Trivalent zirconium and hafnium ions in yttria-based transparent ceramics

Electron paramagnetic resonance spectra of transparent yttria-based ceramics with zirconium and hafnium additives contain signals with close parameters due to paramagnetic Zr3+ and Hf3+ ions, which have similar ground-state electron configurations of [Kr]4d 1 and [Xe]5d 1, respectively. © 2013 Pleiades Publishing, Ltd

Magnetic properties and structure of TiO2-Mn (0.73 %) nanopowders: The effects of electron irradiation and vacuum annealing

Nanopowder TiO2-0.73 % Mn was synthesized by the sol-gel method. Thermal treatment of the samples was carried out in vacuum at a temperature of 500°C. Magnetic properties were studied in the temperature range from 2 to 850 K. The effects of electron irradiation and vacuum annealing on the EPR spectra and magnetic properties of TiO2-Mn powder are discussed. It was established that a part of manganese ions in the anatase crystal lattice interacts antiferromagnetically, which causes a decrease in magnetization as compared to the result of the calculation for non-interacting ions. Vacuum annealing leads to the formation of oxygen vacancies and, at the same time, to a noticeable increase in the ferromagnetic contribution to magnetization, especially, after preliminary electron irradiation. We assume that the ferromagnetic contribution to the magnetization appears either due to incomplete compensation of antiferromagnetically directed moments of manganese ions, or due to positive exchange interactions of Mn ions via defects in the TiO2 lattice. It is shown that the temperature of magnetic disordering in samples with a spontaneous magnetic moment exceeds 600°C. © 2019, Institute for Metals Superplasticity Problems of Russian Academy of Sciences. All rights reserved

Unconventional magnetism of non-uniform distribution of Co in TiO2 nanoparticles

High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) analysis, electron paramagnetic resonance (EPR), X-ray absorption spectroscopy (XAS), magnetic methods, and density-functional theory (DFT) calculations were applied for the investigations of Co-doped anatase TiO2 nanoparticles (∼20 nm). It was found that high-spin Co2+ ions prefer to occupy the interstitial positions in the TiO2 lattice which are the most energetically favourable in compare to the substitutional those. A quantum mechanical model which operates mainly on two types of Co2+ – Co2+ dimers with different negative exchange interactions and the non-interacting paramagnetic Co2+ ions provides a satisfactorily description of magnetic properties for the TiO2:Co system. © 2020 Elsevier B.V.Russian Foundation for Basic Research. Ministry of Science and Higher Education of the Russian Federatio

Efficient Certified Resolution Proof Checking

We present a novel propositional proof tracing format that eliminates complex processing, thus enabling efficient (formal) proof checking. The benefits of this format are demonstrated by implementing a proof checker in C, which outperforms a state-of-the-art checker by two orders of magnitude. We then formalize the theory underlying propositional proof checking in Coq, and extract a correct-by-construction proof checker for our format from the formalization. An empirical evaluation using 280 unsatisfiable instances from the 2015 and 2016 SAT competitions shows that this certified checker usually performs comparably to a state-of-the-art non-certified proof checker. Using this format, we formally verify the recent 200 TB proof of the Boolean Pythagorean Triples conjecture

NATURAL HYDROXYAPATITE AS A DETECTOR OF THE ACCUMULATED DOSE OF IONIZING RADIATION

The purpose of the present study is developing a new dosimeter detector based on biological hydroxyapatite having several advantages over the existing analogs, and methods of its application. Properties of the biological materials were studied by continuous and pulsed EPR in order to determine their suitability for application as dosimetric materials. Possible differences in the mechanisms of formation of radiation-induced stable free radicals in the biological hydroxyapatite of different origin were considered, and radiation sensitivity of this materials was determined. Studies were also aimed at finding a binder having the properties of neutrality to radiation and biocompatibility. A test batch of artificial radiation detectors based on the chosen material, epoxy resin, was produced and tested. Detectors were tested for their usefulness in the calibration of artificial radiation beams as well as for radioecological studies

Research of Dosimetric Characteristics of Human Hair Depending on the Content of Melanine

Purpose: Investigation of paramagnetic properties of radiation-induced centers that occur when hair samples are irradiated with ionizing radiation, depending on the color of the sample. Material and methods: A Bruker Elexsys E580 electron paramagnetic resonance spectrometer was used. To improve the signal-to-noise ratio, the spectrum was recorded with three accumulations with a constant scan time equal to one minute. Measurements were made using a highly sensitive rectangular Bruker SuperHighQ resonator. For irradiation of samples, the linear electron accelerator UELR-10-10С2 of the innovation and implementation center for radiation sterilization of the Urals Federal University (Institute of Physics and technology) was used. Results: Research of the EPR signal parameters of the melanin in hair samples of different colors (black, brown, red and gray with different degrees of pigmentation) showed that the intensity of the EPR signal varies depending on the hair color. The higher the radiation sensitivity of the hair, the lighter the color of the hair. The melanin signal, which is the background for the radiation-induced signal, increases with increasing intensity of hair color. © 2022 State Research Center, Burnasyan Federal Medical Biophysical Center of Federal Medical Biological Agency. All rights reserved.Federal Medical and Biological Agency of RussiaSouth Ural Regional Medical and Dosimetric Emergency CenterMinistry of Education and Science of the Russian Federation, Minobrnauka, (AAAA-A18-118020290104-2)The author declare no conflict of interest. The work was carried out within the framework of state contract No. 11.310.19.2 on the topic “Improving the provision of emergency preparedness and response of the South Ural Regional Medical and Dosimetric Emergency Center in the event of radiation accidents” (code “Response-19”), funded by the Federal Medical and Biological Agency of Russia. EPR measurements were partly carried out within the framework of the state order of the Ministry of Education and Science of Russia (topic "Spin", No. AAAA-A18-118020290104-2). Article was prepared with equal participation of the authors 15.03.2022. 23.04.202

Magnetism and temperature dependence of nano-TiO2: Fe EPR spectra

Nanocrystalline TiO2 samples of various compositions (up to 5 at.% Fe) with anatase structure and an average particle size of about 20 nm were synthesized using sol-gel technology. The magnetic properties of nano-TiO2: Fe was studied by electron paramagnetic resonance (EPR) and Faraday balance. The existence of an inhomogeneous magnetic state in TiO2: Fe samples of different compositions were revealed by EPR spectroscopy in a wide temperature range. The analysis of the EPR spectra in the L -, X - and Q-bands allowed us to calculate the quadratic fine structure (D, E) parameters, “axial” and “rhombic” ones, respectively. The value of D turned out to be quite small, which indicates an insignificant anisotropy, which can be ignored describing the magnetic properties of TiO2:Fe. It was shown that the temperature behavior of different separate components of the integral EPR spectra can be qualitatively interpreted in the model of coexistence in the TiO2: Fe system, mainly, dimers with a strong negative exchange interaction and isolated paramagnetic centers. No ferromagnetic state in TiO2: Fe-based samples after etching of aE-prepared state were detected. © 202

MAGNETISM AND EPR OF COBALT-DOPED TIO2 NANOPOWDERS, IN VARIOUS TREATMENTS

The existence of different nature defects and carriers of a magnetic moment, based on Ti3+ or Co2+ on the surface of a nanoparticle, is a necessary condition for the realization of exchange interactions leading to the appearance of a spontaneous magnetic moment.Авторы выражают благодарность Российскому научному фонду за финансовую поддержку исследований (грант № 16-12-10004)