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Ткаля, Евгений Викторович

Организационные подразделения

Организационная единица

Институт лазерных и плазменных технологий

Стратегическая цель Института ЛаПлаз – стать ведущей научной школой и ядром развития инноваций по лазерным, плазменным, радиационным и ускорительным технологиям, с уникальными образовательными программами, востребованными на российском и мировом рынке образовательных услуг.

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Ткаля

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Евгений Викторович

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Теперь показываю 1 - 10 из 18

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Chemical bonding between thorium atoms and a carbon hexagon in carbon nanomaterials
(2020) Bibikov, A. V.; Nikolaev, A. V.; Tkalya, E. V.; Николаев, Александр Васильевич; Ткаля, Евгений Викторович
We explore the unusual nature of chemical bonding of thorium atoms with a ring of six carbon atoms (hexagon) in novel carbon materials. Our ab initio calculations of Th-based metallofullerenes (Th@C60 and Th@C20) and Th bound to benzene or coronene at the Hartree-Fock level with the second order perturbation (MP2) correction accounting for the van der Waals interactions demonstrate that the optimal position of the thorium atom is where it faces the center of a hexagon and is located at a distance of 2.01-2.07 Å from the center. For Th encapsulated in C60 it is found at 2.01 Å, whereas the other local energy minima are shifted to larger energies (0.22 eV and higher). Inside C60 the highest local minimum at 1.17 eV is observed when Th faces the center of the five member carbon ring (pentagon). Based on our calculations for Th with benzene and coronene where the global minimum for Th corresponds to its position at 2.05 Å (benzene) or 2.02 Å (coronene) from the hexagon center, we conclude that a well pronounced minimum is likely to be present in graphene and in a single wall carbon nanotube. The ground state of Th is singlet, and other high spin states (triplet and quintet) lie higher in energy (>1.62 eV). We discuss a potential use of carbon nanomaterials with the 229Th isotope having its nuclear transition in the optical range, for metrological purposes.
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Cross section of the Coulomb excitation of Th-229m by low energy muons
(2021) Tkalya, E. V.; Ткаля, Евгений Викторович
The inelastic scattering cross section for muons, mu(-), with energies E = 9-100 eV from the Th-229 nuclei is calculated in the framework of the second order of the perturbation theory for quantum electrodynamics. The dominant contribution to the excitation of the low energy isomer Th-229m(3/2(+), 8.19 +/- 0.12 eV) originates from the E2 multipole. The excitation cross section reaches the value of 10(-12) cm(2) in the range E approximate to 10 eV. This value is four to five orders of magnitude larger than the electron excitation cross section and is sufficient for the efficient excitation of Th-229m on the muon beam at the next generation of muon colliders.
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Internal conversion of the low-energy (229m)qh isomer in the thorium anion
(2020) Tkalya, E. V.; Si, R.; Ткаля, Евгений Викторович
A process of the decay of the anomalously low-lying nuclear isomer Th-229m(3/2(+), 8.28 +/- 0.17 eV) in the thorium anion (Th ) via the internal conversion (IC) channel is studied. We show that the half-life of the nuclear isomer in the 6d(3/2)(3)7s(1/2)(2) ground state and in the 6d(3/2)(3)7s(1/2)(2)7p(1/2)(1) excited state of Th- is approximate to 1.5 and approximate to 1.1 times bigger than in the 6d(3/2)(2)7s(1/2)(2) ground state of the Th atom. The IC probabilities in the anion decreases despite the decay via the additional 6d(3/2) or 7P(1/2) electrons. This counterintuitive result is a consequence (a) of a decrease in the amplitudes of the 6d(3/2) and 7s(1/2) wave functions near the nucleus due to an increase in their diffuseness of upon the addition of extra electron and (b) of mutual compensation in the IC probability due to a kinematic factor, which depends on the energy of the conversion electron in the continuum as E-c(-1/2), and the E-c(1/4) growth of the amplitudes of the electron wave functions.
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Excitation of Th-229m at Inelastic Scattering of Low Energy Electrons
(2020) Tkalya, E. V.; Ткаля, Евгений Викторович
Excitation of the anomalously low lying nuclear isomer Th-229m(3/2(+), 8.28 +/- 0.17 eV) in the process of inelastic electron scattering is studied theoretically in the framework of the perturbation theory for the quantum electrodynamics. The calculated cross sections of Th-229m by the extremely low energy electrons in the range 9-12 eV for the Th atom and Th-1+,Th-4+ ions lie in the range 10(-25)-10(-26) cm(2). Being so large, the cross section opens up new possibilities for the effective nonresonant excitation of Th-229m in experiments with an electron beam or electron (electric) current. This can be crucial, since the energy of the isomeric state is currently known with an accuracy insufficient for the resonant excitation by photons. In addition, the cross section of the time reversed process is also large, and as a consequence, the probability of the nonradiative Th-229m decay via the conduction electrons in metal is approximate to 10(6) s(-1), that is, close to the internal conversion probability in the Th atom.
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A Unique System for Registering One-Photon Signals in the Ultraviolet Range from An Isomeric 229mTh Nucleus Implanted on Thin SiO2/Si Films
(2020) Lebedinskii, Y. Y.; Borisyuk, P. V.; Chubunova, E. V.; Kolachevsky, N. N.; Vasiliev, O. S.; Tkalya, E. V.; Лебединский, Юрий Юрьевич; Борисюк, Петр Викторович; Чубунова, Елена Витальевна; Васильев, Олег Станиславович; Ткаля, Евгений Викторович
© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimCurrently, an urgent task related to creating a nuclear frequency standard is the identification of a low-lying nuclear state in the thorium-229 isotope. Herein, a method for measuring the single-photon energy during the decay of an isomeric thorium-229 nucleus implanted in a wide-gap dielectric SiO2 (Eg = 9 eV) is developed. The proposed method utilizes thin silicon oxide layers obtained by thermal oxidization of the pure silica wafers, which allows measurement of the energy of photons in the ultraviolet (UV) range using an electronic spectrometer. The modeling study of electronic state excitation is provided via UV radiation from Kr, Xe, and D resonance discharging lamps. The obtained spectra are analyzed, and a method for determining the UV photon's energy is proposed.
Открытый доступ
Estimation of the charge state of Th implanted in SiO2in the different atomic environment
(2020) Kurelchuk, U. N.; Borisyuk, P. V.; Nikolaev, A. V.; Tkalya, E. V.; Курельчук, Ульяна Николаевна; Борисюк, Петр Викторович; Николаев, Александр Васильевич; Ткаля, Евгений Викторович
© Published under licence by IOP Publishing Ltd.In this work the investigation of the charge states of thorium implanted in SiO2 is in different atomic environments and at different concentrations is presented.. Th was considered as interstitial and substitutional impurity in model cells of 6, 48 and 96 atoms. The estimations of the Bader effective charges of Th was derived from the electronic charge density n(r) calculated in DFT full relativistic PAW pseudopotential approximation. The change in the electron density of thorium due to the environment in the cells was estimated in comparison with the free atomic state.
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Estimation of the decay rate of Be 7 and Be2 7 encapsulated in C70
(2019) Bibikov, A. V.; Nikolaev, A. V.; Tkalya, E. V.; Ткаля, Евгений Викторович
© 2019 American Physical Society.Electron capture (β-decay) rates of Be7 and Be27 encapsulated in C70 have been estimated by calculating the electron density ρ(0) at the Be7 nucleus and comparing it with ρ(0) and experimental β-decay rates of Be7 inside another fullerene - C60. For that the endohedral fullerenes Be7@C70 and Be27@C70 have been examined by means of the ab initio approach using the Hartree-Fock method with the the second order Møller-Plesset perturbation theory accounting for the Van der Waals foces. Our calculations indicate that the Be27@C70 complex is stable with the binding energy of 1.3 eV and the Be7 dimer bond length 2.30 Å. It has been found that ρ(0) is practically the same in Be7@C70 and Be27@C70, but larger than in an isolated Be7 atom. The increase of ρ(0) however is smaller than in Be7@C60. We also discuss in detail the mechanism underlying the increase of ρ(0) and consequently the decrease of the decay rate in Be7@C70 in comparison with the isolated Be7 atom.
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Excitation of the low-energy Th-229m isomer Th in the electron bridge process via the continuum
(2019) Taichenachev, A. V.; Tolstikhina, I. Yu.; Yudin, V. I.; Borisyuk, P. V.; Kolachevsky, N. N.; Tkalya, E. V.; Борисюк, Петр Викторович; Ткаля, Евгений Викторович
The paper studies the excitation of the Th-229 nucleus to the anomalously low-lying isomeric state 3/2(+)(8.28 +/- 0.17 eV) in the electron bridge process via the continuum of the electron spectrum. Resonant excitation of the nucleus was found to be always possible in the scheme, no matter where the electron levels of an atom or ion were located. Formulas for the excitation cross section by narrow and wide laser lines are obtained. In the resonance, where the process under consideration turns into laser photoionization followed by nuclear excitation in electron capture, the cross section of the process was shown to be comparable in magnitude with that of the photoionization of the thorium atom. Experimental schemes for testing the effect were proposed, which would allow measuring the frequency of the nuclear isomeric transition 3/2(+) -> 5/2(+) to a high precision, which is the first-priority (and still unresolved) task for creating a nuclear clock.
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Decay of the low-energy nuclear Th 229m isomer via atomic Rydberg states
(2019) Tkalya, E. V.; Ткаля, Евгений Викторович
© 2019 American Physical Society.In the paper, a unique process of the decay of the Th229m(3/2+,8.28±0.17 eV) low-energy nuclear isomer via the internal conversion (IC) channel on Rydberg states is considered for the first time. The Rydberg atom Th+229m+eRy- is a unique object where IC is possible exclusively on the Rydberg electron eRy-. It is shown that in the Th4+229m+eRy- system (a) IC on the electron states with relatively small values of the principal quantum number n and the orbital moment l is practically completely suppressed, (b) IC probability, WIC, on the ψns1/2(r) states is proportional to |ψns1/2(0)|2 and can be related with the energy of the hyperfine interaction of the Rydberg electron with the nucleus, (c) WIC decreases rapidly with the increase of n in the range from 10 to 50, and in the range n 150WIC changes as const/n3 typical for hydrogen-like ions, and (d) at n≈10-30, WIC as a function of l has a characteristic "knee" between l=3 and l=4, i.e., a decrease of three orders of magnitude in WIC due to the qualitative change in the ratio between the centrifugal and shielding potentials.
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Autoelectronic emission and charge relaxation of thorium ions implanted into a thin-film silicon oxide matrix
(2021) Borisyuk, P. V.; Chubunova, E. V.; Kolachevsky, N. N.; Lebedinskii, Y. Y.; Tkalya, E. V.; Vasilyev, O. S.; Yakovlev, V. P.; Борисюк, Петр Викторович; Чубунова, Елена Витальевна; Лебединский, Юрий Юрьевич; Ткаля, Евгений Викторович; Васильев, Олег Станиславович; Яковлев, Валерий Петрович
An ensemble of thorium-229 ions embedded by pulsed laser implantation into a matrix of a broadband dielectric-silicon oxide is studied. The results of the experimental investigation of thorium ions' lifetime as charged components of the Th+/SiO2/Si system formed immediately after laser implantation are presented. The modelled theoretical description takes into account the instantaneous charging of the surface via laser implantation followed by charge relaxation due to the effect of autoelectronic emission that leads to time dependent partial neutralization of the surface charge by tunneling electrons. It was found that the lifetime of Th+ ions on the SiO2 surface can exceed 10 s, which would be an attractive opportunity for studying the nuclear low-lying isomeric transition in the thorium-229 isotope.