Defense of the dissertation of Malikova Jadra for the degree of Doctor of Philosophy (PhD) in the specialty «8D05323 - Technical Physics»

L.N. Gumilyov Eurasian National University, a dissertation defense for the degree of Doctor of Philosophy (PhD) by Malikova Jadra on the topic «Defect formation of pure and activated LiF crystals caused by pulsed electron beam and ion flow» to the educational program «8D05323 – Technical Physics».

The dissertation was carried out at the «Technical Physics education department» of L.N. Gumilyov Eurasian National University.

The language of defense is russian

Official reviewers:

Daulet Sergeev – Candidate of Physical and Mathematical Sciences, Associate Professor, Lieutenant Colonel, Head of the Department of Design and Operation of Radio-Electronic Equipment at the Republican State Institution “T. Ya. Begeldinov Military Institute of the Air Defense Forces” of the Ministry of Defense of the Republic of Kazakhstan, Aktobe, Republic of Kazakhstan;

Gulbanu Kaptagay – PhD, Associate Professor of the Department of Physics, Kazakh National Women’s Teacher Training University, Almaty, Republic of Kazakhstan.

Temporary members of the Dissertation Council:

Kuanyshbek Shunkeev – Doctor of Physical and Mathematical Sciences, Professor, Director of the Scientific Center “Radiation Physics of Materials,” K. Zhubanov Aktobe Regional University, Aktobe, Republic of Kazakhstan;

Adolf Nogay – Doctor of Physical and Mathematical Sciences, Professor of the Department of Radio Engineering, Electronics and Telecommunications, S. Seifullin Kazakh Agrotechnical Research University, Astana, Republic of Kazakhstan;

Anuar Aldongarov – Doctor of Philosophy (PhD), Associate Professor of the Department of Technical Physics, L.N. Gumilyov Eurasian National University, Astana, Republic of Kazakhstan.

Scientific advisors:

Abdirash Akilbekov – Doctor of Physical and Mathematical Sciences, Professor of the Department of Technical Physics, L.N. Gumilyov Eurasian National University, Astana, Republic of Kazakhstan;

Anatoliy Popov – Doctor of Physics, PhD, Professor at the University of Latvia, Leading Researcher at the Institute of Solid State Physics, Riga, Latvia.

The defense will take place on April 11, 2026, at 02:00 PM in the Dissertation Council for the training direction «8D053 – Physical and chemical sciences» in the specialty «8D05323 – Technical Physics» of L.N. Gumilyov Eurasian National University. The dissertation council meeting will be held in offline and online formats.

Link: https://clck.ru/3RyhCd 

Address: Astana, Kazhymukan Street, 13, auditorium No. 310 

Abstract (English): The purpose of the dissertation research. The objective of the research is a comprehensive experimental and theoretical study of the formation, evolution, and thermal annealing of radiation defects in pure and activated LiF crystals under electron, ion, and neutron irradiation. Research objectives. 1. To investigate the initial characteristics of pure and activated LiF crystals and to determine the composition of their impurity–defect subsystem prior to irradiation. 2. To identify radiation-induced defects in LiF under electron, neutron, and ion irradiation and to establish their spectral characteristics. 3. To analyze the influence of the type, energy, and fluence of irradiation, as well as the values of Sₑ and Sₙ, on the formation of F and aggregated Fₙ centers and on the change in the optical and IR spectra. 4. To investigate the stepwise thermal annealing of F centers based on optical absorption data, to determine the kinetic parameters (activation energies and pre-exponential factors), and to establish the features of recovery for different irradiation regimes. 5. To analyze the broad Fₙ absorption bands, to trace the temperature evolution of the contributions of F₂, F₃, F₃⁺, and F₄⁻ centers, and to establish the sequence of their transformations up to the formation of lithium colloidal clusters. 6. To develop a diffusion–reaction model of the thermal evolution of F and Fₙ centers, as well as impurity–defect complexes, and to compare the calculated annealing curves with the experimental data. 7. To establish relationships between the mechanisms of radiation defect formation and annealing and the optical and dosimetric characteristics of LiF, and to formulate recommendations for optimizing irradiation and heat-treatment regimes. Research methods. High-purity LiF crystals grown by the Bridgman–Stockbarger and Kyropoulos methods were investigated in this dissertation. Irradiation of the samples was carried out at the DC-60 accelerator (Astana) and the GSI accelerator complex (Darmstadt) using ions ¹⁶O (28 MeV), ¹⁴N (23 MeV), ⁸⁴Kr (150 MeV), and ²³⁸U (2640 MeV), as well as thermal neutrons in the IRT-2000 research reactor and pulsed electron beams with an energy of 250 keV. The optical properties and concentrations of F and Fₙ centers were measured using UV–visible spectroscopy on SPECORD 250, PERSEE T8DCS, and SF-2000 spectrophotometers. Identification of hydroxyl centers and radiolysis products was performed using IR spectroscopy on Specord 75-IR and Vertex 70V instruments. Stepwise thermal annealing in the temperature range 293–870 K was carried out in an SNOL furnace with a controlled heating rate of 5 K/s, followed by cooling and repeated spectral measurements to determine the temperature intervals of decay and aggregation of color centers. Numerical modeling of defect relaxation kinetics, diffusion–reaction processes, and migration energetics of F centers was performed on the LASC supercomputing complex using a diffusion–reaction model. This made it possible to obtain quantitative estimates of migration energies, aggregation rates, and temperature ranges of thermal stability of radiation defects. The main provisions submitted for defense. Neutron irradiation of LiF:OH leads to the emergence of dose-dependent infrared (IR) absorption bands of hydroxyl and hydrogen-related centers, which are directly associated with ⁶Li(n,α)³H nuclear reaction and the initial coordination of the OH impurity. Stepwise annealing of F centers after electron and ion irradiation is governed by diffusion-controlled kinetics; the activation energies and pre-exponential factors define the E_a "-" Xcorrelation characteristic of disorder-controlled diffusion. The kinetic theory of annealing of isolated F and aggregated Fₙ centers, consistent with experimental data, quantitatively describes the cascade of diffusion–reaction stages and enables prediction of the temperature ranges of LiF recovery after different types of irradiation. Description of the main results. 1. For the first time, a comparative of studies of radiation-induced defects in LiF under three fundamentally different types of irradiation —swift heavy ions, neutrons, and intense pulsed electron beams—has been carried out. It is shown how variations in energy deposition mechanisms (Se, Sn) and radiation spectra define different scenarios of primary and aggregated defect formation. 2. Based on IR spectroscopy of neutron-irradiated LiF:OH crystals, the role of hydroxyl and hydrogen centers (U, U₁, U₂, U₃, OH⁻…Fᵢ complexes) in radiation defect formation has been revealed. It is shown that thermal neutrons make the dominant contribution to the generation of such defects via the ⁶Li(n,α)³H reaction, causing dose-dependent shifts of OH absorption bands that reflect changes in the local structure. 3. For the first time, activation energies of thermal annealing processes of F centers in LiF crystals were experimentally obtained and analyzed for different regimes of electron and ion irradiation. It is shown that the Ea values and pre-exponential factors form a consistent correlation, interpreted as a manifestation of disorder-controlled diffusion. 4. A stepwise annealing model of F and Fn centers in LiF has been introduced and implemented, allowing determination of activation energies and pre-exponential factors for various channels of defect migration and coagulation based on optical absorption and recovery kinetics, and enabling a quantitative description of the cascade of diffusion–reaction stages. 5.Based on Gaussian decomposition of broad absorption bands in the 1.7–4.2 eV region, the transformation sequence F → F₂ → F₃/F₃⁺ → F₄ → lithium colloidal clusters was traced for the first time within a single experimental framework for irradiation with light (¹⁴N, ¹⁶O) and heavy (⁸⁴Kr, ²³⁸U) ions. It was shown that F₃⁺ and F₄ centers represent pre-colloidal states characteristic of regions with maximum track-induced disorder density. 6.Practically significant annealing temperature intervals were determined for different defect types and irradiation regimes, providing a basis for controlled thermal treatment of LiF crystals, recovery of their optical properties, and targeted regulation of color center concentrations in dosimetric and optical applications. Description of the novelty and importance of the results obtained. The obtained results define practical temperature windows for LiF recovery after irradiation, clarify how electronic stopping governs the competition between defect aggregation and recombination, and establish quantitative kinetic parameters (activation energy Ea and pre-exponential factor X) of defect annealing processes. These parameters can serve as a basis for post-irradiation thermal treatment and for controlled tuning of color center concentrations in LiF-based optical and dosimetric applications. Description of the applicant's contribution to the preparation of each publication. The main results of the dissertation research are published in 11 scientific works corresponding to the dissertation topic, including 3 articles in peer-reviewed journals indexed in Scopus and Web of Science and 8 conference papers and abstracts presented at international scientific conferences. List of Publications: Influence of Neutron Irradiation Conditions on Maximal Frequency of IR Absorption Spectra of LiF:OH Single Crystal // Physica Status Solidi (A), 2023, Vol. 220(10) (Q3, percentile 51%, IF 1.9). Thermal Annealing of Radiation Damages Produced by Swift ¹⁴N and ¹⁶O Ions in LiF Crystals // Materials Research Express, 2024, Vol. 11(7) (Q3, percentile 51%, IF 2.1). Thermal Stability of Color Centers in Lithium Fluoride Crystals Irradiated with Electrons and N, O, Kr, U Ions // Materials, 2025, Vol. 18(19), 4441 (Q1, percentile 79%, IF 3.2). Applicant’s Contribution: A thorough review of the existing literature on the research topic was conducted; experiments were performed and the obtained data were processed; and the original manuscript drafts were prepared in compliance with scientific publication requirements. The applicant made a direct and substantial contribution at all key stages of the research.

Dissertation

List of Scientific Works

Consultant's Review

Foreign Consultant's Review

Conclusion of the Research Ethics Committee

Official Reviewer's Review

Official Reviewer's Review