Virtual Compton scattering at low energies with a positron beam

The European Physical Journal A - Using a transport model that includes a first-order chiral phase transition between the partonic and the hadronic matter, we study the development of density...     

Stochastic dynamics of multiple scattering and energy losses of channeled particles

A system of equations describing the evolution of the mean-square quantum fluctuations of the transverse coordinate and momentum operators and the evolution of the mean-square fluctuations of the transverse coordinate and momentum with respect to the classical trajectory of channeled particle is constructed using linearized Heisenberg equations. The energy losses of channeled particles on crystal electrons and the mean-square fluctuations of the transverse coordinate and momentum are calculated within the same formalism.     

Energy losses of channeled particles at high energies

The ratio of the energy loss of channeled particles to the enrgy loss in the amorphous medium has been calculated including relativistic corrections. In the limit of high velocities, the ratio has been shown not to tend to unity.     

Nuclear Rms charge radii from relative electron scattering measurements at low energies

The nuclear rms charge radii measured by low energy electron scattering at Darmstadt are summarized. Improvements in the experimental equipment and method permitted a redetermination of the¹²C radius which yieldedR _m (¹²C)=2.462 ± 0.022fm. This value has been used to recalibrate the radii measured relative to¹²C.     

The electron energy loss spectrum of tin at low primary beam energies

The electron energy loss spectra of clean and oxidised tin have been measured for primary energies in the range 100–1000 eV. The structure found for clean tin is similar to published spectra recorded with low primary energies except for the presence of a small peak at 4.7 eV. Differences between the reported volume plasmon energy recorded with low and high primary beam energies were noted and a model is presented to explain these differences in terms of plasmon dispersion.     

Three-body Coulomb Green function and the reactions with charged particles at low energies

It has been shown that the inclusion of all possible Coulomb rescatterings of three charged particles in intermediate state results in an infinite series of diagrams which have a pole located at the same place as the pole of the pole diagram. The contribution of the pole terms of such infinite series has explicitly been singled out and summed-up. Renormalization of the pole diagram amplitude due to all the possible Coulomb rescatterings of particles in intermediate state has been found. The result obtained means that the three-body Coulomb Green function entering the expression for the reaction amplitude may be written in the form of the renormalized free Green function plus the residue which behaves as in the case of short-range interactions.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.     

Total cross sections scattering at of positron-sodium low energies

A new calculation for the total cross section of positron-sodium scattering is performed in an energy range down to a few tenths of one electron volt using the coupled-channel optical method.The ionization continuum and the positronium formation channels are included via an equivalent-local complex potential.The role played by the break-up and rearrangement processes in the low energy positron-sodium scattering is also investigated.The total scattering cross section is reported and compared with the available theoretical and experimental data.     

Gravitational scattering in the ADD model at high and low energies

Gravitational scattering in the ADD model is considered at both sub- and transplanckian energies using a common formalism. By keeping a physical cut-off in the KK tower associated with virtual KK exchange, such as the cut-off implied by a finite brane width, troublesome divergences are removed from the calculations in both energy ranges. The scattering behavior depends on three different energy scales: the fundamental Planck mass, the collision energy and the inverse brane width. The result for energies low compared to the effective cut-off (inverse brane width) is a contact-like interaction. At high energies the gravitational scattering associated with the extra dimensional version of Newton’s law is recovered.     

Radiative charge transfer and radiative association of protons colliding with Na at low energies

Using the fully quantum-mechanical approach, the radiative charge transfer for H⁺ + Na(3s) collisions has been investigated. The charge transfer emission spectra are analyzed at resonant and non-resonant collision energies. The radiative association cross sections, obtained by subtracting the radiative charge transfer part from total radiative decay cross sections calculated by the optical potential method, are presented in the energy range 10⁻⁶-1 eV.     

Total cross sections of positronben sodium scattering at low energies

A new calculation for the total cross section of positron-sodium scattering is performed in an energy range down to a few tenths of one electron volt using the coupled-channel optical method. The ionization continuum and the positronium formation channels are included via an equivalent-local complex potential. The role played by the break-up and rearrangement processes in the low energy positron-sodium scattering is also investigated. The total scattering cross section is reported and compared with the available theoretical and experimental data.     

High energy scattering of composite particles II. Classification of multiple scattering contributions

All inequivalent multiple scattering contributions are found for the collision of two composite particles, each of them consisting of less than five elements. The cross-section for high energy- scattering is calculated as an example. Some properties of multiple scattering are briefly discussed.Dedicated to Professor V. Votruba on his sixtieth birthday.On leave fromCharles University, Prague, Czechoslovakia.The author thanks Professor H. Rollnik for hospitality at the Institute and for the financial support from the Heinrich-Hertz-Stiftung. He would also like to thank Dr. T. P. Kokott for substantial assistance in running the computer PDP 10.     

On the average energy of sputtered particles

Summary The correct expression for the average energy of sputtered particles in the linear regime has, for the first time, been derived. The theoretical results are compared with recent data from computer simulation studies and it is shown that the average sputtered energy can only be evaluated by precisely determining both the maximum energy and the threshold of the sputtered particles.

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Riassunto è stata derivata per la prima volta l’espressione corretta nel regime lineare dell’energia media delle particelle emesse da solidi durante bombardamento ionico. I risultati teorici sono stati confrontati con alcuni dati ottenuti recentemente mediante simulazione al calcolatore. è stato inoltre evidenziato che l’energia media delle particelle emesse può essere calcolata in modo preciso solo se si determinano contemporaneamente l’energia massima delle particelle emesse e la soglia per il processo di emissione.

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Резюме Впервые выводится правильное выражение для средней энергии распыленных частиц в линейном режиме. Теоретические результаты сравниваются с недавними данными численного моделирования на ЭВМ. Показывается, что средняя распыленная энергия может быть оценена только при условии, если точно определены одновременно максимальная энергия распыленных частиц и порог для процесса распыления.

     

Spin rotation at multiple scattering of high energy particles by atomic strings in a crystal

It is shown that an appreciable rotation of a high energy particle spin can occur when the beam passes through a crystal at a small angle with its axis.     

Photoelectron diffraction at low energies: the applicability of single scattering calculations

The energy dependence of the 4f core level photoemission intensity from Ta(100) has been modeled at low electron kinetic energies using the single scattering cluster (SSC) approximation. The results show a strikingly similar shape to that of a full multiple scattering calculation, particular at electron kinetic energies less than 75 eV. A comparison with the experimentally measured surface/bulk core level intensity oscillations indicates that the first interlayer spacing of the Ta(100) surface is contracted by 11 ± 3%, consistent with previous determinations. These results suggest that SSC calculations can model low energy photoelectron diffraction data from surface shifted core levels with sufficient accuracy to enable a quantitative structural determination of clean, unreconstructed surfaces.     

The measurement of energy spectra of neutral particles in low energy ion scattering

An apparatus is described for low energy (0.1–10 keV) ion scattering (LEIS) experiments. A time of flight (TOF) spectrometer is incorporated in the system to be able to measure the energy of particles in the neutral state after scattering. The energy resolution ΔE/E of the TOF spectrometer is discussed and found to be 0.5% (FWHM). This is sufficient for our scattering experiments. An electrostatic analyzer (ESA) is used to measure the energy of scattered ions [ΔE/E=0.5% (FWHM)]. Experiments show that in general the ion dose needed to obtain a TOF spectrum (2×10¹⁰ ions/cm²) is much smaller than the dose needed for an ESA-spectrum (6×10¹³ ions/cm²). The ion spectra measured with the TOF spectrometer, by subtracting the neutral yield from the total yield, as well as with the ESA are found to agree quite well. This provides a way to calibrate the TOF spectrometer. The determination of the ion fraction of scattered particles is discussed [10 keV⁴⁰Ar⁺ on Cu(100), scattering angle 30°]. It is shown that the TOF spectrometer is able to measure light recoil particles (e.g. hydrogen) from a heavy substrate. In the analysing system is, in addition to the TOF spectrometer, also incorporated a stripping cell to measure the energy of neutral scattered particles. An energy spectrum of neutral scattered particles measured with both methods is shown.     

A certain approximation for the resonance interaction of particles at low energies

Using equations proposed earlier [1] we obtain an approximate equation for the scattering amplitude at low energies. A connection is established between the scattering length and effective radius and the parameters characterizing the strong-interaction potential V(q²) for small values of transmitted momentum q².Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 36–40, May, 1973.     

Pion small-angle multiple scattering at energies spanning the (3,3) resonance

The small-angle multiple scattering of positive and negative pions has been measured for C, Al, Cu and Pb targets throughout an energy range spanning the (3, 3) resonance. The measurements were made using two-dimensional multiwire proportional counters placed in the pion beam. All previous multiple scattering data for electrons and protons as well as these new data for pions are used to recalculate the empirical terms in the Moliere theory of multiple scattering. A second-order Born approximation multiple scattering theory has been devised for spin zero particles. Modified Moliere theory gives a better fit to the experimental data than the second-order Born calculation. Because the updated Moliere theory contains much simpler equations and gives closer agreement with experiment, it is recommended in place of the more sophisticated theory for the interpretation of new experimental data.     

Ranges of interaction inp\bar p scattering at low energies

Thep¯ p cross sections at low energies are analysed in the framework of the optical model. It is shown that the annihilation range is closely related to the size of the proton as measured in electromagnetic and hadronic interactions. At larger distances thep¯ p interaction has the similar character as the NN one.