Abstract
The beta 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 - The recoil-particle method and the beta-neutron coincidence method. ^9Li nuclei were produced by the ^(18)O (^7Li, ^9Li)^(16)O reaction with a 20 MeV bombarding energy and by the t(^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 also measured and was found to be 177 ± 3 msec. 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 ± 0.125 MeV was observed. The branching ratios and the log ft values were found to be; (65.0^(+2.7)_(-2.4))%, (32.0^(+2.7)_(-3.7))%, (3.0^(+2.7)_(-0.3))% and (5.12^(+0.01)_(-0.02)), (5.00^(+0.04)_(-0.05)), (5.97^(+0.05)_(-0.28)) to the ground state, the 2.43 MeV and the 2.78 MeV states, respectively. The observed properties of the 2.78 MeV state favor an assignment of ½^-. It decays mainly by p-wave neutron emission to the ground state of ^8Be and has center-of-mass width of 1.1 ± 0.125 MeV. The fraction of the decays of the 2.43 MeV state in ^9Be involving emission of an f-wave neutron to the ground state of ^8Be was found to be (6.4 ± 1.2)%.
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