MEASURING THE NEON-20 RADIATIVE PROTON CAPTURE RATE AT DRAGON by Jonathan Karpesky c Copyright by Jonathan Karpesky, 2020 All Rights Reserved A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Physics). Golden, Colorado Date Signed: Jonathan Karpesky Signed: Dr. Uwe Greife Thesis Advisor Golden, Colorado Date Signed: Dr. Uwe Greife Professor and Head Department of Physics ii ABSTRACT Understanding the abundance levels of isotopes produced in oxygen-neon (ONe) novae within our galaxy requires accurate measurements of nuclear reaction rates within their associated reaction networks. During these cataclysmic events, the produced radioisotope 22Na is ejected into the interstellar medium and β-decays predominately to the first excited state in 22Ne leading to a characteristic 1.275 MeV γ-ray. To date, there has been no astronomical observation of this characteristic γ-ray that can be a potential probe into the physics occuring within novae. The production of 22Na in classical novae is limited by the 20Ne(p,γ)21Na nuclear reaction that is the focus of this experiment. Using the DRAGON recoil separator, new measurements of the 20Ne(p,γ)21Na reaction are performed at center-of- mass energies ranging from 265.5 - 519.6 keV that reach towards the astrophysically relevant energy ranges. The goal is to reduce experimental uncertainties in the 20Ne(p,γ)21Na reaction rate in order to be able to constrain the astrophysical S-factor. In addition, in the frame of this thesis a differential cross-section measurement was performed of 3He + p scattering to test the performance of the new Colorado School of Mines designed and built SONIK scattering chamber. iii TABLE OF CONTENTS ABSTRACT ......................................... iii LISTOFFIGURES .....................................vii LISTOFTABLES ..................................... xvii ACKNOWLEDGMENTS .................................xviii PART I SCIENTIFIC RESULT: DIRECT MEASUREMENT OF RADIATIVE PROTON CAPTURE ON NEON-20 WITHIN THE ASTROPHYSICALLY RELEVANT ENERGY RANGE FOR STELLAR NUCLEOSYNTHESIS IN NOVAE . 1 CHAPTER1 INTRODUCTION ...............................2 1.1 Stellarevolution................................ ....2 1.1.1 Starformation ................................3 1.1.2 Mainsequencestars ............................. 4 1.2 Stellarnucleosynthesis . ..... 10 1.3 NeNacycle .....................................12 1.4 Existingandfuturemeasurements. ...... 14 CHAPTER 2 RADIATIVE CAPTURE THEORY . 19 2.1 Cross-section ................................... 19 2.2 TheGamowwindow ................................ 21 2.3 StellarReactionRates . 23 2.4 Non-resonantreactionrates . .... 25 2.5 Resonantreactionrates. .... 28 iv 2.6 Subthresholdresonances . .... 29 2.7 Reactionyields .................................. 30 2.8 Kinematics .....................................35 2.9 SelectionRules .................................. 38 2.10 Reactionproductstates . .... 40 CHAPTER3 EXPERIMENTALMETHODS . 42 3.1 TRIUMFandBeamDelivery ........................... 42 3.2 DRAGON......................................45 3.2.1 DRAGONHead............................... 48 3.2.2 DRAGONEMS............................... 52 3.2.3 DRAGONTail ............................... 56 CHAPTER 4 ANALYSIS METHODS . 59 4.1 BeamNormalization ................................ 59 4.2 StoppingPower ................................... 61 4.3 BGOCalibration .................................. 62 4.3.1 FirstCalibration .............................. 66 4.3.2 SecondCalibration ............................. 67 4.3.3 FinalCalibration .............................. 68 4.4 BGOResolution................................... 69 4.5 Photopeakefficiency ............................... 75 4.6 TrueCoincidenceSumming . 78 4.7 RecoilDetectionEfficiency. .... 83 4.7.1 BGOArrayEfficiency ........................... 88 v 4.8 ParticleIdentification. ..... 90 CHAPTER5 RESULTS .................................. 94 5.1 YieldMeasurements ................................ 94 5.2 TotalS-factor ................................... 96 5.3 GroundStateTransitionS-factor . ...... 99 5.3.1 TransitionRatios ............................. 100 5.3.2 DC 0keVS-factor ........................... 102 → 5.3.3 BGOResolutionComparison . 103 5.4 Subthreshold and DC 332keVTransitionS-factors. 104 → PART II SCIENTIFIC RESULT: ELASTIC SCATTERING IN INVERSE KINEMATICS OF PROTONS FROM HELIUM-3 USING THE SONIK DETECTOR .................................. 110 CHAPTER6 SONIK ................................... 111 6.1 ElasticScatteringYield. 113 6.2 G-FactorSimulation .............................. 116 6.2.1 SimulationMethods ........................... 118 6.3 Results....................................... 124 CHAPTER 7 SUMMARY AND CONCLUSION . 137 REFERENCESCITED .................................. 140 vi LIST OF FIGURES Figure 1.1 The abundance level of elements within the solar system as a function of atomic mass number with abundances normalized to 1 million parts ofsilicon.Figurefrom..............................3 Figure 1.2 The reaction network pathways for the CNO-I, CNO-II, and CNO-III cycles.Figuretakenfrom . .8 Figure 1.3 The reaction network pathways for the hot CNO cycle. Figure taken from ......................................10 Figure 1.4 The binding energy per nucleon as a function of atomic mass number. The vertical black dashed line represents the fusion / fission boundary where isotopes on the left of the line will release energy during fusion while isotopes on the right will release energy during fission. The binding energy per nucleon peaks near 56Fe shown by the red star marker......................................13 Figure 1.5 The pathways for nucleosynthesis in the NeNa cycle, a hydrogen burning cycle that occurs beyond the hot CNO cycle. Figure taken from.......................................14 Figure 1.6 The astrophysical S-factor for the 20Ne(p,γ)21Na as determined by Mukhamedzhanov et al.. The black dotted line is the subthreshold S-factor, the black dashed line is the ground state transition, and the solid black line is the total S-factor calculated from the indirect 20Ne(3He,d)21Na transfer reaction in . The data points shown by open and closed squares are from representing the direct capture to the ground state and to the subthreshold state, respectively. Of note is the representation of the results from Rolfs et al. appears to be representing the energy scale incorrectly with the measured energies being lower when compared to the original publication. Figure taken from ...... 15 Figure 1.7 The astrophysical S-factor for the three transitions of interest with corresponding R-matrix analysis in the 20Ne(p,γ)21Na reaction as measured by Lyons et al. The data points in solid black triangles are from . The solid red lines represent the R-matrix fit on the measured S-factor data. Figure taken from and the results are mislabeled in that they are actually the differential S-factor that needs to be multiplied by 4π to obtain the actual S-factor result. In addition, several data points takenfrom aremisrepresented. 17 vii Figure 2.1 The two predominant probability factors that determine the relevant stellar energies for the 20Ne(p,γ)21Na reaction for a ONe surface temperature of 0.4 GK. The Gamow factor (e−2πη) represents the penetrability probability shown by the orange line. The Maxwell-Boltzmann factor (e−E/kT ) is shown by the blue line. The Gamow window is the product of the two factors and is characterized by the green line. The relative probability is the unscaled value from thegivenfactordistributions. 22 Figure 2.2 The Gamow window of the 20Ne(p,γ)21Na reaction for a ONe surface temperature of 0.4 GK determined by the product of the two main probability factors. The Gamow window can be approximated by a Gaussian distribution as shown by the red dashed line. A more precise approximation for this reaction can be made using an exponentially modified Gaussian distribution as shown by the green dashed line. The relative probability is the scaled Gamow window by the sum of the distributionoverthegivenenergyrange. 23 Figure 2.3 The astrophysical S-factor of the radiative proton capture reaction on 20Ne calculated by converting the cross-section values from Equation (2.32) into a S-factor. The solid circle data points are direct capture to the ground state measurements from . Figure taken from . 31 Figure 2.4 Excited state diagram for 21Na. The subthreshold state is shown here at 2.425 MeV and is within 7 keV of the reaction binding energy. Figuretakenfrom. .............................. 41 Figure 3.1 ISAC-I experimental hall schematic. Figure taken from........... 43 Figure 3.2 Schematic of the inner components of DRAGON’s windowless gas target.Figuretakenfrom. 44 Figure 3.3 SONIK scattering chamber 3-D model using SolidWorks R . Figure from . ........................................45 Figure 3.4 Schematic of the recirculation system used by DRAGON’s windowless gastarget.Figuretakenfrom.. 46 Figure 3.5 Upstream and downstream schematic of the pumping tubes and apertures for DRAGON’s windowless gas target. Figure taken from.. 47 Figure 3.6 Schematic of DRAGON’s BGO γ array consisting of 30 individual BGO detectors that surround the windowless gas target. Figure takenfrom. 47 viii Figure 3.7 Schematic of DRAGON’s optical layout with elements labeled within the electromagnetic separator portion. Figure taken from . ....... 48 Figure 3.8 Schematic of DRAGON’s