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Angular anisotropy of cascade photons in processes of dielectronic ion recombination

Balashov V. V., Bodrenko I. V., V.K. Dolinov, Strakhova S. I.

Published Jan 1, 1994• 0 citations
OpenAlex

Abstract

The method for calculating the function of angular photon correlation and the angular distribution of photons emitted in the process of dielectronics recombination at any phase of a cascade of radiative and Auger transitions was presented. This method was developed incorporating the formalism of the spin density matrix and the kinetic Pauli equation as the basis. The calculations conducted revealed that the effect of alignment transfer in a cascade can have a strong impact on the shape of angular correlation of cascade photons.

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The method for calculating the function of angular photon correlation and the angular distribution of photons emitted in the process of dielectronics recombination at any phase of a cascade of radiative and Auger transitions was presented. This method was developed incorporating the formalism of the spin density matrix and the kinetic Pauli equation as the basis. The calculations conducted revealed that the effect of alignment transfer in a cascade can have a strong impact on the shape of angular correlation of cascade photons.
The radiative recombination of a free electron into excited states of bare, high- Z ions and the subsequent photon decay are studied in the framework of the density matrix theory. Emphasis is placed, in particular, on the angular correlation between the recombination and the decay photons. The general expression for the photon–photon angular correlation function is derived, based on Dirac's equation as appropriate for high- Z ions. Computations for the dependence of the photon–photon correlation function on the nuclear charge and the projectile energies are carried out for the capture into the 2p 3/2 level and the subsequent Lyman -α 1 (2p 3/2 → 1s 1/2 ) radiation.
New details of a well-known physical process—cascade transition—have been considered. The wave function of a system of two photons emitted in a cascade transition in the absence of a shift of the phase of the intermediate state was studied. The joint energy distribution density for two such photons is obtained by numerical calculation, and a correlation between their energies at certain probabilities of radiative transitions is ascertained. This phenomenon can be used to diagnose the plasma density.
The two-photon decay of highly charged hydrogenlike ions is studied within the framework of second-order perturbation theory, based on Dirac's equation. Attention has been paid to the angle-angle correlations between the two emitted photons. In particular, the density matrix theory is applied in order to explore how these angle-angle correlations are affected by the alignment of the excited states of the ions. Detailed computations have been carried out for the $3{d}_{5∕2}\ensuremath{\rightarrow}1{s}_{1∕2}$ transition in hydrogenlike uranium U91+{\mathrm{U}}^{91+}U91+ ions for different (degrees of) initial alignment. It is shown that the angular correlation function is very sensitive to the alignment of the 3d5∕23{d}_{5∕2}3d5∕2​ state, an effect which has to be accounted for in the analysis of all (future) two-photon decay experiments, for which the excited state of the ions is produced by relativistic ion-atom collisions.
We have studied two-electron one-photon transitions in dielectronic recombination with H-like ions (Z=5−−54Z=5--54Z=5−−54) within ab initio QED theory. It was found that interference between dielectonic recombination with two-electron one-photon transitions and radiative recombination is prominent for light and medium ions being large enough for experimental observation. The interference manifests itself firstly in a sharp Fano-like resonance structure and secondly in a noticeable distortion of the photon angular distribution of the radiative recombination.
The density matrix theory is applied to establish a connection between the configuration of the excited atomic states and the intensity and polarisation of the cascade photons emitted during the decay process. Explicit expressions are obtained for the P, D and F states of hydrogen and helium atoms. These formulae can be used to assist experimental design for the most efficient and revealing measurements. In addition, formulae for the integrated polarisation of the emitted photons from the P, D, F and G states of hydrogen and helium are presented in terms of partial excitation cross sections.
We illustrate the possibility for calculation of bremsstrahlung tip angular destributions and polarization correlations from corresponding photoeffect results with an extension of the method for connecting bremsstrahlung tip and direct-radiative-recombination (DRR) cross sections developed by Lee and Pratt. The agreement between results obtained with this method and results from our numerical partial-wave calculations is, in general, satisfactory. We note features of the distributions and correlations, and once again point out the inadequacies of the nonrelativistic dipole approximation for the evaluation of bremsstrahlung or DRR angular distributions.