Elastic scattering and transfer in the6He+209Bisystem below the Coulomb barrier

Abstract

The interaction of 6 He with 209 Bi has been studied over a range of energies well below the nominal Coulomb barrier. A 4 He group of remarkable intensity, first observed in a previous experiment at near-barrier energies, continues to dominate the reaction in the sub-barrier regime. A total cross section of nearly 200 mb was measured for this group at 5 MeV below the barrier. This very large value is shown to be consistent with the total reaction cross section deduced from a simultaneouslymeasured elastic scattering angular distribution.

Scattering of6He at energies around the Coulomb barrier

“…The Coulomb component was explicitly included in the calculations. This result is in accordance with previous experimental works [12,13,14].…”

Extended optical model analyses of elastic scattering and fusion cross sections for theLi6+Pb208system at near-Coulom

“…As a consequence, the resulting total polarization potential dominated by the DR potential becomes rather smooth as a function of the incident energy. This has explained the reason why the threshold anomaly is not seen in the optical potentials determined for systems involving loosely bound projectiles such as 6 He, 6 Li, and 9 Be [2,10,15].…”

“…In order to test this idea, we have thus carried out [8,9] simultaneous χ 2 analyses of elastic scattering and fusion cross section data for the 6 He+ 209 Bi [10,11,12], 6 Li+ 208 Pb [2,13,14], and 9 Be+ 209 Bi [15,16] systems at near-Coulomb-barrier energies in the framework of the extended optical model [17,18,19] that introduces two types of complex polarization potentials, the DR and fusion potentials. In such analyses, in addition to the elastic scattering cross sections dσ exp E /dΩ, the measured fusion cross section σ exp F , was taken into account together with the total experimental DR cross section, σ exp D , if available, or the semi-experimental DR cross section, σ semi−exp D , if σ exp D was not available.…”

Recent results in reactions using radioactive ion beams

“…Several direct processes can also occur in this system: the projectile can break up, leading to a final state where the target remains unchanged, with an alpha particle and two neutrons flying away; also, there can be a one neutron transfer to the target, in which case the remaining 5 He immediately decays into an alpha and a neutron, both of which fly away independently; finally, two neutrons can be transferred to the target, with an alpha particle flying away. All three processes produce at the end one alpha particle, so by counting these alphas the inclusive transfer-or-breakup (tr/bu) yield was determined [9,10]. This was done at several near and sub-barrier energies, where the elastic channel was also measured.…”

“…Recent results in reactions using RIB's Elí F. Aguilera , transfer/breakup [9,10], and total reaction cross sections [9,10] for the 6 He + 209 Bi system.…”