Hannover 2013 – wissenschaftliches Programm

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A: Fachverband Atomphysik

A 25: Precision spectroscopy of atoms and ions V (with Q)

A 25.4: Vortrag

Mittwoch, 20. März 2013, 11:45–12:00, B 302

Pair production processes by nuclear decay and in muonic atoms — •Nikolay A. Belov¹ and Zoltán Harman^{1, 2} — ¹Max Planck Institute for Nuclear Physics, Saupfercheckweg 1, 69117 Heidelberg, Germany — ²ExtreMe Matter Institute (EMMI), Planckstraße 1, 64291 Darmstadt, Germany

The pair production process by γ-emission of nuclei has been investigated so far both theoretically and experimentally. But, in all works only the production of a free electron and positron was considered. The case when an electron is "born" in a bound state of atom has been neglected as a relatively small effect. We investigate this bound-free pair conversion process for different multipolarities of nuclear γ decay. We use a relativistic description of the electron and positron wave functions as it is necessary for heavy elements. It appears that the contribution of this bound-free process for bare heavy ions at low γ-energies close to 2m_ec² gives a contribution comparable to or stronger than the free-free process and that it may be the dominant electromagnetic decay channel in case of E0 nuclear transitions.

We also investigate the similar bound-free pair production process in electromagnetic muonic transitions in muonic atoms. In this case, all matrix elements can be calculated exactly. Photon energies have the same order as the γ-energies in the nuclear case, so one expects a similar dominance of the bound-free process over the free-free process at low transition energies (for transitions between excited muonic states). Our calculations have confirmed this behaviour.