NEUTRON HALO IN BE-11 STUDIED VIA REACTION CROSS-SECTIONS

Reaction cross sections (sigma-R) and fragmentation cross sections (sigma-F) of reactions of a Be-11 beam on C, Al targets were measured by a transmission method at 33A MeV. The sigma-R have been determined to be 1.56 +/- 0.03 b for Be-11 + C-12, and 2.27 +/- 0.05 b for Be-11 + Al-27. These values are extremely large compared with the systematics of stable nuclei. A large sigma-F has also been observed for the Be-11 --> Be-10 channel. Model calculations using present and 790A MeV data confirm the long neutron tail (neutron halo) in the Be-11 density distribution.