Abstract
The effects of unusual structures of nuclei, such as neutron halos, on nuclear reaction mechanisms are not well understood, particularly at near barrier energies. Using the SOLEROO Radioactive Ion Beam facility at the Australian National University, below-barrier reactions with 8 Li incident on 209 Bi have been performed. Beam purities of about 95% are achieved by rejecting unwanted beam species using a solenoidal separator along with tracking and tagging the secondary beam with two parallel plate avalanche counters (PPACs) placed immediately after the solenoid. However, the radioactive ion beam exiting the solenoid is not parallel to the primary beam axis. To obtain a precise angular distribution of elastic scattering, the tracking facility is used to deduce the true scattering angle on an event-by-event basis. The elastic cross-section for 8 Li on 209 Bi is then extracted, verifying the capability of the facility to perform precise cross-section measurements.
Highlights
A suppression of complete fusion at above barrier energies has been observed in reactions with light, weakly bound nuclei
The SOLEROO Radioactive Ion Beam (RIB) facility at the Australian National University is based on a super-conducting solenoidal separator [14,15,16,17] which produces RIBs by in-flight transfer reactions via interactions with a primary target
To derive a relationship between θGeom and θRIB, an intermediate angle, θParallel is reconstructed using a routine in the software, where θParallel is the scattering angle of any event if the incident RIB is parallel to the primary beam axis
Summary
A suppression of complete fusion at above barrier energies has been observed in reactions with light, weakly bound nuclei. The impact of breakup on fusion with weakly bound radioactive nuclides is not yet clear In exotic nuclei such as 8Li or 6He, containing weakly bound neutrons around a relatively tightly bound core, the nucleon density distribution has an extensive tail which may help the attractive nuclear forces begin to act at large distances between the projectile and the target. This may lower the barrier and enhance fusion cross-sections, in the sub-barrier energy region [9, 10]. This may prevent or hinder complete fusion of the projectile with the target [11, 12]
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