Luận án tiến sĩ: Nghiên cứu parametrization cross-section photofission 238U và mô phỏng GEANT4 cho thiết kế IGISOL - Lê Tuấn Anh

MINISTRY OF EDUCATION AND VIETNAM ACADEMY OF TRAINING SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY ----------------------------- LÊ TUẤN ANH STUDY ON PARAMETRIZATION OF PHOTOFISSION CROSS-SECTION OF 238U AND OPTIMIZATION SIMULATION USING GEANT4 FOR DESIGN OF THE IGISOL FACILITY AT ELI-NP PROJECT PhD THESIS IN ATOMIC AND NUCLEAR PHYSICS Hanoi – 2021 luan an MINISTRY OF EDUCATION AND VIETNAM ACADEMY OF TRAINING SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY ----------------------------- LÊ TUẤN ANH STUDY ON PARAMETRIZATION OF PHOTOFISSION CROSS-SECTION OF 238U AND OPTIMIZATION SIMULATION USING GEANT4 FOR DESIGN OF THE IGISOL FACILITY AT ELI-NP PROJECT Major: Atomic and Nuclear physics Code: 9440106 PhD THESIS IN ATOMIC AND NUCLEAR PHYSICS SUPERVISORS: 1. Dr, PHAN VIET CUONG 2. BALABANSKI Hanoi – 2021 luan an LỜI CAM ĐOAN Tôi xin cam đoan đây là công trình nghiên cứu mà phần chủ yếu do tôi trực tiếp thực hiện, phần còn lại có sự tham gia hỗ trợ của các đồng nghiệp tại nhóm RA4, thuộc dự án ELI-NP tại Romania. Các kết quả nghiên cứu là trung thực và chưa từng được sử dụng trong bất kỳ công trình nào khác.

Luận án cũng sử dụng một số thông tin, số liệu thực nghiệm từ nhiều nguồn số liệu khác nhau và chúng đều được trích dẫn rõ nguồn gốc. Lê Tuấn Anh i luan an Acknowledgements First and foremost, I gratefully express my best thanks to my supervisors, Dr. Phan Viet Cuong at Research and Development Center for Radiation Technology and Prof. Balabanski at ELI-NP Romania for giving me an opportunity to join ELI-NP project, to work in an international researching environments, and for their limitless support and help me when I was in need.

I would like to thank Dr. Paul Constantin in RA4-ELI-NP group, who was alway ready to spend his treasure time to help me through when I got problem not in this work but also daily life in Romania. And I am also grateful to Dr. Bo Mei, Dr.

Deepika Choudhury, and all the members of RA4, as well as ELI-NP, who help me a lot when I was at Romania. I would like to thank the Board of Directors and all members of Graduate University of Science and Technology for helping me during the process of doing my thesis. I also would like to thank my colleagues and friends in the VNU University of Science, in Centre of Nuclear Physics, Institute of Physics, and in Vietnam Atomic Energy Institute for their friendships and encouragements. I would like to express my special thank to all my colleagues at Research and Development Center for always giving me convenience to finish my work.

I would like to thank to all my colleagues at Institute for Nuclear Science and Technology for their unlimited supports. I would like to give my deep gratitude to my parents, my grandma, brother and other members in my big family for their encouragements at all time. And aftermost, I would like to express the most special thank to my wife who has been always beside me, taken care of my two angel babies, to my beloved children who are the motivation of my working. ii luan an This work was supported by Extreme Light Infrastructure Nuclear Physics (ELI- NP) Phase II, a project co-financed by the Romanian Government and the European Union through the European Regional Development Fund -the Competitiveness Oper- ational Program (1/07.

iii luan an Contents Acknowledgements. vii List of tables. viii List of figures. xi Abstract 1 Introduction 2 1 OVERVIEW 4 1.1 The Extreme Light Infrastructure Nuclear Physics facility .1 Gamma Beam System .2 Methods for production of RIB .1 The ISOL technique .2 The in-flight method .3 Ion guide isotope separation online technique .4 Method for production of RIB at ELI-NP .3 The future ELI-NP IGISOL .4 Introduction of Geant4 toolkit .1 Energy loss of ions .2 Physics processes for e− and e+.

21 iv luan an 1.3 Processes induced by gamma beam .4 Mandatory method and classes of a Geant4-based application .6 Purposes of the Thesis. 28 2 STUDY ON PARAMETRIZATION OF PHOTOFISSION CROSS- SECTION OF 238 U 30 2.1 Empirical parametrization for total cross-section, mass yield and isobaric charge distribution of 238 U photofission .1 Parametrization for total cross-section .2 Parametrization for photofission mass yield .3 Parametrization for isobaric charge distributions .2 Validation of the empirical parametrization .3 Prediction of neutron-rich nuclei yield. 47 3 OPTIMIZING THE DESIGN OF CRYOGENIC STOPPING CELL FOR IGISOL FACILITY AT ELI-NP 48 3.1 The structure of the implemented Geant4-based code .2 Implementation of photofission process into Geant4 .3 Ionic effective charge .4 Target geometry optimization .1 The beam spot size .3 Optimize the thinkness of foil targets .4 The thinkness of backing layers .5 The dependence of the photofission fragment release rate on foil transverse size A, the foil tilting angle a, and the inter-foil distance 60 3.6 Remarks for target geometry .5 The stopping length of photofission fragments in Helium gas. Guidance for choosing the width of CSC .1 The characteristics of release photofission fragments from back- ing layers .2 Ion stopping in the gas cell.

Choosing the width of CSC .6 The extraction of photofission fragments out of CSC. 71 Conclusion 73 Bibliography 75 Publications 81 Appendix 82 vi luan an Abbreviations ELI Extreme Light Infrastructure ELI-NP Extreme Light Infrastructure-Nuclear Physics RIB Radioactive Ion Beam ISOL Isotope Separation On-line IGISOL Ion Guide Isotope Separation On-line CSC Cryogenic Stopping Cell LIP Low energy Interaction Point HIP High energy Interaction Point DC Direct Current RF Radio Frequency HPLS High-Power Laser System PW Peta-Watt CBS Compton Backscattering GBS Gamma Beam System NRF Nuclear Resonance Fluorescence SM Symmetric Mode ASM Asymmetric Mode KE Kinetic energy PS Potential Energy Surface GDR Giant Dipole Resonance GSI The GSI Helmholtz Centre for Heavy Ion Research vii luan an List of Tables 2.1 The values of constants used in the empirical parametrization for 238 U photofission total cross-section.2 The values of constants used in the empirical parametrization for 238 U photofission mass yield.3 The values of constants used in the empirical parametrization for 238 U photofission isobaric charge.1 Results for target geometry .2 Gas density dependence of various parameters. 68 viii luan an List of Figures 1.1 Sketch of the ELI-NP machines and experimental areas .2 Geometry of the inverse Compton scattering of a laser photon on a relativistic electron.3 Energy-angle correlation for two gamma beams .4 The energy spectra of two gamma beams .5 Scheme of ISOL and In-Flight techniques [13, 14].6 Boiling and melting point of elements .7 The principle of IGISOL method [15] .8 Gamma source schemetic layout .9 Main components of the IGISOL beamline at ELI-NP .10 Layout of the IGISOL facility in the ELI-NP laboratory building .11 The Top Level Category Diagram of the Geant4 toolkit .12 The experimental photofission cross sections of 238 U .1 The 238 U photofission cross sections .2 Measured mass yields for 238 U photofission .3 The most probable charge Zprob .4 Comparison of the elemental yields Y (Z) = Y (A, Z) measured in two 238 U photofission experiments .5 Comparison between the mass yields measured in two experiments at GSI 41 ix luan an 2.6 Ratio of independent yields of 238 U photofission fragments Y(A,Z) .7 Ratio of independent yields of 238 U photofission fragments Y(A,Z) .8 Comparison of the isotopic yields .9 Cross sections of fragments produced by photofission calculated by the developed parametrization .1 The structure of the implemented Geant4 code.2 Kinetic energy versus atomic mass A of photofission fragments produced with our implementation.3 Kinetic energy versus emitted angle θ of photofission fragments produced with our implementation.4 Gamma beam transversal distribution .5 View of the yz-plane of the target geometry inside the gas cell .6 The dependence on the 238 U foil thickness t of the photofission rate .7 The dependence of PB on the backing foil thickness-B.8 Dependence of the fragment release rate Nr on the γ beam threshold energy.9 The (Z,A) distributions of fission fragment at the time created inside foils 63 3.10 The (Z,A) distribution of release fragments .11 Kinetic energy KE distribution of photofission fragments .12 Stopping length L of the released photofission fragments in He gas at 0.206 mg/cm3 density.13 Stopping length for various densities of the He gas .14 Vertices of ionization processes .15 Schematic drawing of the gas cell for the proposed IGISOL facility at ELI-NP. 71 xi luan an ABSTRACT The main focus of the thesis will be the optimization simulation using Geant4 for the design of a Cryogenic Stopping Cell (CSC) for a future IGISOL (Ion guild Iso- tope separation On-line) facility at ELI-NP (the Extreme Light Infrastructure: Nuc- lear Physics).

This proposed IGISOL facility will be dedicated to the study of exotic neutron-rich nuclei produced via photofission of U 238 target inside CSC. A new reli- able empirical parametrization for total cross-section, mass yield, and isobaric charge distribution was developed in this study. A Geant4-based code was implemented for the simulation of the photofission as well as the stopping of fission fragments inside the target foils and Helium gas. The simulation results have established the optimization of CSC’s parameters, as well as those of the target configuration inside.

1 luan an 2 INTRODUCTION The Extreme Light Infrastructure (ELI), which is marked on the European Strategy Forum on Research Infrastructures (ESFRI) Roadmap as one of the prior- ity research infrastructure projects for Europe, will be the world’s first international laser research infrastructure, pursuing unique science and research applications for international users. ELI has three main research center located in three different coun- tries: ELI-Beamlines facility in the Czech, the ELI-ALPS facility in Hungary, and ELI-Nuclear Physics (ELI-NP) in Romania [1, 2, 3, 4]. ELI-NP is expected to be the most advanced research facility in the world in the field of photonuclear physics, and a new interdisciplinary research field that brings together, for the first time, high-power lasers and nuclear physics. ELI-NP will offer a highly-polarized tunable mono-energetic γ beam in the range from 200 keV to 19.

This kind of beam will open new possibilities for high-resolution spectroscopy at higher nuclear excitation energies. This will lead to a better understanding of nuclear structure at higher excitation energies with many doorway states, their damping widths and chaotic behaviour, but also new fluctuating properties in the time and energy domain. Besides, the ELI-NP gamma beam is also suitable for the production of the radioactive ion beam (RIB) through photofission of Uranium. The advance in the understanding of nuclear structure far from stability using RIB is one of the top priorities defined by the nuclear physicist community in the world.

To support this idea, an IGISOL (Ion guide isotope separation on-line) facility will be constructed to extract the photofission fragments to form RIBs at ELI-NP. The heart of the IGISOL is a Cryogenic Stopping Cell (CSC), where the photofission process takes place. At ELI-NP, the development of a CSC is considered [2, 5]. For producing neutron-rich nuclei, designing nuclear physics experiments, as well as a target system in CSC, an accurate calculation for production cross-section of photofission fragments is crucial.

Therefore, it is necessary to develop a reliable luan an 3 tool for this job. This tool will be useful for estimating the yield of neutron-rich nuclei from photofission process, designing nuclear physics experiments and many other applications not only at ELI-NP but also at other photofission facilities worldwide. Moreover, It is important to do series of prerequisite calculations and simulations to lead to the conceptual design for the particular case of the CSC at ELI-NP IGISOL facility. The works in this thesis aim to fulfill two goals: i) the first one is to develop a reliable empirical parametrization for the calculation of photofission cross-section over a wide energy range below 30MeV.

ii) The second one is to implement a Geant4-based code and carry out a series of simulations to optimize the design of CSC at ELI-NP.