We present the results from e+e- coincidence measurements in 238U + 206Pb collisions at a beam energy of 5.93 MeV/u, using an improved experimental setup at the double-Orange spectrometer of GSI. The capability of our device to detect Internal-Pair-Conversion (IPC) e+e- pairs from discrete nuclear transitions of a moving emitter is demonstrated by investigating the known 1.844 MeV (E1) transition in 206Pb and the 1.770 MeV (M1) transition in 207Pb, excited via Coulomb excitation and a neutron transfer reaction, respectively. The Doppler-shift corrected e+- sum-energy spectra show weak lines at the expected energies with cross sections being consistent with the measured excitation cross sections of the corresponding γ lines and the theoretically predicted IPC coefficients. No other e+e- sum-energy lines were found in the measured spectra. The observed transfer cross sections show a strong dependence on the distance of closest approach (R_min), thus signaling also a strong dependence on the bombarding energy close to the Coulomb barrier.
@article{arxiv.nucl-ex/9612006,
title = {e+e- pairs from 238U + 206Pb collisions},
author = {S. Heinz and E. Berdermann and F. Heine and O. Joeres and P. Kienle and I. Koenig and W. Koenig and C. Kozhuharov and U. Leinberger and M. Rhein and A. Schroeter and H. Tsertos},
journal= {arXiv preprint arXiv:nucl-ex/9612006},
year = {2007}
}
Comments
12 pages, standard LaTeX with 3 included PS figures; Submitted to Physics Letters B