Progress on elastic scattering and breakup of radioactive nuclei based on the HIRFL-RIBLL1

Studying reaction mechanisms and structures of radioactive nuclei is an important frontier of current nuclear physics studies. Research progress on elastic scattering and breakup reactions induced by neutron-rich nucleus Be-11 and proton-rich nucleus B-8 is reviewed in this paper. A novel method is presented for the measurement of elastic scattering and breakup reactions angular distributions induced by radioactive ion beams (RIBs) at HIRFL-RIBLL1 (Radioactive Ion Beam Line in Lanzhou, Heavy-Ion Research Facility in Lanzhou). RIBLL1 is a typical projectile fragmentation (PF) type facility, which has the advantage of providing the short lifetime RIBs and the disadvantage of a broad beam profile. The disadvantage of this production mechanism was overcome through the proposal of a new experimental method. The radioactive beams were identified by applying a time-of-flight and energy loss (TOF-Delta E) technique with a certain magnetic rigidity B rho value in which the TOF was measured using two plastic scintillation detectors. Two position detectors, named PPAC (parallel-plate avalanche counter) or thin DSSD (double-sided silicon strip detector), were used to measure the position and the direction of the incoming beam. A telescope array consisting of DSSDs and SSDs (single silicon detectors) was used to identify the reaction events and measure the scattered angle. The data normalization and small corrections for the misalignment of detectors were performed by assuming the ratio of the elastic cross section to the Rutherford cross section is approximately equal to 1 at small angles. A set of experimental studies of elastic scattering and breakup reactions induced by both of neutron-rich and proton-rich radioactive nuclei at the energies above the Coulomb barriers were performed at HIRFL-RIBLL1. The Be-11 elastic scattering angular distribution shows a strong breakup coupling effect at a relatively high incident energy for the first time, in contrast to what was observed for proton-rich nuclei at similar energies. The results for proton-rich nuclei show only modest effects of the structure on the reaction dynamics at the energies both close to and above the Coulomb barriers. The possible reason of the difference is the Coulomb interactions for valence-core and valence-target as well as the presence of the centrifugal barriers in the ground state of B-8. Angular distributions of breakup reactions for Be-11 and B-8 were measured and analyzed by continuum discretized coupled channel (CDCC) calculations and the IAV (Ichimura, Austern and Vincent) model. The combination of elastic breakup (EBU) and nonelastic breakup (NEB) calculations reproduced the measured breakup angular distributions very well for Be-11 and B-8. The results revealed the importance of the NEB contributions for an understanding of experimental data at backward angles. The integrated breakup cross section of B-8 is approximately only one-fourth of that for Be-11 at similar energies and the same target, which suggests that the presence of Coulomb and centrifugal barriers may suppress the breakup probability.