Tuned electron-nucleus resonance as a tool of producing the 229mTh isomer

The possibility of refining the energy of the 8.36-eV 229mTh nuclear isomer -- the most likely candidate for the role of a nuclear frequency standard -- by means of resonant optical pumping is discussed. Attention is focused on considering the broadening of the resonance in order to reduce scanning time. The two-photon method proposed exploits the radical broadening of the isomer line due to mixing with the electron transition. This is not burdened with the cross-section reduction, in contrast with internal-conversion-based resonance broadening or intended extra-broadening of the spectral line of a pumping laser. In the case under consideration, according to the calculations, it turns out to be two orders of magnitude more efficient. It is applicable to both ionized and neutral thorium atoms. Realization of the method supposes excitation of the both nucleus and electron shell in the final state.