Levels and transitions in140Ba populated following the decay of140Cs

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Abstract
Levels in 140Ba were populated following the beta decay of 140Cs (T12/=64 s) which was produced by the online fission product mass separator OSTIS at the Institut Laue-Langevin. Gamma data were recorded in an event-by-event mode and the coincidence results enable a decay scheme with 52 levels up to 5.8 MeV to be established. Directional correlation measurements were made on 14 direct cascades and 11 skip cascades, all in coincidence with the 21+ to 01+ ground state transition. Definite spin assignments were made for 14 levels and tentative assignments for 5 levels, with multipole mixing ratios being extracted where applicable. In addition, approximate log ft values were calculated for all the beta -fed levels and these, together with the relevant modes of decay, were used as a bias for tentative assignments for all but two of the levels not studied using the correlation technique. The experimental data for the neutron-rich barium isotopes 140-146Ba have been fitted using IBM-2 and the 2+ level at 1994 keV in 140Ba is identified as a mixed-symmetry state.