Researchers from the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences have reported new experimental results that advances our understanding of reaction dynamics and exotic nuclear structures of weakly bound nuclei.
The findings were published in Physics Letters B.
Weakly bound nuclei are characterized by their extremely low binding energy of protons and neutrons. Investigating their reaction mechanisms and exotic structures represents a frontier field in nuclear physics.
Among weakly bound nuclei, the neutron-halo nucleus beryllium-11 and the proton-halo nucleus boron-8 have attracted particular interest. Due to their exceptionally low binding energies and unique nuclear structures, they demonstrate strong coupling effects in nuclear reactions. In particular, the breakup coupling significantly influences elastic scattering. Understanding these effects is crucial for unraveling the structure and reaction mechanisms of atomic nuclei.
To investigate these mechanisms, the researchers conducted a series of experiments at the Radioactive Ion Beam Line in Lanzhou (RIBLL), part of the Heavy Ion Research Facility in Lanzhou (HIRFL). They bombarded a nickel-58 target with secondary beams of beryllium-7, -10, -11 and boron-8 and measured the angular distributions of elastic scattering at energies approximately six times the Coulomb barrier.
By analyzing the measurements with theoretical calculations, the researchers found that the elastic scattering angular distribution of beryllium-11 exhibits significant suppression of the Coulomb-nuclear interference peak due to the breakup coupling, indicating strong coupling effects caused by its neutron-halo structure. In contrast, boron-8, despite its lower binding energy, shows much weaker coupling effects, as the Coulomb and centrifugal barriers suppress the breakup probability of its valence proton.
Additional measurements revealed that beryllium-7 and beryllium-10 behave similarly to other weakly bound isotopes, but their coupling effects are notably weaker. The results indicate that coupling effects intensify with increasing mass number of the target nucleus, a trend validated by scattering data of beryllium-11 and boron-8 on different targets.
"From both experimental and theoretical perspectives, we have completed a systematic investigation of coupling effects in elastic scattering for neutron-halo and proton-halo nuclei at energies above the Coulomb barrier," said Associate Prof. WANG Kang of IMP, first author of the study. "These results provide important insights into the reaction mechanisms of weakly bound nuclei."
The study was carried out in collaboration with researchers from Beihang University and Anhui University, with support from the National Key R&D Program of China and the National Natural Science Foundation of China.
Comparison of elastic scattering differential cross sections of beryllium-11 and boron-8 on different targets at various energies with theoretical calculations. (Image by IMP)
