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Abstract

The β-decay of the 9Li nucleus and the subsequent particle decays of the unbound states of the 9Be nucleus have been investigated with two complementary techniques, a recoil-particle method and a beta-neutron coincidence method. 9Li nuclei were produced by the 18O(7Li, 9Li) 16O reaction at a bombarding energy of 20 MeV and by the 3H(7Li, 9Li)p reaction with a 14 MeV bombarding energy. The energy spectrum of the delayed alphas and the time-of-flight spectrum of the delayed neutrons were obtained. The half-life was measured to be 177±3 ms. Besides the known decay branches to the ground state and to the 2.43 MeV state in 9Be, a new decay branch to an unbound state in 9Be at an excitation energy of 2.78±0.12 MeV was observed. The branching ratios and the log ft values were found to be (65.0−2.4+2.7) %, (32.0−3.7+2.7)%, (3.0−0.3+2.7)% and 5.12−0.02+0.01, 5.00−0.05+0.04, 5.97−0.28+0.05 to the ground state, the 2.43 MeV state and the 2.78 MeV state, respectively. The observed properties of the 2.78 MeV state favor an assignment of 12−. This state decays mainly by neutron emission to the ground state of 8Be and has a c.m. width of 1.10±0.12 MeV.The fraction of the decays of the 2.43 MeV state in 9Be involving emission of a neutron to the ground state of 8Be was found to be (6.4±1.2)%.