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Nghiên cứu thực nghiệm cấu trúc phổ năng lượng kích thích của các hạt nhân 172Yb và 153Sm trên kênh nơtron của lò phản ứng hạt nhân Đà Lạt (Luận án tiến sĩ)Nghiên cứu thực nghiệm cấu trúc phổ năng lượng kích thích của các hạt nhân 172Yb và 153Sm trên kênh nơtron của lò phản ứng hạt nhân Đà Lạt (Luận án tiến sĩ)Nghiên cứu thực nghiệm cấu trúc phổ năng lượng kích thích của các hạt nhân 172Yb và 153Sm trên kênh nơtron của lò phản ứng hạt nhân Đà Lạt (Luận án tiến sĩ)Nghiên cứu thực nghiệm cấu trúc phổ năng lượng kích thích của các hạt nhân 172Yb và 153Sm trên kênh nơtron của lò phản ứng hạt nhân Đà Lạt (Luận án tiến sĩ)Nghiên cứu thực nghiệm cấu trúc phổ năng lượng kích thích của các hạt nhân 172Yb và 153Sm trên kênh nơtron của lò phản ứng hạt nhân Đà Lạt (Luận án tiến sĩ)Nghiên cứu thực nghiệm cấu trúc phổ năng lượng kích thích của các hạt nhân 172Yb và 153Sm trên kênh nơtron của lò phản ứng hạt nhân Đà Lạt (Luận án tiến sĩ)Nghiên cứu thực nghiệm cấu trúc phổ năng lượng kích thích của các hạt nhân 172Yb và 153Sm trên kênh nơtron của lò phản ứng hạt nhân Đà Lạt (Luận án tiến sĩ)
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 ix 3.4 3.3.1 Comparison with other experimental data 108 3.3.2 Comparison with theoretical models 111 3.3.2.1 Nuclear level density 111 3.3.2.2 Radiative strength function 111 Conclusion of chapter 114 Summary and outlook 115 List of publications 117 References 118 xi List of Figures 1.1 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14 2.15 2.16 β − -decay with from 60 Nuclear level scheme of 60 27 Co33 28 Ni32 T1/2 =1925.8 days extracted from ENSDF library The horizontal cross-section view of the DNRR The detail structure of the neutron beam-port No Two-step gamma cascades corresponding to the decays from a compound state The γ − γ coincidence electronics The TAC amplitude spectrum measured with 60 Co The channel-energy relationship of the two detectors Data of the detector B has an offset of 1000 on y-axis The energy resolution of the two detectors in the energy range from 0.5 MeV to MeV The relative efficiencies of the two detectors Experimental setup for measuring the γ − γ coincidences Experimental system at the neutron beam-port No of the DNRR An illustration for a three-step cascade Illustration of the cross talk effect BS: Compton backscattered photon; Ann: annihilation photon Data analysis procedure The discrepancy between two datasets Dataset A is collected from detector A and dataset B is collected from detector B Dataset B is corrected according to dataset A Summation spectrum for 171 Yb(n,2γ) reaction E1 +E2 is sum of energies measured from two detectors Energies (in keV) of the final levels in the cascades are pointed near the peaks of the full absorption energy The notations SE and DE correspond to the single- and double-escape peaks, respectively 15 40 40 42 45 47 48 48 49 50 51 52 54 57 58 59 60 xii 2.17 Summation spectrum for 152 Sm(n,2γ) reaction E1 + E2 is sum of energies measured from two detectors Energies (in keV) of the final levels in the cascades are pointed near the peaks of the full absorption energy 2.18 Explanation of the input variables used in the procedure of obtaining the TSC spectra given in Fig 2.19 2.19 Detail procedure for obtaining the TSC spectra 2.20 a experimental TSC spectrum; b simulated TSC spectrum, c unresolved TSC spectrum with noise line, d unresolved TSC spectrum without noise line corresponding to the decays from the compound state to the ground state of 172 Yb 2.21 Procedure of extracting the NLD and RSF 2.22 Illustration of the shifting procedure for 172 Yb nucleus with Em = 3.625 MeV, Em = 3.875 MeV and Efmax = 1.198 MeV The superposed energy range is between the two vertical arrows The curve (1) simulates the standard dataset (circle), while the curve (2) models the to-be-shifted dataset (triangle) The k factor is the ratio between the area under the curve (1) and that under the curve (2) The two curves have the form of an exponential function C0 exp(C1 E), whose parameters (C0 , C1 ) are obtained via the fitting to the corresponding datasets 2.23 The final dataset describes the functional form of γ-rays transmission coefficient of 172 Yb nucleus in the energy region from 0.5 to 7.5 MeV The line is the average values over an 250 keV energy interval 2.24 Comparison of the γ-rays transmission coefficients of 172 Yb nucleus obtained by different starting excitation-energy bins Histogram with black color is the average of the γ-rays transmission coefficients obtained by all the starting excitation-energy bins from 2.125 MeV to 5.375 MeV The corresponding uncertainties are given by upper and lower lines 3.1 3.2 TSC spectrum corresponding to the ground state of 172 Yb TSC spectrum corresponding to the final level with the energy Ef = 78.8 keV of 172 Yb 60 62 64 68 71 73 75 76 88 89 xiii 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 Experimental level scheme of 172 Yb obtained within the gamma cascades from compound state to six distinct low-lying discrete levels with spin from 0¯ h to 2¯h Explanation of the figure is given in text TSC spectrum corresponding to the final levels with energies Ef = and 7.8 keV of 153 Sm TSC spectrum corresponding to the final level with the energy Ef = 35.8 keV of 153 Sm NLS of 153 Sm obtained within this present work Explanation of the figure is the same as in Fig 3.3 The gamma cascade intensity distributions of 172 Yb obtained within the present work The extracted NLD and RSF of 172 Yb obtained within the present work Comparison between the experimental gamma cascade intensity distributions and the calculated one obtained from the extracted NLD and RSF Comparison between the NLD obtained within the present work and the other experimental data Explanation for this figure is given in text Comparison between the RSF obtained within the present work and the other experimental data Explanation of this figure is given in text Comparison between the NLD obtained within the present work and a few common theoretical models Comparison between RSF obtained within this work and few theoretical models See explanation of the figure in text 91 95 95 96 98 106 107 109 110 112 113 ... 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... 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... Dalat Nuclear Research Reactor Kadmenskij Markushev Furman model Two- Step Cascade Luận án đủ file: Luận án full