Andrey V. Krasavin

Generation of thorium ions by laser ablation and inductively coupled plasma techniques for optical nuclear spectroscopy

Single- and double-charged 232Th and 229Th ions were produced by laser ablation of solid-state thorium compounds and by inductively coupled plasma techniques with mass-spectrometry analysis from liquid solutions of thorium. The latter method was found to be more applicable for producing ions of radioactive 229Th for laser experiments when searching for the energy value of the isomeric nuclear transition.

Multisectional linear ion trap and novel loading method for optical spectroscopy of electron and nuclear transitions

There is a growing need for the development of atomic and nuclear frequency standards because of the important contribution of methods for precision time and frequency measurements to the development of fundamental science, technology and the economy. It is also conditioned by their potential use in optical clocks and quantum logic applications. It is especially important to develop a universal method that could allow one to use ions of most elements effectively (including ones that are not easily evaporated) proposed for the above-mentioned applications. A linear quadrupole ion trap for the optical spectroscopy of electron and nuclear transitions has been developed and evaluated experimentally. An ion source construction is based on an ultra-high vacuum evaporator in which a metal sample is subjected to an electron beam of energy up to 1 keV, resulting in the appearance of gaseous atoms and ions of various charge state. The linear ion trap consists of five successive quadrupole sections including an entrance quadrupole section, quadrupole mass filter, quadrupole ion guide, ion-trap section and exit quadrupole section. The same radiofrequency but a different direct current voltage feeds the quadrupole sections. The instrument allows the mass- and energy-selected trapping of ions from ion beams of various intensities and their localization in the area of laser irradiation. The preliminary results presented show that the proposed instrument and methods allow one to produce effectively up to triply charged thorium ions as well as to trap ions for future spectroscopic study. The instrument is proposed for future use in optical clocks and quantum logic application development.

The band structure of submonolayer thorium coatings on a silicon oxide surface

Data are reported on the electronic structure of thorium-containing clusters formed on the surface of natural silicon oxide via electrochemical deposition. The mutual arrangement of bands in the clusters and silicon oxide substrate is restored with the use of X-ray photoelectron spectroscopy and electron energy loss spectroscopy. It is concluded that the studied cluster/substrate system may be promising for investigating the low-lying isomeric nuclear transition in 229Th isotope.

The size dependence of thermal EMF for Au, Pd, and Pt nanoclusters deposited onto highly oriented pyrolitic graphite surface

Data are presented on the tunnel current-voltage characteristics of gold, palladium, and platinum nanoclusters formed by pulsed laser deposition on the surface of highly oriented pyrolytic graphite. Differential tunnel current-voltage characteristics measured by scanning tunnel spectroscopy have been used to restore the size dependences of the thermal emf values of the studied nanoclusters. The behavior of the thermal emf of the nanoclusters as depending on their sizes has been found to depend on the nature of a metal. The data obtained have been analyzed.

Calculation of density of states of transition metals: From bulk sample to nanocluster

A technique is presented of restoring the electronic density of states of the valence band from data of X-ray photoelectron spectroscopy (XPS). The originality of the technique consists in using a stochastic procedure to solve an integral equation relating the density of states and the experimental X-ray photoelectron spectra via the broadening function. To obtain the broadening function, only the XPS spectra of the core levels are needed. The results are presented for bulk sample of gold and tungsten and nanoclusters of tantalum; the possibility of using the results to determine the density of states of low-dimensional structures, including ensembles of metal nanoclusters, is demonstrated.

Experimental treatments for the investigation of nuclear optical transition in Thorium-229

An original preparation technique of the thorium films by electrochemical deposition from thorium nitrate solution on different substrate is reported. It was found that electrochemical deposition of thorium on the metal surface provides the formation of adherent continuous films, while the deposition on the semiconductor substrates leads to the formation of thorium island films. The origin of the observed thorium films formation and the results on the investigation of thorium films on Si(111) and polycrystalline Cu surfaces by XPS and LEIS are discussed.

Asymptotically Exact Method for Calculation of Density of States in HTSC

The work presents the method of restoring a spectral density from known Green’s function. The method is based on a combination of Monte Carlo and gradient descent algorithms, which avoids the problem of distortion of the equation by nonlinear terms and, therefore, analyzes the most representative range of small deviations. Furthermore, the method does not contain sources of systematic errors and, in principle, any spectral function can be parameterized with any desired accuracy. With the use of the method, the spectral density of states was restored for FeAs-based superconductors. The method works well also for metal nanoclusters and many other systems.

Calculation of Density of States for FeAs-based Superconductors

Received 28.12.2016, received in revised form 16.01.2017, accepted 28.02.2017 The spectral and the total density of states were calculated for two-dimensional FeAs-clusters within the limits of the two-orbital model, which is widely used for modeling iron-based superconductors. The spectra were restored by means of an asymptotically exact stochastic procedure, which was modified to restore the kernel of the integral equation relating the Matsubara Green’s function and the spectral density. The data for Matsubara Green’s function were obtained with the use of the generalized quantum world-line Monte Carlo algorithm adapted for the two-orbital model. The calculations were made for clusters with sizes up to 10×10 FeAs-cells. The data are presented for the distribution profiles along the main crystallographic directions and for the entire Brillouin zone. The analysis of the doped state revealed differences in the electron and hole states of the system that is correlated with known experimental data.

Thorium silicate compound as a solid-state target for production of isomeric thorium-229 nuclei by electron beam irradiation

In this paper, we discuss an idea of the experiment for excitation of the isomeric transition in thorium-229 nuclei by irradiating with electron beam targets with necessary physical characteristics. The chemical composition and bandgap of ThSi10O22 were determined by X-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy. It was found that the energy gap is equal to 7.7 eV and does not change when the target is exposed to a medium energy electron beam for a long time. This indicates that the compound possesses high electron-beam resistance. A quantitative estimation of the output function of isomeric thorium-229 nuclei generated by interaction of nuclei with the secondary electron flow formed by irradiating the solid-state ThSi10O22-based target is given. The estimation shows that ThSi10O22 is a promising thorium-containing target for investigating excitation of the nuclear low-lying isomeric transition in the thorium-229 isotope using medium-energy electrons.

229Th and 232Th optical spectroscopy system for nuclear frequency standard

The results of developing of the laboratory complex for optical spectroscopy of multiply charged thorium ions are presented. The preliminary experimental results on producing single, double and triple charged ions from solid compounds of thorium nitrate by electron beam evaporation technique are reported. It is shown that the proportion of triple and double charged thorium ions obtained by this method to single ones exceeds the values for the laser ablation technique. The electron beam evaporation technique is the basis of the developed complex.