INVARIANT-MASS SPECTROSCOPY OF LI-10 AND LI-11

Break-up of secondary Li-11 ion beams (280 MeV/nucleon) on C and Pb ta rgets into Li-9 and neutrons is studied experimentally. Cross sections and neutron multiplicity distributions are obtained, characterizing d ifferent reaction mechanisms. Invariant-mass spectroscopy for Li-11 an d Li-10 is performed. The E1 strength distribution, deduced from elect romagnetic excitation of Li-11 up to an excitation energy of 4 MeV com prises similar to 8% of the Thomas-Reiche-Kuhn energy-weighted sumrule strength. Two low-lying resonance-like structures are observed for Li -10 at decay energies of 0.21(5) and 0.62(10) MeV, the former one carr ying 26(10)% of the strength and likely to be associated with an s-wav e neutron decay. A strong di-neutron correlation in Li-11 can be disca rded. Calculations in a quasi-particle RPA approach are compared with the experimental results for Li-10 and Li-11. (C) 1997 Elsevier Scienc e B.V.