New results on the halo structure of "8B

The longitudinal momentum distribution of "7Be fragments after fragmentation of "8B and the one-proton removal cross section (#sigma#_-_1_p) in a carbon target were measured at 1440 MeV/u with the fragment separator FRS used as an energy-loss spectrometer. The results show a narrow momentum distribution with a FWHM value of 91#+-#5 MeV/c and a large cross-section, #sigma#_-_1_p=98#+-#6 mb. Both these results support the interpretation of a spatially extended proton orbit forming a halo in the "8B ground state. The momentum distribution and the one-proton removal cross section are shown to be reproduced with a three-body wave function for "8B where the target is treated as a black disc in the breakup process. (orig.)Available from TIB Hannover: RO 801(99-09) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Neutron angular distributions from the core break-up reactions of the 11^{11}Be and 11^{11}Li halo nuclei

International audienceThe halo nuclei 11Be and 11Li have been studied through core break-up reactions, where the halo neutrons are detected in anti-coincidence with the core of the halo nucleus. In this particular channel, the halo neutrons are not expected to participate in the reaction and should therefore show the same properties as when situated inside the halo nucleus. The widths of the halo neutron momentum distributions have been extracted in coincidence with He fragments, Γ = 32±4 MeV/c, and Li fragments, Γ = 42±4 MeV/c for 11Be and with He fragments, Γ = 42±6 MeV/c for 11Li. An experimental value of the shadow effect for 11Be when breaking up to Li and He fragments has been obtained to be 0.63. A simple theoretical calculation to reproduce this value is given