Dominance of direct reaction channels at deep sub-barrier energies for weakly bound nuclei on heavy targets: The case B-8 + Pb-208

We report the first evidence of breakup dominance at deep sub-barrier energies for the proton halo nucleus B-8 on a heavy target. Angular distribution measurements of the B-8 breakup fragment, Be-7, on lead were performed at the TwinSol facility of the University of Notre Dame at a beam energy of 30 MeV, 58% of the Coulomb barrier and corresponding to a distance of closest approach of 20.5 fm. The Be-7 yield was observed in two double sided silicon strip detector telescopes symmetrical to the radioactive beam and normalized using the B-8 Rutherford scattering. The results are in excellent agreement with continuum discretized coupled channel calculations with a total breakup cross section (326 +/- 84) mb. This is found to exhaust all of the total reaction cross section for the system B-8 + (208)pb, possibly prohibiting a fusion enhancement. This finding is expected to give more insight to the puzzle of fusion suppression at deep sub-barrier energies with possible major consequences on nuclear astrophysics.