Phys. Rev. Lett. 78, 618 - 621 (1997)
Search for Monoenergetic Positron Emission from Heavy-Ion Collisions at Coulomb-Barrier Energies
I. Ahmad et al. (APEX Collaboration)
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I. Ahmad1, Sam M. Austin2, B. B. Back1, R. R. Betts1,3, F. P. Calaprice4, K. C. Chan5, A. Chishti5, C. Conner3, R. W. Dunford1, J. D. Fox6, S. J. Freedman7, M. Freer1,8, S. B. Gazes9, A. L. Hallin10, T. Happ1,11, D. Henderson1, N. I. Kaloskamis5, E. Kashy2, W. Kutschera1, J. Last1, C. J. Lister1, M. Liu10, M. R. Maier2, D. J. Mercer2, D. Mikolas2, P. A. A. Perera12, M. D. Rhein1,11, D. E. Roa6, J. P. Schiffer1,9, T. A. Trainor13, P. Wilt1, J. S. Winfield2, M. R. Wolanski9, F. L. H. Wolfs12, A. H. Wuosmaa1, G. Xu5, A. Young4, and J. E. Yurkon2 (APEX Collaboration) 1Physics Division, Argonne National Laboratory, Argonne, Illinois 60439
2National Superconducting Cyclotron Laboratory and Department of Physics & Astronomy, Michigan State University, East Lansing, Michigan 48824
3Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607
4Physics Department, Princeton University, Princeton, New Jersey 08544
5Wright Nuclear Structure Laboratory, Yale University, New Haven, Connecticut 06520
6Physics Department, Florida State University, Tallahassee, Florida 32306
7Lawrence Berkeley Laboratory, Berkeley, California 94720
8School of Physics and Space Research, University of Birmingham, P.O. Box 363, Birmingham B15 2TT, England
9Department of Physics, University of Chicago, Chicago, Illinois 60637
10Physics Department, Queen's University, Kingston, Ontario, K7L 3N6, Canada
11Gesellschaft für Schwerionenforschung, Planckstrasse 1, 64291 Darmstadt, Germany
12Nuclear Structure Research Laboratory, University of Rochester, Rochester, New York 14627
13Nuclear Physics Laboratory, University of Washington, Seattle, Washington 98195
Received 20 September 1996
Positron production in 238U+232Th and 238U+181Ta collisions near the Coulomb barrier has been studied. Earlier experiments reported narrow lines in the spectra of positrons, accumulated without the requirement of electrons detected in coincidence. No evidence of such structure is observed in the present data. The positron energy spectra are compared with estimates from dynamic atomic processes, and from internal pair conversion of electromagnetic transitions from the excited nuclei.
©1997 The American Physical Society
URL: http://link.aps.org/doi/10.1103/PhysRevLett.78.618
DOI: 10.1103/PhysRevLett.78.618
PACS: 25.70.Bc, 14.80.-j
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