Weak e+e− lines from internal pair conversion observed in collisions of 238U with heavy nuclei |
| |
Authors: | S Heinz E Berdermann F Heine O Joeres P Kienle I Koenig W Koenig C Kozhuharov U Leinberger M Rhein A Schröter H Tsertos |
| |
Institution: | Technische Universit?t München, D–85748 Garching, Germany, DE Gesellschaft für Schwerionenforschung (GSI), D–64291 Darmstadt, Germany, DE University of Cyprus, CY–1678 Nicosia, Cyprus, CY
|
| |
Abstract: | We present the results of a Doppler-shift correction to the measured e+e−–sum-energy spectra obtained from e+e−–coincidence measurements in 238U +206Pb and 238U +181Ta collisions at beam energies close to the Coulomb barrier, using an improved experimental setup at the double-Orange spectrometer
of GSI. Internal-Pair-Conversion (IPC) e+e− pairs from discrete nuclear transitions of a moving emitter have been observed following Coulomb excitation of the 1.844
MeV (E1) transition in 206Pb and neutron transfer to the 1.770 MeV (M1) transition in 207Pb. In the collision system 238U +181Ta, IPC transitions were observed from the Ta-like as well as from the U-like nuclei. In all systems the Doppler-shift corrected
e+e−–sum-energy spectra show weak lines at the energies expected from the corresponding γ–ray spectra with cross sections being
consistent with the measured excitation cross sections of the γ lines and the theoretically predicted IPC coefficients. No
other than IPC e+e−–sum-energy lines were found in the measured spectra. The transfer cross sections show a strong dependence on the distance
of closest approach (Rmin), thus signaling also a strong dependence on the bombarding energy close to the Coulomb barrier.
Received: 22 July 1997 / Revised version: 15 October 1997 |
| |
Keywords: | PACS:14 60 Cd Electrons and positrons – 23 20 Ra Internal pair production – 25 70 Bc Elastic and quasielastic scattering – 25 70 De Coulomb excitation – 25 70 Hi Transfer reaction – 29 30 Aj Charged-particle spectrometers: electric and magnetic |
本文献已被 SpringerLink 等数据库收录! |
|