Персона: Степанов, Сергей Всеволодович
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Институт ядерной физики и технологий
Цель ИЯФиТ и стратегия развития - создание и развитие научно-образовательного центра мирового уровня в области ядерной физики и технологий, радиационного материаловедения, физики элементарных частиц, астрофизики и космофизики.
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Теперь показываю 1 - 9 из 9
- ПубликацияТолько метаданныеPositronium Annihilation in Freshly Defrosted Thawed Water(2023) Zemskaya, L. I.; Ilyukhina, O. V.; Karpov, M. V.; Stepanov, S. V.; Степанов, Сергей Всеволодович
- ПубликацияТолько метаданныеInteraction of positronium with dissolved oxygen in liquids(2020) Stepanov, P. S.; Selim, F. A.; Stepanov, S. V.; Bokov, A. V.; Степанов, Сергей ВсеволодовичThe interaction of positronium (Ps) with molecular oxygen dissolved in liquids is experimentally investigated. Computer software has been developed for fitting the positron annihilation lifetime spectra in liquids using parameters with clear physical meaning: rate constants of the Ps chemical reactions, annihilation rate constants of the different positron states, probability of Ps formation in a quasi-free state, typical formation time of a Ps nanobubble. Such processing of the spectra allowed identification of the dominant interaction of the Ps atom with dissolved oxygen. It turns out to be mainly ortho-para-conversion (Ps -> 1/4 p-Ps + 3/4 o-Ps), but not oxidation (Ps + O-2 -> e(+) + O-2(-)). Values of the reaction rate constants are obtained.
- ПубликацияТолько метаданныеAnnealing of radiation-induced defects in tungsten: Positron annihilation spectroscopy study(2019) Terentyev, D.; Funtikov, Y. V.; Stolbunov, V. S.; Ogorodnikova, O. V.; Dubov, L. Y.; Stepanov, S. V.; Shtotsky, Y. V.; Efimov, V.; Gutorov, K.; Огородникова, Ольга Вячеславовна; Дубов, Леонид Юрьевич; Степанов, Сергей Всеволодович; Штоцкий, Юрий Владимирович; Ефимов, Виталий Сергеевич; Гуторов, Константин Михайлович© 2019 Elsevier B.V. Positron annihilation lifetime spectroscopy (PALS) was applied to study the annealing of radiation-induced defects in polycrystalline tungsten (W) irradiated with 21.6 MeV protons at 100 °C up to a fluence of 5 × 10 15 p/cm 2 . Three components were observed in the measured spectra: short-lifetime of 100–120 ps (positron annihilation in the defect-free W lattice), medium-lifetime of ∼190–330 ps (annihilation at mono-vacancies and small vacancy cluster containing ∼ 2–4 vacancies) and long-lifetime of ∼500 ps (annihilation in large vacancy clusters containing more than 10 vacancies). The irradiation of W with protons at 100 °C, primary, led to the formation of mono-vacancies, self-interstitial defects were created as well but migrated towards sinks during the irradiation. Onset of vacancy diffusion in W starts already at 200 °C before defect recovery stage III. After annealing at ∼400 °C, a sharp drop in the intensity of the positron medium-life component together with a simultaneous increase in positron lifetime from ∼220 to ∼280 ps is observed, and a long-life component appears. This indicates migration and annealing of vacancies and their agglomeration in large vacancy clusters. After annealing at 500–700C, the intensity of long-life component increases indicating the growth of large vacancy clusters but at 900 °C they anneal completely as the mean lifetime recovers nearly to the value measured in the un-irradiated material.
- ПубликацияОткрытый доступПОЗИТРОННАЯ ДИАГНОСТИКА FE-GA СПЛАВОВ(НИЯУ МИФИ, 2025) СТЕПАНОВ, С. В.; ДУБОВ, Л. Ю.; ИЛЮХИНА, О. В.; ШТОЦКИЙ, Ю . В.; АКМАЛОВА, Ю. А.; БУДАЕВА, Л. И.; Штоцкий, Юрий Владимирович; Дубов, Леонид Юрьевич; Степанов, Сергей Всеволодович; Акмалова, Юлия АльфредовнаВ настоящей работе исследована динамика дефектов вакансионного типа в сплавах Fe-Ga (галфенолах) с содержанием галлия от 16,5 до 33%. Методы спектроскопии времени жизни аннигиляции позитронов (PALS), нейтронной дифракции и рентгеновской дифракции (XRD) показывают высокую степень корреляции в изменениях времени жизни позитронов и фазового состава образцов. Сравнение позитронных данных и результатов структурного анализа показывает различное поведение упорядочения дефектов в сплавах с содержанием галлия x выше и ниже 25%. Все исследованные сплавы, закаленные при 1000°С, демонстрируют высокую концентрацию моновакансий железа (> 2·10-4 ат-1). Оказалось, что время жизни в моновакансиях линейно изменяется от ~ 160 пс при x = 16.5 до ~ 180 пс при x = 33. Теоретические оценки времени жизни позитронов в моновакансиях в зависимости от числа атомов NGa в ближайшем окружении дают времена от 183 пс при NGa = 0 до 198 пс при NGa = 8. Для объяснения экспериментальных результатов предложена модель вакансионно-углеродных комплексов.
- ПубликацияТолько метаданныеPositron Study of Fe–Ga Alloys(2025) Dubov, L. Y.; Shtotsky, Y. V.; Ilyukhina, O. V.; Akmalova, Y. A.; Stepanov, S. V.; Дубов, Леонид Юрьевич; Штоцкий, Юрий Владимирович; Акмалова, Юлия Альфредовна; Степанов, Сергей Всеволодович
- ПубликацияОткрытый доступPALS investigation of structural vacancies during phase transitions in Fe-27Ga and Fe-27Ga-0.1Tb alloys(2019) Golovin, I. S.; Palacheva, V. V.; Dubov, L. Y.; Shtotsky, Y. V.; Stepanov, S. V.; Akmalova, Y. A.; Дубов, Леонид Юрьевич; Штоцкий, Юрий Владимирович; Степанов, Сергей Всеволодович; Акмалова, Юлия Альфредовна© 2019 Author(s).Good mechanical properties and relatively low switching magnetic field make Fe-Ga alloys very useful magnetostrictive material for wide range of practical applications. Doping with rare-earth elements (such as Tb) can significantly increase magnetostriction, because Tb rearranges vacancy structure during phase transitions in Fe-27Ga alloys. It was found that A2 and D03 structures in Fe-27Ga have high density of Fe-monovacancies with the positron lifetime ≈180 ps regardless of the presence of Tb. Transition into L12 structure is accompanied by formation of a significant number of larger vacancy defects, which increases the e+ lifetime by 5 %. Addition of 0.2% Tb suppress formation of these large defects at annealing temperatures of 400-550°C. Presence of Tb also decreases concentration of vacancies in D019 structure. After annealing at 650°C D019 volume fraction in Fe-27Ga-0.2Tb decreases to 60 %, (according to the positron measurements) against 95 % in Fe-27Ga. In both alloys at 700°C number of monovacancies increases dramatically during formation of the bcc B2 phase.
- ПубликацияОткрытый доступPositronium in thawed water(2019) Byakov, V. M.; Ilyukhina, O. V.; Bokov, A. V.; Karpov, M. V.; Stepanov, S. V.; Степанов, Сергей Всеволодович© 2019 Author(s).Parameters of the positron annihilation spectra for pure water previously subjected to the freeze-thaw process are mea- sured. It is shown that orthopositronium lifetime in melted water slightly vary with time after melting (typical time is less than few hours) and then reach the value corresponding to ordinary water. This may indicate that molten water is a nonequilibrium system with a rather long relaxation time. This phenomenon may reflect the process of restructurizing of large clusters of water molecules linked through hydrogen bonds.
- ПубликацияОткрытый доступA model for joint processing of LT and CDB spectra of dielectric nano-sized powders(2019) Stepanov, P. S.; Selim, F. A.; Stepanov, S. V.; Byakov, V. M.; Степанов, Сергей Всеволодович© 2019 Author(s).A model that allows interpretation of positron annihilation spectra (LT and CDB) in nanodispersed dielectric powders is developed. Model takes into account e+ capture by vacancy-type defects, formation of e+ surface-bound states, as well as the formation of quasi-free positronium (inside crystallites) which may escape into intergranular space where it becomes thermalized during elastic collisions. The process of annihilation of ortho-Ps is narrowed down to its conversion into the para-state as a result of collisions with oxygen molecules (O2) adsorbed on the surface of crystallites. A computer program for lifetime spectra fitting that accounts on the parameters of the above model is developed (with ROOT framework). Combination of the program with our CDB software allows joint processing of the LT and CDB annihilation spectra of nanopowders.
- ПубликацияОткрытый доступPALS and FTIR study of proton irradiated Si upon ageing(2019) Ilyukhina, O. V.; Funtikov, Y. V.; Khmelevsky, N. O.; Aksenenko, A. Y.; Dubov, L. Y.; Stepanov, S. V.; Shtotsky, Y. V.; Дубов, Леонид Юрьевич; Степанов, Сергей Всеволодович; Штоцкий, Юрий Владимирович© 2019 Author(s).Transformation of radiation defects structure in proton-irradiated silicon during 22 month ageing at room temperature were studied by means of the positron annihilation lifetime spectroscopy and Fourier transformed infrared spectroscopy. Three pairs of irradiated samples were isochronically annealed and measured after 1, 14 and 22 months since irradiation. Significant distinctions in behavior of the positron trapping rate upon annealing were detected. They can be explained by evolution of interstitial clusters in the disordered regions of irradiated Si during long-term ageing at room temperature.