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s-wave scattering lengths for the 7Be+p system from an R-matrix analysis...

Publication Type
Journal
Journal Name
Physical Review C
Publication Date
Page Number
045807
Volume
99
Issue
4

The astrophysical S factor for the radiative proton capture reaction on 7Be (S17) at low energies is affected by the s-wave scattering lengths. We report the measurement of elastic and inelastic scattering cross sections for the 7Be+p system in the center-of-mass energy range 0.474–2.740 MeV and center-of-mass angular range 70∘–150∘. A radioactive 7Be beam produced at Oak Ridge National Laboratory's (ORNL) Holifield Radioactive Ion Beam Facility was accelerated and bombarded a thin polypropylene (CH2)n target. Scattered ions were detected in the segmented Silicon Detector Array. Using an R-matrix analysis of ORNL and Louvain-la-Neuve cross-section data, the s-wave scattering lengths for channel spins 1 and 2 were determined to be 17.34+1.11−1.33 and −3.18+0.55−0.50 fm, respectively. The uncertainty in the s-wave scattering lengths reported in this work is smaller by a factor of 5–8 compared to the previous measurement, which may reduce the overall uncertainty in S17 at zero energy. The level structure of 8B is discussed based upon the results from this work. Evidence for the existence of 0+ and 2+ levels in 8B at 1.9 and 2.21 MeV, respectively, is observed.