explored. It is demonstrated that scattering in the forward and backward directions is dominated by the transverse component. The parallel component contributes to sidescattering, with its influence on total scattering decreasing with particle complexity. We propose that this is due to the inability of complex particles to maintain a standing wave, diminishing much of the sidescattering observed for monocrystals. Comparisons of the far-field scattering properties of complex aggregates using the discrete dipole and Rayleigh–Gans approximations are also presented for x=2 and x=10, along with results obtained using a soft sphere approximation.

Influence of plasma turbulence and exchange-correlation on electron scattering in turbulent plasmas: Spin-interference

The influence of plasma turbulence and exchange corrections due to the spin-channel preference on the electro-electron scattering is investigated in turbulent plasmas. The second-order Eikonal analysis and the effective potential including the far-field interaction term caused by the field fluctuation is applied to obtain the total scattering phase shift in turbulent plasmas. The forward and exchange scattering amplitudes for electron-electron scatterings in the spin-triplet and singlet states are obtained by the Glauber–Eikonal method with the impact-parameter analysis. The differential electron-electron scattering cross section for the total spin states of the scattering system is obtained as a function of the Dupree-turbulence coefficient, impact parameter, collision energy, thermal energy, and Debye length in turbulent plasmas. It is found that the turbulent effect enhances the differential scattering cross section, especially, in forward and backward scattering regions. It is also shown that the differential scattering cross section decreases with an increase of the plasma temperature. In addition, it is found that the influence of spin-dependent quantum interference suppresses the scattering cross section due to the fermionic behavior of plasma electrons.

Calculation and analysis of gamma-induced irradiation damage cross section

Due to the discrepancies of gamma-induced Displacement per Atom (DPA) cross sections among different calculations, the present work identifies the sources of the discrepancies and recommends the computation of displacement cross sections induced by photons, including the stopping power for electrons and positrons, the differential scattering cross sections, and the gamma-matter interactions. The production of electrons and positrons and the corresponding gamma-induced damage cross sections computed with the above methods are validated against Monte Carlo simulations. The damage cross section for Photoelectric Effect (PE) is negligible for incident photon energy higher than 2 MeV. Above 2 MeV, the percentage of atomic displacement for Compton Scattering (CS) decreases with incident energy, while that for Pair Production (PP) increases and becomes more important than CS above 10 MeV. In the PP, it is recommended to differently treat positrons and electrons for damage calculations because positrons produce 68–77% of DPA induced by electrons. 9.8 × 10−10 DPA/year gamma-induced displacement is obtained in the heavy reflector of PERLE experiment using the recommended damage cross sections. Neglecting the influence of moderator on photon flux in reflector, 8.1 × 10−4 DPA/year gamma-induced displacement damage is found in the reflector of Evolutionary Pressurized Reactor (EPR).

Вероятность процессов захвата электронов у атомов аргона ионами -=SUP=-3-=/SUP=-Не-=SUP=-2+-=/SUP=- при различных параметрах удара

AbstractWe have measured the absolute values of total cross sections of capture of one and two electrons by He^2+ ions from argon atoms. The differential scattering cross sections have been determined for fast atoms and singly charged helium ions formed in each of these processes (without and with additional ionization of the formed slow argon ion). Measurements have been taken for He^2+ ions with kinetic energy of 6 keV in scattering angle range 0–2.5°. Based on the measured differential cross sections using different model atomic particle interaction potentials, we have calculated the cross sections of these processes as functions of the impact parameter. The probabilities of realization of these processes with electron density distribution in different shells in the target atom have been compared. The applicability of the expressions for the screened Coulomb interaction potentials in the description of scattering of particles that have captured electrons has been demonstrated.

Differential and Integral Cross Sections of Electron Elastic Scattering by PH3 Molecule in the Energy Ranging from 10 eV up to 20 keV

Differential and integral cross sections for electron elastic scattering by phosphine molecule at the incident energies ranging from 10 eV up to 20 keV are calculated using the well known partial wave expansion formalism. The considered interaction potential is essentially an optical spherical one including a static contribution, exchange and correlation-polarization ones. The first one is numerically calculated considering a single-center Hartree-Fock model, while two expressions of the well-known exchange potential and two others for the correlation-polarization potential are rigorously selected from the literature. The differential and integral cross sections obtained for the four potential combinations investigated in the present work, exhibit a general agreement and show clearly the role played by the exchange and correlation-polarization effects, particularly at lower scattering angles and lower impact energies. In addition, the differential and integral cross sections are compared to the experimental and theoretical results available in the literature and a good agreement is found.

Covariance Matrices for Differential and Angle-Integrated Neutron-Induced Elastic and Inelastic Scattering Cross Sections of 56Fe

Correlations between neutron inelastic scatterings angular distributions are not included in the Joint Evaluated Fission and Fusion (JEFF) nuclear data library, while they are key quantities for uncertainty propagation of nuclear data. By reproducing the angle-integrated cross sections and uncertainties of JEFF-3.1.1, the present work obtains covariance matrix between high energy model parameters using the least square method implemented in the CONRAD code. With this matrix, it is possible to generate correlations between angle-integrated cross sections and angular distributions, which are usually presented by Legendre coefficients. As expected, strong correlations are found, for example, between the Legendre coefficients of elastic and first-level-inelastic scatterings and the angle-integrated total, elastic, total inelastic cross sections.

Imaging inelastic scattering of CO with argon: polarization dependent differential cross sections.

Rotationally inelastic scattering of carbon monoxide (CO) with Argon at a collision energy of 700 cm-1 has been investigated by measuring polarization dependent differential scattering cross sections (PDDCSs) for rotationally excited CO molecules using a crossed molecular beam apparatus coupled with velocity-map ion imaging. A simple and robust (1 + 1' + 1'') VUV (Vacuum Ultra-Violet) REMPI (Resonance Enhanced Multi Photon Ionization) scheme is used and images are obtained by setting the VUV light polarization direction parallel or perpendicular to the scattering plane. Clear differences between the images for the two polarizations are observed, indicating strong collision induced alignment of the rotational angular momentum of scattered CO. A direct image analysis procedure as described in our previously published paper (A. G. Suits et al., J. Phys. Chem. A., 2015, 119, 5925), is employed to extract the fully quantum state resolved alignment-free differential cross sections (DCSs) and the state-to-state angle-dependent alignment moments for each final rotational state. The experimental results are compared with advanced theory, in particular with the predictions of CC QM (Close-Coupling Quantum Mechanical) and QCT (Quasi-Classical Trajectory) calculations. The agreement between experiment and theory is generally found to be quite good throughout the entire scattering angle range for all the final states probed, showing the reliability of the experiment and use of the direct extraction method, as well as the accuracy of the potential surface over the studied collision energy range. A classical kinematic apse (hard shell) model was found to be useful in interpreting the measured collision induced alignment moments.

A search for deviations from the inverse square law of gravity at nm range using a pulsed neutron beam

Recently published results and ongoing experimental efforts to search for deviations from the inverse square law of gravity at the nanometer length scale using slow neutron scattering from the noble gases are discussed. Using the pulsed slow neutron beamline BL05 at the Materials and Life Sciences Facility at J-PARC, we measured the neutron momentum transfer (q) dependence of the differential scattering cross section for the noble gases He, Ne, Ar, Kr, and Xe. By comparing to the distributions obtained using pseudo-experimental Monte Carlo simulations and forming ratios between Xe and He, we placed an upper bound on the strength of a new interaction as a function of interaction length λ which improved upon previous results in the region λ < 0.1 nm, and remains competitive in the larger λ region. Additionally we describe how we are using our technique to extract relative values of the total neutron scattering cross sections of the noble gases, as well as how we plan to measure the neutron-electron scattering length using the NOVA instrument on BL21 at J-PARC.