Hot fusion-evaporation cross sections of Ca44-induced reactions with lanthanide targets
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© 2015 American Physical Society. Background: Previously reported cross sections of Sc45-induced reactions with lanthanide targets are much smaller than Ca48-induced reactions on the same targets. Ca44 is one proton removed from Sc45 and could be used to produce nuclei with a relative neutron content between those produced in the Sc45- and Ca48-induced reactions. Purpose: As part of a systematic investigation of fusion-evaporation reactions, cross sections of Ca44-induced reactions on lanthanide targets were measured. These results are compared to available data for Ca48- and Sc45-induced fusion-evaporation cross sections on the same lanthanide targets. Collectively, these data provide insight into the importance of the survival against fission of excited compound nuclei produced near spherical shell closures. Methods: A beam of Ca6+44 at an energy of ≈5MeV/u was delivered by the K500 superconducting cyclotron at the Cyclotron Institute at Texas A&M University. The desired evaporation residues were selected by the Momentum Achromat Recoil Spectrometer and identified via their characteristic α-decay energies. Excitation functions for the Ca44+Gd158,Tb159, and Dy162 reactions were measured at five or more energies each. A theoretical model was employed to study the fusion-evaporation process. Results: The Ca44-induced reactions have xn cross sections that are two orders of magnitude larger than Sc45-induced reactions but two orders of magnitude smaller than Ca48-induced reactions on the same targets. Proton emission competes effectively with neutron emission for the Ca44+Tb159 and Dy162 reactions. The maximum 4n cross sections in the Ca44+Gd158,Tb159, and Dy162 reactions were 2100±230,230±20, and 130±20μb, respectively. The Ca44+Gd158 and Tb159 cross sections are in good agreement with the respective cross bombardments of Ca48+Gd154 and Sc45+Gd158 once differences in capture cross sections and compound nucleus formation probabilities are corrected for. Conclusions: Excitation functions were measured in Ca44-induced reactions on lanthanide targets. Evaporation residue cross sections were two orders of magnitude larger than Sc45-induced reactions on the same targets due to an increase in the survival probability of the compound nucleus. However, little evidence of cross-sectional enhancement due to shell stabilization of the compound nucleus was observed.
author list (cited authors)
Werke, T. A., Mayorov, D. A., Alfonso, M. C., Tereshatov, E. E., & Folden, C. M.