Isomeric Excitation of Th229 in Laser-Heated Clusters

We consider theoretically isomeric excitation of $^{229}\mathrm{Th}$ in a laser-heated cluster. A $^{229}\mathrm{Th}$ cluster is first radiated by an intense femtosecond laser pulse, causing ionization of the constituting atoms. The cluster will then survive for a time on the order of 1 ps, during which the electrons collide with the nuclei repeatedly and excite them to the isomeric state. Two mechanisms are responsible for the isomeric excitation: nuclear excitation by electron capture (NEEC) and nuclear excitation by inelastic electron scattering (NEIES). By changing the laser intensity, one can tune between NEEC and NEIES continuously. This laser-heated-cluster scheme not only provides a highly efficient means for isomeric excitation, but also provides an approach for the confirmation of the NEEC process, which has been predicted for over forty years without conclusive experimental verifications.