SOLUTION OF THE L-10-PUZZLE - MASS AND EXCITED-STATES

The mass of Li-10 has been measured with two different reactions: Be-9(C-13,N-12)Li-10, E(Lab) = 336MeV, and C-13(C-14,F-17)Li-10, E(Lab) = 337 MeV The mass excess of 33.445(50) MeV is deduced from the Q-value measurement. Li-10 is found to be particle-unstable with respect to one-neutron emission by 0.42(5) MeV. In the analysis of the first reaction a low lying excited state is found at 0.38(8) MeV This state and the ground state can be most probably identified as the 1+/2+-doublet coupled from the [pi 1 p 3/2 x nu 1 p 1/2] configuration, the 1+-state being the ground state. The (C-13, N-12)-reaction populates the 1+-state strongly due to a spin-isospin-flip character of the dominant part of the transition amplitude. The 2+-member corresponds to the mass given by Wilcox et al. A second excited state is observed at 4.05(10) MeV with a width of 0.7(2) MeV, it can be associated with the nu 1 d 5/2-strength. The second reaction is fully supporting the interpretation of the ground state doublet. The excited state at 4.05 MeV is not observed in this reaction and indeed it should not, because the reaction does not populate in first order excited neutron configurations. The levels are well described by mean field calculations including pairing correlations. The lowest resonance in the calculations is the nu 1/2--configuration, whereas the nu 1/2+-configuration shows at the neutron threshold a strong nonresonant contribution.