Photonuclear Population of ^229m,g Th in Th‐Doped Crystals Toward Nuclear Clock Development

ABSTRACT Efficient population of the is essential for advancing nuclear clock technology, whose progress faces strategic challenges related to the finite legacy supply and competing high‐value medical applications of . This study proposes a novel approach to populate via photonuclear reactions in thorium‐doped crystals. Theoretical calculations were performed to evaluate the photonuclear reaction cross‐sections of four thorium isotopes , which show ‐related production cross‐sections reaching hundreds of millibarns. Monte Carlo simulations further analyzed the time‐wavelength distributions of radiative decay signals and Cherenkov radiation backgrounds in thorium‐doped , , and LiF crystals under bremsstrahlung irradiation, revealing the correlation between the signal‐to‐noise ratio (SNR) and incident electron parameter. The results show that crystals achieved an SNR of 10 under irradiation with bremsstrahlung driven by 1 C electrons at 40 MeV, outperforming other materials. Compared to VUV laser direct excitation and X‐ray resonant scattering pumping, this method exhibits unique advantages, including target material flexibility, broad light source compatibility, and higher excitation rates. Moreover, by enabling the conversion of abundant and into ‐doped crystals, photonuclear reactions offer a decentralized production route that is independent of the finite supply derived from regulated inventories. These findings indicate that the photonuclear population is a promising pathway for efficient production and characterization, effectively mitigating future supply constraints for fundamental research.