Preparation technique of thorium films by electrochemical deposition for nuclear optical frequency standard based on thorium-229

Abstract

The increase of the accuracy of optical frequency standards by means of the development of nuclear clocks a novel frequency standard based on the nuclear transition to the long-living isomer nuclear state of Th-229 with energy ~7.6 eV is of great interest. The main problem is the fact that there are no experimental data on the direct measurement of the energy of the isomeric transition in Th-229, and the above result was obtained only by indirect measurements, and has great uncertainty. Low energy ion scattering spectroscopy might be used for more precision investigations of the isomeric transition in Th-229. It is caused by the fact that ion scattering spectra exhibit the fine structure determined by the target surface electronic structure. In the case of low energy nuclear transition it can give the information about the isomer nuclear state of Th-229. To prove this supposition it is necessary to prepare high quality samples with a high thorium surface coverage. An original preparation technique of the thorium films by electrochemical deposition from thorium nitrate solution on Si(111) substrate is reported. It was found that electrochemical deposition of Th on the semiconductor substrates leads to the formation of ThSiO_x island films. The origin of the observed thorium films formation and the results on the investigation of ²²⁹Th and ²³²Th films on Si(111) surface by X-ray photoelectron spectroscopy and low energy ion spectroscopy discussed.