Physics Division Annual Report 2002

Argonne National Laboratory, with facilities in the states of Illinois and Idaho, is owned by the United States Government and operated by The University of Chicago under the provisions of a contract with the Department of Energy. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor The University of Chicago, nor any of their employees or officers, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of document authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof, Argonne National Laboratory, or The University of Chicago. Available electronically at http://www.doe.gov/bridge Available for processing fee to U. S. Department of Energy and its contractors, in paper, from: U.S. Department of Energy Office of Scientific and Technical Information P.O. Box 62 Oak Ridge, TN 37831-0062 Phone: (865) 576-8401 Fax: (865) 576-5728 Email: [email protected] ABOUT THE COVER: An overview of the Canadian Penning Trap apparatus. This instrument is used at ATLAS to make precise measurements of the masses of the short-lived nuclei involved in the processes that create the chemical elements in the cosmos. The ion-stopping technology for this trap was a pioneering development that helped lead to the concept for the Rare Isotope Accelerator. The lower left section of the figure is a side view of the ion trap. ANL-03/23 ARGONNE NATIONAL LABORATORY 9700 S. Cass Avenue Argonne, Illinois 60439-4801 PHYSICS DIVISION ANNUAL REPORT 2002 Donald F. Geesaman Director September 2003 Preceding Annual Reports ANL-00/20 1999 ANL-01/19 2000 ANL-02/15 2001 Edited by Karen J. Thayer ii FOREWORD This report highlights the research performed in 2002 in the Physics Division of Argonne National Laboratory. The Division’s programs include operation of ATLAS as a national user facility, nuclear structure and reaction research, nuclear theory, medium energy nuclear research and accelerator research and development. The great progress that was made in meeting the exciting intellectual challenges of modern nuclear physics reflects the talents and dedication of the Physics Division staff and the visitors, guests and students who bring so much to the research. The focus of research in the Division is on understanding the structure of strongly interacting matter, hadrons and nuclei, and the role nuclear processes take in the cosmos in the energy generation in stars and the formation of the very elements of which we are made. A great strength of these efforts is the critical interplay of theory and experiment. Major strides have been made both in understanding the basis of the strong interaction from quantum chromodynamics, and in realizing how the resulting interactions between protons and neutrons lead directly to the properties of the world around us. These theoretical advances provide a firm foundation to move forward in the science agenda expressed in the Nuclear Science Advisory Committee’s 2002 Long Range Plan for Nuclear Science. Notable results in research at ATLAS include precise measurements of nuclear masses with the Canadian Penning Trap, significant insights into the structure of the heaviest nuclei and the role of new modes of nuclear pairing. The year ended amidst a concerted effort to complete the move of Gammasphere back to ATLAS and everyone is eagerly looking forward to the prospect of the next epoch of exciting results with this, the world’s most powerful instrument for nuclear structure research, in 2003. Under constrained budgets, ATLAS operated for 4416 hours of research in FY2002 while achieving 95% efficiency of beam delivery for experiments. Numerous improvements resulted in increased capabilities for the users, especially in higher beam intensities and reliability. In Medium Energy Physics new measurements of the proton’s elastic form factors will resolve a major puzzle in understanding the distribution of charge and magnetization of the proton and an exciting initiative to search for the violation of time-reversal invariance using trapped Ra atoms has begun. The DOE/NSF Nuclear Science Advisory Committee has recommended that the Rare Isotope Accelerator is the highest priority of our field for major new construction. Argonne continues to lead in the development and exploitation of the new technical concepts that will truly make RIA, in the words of NSAC, “the world-leading facility for research in nuclear structure and nuclear astrophysics.” New classes of superconducting cavities are being fabricated. High power liquid- lithium targets have been prototyped. A full RIA scale gas-catcher system was constructed and has achieved the extraction efficiency projected for the RIA facility. Our science and our technology continue to point the way to this major advance. It is a tremendously exciting time in science for RIA holds the keys to unlocking important secrets of nature. The work described here shows how far we have come and makes it clear we know the path to meet these intellectual challenges. iii iv TABLE OF CONTENTS Page I. HEAVY-ION NUCLEAR PHYSICS RESEARCH....................1 A. REACTIONS OF ASTROPHYSICAL IMPORTANCE USING STABLE AND RADIOACTIVE BEAMS.................................. 3 a.1. Determination of the 8B Neutrino Spectrum............................................................3 a.2. Production of a 8Li Beam with the In-Flight Technique..........................................8 19 a.3. The Branching Ratio Γα/Γγ of the 4.033 MeV State in Ne ...................................8 a.4. The Astrophysical Rate of the 15O(α,γ)19Ne Reactions Studied via 21Ne(p,t)19Ne ..........................................................................................................10 a.5. On the γ Decay of the 2643-keV State in the rp Breakout Nucleus 20Na ..............12 a.6. Study of the Breakout Reaction 18Ne(α,p)21Na .....................................................14 a.7. Ne, Na and Al Burning in Astrophysically Important (p,γ) Reactions..................14 a.8. Production of a Radioactive 37K Beam with the In-Flight Technique...................15 a.9. Measurement of 44Ti Half-Life ..............................................................................15 a.10. Mass Measurements Along the rp-Process Using the Canadian Penning Trap Mass Spectrometer.................................................................................................16 68 a.11. Direct Qβ Measurement of the N = Z rp-Process Waiting-Point Nucleus Se and Its Astrophysical Implications ...............................................................................18 B. STRUCTURE OF NUCLEI VERY FAR FROM THE VALLEY OF STABILITY ......................................................................... 21 B.1. Proton-Rich Nuclear Spectroscopy ....................................................................21 b.1.1. The 56Ni(3He,p) Reaction and the Question of T = 0, T = 1 Pairing in N = Z Nuclei.....................................................................................................................21 b.1.2. Unravelling the Backbends in 68Se and 72Kr: The Quest for np-Pairing ..............23 b.1.3. Structure and Significance of Isomers in Intermediate Mass N = Z Even Even Nuclei............................................................................................................24 b.1.4. Gamma Vibration and Quasiparticle Excitations in 80Sr .......................................25 b.1.5. The Spectroscopy of T = 0 and T = 1 Low-Lying States in Odd-Odd N = Z Nuclei.....................................................................................................................26 b.1.6. Single Particle States in 111,113,115Sb Populated via β-Decay .................................28 b.1.7. Identification of Excited States in 140Dy................................................................30 b.1.8. In-Beam Spectroscopy of the Proton Unbound Nucleus 143Ho .............................31 b.1.9. New Results in Proton Radioactivity.....................................................................33 b.1.10. Proton Decay of Non Axially-Symmetric Deformed Nuclei.................................34 v b.1.11. Limits of the Energy-Spin Phase Space Beyond the Proton Drip Line: Entry Distributions of Pt and Au Isobars...............................................................35 b.1.12. In-Beam γ-Ray Spectroscopy of 172Pt....................................................................36 b.1.13. Triple Shape Co-Existence in 179Hg ......................................................................37 b.1.14. Alpha Decay of 181Pb.............................................................................................40 B.2. Neutron-Rich Nuclear Spectroscopy..................................................................41 b.2.1. Structure of 52,54Ti and Shell Closures in Neutron-Rich Nuclei Above 48Ca ........41 b.2.2. First Observation

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