2026/07/09 by Udeshika C. Perera, H. B. Tran Tan, H. W. T. Morgan +3
#nucl-th #cond-mat.mtrl-sci #physics.atom-ph
We present an ab initio calculation of the band-to-band internal-conversion rate of the ℏω\rm nuc ≈ 8.35 eV isomeric transition in 229ThO2. Because the nuclear transition energy exceeds the electronic band gap of ThO2, the isomer can decay nonradiatively by resonantly promoting a valence electron into the conduction band. We formulate this process as a Brillouin-zone sum over vertical interband transitions weighted by local Th-centered hyperfine matrix elements, which are evaluated directly from all-electron full-potential linearized augmented-plane-wave Bloch spinors. A finite nuclear magnetization model is included to regularize the short-range hyperfine interaction and to account for the Bohr-Weisskopf effect. After applying scissor shifts to span the experimentally reported ThO2 band gaps, we find calculated internal-conversion lifetimes in the range of 1-16~μ\rm s. The lifetime increases strongly as the band gap approaches ω\rm nuc because the resonant interband phase space at the nuclear transition energy is reduced. For the larger reported ThO2 gaps, the calculated lifetime is comparable to the measured conversion-electron Mössbauer lifetime [Nature 648, 300 (2025)]. Our analysis implies that choosing solid-state hosts with band-gap values slightly lower than ω\rm nuc can optimize solid-state nuclear clock performance with internal-conversion electron readout.