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

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 CaF 2 . The chemical state of the atoms and the change of the band structure in the surface layers of Th/CaF 2 system on CaF 2 substrate were investigated by XPS and REELS techniques. It was found that REELS spectra for Th/CaF 2 system include peaks in the region of low energy losses (3-7 eV) which are missing in the similar spectra for pure CaF 2 . 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/CaF 2 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 μs for 6d-electrons, and about 1 μs for 7s-electrons.

Oxidation State of <sup>229</sup>Th Recoils Implanted into MgF<sub>2</sub> Crystals

“…While thorium is typically found as Th 4+ in condensed phases, the presence of thorium in other oxidation states is quite rare [21], it is not known for certain what the chemical environment of the thorium ions is in the solid-state studies conducted so far. The failure to detect emission from the isomeric state in the previous studies could be due to an unsuitable chemical environment, lattice defect sites or impurities could cause the thorium ions to be in lowervalence states or in unsuitable chemical forms [22].…”

Lifetime Measurement of the Th229 nuclear isomer

“…A direct half-life measurement of a photonic decay channel [16] has been controversially discussed [17].Several different experimental approaches have been pursued, aiming for a measurement of the isomer's properties or for an optical laser excitation of the nucleus [18][19][20][21][22][23][24][25][26][27]. However, despite significant experimental effort, no conclusive measurement of the isomeric half-life has been reported so far.As a result of the low excitation energy, the isomer can decay via three decay channels to its ground state, whose occurrence depends on the electronic surrounding of the nucleus [28][29][30][31]: when the binding energy of an electron E B in the surrounding of the nucleus is lower than the excitation energy of the isomer E I , the isomer decays preferably via internal conversion (IC) by emitting an electron with an energy E e − = E I − E B . For the expected isomer energy of 7.8 eV, this channel dominates for neutral 229 Th, which has an ionization energy of 6.3 eV [32].…”

“…As a result of the low excitation energy, the isomer can decay via three decay channels to its ground state, whose occurrence depends on the electronic surrounding of the nucleus [28][29][30][31]: when the binding energy of an electron E B in the surrounding of the nucleus is lower than the excitation energy of the isomer E I , the isomer decays preferably via internal conversion (IC) by emitting an electron with an energy E e − = E I − E B . For the expected isomer energy of 7.8 eV, this channel dominates for neutral 229 Th, which has an ionization energy of 6.3 eV [32].…”

Enhanced Electrochemical Stability of Molten Li Salt Hydrate Electrolytes by the Addition of Divalent Cations

“…The absence of any analogous Al 2p peak for LCH is attributed to a relatively thicker SEI (Figure S1). The peak in the Mg 2p spectra (∼51 eV) 46 can be assigned to MgF 2 in LMH (Figure 4b), and the peak in the Ca 2p spectra at ∼348 eV 47 indicates the formation of CaF 2 in LCH (Figure 4c). We note here that we cannot exclude the possibility for the presence of a small proportion of MgCO 3 or CaCO 3 in these spectra (due to the similar peak position of the carbonates), 48,49 which may be formed through the reduction of a minute amount of O 2 and CO 2 dissolved in LMH and LCH , respectively.…”