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Collective Structure of Neutron-Rich Rare-Earth Nuclei And The World Ends Tomorrow and YOU MAY DIE! Well, no, probably not. but whatever you do, just keep reading! Cover page illustration by: Karin Rönmark The theory of everything Konstfack University College of Arts, Crafts and Design spring exibition 2009. http://www.karinronmark.se/ List of Papers This thesis is based on the following papers, which are referred to in the text by their Roman numerals. I P.-A. Söderström, et al. Spectroscopy of Neutron-Rich 168,170Dy: Yrast Band Evolution Close to the NpNn Valence Maximum. Physical Review C, 81:034310, 2010 II G. M. Tveten, P.-A. Söderström, et al. The neutron rich isotopes 167,168,169Ho studied in multi-nucleon transfer reactions. In manuscript. III P.-A. Söderström, et al. Interaction Position Resolution Simulations and In-beam Measurements of the AGATA HPGe detectors. Nuclear Instruments and Methods in Physics Research, A638:96, 2011. IV P.-A. Söderström, J. Nyberg, and R. Wolters. Digital pulse-shape discrimination of fast neutrons and γ rays. Nuclear Instruments and Methods in Physics Research, A594:79, 2008. V E. Ronchi, P.-A. Söderström, J. Nyberg, E. Andersson Sundén, S. Conroy, G. Ericsson, C. Hellesen, M. Gatu Johnson, M. Weiszflog. An artificial neural network based neutron-gamma discrimination and pile-up rejection framework for the BC-501 liquid scintillation detector. Nuclear Instruments and Methods in Physics Research, A610:534, 2009. Reprints were made with permission from the publishers. Major publications not included in this thesis. 1. K. Straub, et al. Decay of drip-line nuclei near 100Sn. Submitted to the GSI Scientific Report 2010. 2. A. Pipidis, et al. The Genesis of NEDA (NEutron Detector Array): Characterizing its Prototypes. Submitted to the LNL Annual Report 2010. 3. F. C. L. Crespi, et al. Measurement of 15 MeV γ rays with the AGATA cluster detectors. Submitted to the LNL Annual Report 2010. 4. M. ¸Senyigit,˘ et al. AGATA Demonstrator Test with a 252Cf Source: Neutron-Gamma Discrimination. Submitted to the LNL Annual Report 2010. 5. D. D. DiJulio, et al. Electromagnetic properties of vibrational bands in 170Er. Eur. Phys. J., A47:25, 2011. 6. S. Hirayama, et al. Production of protons, deuterons, and tritons from carbon bombarded by 175 MeV quasi mono-energetic neutrons Prog. Nucl. Sci. Tech., 1:69, 2011. 7. B. Cederwall, et al. New spin-aligned pairing phase in atomic nuclei inferred from the structure of 92Pd. Nature, 469:68, 2011. 8. T. S. Brock, et al. Observation of a new high-spin isomer in 94Pd. Phys. Rev. C, 82:061309, 2010. 9. A. Blazhev, et al. High-energy excited states in 98Cd. J. Phys. Conf. Ser., 205:012035, 2010. 10. R. Wadsworth, et al. The northwest frontier: Spectroscopy of N ∼ Z nuclei below mass 100. Acta Phys. Polon., B40:611, 2009. 11. P.-A. Söderström, et al. AGATA: Gamma-ray tracking in seg- mented HPGe detectors. In Proceedings of the 17th International Workshop on Vertex detectors, PoS (VERTEX 2008), page 040. Sissa, 2009. 12. U. Tippawan, et al. Studies of neutron-induced light-ion production with the MEDLEY facility. In O. Bersillon, et al. (editors), Proceedings of the International Conference on Nuclear Data for Science and Technology 2007, page 1347. EDP Sciences, 2008. 13. M. Hayashi, et al. Measurement of light-ion production at the new Uppsala neutron beam facility. In O. Bersillon, et al. (editors), Proceedings of the International Conference on Nuclear Data for Science and Technology 2007, page 1091. EDP Sciences, 2008. 14. M. Hayashi, et al. Neutron-induced proton production from carbon at 175 MeV. In T. Hazama and T. Fukahori (editors), Proceedings of the 2007 Symposium on Nuclear Data November 29-30, 2007, Ricotti, Tokai, Japan, volume JAEA-Conf 2008-008, page 62. Japan Atomic Energy Agency, Tokai-mura, Japan, 2008. 15. P.-A. Söderström. Detection of fast neutrons and digital pulse shape discrimination between neutrons and γ rays. In A. Covello, et al. (editors), Proceedings of the International School of Physics ’Enrico Fermi’, volume 169 Nuclear Structure far from Stability: new Physics and new Technology, page 551. SIF, Bologna and IOS Press, Amsterdam, 2008. 16. M. Hayashi, et al. Effect of nuclear interaction loss of protons in the response of CsI(Tl) scintillator. Engineering Sciences Reports, Kyushu University, 29:374, 2008. Contents 1 Background . ........................................ 1 1.1 Nuclear structure . .................................. 3 1.1.1 The nuclear landscape . ........................ 3 1.1.2 Spin and energy ................................ 5 1.2 Nuclear astrophysics . ............................. 6 1.2.1 S-process ..................................... 8 1.2.2 R-process . ................................. 8 1.2.3 P-process ..................................... 9 1.2.4 Rp-process . ................................. 9 1.2.5 νp-process . ................................. 9 1.3 Radioactive ion beam facilities ......................... 10 Part I: Physics 2 Theory of deformed nuclei . .............................. 13 2.1 Nuclear deformation . ............................. 13 2.1.1 Nilsson model ................................. 15 2.1.2 Particle plus triaxial rotor model ................... 17 2.1.3 Cranking model ................................ 19 2.1.4 Variable moment of inertia model . ............... 20 2.2 Nuclear deformations in the r process . ................ 21 2.3 Heavy-ion induced nuclear reactions .................... 24 3 PRISMA and CLARA experiment ......................... 27 3.1 LNL accelerator complex ............................. 29 3.2 PRISMA . ...................................... 29 3.2.1 MCP . ..................................... 30 3.2.2 Quadrupole and dipole magnets . ................... 32 3.2.3 MWPPAC . ................................. 33 3.2.4 Ionization chambers . ............................ 33 3.2.5 Mass determination . ............................ 35 3.3 CLARA .......................................... 38 3.4 Dysprosium isotopes . ............................. 40 3.5 Holmium isotopes .................................. 42 4 Evolution of collectivity . .............................. 45 4.1 Variable moment of inertia . ......................... 45 4.2 Deformations in odd-A nuclei ......................... 47 4.3 Rigidity and backbending . ......................... 49 Part II: Technology 5 The AGATA HPGe spectrometer .......................... 55 5.1 HPGe crystals . .................................. 56 5.2 Electronics . ...................................... 56 5.3 Pulse-shape analysis . ............................. 58 5.4 Tracking of γ rays .................................. 59 5.5 Data acquisition . .................................. 60 5.6 Position resolution .................................. 61 5.6.1 Reaction selection and simulations . ............... 63 5.6.2 Experiment . ................................. 65 5.7 Neutrons in AGATA . ............................. 67 6 Neutron detector NEDA . .............................. 71 6.1 SPIRAL2 . ...................................... 71 6.2 The Neutron Wall .................................. 72 6.3 The neutron detector array NEDA . .................... 72 6.3.1 The BC-501A and BC-537 liquid scintillators . ...... 73 6.3.2 Geometry . ................................. 74 6.3.3 Detection of scintillation light . ................... 74 6.3.4 Electronics . ................................. 75 6.4 Digital pulse shape analysis . ......................... 76 6.4.1 Charge comparison and zero cross-over .............. 76 6.4.2 Artificial neural networks . ........................ 80 6.4.3 Time resolution ................................ 80 Part III: Discussion 7 Outlook . ............................................ 87 7.1 AGATAatLNL.................................... 87 7.2 AGATAatGSI.................................... 89 7.3 AGATA at SPIRAL2 . ............................. 90 8 Concluding remarks . ................................... 93 9 Kollektiv kärnstruktur hos neutronrika sällsynta jordartsmetaller och nya instrument för gammaspektroskopi ...................... 95 10 Acknowledgements . ................................... 99 Bibliography ............................................ 103 Contribution to the papers .................................. 121 List of Acronyms ACTAR Active Targets ADC analog-to-digital converter AGATA Advanced Gamma Tracking Array AGAVA AGATA VME Adapter ALICE A Large Ion Collider Experiment ANN artificial neural network APD avalanche photodiode ATC AGATA triple-cluster BCS Bardeen, Cooper and Schrieffer BGO bismuth germanate B2FH Burbidge, Burbidge, Fowler and Hoyle CARMEN Cells Arrangement Relative to the Measurement of Neutrons CERN Organisation Européenne pour la Recherche Nucléaire CIME Cyclotron pour Ions de Moyenne Energie CLARA Clover Detector Array CNO carbon, nitrogen and oxygen CPU central processing unit DANTE Detector Array for multi-Nucleon Transfer Ejectiles DAQ data aquisition system DESCANT Deuterated Scintillator Array for Neutron Tagging DESIR Désintégration, Excitation et Stockage des Ions Radioactifs DSP digital signal processor ESS European Spallation Source FAIR Facility for Antiproton and Ion Research FAZIA Four pi A and Z Identification Array FET field-effect transistor FOM figure-of-merit FPGA field programmable gate array FRS fragment separator FWHM full width at half maximum GANIL Grand Accelerateur National d’Ions Lourds GASPARD Gamma Spectroscopy and Particle Detection GDR giant dipole resonance GRETA Gamma Ray Energy Tracking Array GSI Gesellschaft für Schwerionenforschung
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