Final PhD Seminar

Elastic Scattering of 8Li on heavy and medium mass targets with SOLEROO capability

Ms Chandrima Sengupta
Department Nuclear Physics

Exotic nuclide 8Li has a weakly bound neutron loosely bound to a relatively tightly bound core, which has a strong influence on nuclear reaction mechanisms, especially at bombarding energies near the Coulomb barrier. The weak intensity of radioactive beams makes precision measurements challenging, and the results obtained so far regarding the interplay of weak binding, break up and fusion have not 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 90% 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 potentials have to be defined. This can be achieved through measurements of elastic scattering angular distributions. Elastic scattering angular distributions for 8Li on 208Pb, 209Bi and 58Ni at energies near and above the barrier have been measured. 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 scattering angle has been reconstructed on an event-by-event basis which allows reliable extraction of the elastic scattering angular distribution. To normalise this elastic scattering distribution to Rutherford scattering, the experimental beam spot and divergence are fed in to a Monte Carlo simulation which takes in to account any asymmetry in the beam profile and reproduces the effect of that asymmetry in determining the 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 to the optical model results. The obtained reaction cross-sections at above barrier energies have then been compared with the measured reaction cross-sections for 6Li, 7Li and 9Li. The results of the analysis of this elastic scattering data will be discussed during the talk.

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