At L.N. Gumilyov Eurasian National University, Ibadullayev Dastan Alisheruly will defend his dissertation for the degree of Doctor of Philosophy (PhD) on the topic «Investigation of 242Pu + 48Ca and 238U + 48Ca reactions at the JINR Superheavy Element Factory» under the educational program «8D05305 - Nuclear Physics».
The dissertation was carried out at the «Nuclear physics, new materials and technologies education department» of L.N. Gumilyov Eurasian National University.
The language of defense is russian
Official reviewers:
- Timur Zholdybaev Kadirzhanovich – Candidate of Physical and Mathematical Sciences, Associate Professor, Head of the Nuclear Physics Department at the Institute of Nuclear Physics of the Ministry of Energy of the Republic of Kazakhstan (Almaty, Kazakhstan).
- Arkadiy Taranenko Vladimirovich – PhD, Associate Professor, Leading Researcher at the Department of Experimental Methods of Nuclear Physics (No. 11), Institute of Nuclear Physics and Technologies, MEPhI (Moscow, Russian Federation).
Temporary members of the Dissertation council:
- Avazbek Nasirov Karimovich – Doctor of Physical and Mathematical Sciences, Leading Researcher at the Theoretical Nuclear Physics Department of the N.N. Bogolyubov Laboratory of Theoretical Physics, JINR (Dubna, Russian Federation).
- Saule Zhaugasheva Amanbaevna – Candidate of Physical and Mathematical Sciences, Associate Professor at the Department of Theoretical and Nuclear Physics, Al-Farabi Kazakh National University (Almaty, Kazakhstan).
- Orazaly Kalikulov Abilkhasimovich – PhD, Head of the Cosmic Ray Physics Laboratory at the Institute of Nuclear Physics of the Ministry of Energy of the Republic of Kazakhstan (Almaty, Kazakhstan).
Scientific advisors:
- Sholpan Giniyatovna Giniyatova– Candidate of Physical and Mathematical Sciences, Associate Professor at the Department of Nuclear Physics, New Materials, and Technologies, L.N. Gumilyov Eurasian National University (Astana, Kazakhstan). - Kairat Atazhanovich Kuterbekov– Doctor of Physical and Mathematical Sciences, Professor at the Department of Nuclear Physics, New Materials, and Technologies, L.N. Gumilyov Eurasian National University (Astana, Kazakhstan).
- Vladimir Utenkov Klimentyevich – Doctor of Physical and Mathematical Sciences, Head of Sector No. 1, G.N. Flerov Laboratory of Nuclear Reactions, JINR (Dubna, Russian Federation).
The defense will take place on September 04, 2025, at 12:00 PM in the Dissertation Council for the training direction «8D053 – Physical and chemical sciences» under the educational program «8D05305 – Nuclear physics» of L.N. Gumilyov Eurasian National University. The online broadcast will be made on the Microsoft Teams platform.
Link: https://clck.ru/3Mn9cv
Address: Astana, Satpayev St. 2, room 302.
Abstract (English): ANNOTATION of the dissertation work of Ibadullayev Dastan Alisheruly on the topic of " Investigation of 242Pu + 48Ca and 238U + 48Ca reactions at the JINR Superheavy Element Factory ", submitted for the degree of Doctor of Philosophy (PhD) in the educational program: "8D05305 - Nuclear Physics" The dissertation is dedicated to the experimental study of reactions involving 48Ca ions with 244Pu and 238U targets at the new Superheavy Element Factory (SHE Factory) at the Flerov Laboratory of Nuclear Reactions (FLNR), Joint Institute for Nuclear Research (JINR). Relevance of the research topic. The most important data on nuclear properties can be obtained by studying nuclei in extreme states. Examples of such nuclei include those far from the β-stability line with a large excess of neutrons or protons, highly deformed nuclei, nuclei with large angular momentum, etc. The study of the radioactive properties of superheavy nuclei with atomic numbers Z > 100, which contain the largest number of protons and neutrons, is of significant interest. In these nuclei, Coulomb repulsion forces are so strong that only shell effects prevent their immediate fission. Since the 1940s, when the first transuranium elements—neptunium and plutonium—were discovered, the synthesis of new elements has become one of the most relevant areas of research in nuclear physics. These studies deepen our understanding of the strong interaction that binds nucleons within the nucleus and contribute to the development of theoretical nuclear models. They also help reveal patterns in nuclear properties depending on nucleon composition and predict the properties of yet undiscovered nuclei. Due to their relatively short lifetimes, these nuclei do not exist in nature and can only be artificially synthesized—in fusion reactions involving stable, relatively light nuclei accelerated to approximately 0.1 times the speed of light, with radioactive heavy nuclei that can be obtained in reactors. The study of complete fusion reactions of these nuclei allows for a deeper understanding of the fusion process mechanisms—capture of the two nuclei, formation of a nearly spherical compound nucleus, and its subsequent survival through neutron evaporation. According to the shell model, the most stable nuclei have "magic" numbers of protons and neutrons: 2, 8, 20, 28, 50, 82, as well as 126, 152, and 162 for neutrons. Various theoretical models predict magic shells for protons at Z=114−126 and for neutrons at N=184. For half a century, different nuclear models have predicted the existence of the so-called "island of stability" of superheavy nuclei—an area around 298Fl. According to these predictions, the lifetimes of such nuclei could be 1 000, 100 000, or even millions of years. Since 1998, for over 20 years, experiments on the synthesis of superheavy elements (SHE) were conducted at FLNR JINR using the gas-filled separator DGFRS-1 (Dubna Gas-Filled Recoil Separator) in complete fusion reactions of accelerated 48Ca ions with actinide targets. As a result of these experiments, new superheavy elements with Z=113–118 were discovered in reactions involving 48Ca ions with 242,244Pu, 243Am, 245,248Cm, 249Bk, and 249Cf. Throughout these experiments, it was established that the highest cross-sections were obtained for the synthesis of elements 114 and 115 (≈ 10 pb, where 1 pb = 10−36 cm²). For heavier nuclei, cross-sections decrease to 4.5 pb (Z=116), 2.5 pb (Z=117), and 0.5 pb (Z=118). According to calculations made within self-consistent microscopic models, the next magic proton shells are expected at Z = 120, 124, and 126. Further use of calcium ions as projectiles does not allow the synthesis of elements heavier than Og, as no sufficient amounts of target materials heavier than Cf are available. To conduct experiments on the synthesis of elements 119 and 120, it was proposed to use 50Ti and 54Cr ion beams. To facilitate further research on superheavy elements, the SHE Factory at FLNR JINR was commissioned, based on the new DC-280 heavy-ion accelerator. The designed beam intensity of 48Ca ions is 10 pµA (6×1013 ions per second), which is ten times higher than the intensity achieved at the U-400 accelerator used in previous experiments. The first experimental facility of the SHE Factory was the new gas-filled separator DGFRS-2 with a QDQQD magnetic element configuration (Q – quadrupole lens, D – dipole magnet). This dissertation presents the results of the second and third experiments conducted at DGFRS-2 using 238U and 242Pu targets. These experiments, along with the previous study of the 243Am + 48Ca reaction, allowed the verification and optimization of the SHE Factory's capabilities in synthesizing and studying new isotopes of known superheavy elements up to Og (Z=118), as well as initiating the synthesis of new elements with Z>118 at a higher sensitivity level. Due to the relatively long lifetimes of Fl isotopes produced in the 242Pu + 48Ca reaction, this reaction is planned to be used for further studies of the chemical properties of element Fl. Compared to experiments on the synthesis and decay property studies of SHE conducted using electromagnetic separators, studying the chemical properties of SHE poses challenges related to the longer transportation time of atoms from the target to the detectors and, consequently, lower efficiency in delivering decaying atoms to the detectors. For the preparation and execution of such experiments on Fl chemistry, it was necessary to determine more precisely the cross-section at the excitation function maximum of the 242Pu(48Ca, 3n) reaction, as well as the decay properties of 287Fl (T1/2≈0.5 s) and its daughter nuclei. Additionally, for future experiments on the synthesis of new elements, it was important to test the stability of the target under increased ion beam intensity. Target stability was verified in an experiment on the synthesis of 283Cn in the 238U + 48Ca reaction. The purpose of this dissertation is to conduct a more detailed study of the decay properties of Fl and Cn isotopes and their daughter nuclei formed in the complete fusion reactions 242Pu + 48Ca and 238U + 48Ca, as well as to determine the reaction cross-sections. Additionally, the study aims to assess the efficiency of the Superheavy Element Factory at FLNR JINR and to evaluate the stability of the target under high-intensity 48Ca ion beams. Research objectives: To achieve the stated goal, the following objectives were defined: 1. To verify the efficiency of the new DGFRS-2 separator in the reactions 242Pu + 48Ca and 238U + 48Ca, as well as to test the digital and analog data acquisition systems. 2. In the 242Pu + 48Ca reaction in the 3-4n evaporation channels: a) Measurement of the excitation function; b) Measurement of the energies and decay times of the 286-287Fl isotopes and their daughter nuclei with high statistics; c) Calculation of the half-lives of 286-287Fl isotopes for studying the chemical properties of Fl; d) Attempt to detect two states of 287Fl leading to different decay modes of 279Ds; e) Attempt to detect the decay of 286Fl to the rotational level 282Cn; f) Attempt to detect the alpha line of 286Fl with an energy of 9.6 MeV. 3. In the 238U + 48Ca experiment, to study the target stability at high 48Ca ion beam intensity up to 6.5 pµA. 4. In the 238U + 48Ca reaction in the 3n evaporation channel: a) Measurement of the excitation function; b) Measurement of the energies and decay times of the 282Cn isotope and its daughter nuclei with high statistics. 5. For analog electronics, to develop a new program for searching for "active correlations" to register decay chains of superheavy elements under significantly reduced background conditions and to test it in the 242Pu + 48Ca and 238U + 48Ca experiments. Object of study. The research objects were the isotopes of superheavy nuclei 286Fl, 287Fl, 282Cn, and their daughter nuclei, as well as the 242Pu and 238U targets irradiated with high-intensity Ca ion beams. Subject of study. The research subject includes the decay properties of the superheavy elements flerovium (Fl) and copernicium (Cn), as well as their daughter nuclei formed in the fusion reactions of 48Ca with 242Pu and 238U, respectively. Particular attention is given to studying the excitation functions of reactions, energy spectra, time distributions, half-lives, as well as the search for possible new states of superheavy nuclei and the determination of the efficiency of the DGFRS-2 separator. Research methods. To accomplish these objectives, the following research methods were used: 1.Conducting nuclear physics experiments using a heavy ion accelerator and the gas-filled separator DGFRS-2 at the Superheavy Element Factory of the Flerov Laboratory of Nuclear Reactions (FLNR) JINR. 2.Applying the method of registering nuclear decay chains using digital and analog data acquisition systems at the DGFRS-2 separator. 3.Measuring reaction excitation functions by detecting reaction products. 4.Constructing energy spectra of alpha particles and decay time distributions of synthesized nuclei. 5.Applying the method of correlated events to identify the decay of superheavy nuclei. 6.Developing and testing specialized software for searching for active correlations in the analog registration system. Main provisions submitted for defense: 1. The properties of nuclei in the decay chains of 286-287Fl and 283Cn were measured with high statistics. In the 242Pu(48Ca,3-4n)286-287Fl experiment, 94 decay chains of 286-287Fl were registered, three times more than in all previous experiments combined. In the 238U(48Ca,3n)283Cn experiment, 16 decay chains of 283Cn were registered, bringing the total number to 85 when combined with the 242Pu(48Ca,3n)287Fl → 283Cn results. 2. Data were obtained for the first time indicating the possible decay of 286Fl to the first rotational level 2+ of the 282Cn isotope. 3. Data were obtained for the first time indicating the possible existence of two different alpha transitions in the decay chains starting from 287Fl, leading either to the alpha decay of 279Ds or its spontaneous fission. 4. The excitation functions of the reactions 242Pu(48Ca,3-4n)286-287Fl and 238U(48Ca,3n)283Cn were measured at 48Ca beam energies of 242.5 and 247.5 MeV for the 242Pu experiment, and 231.1 and 234.4 MeV for the 238U experiment. The cross-section for the 3n evaporation channel in the 242Pu experiment was found to be three times higher than previously measured. 5. High target stability was demonstrated – 97% of the target material was retained on the substrate in the 238U(48Ca,3n)283Cn experiment, where a 48Ca beam intensity of 6.5 pµA (4×1013 particles per second) was achieved for the first time. Scientific novelty. • 94 decay chains of 286,287Fl and 16 decay chains of 283Cn were registered, allowing for a more detailed determination of the decay properties of eight previously known isotopes from 286,287Fl to 267Rf. • The excitation functions of the 48Ca + 242Pu and 48Ca + 238U reactions were measured, forming 286,287Fl and 283Cn in the excitation energy range of 290Fl – 37.1-44.8 MeV and 286Cn – 30.7-37.1 MeV, respectively. It was shown that the cross-section of the 242Pu(48Ca,3n)287Fl reaction is three times higher than previously measured. • For the first time, data indicating the possible decay of 286Fl to the first rotational state 2+ of the 282Cn isotope were obtained. • New data on the possible existence of two different states in the 287Fl and 283Cn isotopes were obtained, confirmed by two distinct alpha transitions in their decay chains. • For the first time, a high 48Ca beam intensity (6.5 pµA) was achieved at the Superheavy Element Factory, demonstrating target stability under high-intensity ion beam irradiation. Scientific and practical value of the work. 1. The results of this study contribute to a deeper understanding of the structure and properties of superheavy elements, particularly flerovium (Fl) and copernicium (Cn), as well as their daughter nuclei, which is of fundamental importance for nuclear physics of superheavy elements. 2. The measurement of excitation functions of reactions allows for a deeper understanding of the mechanisms of nucleus formation in complete fusion reactions. 3. The obtained data on half-lives, energy spectra, and possible new states of superheavy nuclei can be used for further modeling and prediction of the properties of isotopes of elements with higher atomic numbers. 4. The results of cross-section measurements of nuclear formation and radioactive properties can be utilized in experiments studying the chemical properties of elements 114 and 112, as well as in nuclear structure research. 5. The verification and demonstration of the efficiency of the DGFRS-2 separator and the stability of targets under high-intensity beam conditions have practical significance for improving technical capabilities and increasing the efficiency of experiments at the Superheavy Element Factory of JINR. 6. A program for online searching of correlated events of the type ER-α for the analog electronics of the DGFRS-2 separator was developed. Upon detecting such a correlation, the program disables the DC-280 accelerator beam for 100 seconds, ensuring the registration of superheavy isotope decay chains at an extremely low background level. Personal contribution of the author. The results presented in the dissertation were obtained by the author in collaboration with colleagues from the Flerov Laboratory of Nuclear Reactions at JINR (Dubna, Russian Federation) and are reflected in joint publications. The author's personal contribution includes participation in setting research objectives and planning experiments, conducting a comprehensive set of experimental studies, processing experimental results, preparing scientific publications, and presenting findings at seminars and conferences. Reliability of work results The validity and reliability of the obtained results are confirmed by the strong agreement of the experimental data with previous studies on the synthesis of elements 114 and 112 conducted using the DGFRS-1, GARIS-II, BGS, and SHIP separators. The measured excitation functions of the studied reactions also show good agreement with theoretical calculations. Approbation of work. The materials of the dissertation work were presented and reported at the following republican and international conferences: – LXXII International conference "Nucleus-2022: Fundamental problems and applications", Lomonosov Moscow State University, Moscow, Russia, 2022. Participation with an oral presentation. – IV International Scientific Forum “Nuclear science and technologies”, Almaty, Kazakhstan, 2022. Participation with an oral presentation. – The V International Scientific Forum “Nuclear Science and Technologies”, Almaty, Kazakhstan, 2024. Participation with an oral presentation. Publications. A total of 14 papers have been published on the dissertation topic, of which 11 articles have been published in journals with a non-zero impact factor indexed in the Scopus database and 3 articles in the proceedings of the international conferences. The structure and scope of the thesis. The dissertation consists of an introduction, six chapters, a conclusion, and a list of references comprising 119 sources. The total length of the work is 80 pages, including 7 tables and 26 figures. The introduction highlights the relevance of the research, provides an overview and formulation of the problem under study, defines the objectives, outlines the novelty of the obtained results, and justifies their scientific and practical significance. The main findings submitted for defense, the author's personal contribution, the approbation, and a brief summary of the dissertation are also presented. The first chapter of the dissertation is dedicated to reviewing experimental studies on the synthesis of flerovium (Fl) and copernicium (Cn) isotopes, as well as the history of the discovery of these elements. The second chapter presents the main characteristics of the experimental setup for synthesizing and studying the properties of superheavy nuclei. The design and systems of the DGFRS-2 separator, along with the data acquisition and processing system, are described in detail. The third chapter includes the results of experiments on the reactions 242Pu + 48Ca and 238U + 48Ca. It lists the parameters of the targets and 48Ca ion beams and provides results on the stability of the targets in these experiments. The fourth chapter presents an analysis of the energy spectra and decay time distributions of decay chains of the odd-even isotopes 287Fl and 283Cn. The dependence of the decay properties of isotopes 287Fl, 283Cn, and 279Ds on the excitation level scheme is demonstrated. The spontaneous fission process of isotope 283Cn is discussed. The fifth chapter is devoted to analyzing the energy spectra and decay time distributions of the even-even isotope 286Fl. The observation of decay to the first rotational state 2+ of isotope 282Cn is examined. The sixth chapter presents the results of excitation function measurements. A comparison of the experimental data on the cross-sections of the formation of isotopes 286Fl, 287Fl, and 283Cn with theoretical calculations is conducted. The conclusion summarizes the key findings derived from the performed experiments and their analysis.
Conclusion of the Research Ethics Committee
Defense of the dissertation: https://www.youtube.com/watch?v=s_8_VdIFYJw&ab_channel=ENUOFFICIAL
