Highly Excited States in C11. Elastic Scattering of Protons by B10

Abstract

Excitation functions for the elastic scattering of protons by B10 have been measured at center-of-mass scattering angles near 90°, 125°, and 160° for proton energies between Ep=0.15 MeV and Ep=3.0 MeV. Scattering angular distributions were measured at 43 selected energies in this range. An excitation function for the reaction B10(p, α0)Be7 was also measured between Ep=1.5 MeV and Ep=2.6 MeV at a laboratory angle of 90°. The atomic stopping cross section of boron for protons has been determined between Ep=0.1 MeV and Ep=3.0 MeV. The elastic scattering excitation functions exhibit conspicuous anomalies at Ep=1.50 MeV and Ep=2.180 MeV. The α0 transition to the ground state of Be7 is also resonant at Ep=2.180 MeV. The behavior of the cross sections in these regions has been analyzed in terms of compound states of C11. Satisfactory agreement is achieved with level assignments of Jπ=7/2+ with ER=1.50 MeV, Γp=90 keV, ΓT=250 keV; and Jπ=9/2+ with ER=2.180 MeV, Γp=100 keV, Γα0=100 kev, and ΓT=200 keV. Although complete analysis of the scattering is hindered by the influence of unknown background processes, the negative parity assignment for the previously reported state at Ep=1.17 MeV, derived from other reaction experiments, appears inconsistent with the scattering.

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