Luận án TS Vật lý: Cấu trúc phổ năng lượng 172Yb, 153Sm lò hạt nhân Đà Lạt

MINISTRY OF EDUCATION AND MINISTRY OF SCIENCE AND TRAINING 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 MINISTRY OF SCIENCE AND TRAINING 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: 9 44 01 06 Supervisors: 1. Nguyễn Xuân Hải 2. 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. Phạm Đình Khang for their guidance, support and encouragement during my research work.

They provided me not only the mo- tivation 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. Sukhovoj for his great guidance. He taught me how to become an honest and effective analyst.

I would like also to thank Assoc. Nguyễn Quang Hưng for his interest- ing conversations and his important suggestions for my research since 2016. 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 1 Theory 11 1.1 Compound nuclear reaction .1 Bohr-independence hypothesis .2 Nuclear level scheme .3 Nuclear level density .1 Fermi-gas model .1 Systematics of the Fermi-gas parameters .2 Constant temperature model .3 Gilbert-Cameron model .4 Generalized superfluid model .5 Microscopic-based models .4 Radiative strength function .5 Conclusion of chapter 1. 37 viii 2 Experiment and data analysis 39 2.1 Experimental facility and experimental method .1 Dalat Nuclear Research Reactor and the neutron beam-port No.2 The γ − γ coincidence method .1 Electronic setup and operation principle .4 Experimental setup and target information .5 Sources of “systematic” errors in γ − γ coincidence method 51 2.2 Two-step cascade spectra .3 Determination of gamma cascade intensity .4 Construction of nuclear level scheme .5 Determination of gamma cascade intensity distributions .6 Extraction of nuclear level density and radiative strength function .1 Basic ideas and underlying assumption .2 Determination of the functional form of the γ-rays transmission coefficient .3 Determination of nuclear level density .4 Determination of radiative strength function .3 Conclusion of chapter 2.

79 3 Results and discussion 81 3.1 Nuclear level scheme of 172 Yb and 153 Sm .2 Gamma cascade intensity distributions of 172 Yb .3 Nuclear level density and radiative strength function of 172 Yb .1 Comparison with other experimental data .2 Comparison with theoretical models .1 Nuclear level density .2 Radiative strength function .4 Conclusion of chapter 3. 114 Summary and outlook 115 List of publications 117 References 118 xi List of Figures 1.1 Nuclear level scheme of 60 28 Ni32 from 60 27 Co33 β − -decay with T1/2 =1925.8 days extracted from ENSDF library.1 The horizontal cross-section view of the DNRR.2 The detail structure of the neutron beam-port No.3 Two-step gamma cascades corresponding to the decays from a compound state.4 The γ − γ coincidence electronics.5 The TAC amplitude spectrum measured with 60 Co.6 The channel-energy relationship of the two detectors. Data of the detector B has an offset of 1000 on y-axis.7 The energy resolution of the two detectors in the energy range from 0.5 MeV to 8 MeV.8 The relative efficiencies of the two detectors.9 Experimental setup for measuring the γ − γ coincidences.10 Experimental system at the neutron beam-port No. 3 of the DNRR.11 An illustration for a three-step cascade.12 Illustration of the cross talk effect.

BS: Compton backscattered pho- ton; Ann: annihilation photon.13 Data analysis procedure.14 The discrepancy between two datasets. Dataset A is collected from detector A and dataset B is collected from detector B.15 Dataset B is corrected according to dataset A.16 Summation spectrum for 171 Yb(n,2γ) reaction. E1 +E2 is sum of en- ergies measured from two detectors. Energies (in keV) of the final levels in the cascades are pointed near the peaks of the full absorp- tion energy.

The notations SE and DE correspond to the single- and double-escape peaks, respectively.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.18 Explanation of the input variables used in the procedure of obtain- ing the TSC spectra given in Fig.19 Detail procedure for obtaining the TSC spectra. experimental TSC spectrum; b.

simulated TSC spectrum, c. un- resolved TSC spectrum with noise line, d. unresolved TSC spec- trum without noise line corresponding to the decays from the com- pound state to the ground state of 172 Yb.21 Procedure of extracting the NLD and RSF.22 Illustration of the shifting procedure for 172 Yb nucleus with Em = 3.875 MeV and Efmax = 1. The su- perposed energy range is between the two vertical arrows.

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 func- tion C0 exp(C1 E), whose parameters (C0 , C1 ) are obtained via the fitting to the corresponding datasets.23 The final dataset describes the functional form of γ-rays transmis- sion coefficient of 172 Yb nucleus in the energy region from 0. The line is the average values over an 250 keV energy interval.24 Comparison of the γ-rays transmission coefficients of 172 Yb nu- cleus obtained by different starting excitation-energy bins. His- togram with black color is the average of the γ-rays transmission coefficients obtained by all the starting excitation-energy bins from 2.

The corresponding uncertainties are given by upper and lower lines.1 TSC spectrum corresponding to the ground state of 172 Yb.2 TSC spectrum corresponding to the final level with the energy Ef = 78.8 keV of 172 Yb.3 Experimental level scheme of 172 Yb obtained within the gamma cascades from compound state to six distinct low-lying discrete levels with spin from 0h̄ to 2h̄. Explanation of the figure is given in text.4 TSC spectrum corresponding to the final levels with energies Ef = 0 and 7.8 keV of 153 Sm.5 TSC spectrum corresponding to the final level with the energy Ef = 35.8 keV of 153 Sm.6 NLS of 153 Sm obtained within this present work. Explanation of the figure is the same as in Fig.7 The gamma cascade intensity distributions of 172 Yb obtained within the present work.8 The extracted NLD and RSF of 172 Yb obtained within the present work.9 Comparison between the experimental gamma cascade intensity distributions and the calculated one obtained from the extracted NLD and RSF.10 Comparison between the NLD obtained within the present work and the other experimental data. Explanation for this figure is given in text.11 Comparison between the RSF obtained within the present work and the other experimental data.

Explanation of this figure is given in text.12 Comparison between the NLD obtained within the present work and a few common theoretical models.13 Comparison between RSF obtained within this work and few the- oretical models. See explanation of the figure in text. 113 xv List of Tables 2.1 Selected parameters of the electric modules.2 Parameters of the relative efficiency functions.1 Primary and secondary gamma-ray energies and absolute inten- sities obtained from the 171 Yb(nth , γ) reaction. The experimental values are compared with the ENSDF data.2 Primary and secondary gamma-ray energies and absolute inten- sities obtained from the 152 Sm(nth , γ) reaction.

The experimental values are compared with the ENSDF data.3 The gamma cascade intensity distribution of 172 Yb and the contri- bution of the resolved cascades. 99 xvii List of Abbreviations NLS Nuclear Level Scheme NLD Nuclear Level Density RSF Radiative Strength Function CTM Constant Temperature Model BSFG Back-Shifted Fermi Gas GSM Generalized Superfluid Model ENSDF Evaluated Nuclear Structure Data File HFBCS Hartree-Fork plus Bardeen-Cooper-Schrieffer DNRI Dalat Nuclear Research Institute DNRR Dalat Nuclear Research Reactor KMF Kadmenskij Markushev Furman model TSC Two- Step Cascade Luận án đủ ở file: Luận án full