XPS study of ion irradiated and unirradiated CeO2 bulk and thin film samples

This work considers the effect of fission-energy ion irradiation on the electronic structure at the surface of bulk and thin film samples of CeO2 as a simulant for UO2 nuclear fuel. For this purpose, thin films of CeO2 grown on Si substrates and bulk CeO2 samples were irradiated by Xe ions (92 MeV, 4.8 × 1015 ions/cm2) to simulate the fission damage that occurs within nuclear fuels. The irradiated and unirradiated samples were characterized by X-ray photoelectron spectroscopy. A technique of the quantitative evaluation of cerium ionic composition on the surface of the samples has been successfully applied to the obtained XPS spectra. This technique is based on the intensity of only one of the reliably identifiable high-energy peak at 916.6 eV in the Ce 3d XPS spectra. The as-produced samples were found to contain mostly the Ce4+ ions with a small fraction of Ce3+ ions formed on the surface in the air or under X-rays. The core-electron XPS structure of CeO2 was associated with the complex final state with vacancies (holes) resulting from the photoemission of an inner electron. The Xe ion irradiation was found to increase the Ce3+ content in the samples of CeO2, with the thin films being more sensitive than the bulks samples

Quantum noise limited interferometric measurement of atomic noise: towards spin squeezing on the Cs clock transition

We investigate theoretically and experimentally a nondestructive interferometric measurement of the state population of an ensemble of laser cooled and trapped atoms. This study is a step towards generation of (pseudo-) spin squeezing of cold atoms targeted at the improvement of the Caesium clock performance beyond the limit set by the quantum projection noise of atoms. We calculate the phase shift and the quantum noise of a near resonant optical probe pulse propagating through a cloud of cold 133Cs atoms. We analyze the figure of merit for a quantum non-demolition (QND) measurement of the collective pseudo-spin and show that it can be expressed simply as a product of the ensemble optical density and the pulse integrated rate of the spontaneous emission caused by the off-resonant probe light. Based on this, we propose a protocol for the sequence of operations required to generate and utilize spin squeezing for the improved atomic clock performance via a QND measurement on the probe light. In the experimental part we demonstrate that the interferometric measurement of the atomic population can reach the sensitivity of the order of N_at^1/2 in a cloud of N_at cold atoms, which is an important benchmark towards the experimental realisation of the theoretically analyzed protocol.Comment: 12 pages and 9 figures, accepted to Physical Review