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Capture Cross Sections for the Astrophysical P Process CAPTURE CROSS SECTIONS FOR THE ASTROPHYSICAL P PROCESS By Stephen J. Quinn A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of Physics - Doctor of Philosophy 2015 ABSTRACT CAPTURE CROSS SECTIONS FOR THE ASTROPHYSICAL P PROCESS By Stephen J. Quinn This dissertation includes the design and development of the Summing NaI (SuN) 4π γ-ray detector at the National Superconducting Cyclotron Laboratory to measure proton and α radiative capture reactions relevant in the astrophysical p process. Discussions of p-process nucleosynthesis, the relevant nuclear reaction theory, experimental details, and analysis procedures are included. All reaction measurements were performed at the Nuclear Science Laboratory of the University of Notre Dame. The commissioning experiments in both regular and inverse kinematics were done using known resonances in the 27Al(p,γ)28Si and 58Ni(p,γ)59Cu reactions, and the results agree well with previous literature values. The success of these proof-of-principle measurements marks the first time that the γ-summing technique has been implemented in inverse kinematics. Furthermore, in an effort to inves- tigate the synthesis of the light p-process nuclei, the 74Ge(p,γ)75As, 74Ge(α,γ)78Se, and 90,92Zr(α,γ)94,96Mo reactions were measured and compared to theoretical calculations using the nuclear statistical model. It was found that the new 74Ge(p,γ)75As measurements cause an enhancement in the overproduction of 74Se in p-process models, and that the updated 90Zr(α,γ)94Mo reaction rate seems to confirms the p-process branching point at 94Mo. Fi- nally, the 58Ni(α,γ)62Zn reaction was measured for its role in nucleosynthesis in type Ia supernovae. The measurements here lower the reaction rate used in astrophysical models, which leads to a 5% reduction in the calculated abundances of several isotopes. All of the measurements in this dissertation greatly reduce the uncertainty in the reaction cross section. When the Yankees beat the Red Sox all is right in the world. iii ACKNOWLEDGMENTS This is my favorite section of all because it gives me an opportunity to thank everyone who contributed to this thesis. First of all, special thanks must go to my advisor, Artemis Spyrou, for her guidance, kindness, and support during my time in graduate school. I absolutely could not have worked with a better professor, a more brilliant scientist, or on a more interesting project, and I am extremely grateful for the many opportunities that she has given me that are far too numerous to list here. Thank you, Artemis! It has been a pleasure working alongside all of the SuN group members, including Jorge, Farheen, Alex, Debra, Alicia, and the many brilliant undergraduate students. In particular, I would like to single out Anna Simon for her countless contributions to this thesis. She has been an incredible source of information when I had little experience, as well as serving as a wonderful mentor and friend. Overall, it has been a pleasure to take part in the creation of the SuN group and it is wonderful to see the SuN detector shine as brightly as it is today. The experiments comprising this thesis would not have been possible without the hard work of many scientists and they all deserve recognition. It is a large fear of mine that I will forget someone! At the NSCL, thanks to John Yurkon for his vast knowledge and patience in teaching me the art of target making, and thanks to Renan Fontus for designing the beam pipe for the SuN detector. I would also like to thank Sean Liddick, Jeromy, Chris, Nicki, and Scott for their time and assistance with DDAS; they are true superstars. At Notre Dame, thanks to the many graduate students who helped operate the accelerator, the technicians who assisted in the setup, and everyone who makes Notre Dame such a welcoming place for external experimenters. A special thanks is in order for Man¨oel Couder, Dan Robertson, Ed Stech, Wanpeng Tan, and Antonios Kontos for going above and beyond the call of duty, and iv whose help was critical for a successful experimental campaign. At Hope College, I express my gratitude to Paul DeYoung, Graham Peaslee, and Dave Daugherty for their time and expertise with target thickness measurements. Additionally, I would like to thank Thomas Rauscher and Eduardo Bravo for their collaboration and contribution to this work. I greatly appreciate the assistance of Professors Ed Brown, Jim Linnemann, Filomena Nunes, and Michael Thoennessen through their knowledge, questions, and, most of all, gen- erosity in agreeing to give up their valuable time to serve on my guidance committee. I also would like to acknowledge the National Science Foundation, the Joint Institute for Nuclear Astrophysics, and the Michigan State University Graduate School for financial support. Truthfully, my time in graduate school has been wonderful and I am very fortunate to have many friends that have made it so enjoyable. I will miss my officemates, roommates, teammates, and everyone from the daily lunches, Happy Hours, tailgates, and parties that have kept me laughing since I arrived at MSU. A “merci beaucoup” to Yari and Bazzy for their support and motivation during the more difficult first few years of trying to balance classes, exams, teaching, and research. Finally, and most importantly, I would like to thank my family. I have been incredibly blessed with unquestionably the greatest family of all time, and I would like to thank them for putting up with me. Thanks Mom and Dad for being such awesome role models, and thanks Lassu and Mollister for being my two favorite people in the world. As Yogi Berra would say, “I just want to thank everyone for making this day necessary.” v TABLE OF CONTENTS LIST OF TABLES .................................... ix LIST OF FIGURES ................................... xi Chapter 1 Introduction ................................ 1 1.1 Elements...................................... 2 1.2 Abundances .................................... 4 1.3 Nucleosynthesis .................................. 6 1.3.1 Big Bang Nucleosynthesis . 7 1.3.2 Quiescent Stellar Burning . 7 1.3.3 Supernovae ................................ 8 1.3.4 Nuclear Statistical Equilibrium . 10 1.3.5 Nucleosynthesis of the Heavy Elements . 11 1.4 ProductionofthepNuclei............................ 14 1.4.1 νpprocess................................. 14 1.4.2 rpprocess ................................. 15 1.4.3 pprocess ................................. 15 1.4.4 Uncertainties . 21 1.5 LookingAhead .................................. 25 Chapter 2 Nuclear and Astrophysical Quantities ................ 27 2.1 CrossSection ................................... 27 2.2 StellarReactionRate............................... 29 2.3 AstrophysicalSfactor .............................. 31 2.4 GamowWindow ................................. 33 2.5 Qvalue ...................................... 35 Chapter 3 Theoretical Considerations ....................... 37 3.1 ResonantReactions................................ 37 3.1.1 InStars .................................. 38 3.1.2 IntheLaboratory............................. 39 3.2 NuclearStatisticalModel. .. .. 44 3.3 ReciprocityTheorem ............................... 49 Chapter 4 Experimental Techniques ........................ 53 4.1 MeasuringtheCrossSection . 53 4.1.1 Activation . 54 vi 4.1.2 γ-InducedReactions ........................... 55 4.1.3 In-BeamMethods............................. 55 4.1.3.1 Angular Distributions Method . 57 4.1.3.2 γ-Summing Technique . 58 4.1.4 Techniques in Inverse Kinematics . 60 4.2 TargetProductionandCharacterization . ... 62 4.2.1 Evaporation................................ 62 4.2.2 ThicknessMeasurements . 65 4.2.2.1 Experimental Details . 67 4.2.2.2 Calibrations . 69 4.2.2.3 RBS Analysis . 70 4.2.2.4 ERD Analysis . 72 4.3 ExperimentalSetup................................ 76 4.3.1 BeamProduction............................. 77 4.3.2 Acceleration . 79 4.3.3 Ion Selection . 80 4.3.4 ExperimentalEndstation. 82 Chapter 5 The SuN Detector ............................ 84 5.1 Design....................................... 84 5.2 Detection ..................................... 86 5.3 DataAcquisition ................................. 89 5.3.1 PMT signals . 90 5.3.2 NSCLDDAS ............................... 91 5.3.3 ExternalTriggering............................ 96 5.4 RadiationSourceTesting............................. 98 5.5 GEANT4 Simulation . 101 Chapter 6 Analysis ................................... 107 6.1 Gain Matching and Calibration . 107 6.2 Thresholds..................................... 114 6.3 SumPeakAnalysis ................................ 117 6.3.1 Isomericstates .............................. 119 6.3.2 Dopplerreconstruction . 121 6.4 γ-SummingEfficiency............................... 123 Chapter 7 27Al(p,γ)28Si ................................ 128 Chapter 8 74Ge(p,γ)75As ............................... 135 Chapter 9 58Ni(α,γ)62Zn ............................... 147 vii Chapter 10 Additional (α,γ) Measurements .................... 158 10.1 90Zr(α,γ)94MoResults .............................. 161 10.2 92Zr(α,γ)96MoResults .............................. 163 10.3 74Ge(α,γ)78SeResults .............................. 165 10.4Discussion..................................... 166 10.4.1 90Zr(α,γ)94Mo .............................. 168 10.4.2 92Zr(α,γ)96Mo .............................. 170 10.4.3 74Ge(α,γ)78Se............................... 172 10.5Conclusions .................................... 173 Chapter 11 Measurements
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