Abstract
The partial cross sections of heavy residual nuclei produced in the heavy ion fusion of12C+20Ne have been measured atE c.m.=6–15 MeV viaγ-ray spectroscopy with a Ge(Li) detector. Windowless and recirculating gas target systems have been used. The dominant residual nuclei are24Mg,27Al,28Si,30Si,30P and31P, which arise from two- and three-body breakups in the exit channels. The observed excitation functions are smooth in their energy dependence and give no indications for the existence of pronounced resonance structures, in contrast to theoretical predictions. The Coulomb excitation of20Ne served as an intrinsic calibration standard in the determination of absolute partial and total fusion cross sections. The same experimental set-up was also used in the reaction studies of16O+16O atE c.m.=7–14 MeV, going through the same compound nucleus32S at similar excitation energies. The observed energy dependence in the excitation functions is in good agreement with previous work. The total fusion cross section agrees fairly well with two sets of values reported previously, but deviates significantly from other reported absolute cross section values. The relative evaporation distributions of the residual nuclei are similar for both heavy ion reactions. However, the ratio of their total fusion cross sections deviates from model predictions and suggests that compound nucleus formation does depend on the microscopic structure of the colliding nuclei in the entrance channel. From the observed energy dependence of the above ratio, particularly at subcoulomb energies, geometrical effects in the entrance channel (due to deformed and spherical nuclei) appear to be weak. The astrophysical aspects of the data in the context of late stellar nucleosynthesis are discussed.
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Supported in part by the Deutsche Forschungsgemeinschaft [Ro 429/7–12]
The authors greatly appreciate the help of H.W. Becker, L. Buchmann, J. Görres, K.U. Kettner, W.E. Kieser. P. Schmalbrock and M. Wiescher during the course of the experiments. We would like to thank W. Verhoeven and the mechanical workshop for their work on the apparatus as well as J.W. Hammer (Stuttgart) for the loan of the jet target chamber. The travel support to the laboratory at Bochum was provided by the Westfälische Wilhelms-Universität and is highly acknowledged. One of the authors (C.R.) thanks Prof. C.A. Barnes for many fruitful discussions as well as the provision of the16O+16O data prior to publication. C.R. also wishes to thank the California Institute of Technology and Prof. T.A. Tombrello for an appointment as Visiting Associate, during which time the present manuscript was prepared. Finally, Prof. F. Riess is thanked for calculations of the12C+20Ne Coulomb excitation and Prof. H.J. Krappe for helpful comments on the manuscript.
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Hulke, G., Rolfs, C. & Trautvetter, H.P. Comparison of the fusion reactions12C+20Ne and16O+16O near the Coulomb barrier. Z Physik A 297, 161–183 (1980). https://doi.org/10.1007/BF01421473
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DOI: https://doi.org/10.1007/BF01421473