LABORATORI NAZIONALI DI LEGNARO
Exotic nuclei such as 8Li and 6He have weakly bound neutrons around a relatively tightly bound core and have a strong influence on nuclear reaction mechanisms, especially at bombarding energies near the Coulomb barrier region. The weak intensity of these radioactive beams makes precision measurements challenging and the results obtained so far regarding the interplay of weak binding, break up and fusion have not so far been conclusive. To achieve a better understanding about these nuclei, the SOLEROO (Solenoidal Exotic Rare Isotope Separator) radioactive ion beam (RIB) capability has been developed at the Australian National University (ANU). This capability is based on a 6.5 T superconducting solenoidal separator which produces RIBs by in-flight transfer reaction via interactions with a primary target. Following production, all the reaction products enter the solenoidal separator and the desired RIBs are separated using a 6.5 T axial magnetic field and focussed on to a secondary target. The secondary beam is tracked with two parallel plate avalanche counters (PPACs) placed immediately after the solenoid. Beam purities of about 98% can be achieved by rejecting unwanted beam species using this tracking facility. Surrounding the secondary target, high efficiency double sided silicon strip detectors are placed in a wide angular range to measure reaction products. Each component of this capability has been optimised to produce the maximum output from this capability. Before studying any complicated reaction mechanism of these exotic nuclei, the interaction potential have to be defined. It can be achieved by fitting the measured elastic scattering angular distribution with some theoretical model. To define the interaction potential, elastic scattering angular distributions for 8Li on 208Pb, 209Bi and 58Ni at energies near and above the barrier have been extracted. The secondary beam of 8Li incident on the secondary target has a finite divergence and a finite beam spot size. Using the tracking information, the true scattering angle has been reconstructed on an event-by-event basis which allows to extract a reliable elastic scattering angular distribution. To normalise this elastic scattering distribution with Rutherford distribution, the beam spot and divergence in the experiment are fed in to a Monte Carlo simulation which essentially takes in to account any kind of asymmetry in the beam profile and reproduces the effect of that asymmetry in determining the true scattering angle. Detailed optical model calculations have then been performed to extract reaction cross-sections for the above systems. Considering the complexity of measuring elastic scattering angular distribution, the reaction cross-sections have also been extracted with Sum-of-Differences (SOD) method and have been compared. The obtained reaction cross-sections at above barrier energies have then been compared with the measured reaction cross-sections for 6Li and 7Li. The results of the analysis of this elastic scattering data will be discussed during the talk.

DATA: 14-06-2019