Isomer Triggering via Nuclear Excitation by Electron Capture

Triggering of long-lived nuclear isomeric states via coupling to the atomic shells in the process of nuclear excitation by electron capture (NEEC) is studied. NEEC occurring in highly charged ions can excite the isomeric state to a triggering level that subsequently decays to the ground state. We present total cross sections for NEEC isomer triggering considering experimentally confirmed low-lying triggering levels and reaction rates based on realistic experimental parameters in ion storage rings. A comparison with other isomer triggering mechanisms shows that, among these, NEEC is the most efficient.

Figure 1

Partial level scheme of ${}_{42}{}^{93}\mathrm{Mo}$. As a general notation, the isomeric state ($I$) can be excited to the triggering level ($T$). The triggering level subsequently decays back to $I$ or to a level $F$ which initiates a cascade via different intermediate states (dashed line) to the ground state (GS). $E4$ denotes a strongly hindered nuclear ($\gamma$) transition.