Dominance of direct reaction channels at deep sub-barrier energies for weakly bound nuclei on heavy targets: The case <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mmultiscripts><mml:mi mathvariant="normal">B</mml:mi><mml:mprescripts/><mml:none/><mml:mn>8</mml:mn></mml:mmultiscripts><mml:mo>+</mml:mo><mml:mmultiscripts><mml:mi>Pb</mml:mi><mml:mprescripts/><mml:none/><mml:mn>208</mml:mn></mml:mmultiscripts></mml:mrow></mml:math>
A. Pakou, L. Acosta, P. D. O’Malley, Sérgio Luiz Cruz Aguilar, E. F. Aguilera, Matthew Baines, D. W. Bardayan, F. D. Becchetti, Ch. Boomershine, M. Brodeur, F. Cappuzzello, S. Carmichael, L. Caves, E. Chávez, C. Flores-Vázquez, A. Gula, J. J. Kolata, B. Liu, D. J. Marı́n-Lámbarri, Felipe Morales, К. Rusek, Á. M. Sánchez-Benítez, O. Sgouros, Vijay R. Sharma, V. Soukeras, G. Souliotis
Abstract
We report the first evidence of breakup dominance at deep sub-barrier energies for the proton halo nucleus $^{8}\mathrm{B}$ on a heavy target. Angular distribution measurements of the $^{8}\mathrm{B}$ breakup fragment, $^{7}\mathrm{Be}$, 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 $^{7}\mathrm{Be}$ yield was observed in two double sided silicon strip detector telescopes symmetrical to the radioactive beam and normalized using the $^{8}\mathrm{B}$ Rutherford scattering. The results are in excellent agreement with continuum discretized coupled channel calculations with a total breakup cross section $(326\ifmmode\pm\else\textpm\fi{}84)\phantom{\rule{0.28em}{0ex}}\mathrm{mb}$. This is found to exhaust all of the total reaction cross section for the system $^{8}\mathrm{B}+^{208}\mathrm{Pb}$, 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.