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Download PDF (1.21 High Precision Measurement of the 19Ne Lifetime by Leah Jacklyn Broussard Department of Physics Duke University Date: Approved: Albert Young Calvin Howell Kate Scholberg Berndt Mueller John Thomas Dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Physics in the Graduate School of Duke University 2012 Abstract (Nuclear physics) High Precision Measurement of the 19Ne Lifetime by Leah Jacklyn Broussard Department of Physics Duke University Date: Approved: Albert Young Calvin Howell Kate Scholberg Berndt Mueller John Thomas An abstract of a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Physics in the Graduate School of Duke University 2012 Copyright c 2012 by Leah Jacklyn Broussard All rights reserved except the rights granted by the Creative Commons Attribution-Noncommercial Licence Abstract The lifetime of 19Ne is an important parameter in precision tests of the Standard Model. Improvement in the uncertainty of experimental observables of this and other 1 T = 2 mirror isotopes would allow for an extraction of Vud at a similar precision to that obtained by superallowed 0+ → 0+ Fermi decays. We report on a new high precision measurement of the lifetime of 19Ne, performed at the Kernfysich Versneller MeV 19 Instituut (KVI) in Groningen, the Netherlands. A 10.5 A F beam was used to 19 produce Ne using inverse reaction kinematics in a H2 gas target. Contaminant productions were eliminated using the TRIμP magnetic isotope separator. The 19Ne beam was implanted into a thick aluminum tape, which was translated to a shielded detection region by a custom tape drive system. Collinear annihilation radiation from the emitted decay positrons were detected by two high purity germanium (HPGe) detectors. Event pulse waveforms were digitized and stored using a CAEN V1724 Digitizer. Systematic studies were performed to characterize rate-dependent data ac- quisition effects, diffusion, backgrounds, and contamination from the separator. We have obtained the result for the lifetime of τ =24.9344 ± 0.0073(stat) ± 0.0083(sys) seconds. iv Contents Abstract iv List of Tables viii List of Figures ix Acknowledgements xi Introduction 1 1 Motivation 3 1.1TheoreticalBackground......................... 3 1.1.1 Weakinteraction......................... 3 1.1.2 Nuclearbetadecay........................ 5 1.1.3 Superalloweddecays....................... 7 1.1.4 Theoreticalcorrections...................... 9 1.2TestsoftheStandardModel....................... 11 1.2.1 CKM unitarity .......................... 11 1.2.2 CVChypothesis.......................... 13 1.2.3 Left-Rightsymmetry....................... 13 1.3 Status of the 19Nesystem........................ 17 2 Experimental Method 24 2.1Method.................................. 25 2.2 Implantation ............................... 29 v 2.2.1 Tapematerial........................... 29 2.2.2 Depthsimulation......................... 30 2.3Tapedrivesystem............................. 32 2.3.1 Prototype............................. 32 2.3.2 Finaldesign............................ 39 2.4Lifetimemeasurement.......................... 44 2.4.1 Detectionsystem......................... 44 2.4.2 Dataacquisition.......................... 47 3 Production of 19Ne 52 3.1Productionmechanism.......................... 52 3.2 TRIμPisotopeseparator......................... 54 3.3LISE++predictions........................... 58 3.4Measurementresults........................... 61 4 Analysis 67 4.1Method.................................. 69 4.2Statisticalbias.............................. 71 4.3Detectionefficiency............................ 77 4.3.1 Deadtime............................. 78 4.3.2 Accidentalclovercoincidences.................. 81 4.3.3 Energy determination ....................... 85 4.3.4 Pulse pile-up ........................... 89 4.4Diffusion.................................. 94 4.5Ambientbackground........................... 99 4.6Contamination.............................. 100 5 Result and Implications 105 vi Bibliography 110 Biography 118 vii List of Tables 1.1FermiandGamow-Tellerselectionrules................. 8 1.2 Theoretical corrections in 19Nesystem.................. 17 1.3 Previous 19Nehalf-lifemeasurements................... 18 1.4 Experimental inputs in the 19Nesystem................. 22 19 1.5 Previous Ne Aβ measurements..................... 23 dE → 3.1 Isotope dx E transitions in silicon. .................. 60 3.2 Effect of degrader in separator. ..................... 62 3.3Contaminantidentificationatseparatorexit............... 65 3.4 Limits on contamination obtained from the silicon detector at separa- torexit................................... 66 4.1 Limits on contamination obtained from lifetime fits. ........ 103 5.1Systematicuncertainties.......................... 106 viii List of Figures 1.1Feynmandiagramofneutrondecay.................... 4 1.2 Vud from independent systems. ..................... 12 1.3 Previous 19Nehalf-lifemeasurements................... 20 1.4 Level diagram for 19Ne........................... 21 2.1Experimentoverview............................ 27 2.2 Simulated average implantation depth in Mylar and aluminum. .... 30 2.3 Simulated distribution of implantation depth in aluminum. ...... 31 2.4Prototypetapedrive............................ 33 2.5Drivemechanism.............................. 35 2.6 Supply reel. ................................ 36 2.7 Separator exit coupling. ......................... 37 2.8Upgradedtapedrive............................ 40 2.9 Upgraded tape supply reel assembly. .................. 41 2.10Upgradeddrivemechanism........................ 43 2.11Detectionsystem.............................. 45 2.12Leadshieldingbackgroundspectrum................... 46 2.13DAQelectronicsdiagram......................... 48 3.1 19F(p,n)19Ne cross section. ........................ 53 3.2Evs.TOFofisotopesintheseparator.................. 56 dE 3.3 dx vs.TOFofisotopesintheseparator................. 57 ix 3.4 TriμPseparator.............................. 58 3.5 Simulated E vs. TOF in stage one silicon detector. ........... 59 3.6 Observed E vs. Bρ in stage one silicon detector. ............ 63 3.7 Observed energies at separator exit using 30μmdegrader........ 64 4.1Analysismethodflowchart........................ 68 4.2Simulatedbiasinanalysismethod.................... 74 4.3Simulatedbiasinalternateanalysismethod............... 75 4.4 Goodness of fit of function approximation to sample size bias. .... 76 4.5Interpolationoffitintervalbias...................... 77 4.6Deadtimesimulation............................ 80 4.7 Segment coincidence timing. ....................... 84 4.8 Example piled-up event. ......................... 87 4.9Detectorgaindrift............................. 88 4.10Cloversegmentenergyspectrum..................... 89 4.11 Energy spectrum distortion due to pile-up. ............... 91 4.12Energylowerthresholdcut........................ 93 4.13Energyhigherthresholdcut........................ 94 4.14 Function fit to simulated distribution of implantation depths. ..... 95 4.15Simulatedlossduetodiffusion...................... 97 4.16Simulatedbiasinlifetimeduetodiffusion................ 98 4.17 Measured lifetime at various implantation depths. ........... 98 4.18Measuredbackgroundrates........................ 100 4.19 Isotope concentration in sample during implantation. ........ 102 5.1 New half-life result for 19Ne........................ 107 x Acknowledgements I would like to thank the many people who made this work possible. First, I would like to thank my advisor, Albert Young, for the countless discussions and debates on seemingly impossible problems, for keeping me from getting lost in the finer details, and for pushing me to take on bigger challenges than I thought I could handle. I know that I am a better physicist today because you demanded it. I would also like to thank my co-advisor Calvin Howell, whose uncanny knack for seeing to the heart of the problem and careful attention to detail was more than welcome during this project’s most difficult challenges. I am grateful to everyone who helped to pull this project together. Robby Pattie Jr. was an essential part of this project, not only because of the countless hours spent on developing the data acquisition system, but also because he made sure I occasionally got out of the lab to enjoy Europe. I was able to sleep at night during shift-taking knowing that the experiment was in good hands. I also must thank Henning Back for his many contributions to this project, but especially for taking me under his wing when I was first getting started and hopelessly lost. Melissa Boswell paved the way for this project with her early work on the gas target and even returned to help take shifts during the measurement. Alex Crowell had many useful insights into our myriad of computing problems, and graciously performed many thankless tasks. I have the great pleasure of thanking my dear friend Mary Kidd, who worked shifts even though she was not a part of the project, and almost xi certainly kept me from going insane. I owe many thanks to the TUNL technical staff, especially Bret Carlin, John Dunham, Patrick Mulkey, and Richard O’Quinn, not only for their work creating a very snazzy tape drive interface, but for their cheerful guidance throughout the development of the project. I also want to thank Matthew Busch for his tremendous improvements to the tape drive system. On the other side of the globe,
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