Bound internal conversion versus nuclear excitation by electron transition: Revision of the theory of optical pumping of the ~(229m)Th isomer

摘要

Two-photon optical pumping of the 7.6-eV nuclear isomer in the singly ionized atoms of ~(229)Th is considered. Differences between two mechanisms of the pumping, nuclear excitation in the electronic transition (NEET) and bound internal conversion (BIC), are derived and analyzed numerically. The BIC mechanism turns out to be more effective, by orders of magnitude, in accordance with previous calculations. Moreover, a numerical smallness in the NEET scheme is explicitly pointed out concerning singly and doubly charged ions. That is related to the smallness of the final vertex, responsible for conservation of energy. In the case of BIC, the calculated pumping rate of the isomer for the most effective scheme may be as high as 0.03 s~(-1).