TWO-PHOTON RESONANCE MECHANISM OF OPTICAL PUMPING OF THE 8.3-eV ISOMER 229mTh IN NEUTRAL ATOMS

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