Band structure and decay channels of thorium-229 low-lying isomeric state for ensemble of thorium atoms adsorbed on calcium fluoride

TL;DR

This study investigates the electronic structure and decay channels of thorium-229's low-lying isomeric state in thorium atoms adsorbed on calcium fluoride, revealing chemical bonding effects and estimating nuclear decay times.

Contribution

It provides new insights into the electronic configuration and decay mechanisms of thorium-229 in a surface-adsorbed state, combining experimental spectroscopy with decay time estimation.

Findings

REELS spectra show low-energy peaks linked to thorium chemical bonds.

Decay time of thorium-229's excited state estimated at 40 μs for 6d-electrons.

Decay time estimated at 1 μs for 7s-electrons.

Abstract

The results are presented on the study of the electronic structure of thorium atoms adsorbed by the liquid atomic layer deposition from aqueous solution of thorium nitrate on the surface of CaF2. The chemical state of the atoms and the change of the band structure in the surface layers of Th/CaF2 system on CaF2 substrate were investigated by XPS and REELS techniques. It was found that REELS spectra for Th/CaF2 system include peaks in the region of low energy losses (3-7 eV) which are missing in the similar spectra for pure CaF2. It is concluded that the presence of the observed features in the REELS spectra is associated with the chemical state of thorium atoms and is caused by the presence of uncompensated chemical bonds at the Th/CaF2 interface, and, therefore, by the presence of unbound 6d- and 7s-electrons of thorium atoms. Assuming the equivalence of the electronic configuration of thorium-229 and thorium-232 atoms, an estimate was made on the time decay of the excited state of thorium-229 nuclei through the channel of the electron conversion. It was found that the relaxation time is about 40 {\mu}s for 6d-electrons, and about 1 {\mu}s for 7s-electrons.