MINISTRY OF EDUCATION AND TRAINING MINISTRY OF SCIENCE AND TECHNOLOGY Vietnam Atomic Energy Institute ——————— NGUYỄN NGỌC ANH EXPERIMENTAL STUDY ON LEVEL STRUCTURE OF EXCITED 172 Yb AND 153 Sm NUCLEI USING NEUTRON BEAM FROM DALAT NUCLEAR RESEARCH REACTOR DOCTORAL DISSERTATION IN PHYSICS HÀ NỘI - 2018 MINISTRY OF EDUCATION AND TRAINING MINISTRY OF SCIENCE AND TECHNOLOGY Vietnam Atomic Energy Institute ——————— NGUYỄN NGỌC ANH EXPERIMENTAL STUDY ON LEVEL STRUCTURE OF EXCITED 172 Yb AND 153 Sm NUCLEI USING NEUTRON BEAM FROM DALAT NUCLEAR RESEARCH REACTOR DOCTORAL DISSERTATION IN PHYSICS Subject: Atomic and Nuclear Physics Code: 44 01 06 Supervisors: Dr Nguyễn Xuân Hải Assoc Prof Dr Phạm Đình Khang HÀ NỘI - 2018 iii Declaration of Authorship I declare that this thesis titled, “Experimental study on level structure of excited 172 Yb and 153 Sm nuclei using neutron beam from Dalat nuclear research reactor” and the work presented in it are my own under the guidance of my supervisors, and have not been published by anyone else in any other works or articles A part of the results has been published in a peer-review journal and proceeding of 23rd International Seminar on Interaction of Neutrons with Nuclei held in Dubna, Russia written in co-authorship with my supervisors and collaborators The other part is in preliminary, and we expect to collect more experimental data before publishing v Acknowledgements I would like to express my deep gratitude to my supervisors, Dr Nguyễn Xuân Hải and Assoc Prof Dr Phạm Đình Khang for their guidance, support and encouragement during my research work They provided me not only the motivation and the important knowledge, but also the financial support for my life from 2013 to 2015 in Đà Lạt I would like to thank Dr A M Sukhovoj for his great guidance He taught me how to become an honest and effective analyst I would like also to thank Assoc Prof Dr Nguyễn Quang Hưng for his interesting conversations and his important suggestions for my research since 2016 I thank Assoc Prof Dr Nguyễn Mậu Chung, my graduate supervisor for the valuable fundamental knowledge that he gave me during my graduate studies I am grateful to Dalat Nuclear Research Institute and Nuclear Training Center, Vietnam Atomic Energy Institute for their significant supports to my research I also thank my colleagues at Center for Nuclear Physics and Nuclear Electronics, Training and Education Center, and Reactor Center for their kind help during my experiment I am thankful to Ms Nguyễn Thúy Hằng and Ms Nguyễn Thị Diệu Huyền for their kind assistant during my PhD study I also wish to thank Lâm’s photocopy shop, 27 Nguyễn Công Trứ, Đà Lạt, for financial support to print my dissertation Finally, I am deeply indebted to my family for their continuous encouragement and constant confidence in me vii Contents Declaration of Authorship iii Acknowledgements v List of Figures xi List of Tables xv List of Abbreviations xvii Introduction 1 Theory 11 1.1 Compound nuclear reaction 11 1.1.1 Bohr-independence hypothesis 11 1.1.2 Reciprocity theorem 13 1.2 Nuclear level scheme 13 1.3 Nuclear level density 16 1.3.1 Fermi-gas model 18 1.3.1.1 Systematics of the Fermi-gas parameters 21 1.3.1.2 Parity ratio 24 1.3.2 Constant temperature model 25 1.3.3 Gilbert-Cameron model 26 1.3.4 Generalized superfluid model 27 1.3.5 Microscopic-based models 29 1.4 Radiative strength function 33 1.5 Conclusion of chapter 37 viii Experiment and data analysis 39 2.1 39 Experimental facility and experimental method 2.1.1 2.2 2.3 Dalat Nuclear Research Reactor and the neutron beam-port No.3 39 2.1.2 The γ − γ coincidence method 41 2.1.3 γ − γ coincidence spectrometer 44 2.1.3.1 Electronic setup and operation principle 44 2.1.3.2 Main properties 46 2.1.4 Experimental setup and target information 49 2.1.5 Sources of “systematic” errors in γ − γ coincidence method 51 Data Analysis 56 2.2.1 Pre-analysis 57 2.2.2 Two-step cascade spectra 61 2.2.3 Determination of gamma cascade intensity 65 2.2.4 Construction of nuclear level scheme 66 2.2.5 Determination of gamma cascade intensity distributions 67 2.2.6 Extraction of nuclear level density and radiative strength function 69 2.2.6.1 Basic ideas and underlying assumption 69 2.2.6.2 Determination of the functional form of the γ-rays transmission coefficient 72 2.2.6.3 Determination of nuclear level density 76 2.2.6.4 Determination of radiative strength function 78 Conclusion of chapter 79 Results and discussion 3.1 Nuclear level scheme of 172 Yb and 153 Sm 81 81 3.1.1 172 Yb 81 3.1.2 153 Sm 92 3.2 Gamma cascade intensity distributions of 172 Yb 97 3.3 Nuclear level density and radiative strength function of 172 Yb 105 117 List of publications Nguyen Ngoc Anh, Nguyen Xuan Hai, Pham Dinh Khang, Nguyen Quang Hung, Ho Huu Thang, Updated level scheme of 172 Yb from 171 Yb(nth ,γ) reaction studied via gamma–gamma coincidence spectrometer, Nucl Phys A 964 (2017) 55–68 Nguyen Ngoc Anh, Nguyen Xuan Hai, Pham Dinh 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