title: Nuclear Excitation by Two-Photon Electron Transition.
abstract: A new mechanism of nuclear excitation via two-photon electron transitions (NETP) is proposed and studied theoretically. As a generic example, detailed calculations are performed for the E1E1 1s2s^{1}S_{0}→1s^{2}^{1}S_{0} two-photon decay of a He-like ^{225}Ac^{87+} ion with a resonant excitation of the 3/2+ nuclear state with an energy of 40.09(5) keV. The probability for such a two-photon decay via the nuclear excitation is found to be P_{NETP}=3.5×10^{-9} and, thus, is comparable with other mechanisms, such as nuclear excitation by electron transition and by electron capture. The possibility for the experimental observation of the proposed mechanism is thoroughly discussed.
authors.affiliation: Helmholtz-Institut Jena, D-07743 Jena, Germany.|Department of Physics, St. Petersburg State University, 198504 St. Petersburg, Russia.
authors.forename: A V
authors.initials: AV
authors.lastname: Volotka
authors.affiliation: Physikalisch-Technische Bundesanstalt, D-38116 Braunschweig, Germany.|Technische Universität Braunschweig, D-38106 Braunschweig, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Surzhykov
authors.affiliation: Helmholtz-Institut Jena, D-07743 Jena, Germany.|Institut für Optik und Quantenelektronik, Friedrich-Schiller-Universität, D-07743 Jena, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Trotsenko
authors.affiliation: Institut für Theoretische Physik, Technische Universität Dresden, D-01062 Dresden, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Plunien
authors.affiliation: Helmholtz-Institut Jena, D-07743 Jena, Germany.|Institut für Optik und Quantenelektronik, Friedrich-Schiller-Universität, D-07743 Jena, Germany.|GSI Helmholtzzentrum für Schwerionenforschung, D-64291 Darmstadt, Germany.
authors.forename: Th
authors.initials: T
authors.lastname: Stöhlker
authors.affiliation: Helmholtz-Institut Jena, D-07743 Jena, Germany.|Theoretisch-Physikalisches Institut, Friedrich-Schiller-Universität, D-07743 Jena, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Fritzsche