Title: Nonradiative annihilation of a positron on bound electrons   

Speaker: Dr. Bennaceur Najjari (Institute of Modern Physics)   

Time: 16:00pm, Sep. 28 (Tuesday), 2021  

Place:  Room 666, Building 5   

Abstract:   

We consider radiation less annihilation of a positron on bound electrons in the field of a heavy nucleus. This process occurs due to the interaction of the annihilating positron-electron pair with a second bound electron which is emitted carrying away the energy release. We present the fully relativistic treatment which employs exact Dirac wave functions to describe the motion of the leptons in the field of the nucleus and regards the interaction between the leptons as a perturbation. The total cross sections for this process are calculated for various elements ranging from silver to fermium. Our results substantially deviate from those previously reported in the literature, both in absolute values of the cross section and its dependence on the positron energy. However, when we apply the principle of detailed balance (DB) to our results to obtain the cross section for the inverse process (negative-continuum dielectronic recombination), a very good agreement is found with the existing results obtained by direct calculations. We also compare nonradiative annihilation with radiative annihilation with emission of a single photon and show that the cross sections for the former are much smaller.