More efficient nuclear-excitation mechanisms and unrecognized high-order effects

Determine whether nuclear-excitation mechanisms more efficient than nuclear excitation by radiative electron-ion recombination exist and whether additional important high-order effects in nuclear excitation and in the interplay between atomic and nuclear degrees of freedom remain to be identified.

Background

The paper introduces nuclear excitation by radiative electron-ion recombination (NERER), a third-order process in which an electron recombines into an atomic vacancy while emitting a real photon and simultaneously exciting the nucleus. For highly charged ions, the calculated NERER cross section for producing the 8.4 eV clock isomer of 229Th can exceed that of the lower-order nuclear excitation by inelastic electron scattering (NEIES) by more than an order of magnitude.

After presenting these results, the authors explicitly leave unresolved whether mechanisms with still higher nuclear-excitation efficiency exist and whether other significant high-order atomic–nuclear effects have yet to be recognized. The unresolved issue is therefore broader than a computational refinement of NERER: it concerns the discovery and assessment of additional efficient excitation pathways and high-order couplings.