Abstract
Velocity distributions of heavy residuesA Res>A tar,Z Res>Z tar identified by means ofα spectroscopy, have been investigated at the velocity filter SHIP in reactions20Ne+208Pb at projectile energies E/A=8.6, 11.4 and 15.0 MeV/u. Besides products from complete or nearly complete fusion, characterized by velocity distributions peaking atν/ν CN≅0.8–1.0, heavy residues with mean velocities of about half of the compound nucleus velocity were observed. The Z-distribution of this component was found to peak atZ=87. It is interpreted as residues from fusion of target nuclei with projectile fragments produced by nearly symmetric break-up. The experimental results were compared with predictions of theoretical models: cross sections for incomplete fusion were calculated using the sum-rule model of Wilcynski et al., while residue cross sections were calculated using the evaporation code HIVAP. A fair agreement between experimental and calculated mass distributions of heavy residues and transferred projectile fragments is achieved if an energy dissipation of ≅23% (at E/A=8.6 MeV/u) and ≅8% (at E/A=11.4 MeV/u) of the incident projectile energy is introduced. The observed peak of theZ-distribution atZ=87 is predominantly effected due to a higher fission probability of products withZ>87 during the deexcitation process and experimental limitations in the identification of products withZ≦86 by means of a spectroscopy, which cause a decrease of the observed production rates towards lowerZ.
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We express our gratitude to P. Armbruster for his interest, encouragement and valuable discussions. We further thank H. Folger and his team for producing the large area Pb-targets.
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Heßberger, F.P., Ninov, V., Hofmann, S. et al. ‘Slow’ residues observed in the reaction20Ne+208Pb at E/A=8.6, 11.4 and 15.0 MeV/u. Z. Physik A - Hadrons and Nuclei 348, 301–309 (1994). https://doi.org/10.1007/BF01305889
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DOI: https://doi.org/10.1007/BF01305889