Nuclear spectroscopy of 140Ba, 124Te and 76Se

The experimental techniques of gamma-gamma directional correlation and nuclear orientation have been used to study the nuclei 140Ba, 124Te and 76Se. A nuclear orientation facility has been developed at the N.S.F. Daresbury, together with the associated data collection and analysis systems. An extensive decay scheme has been established for 140Ba following the β-decay of mass separated 140Cs and many multipole mixing ratios have been extracted. Levels and transitions in 124Te have been studied following both thermal neutron capture by 123Te and the β-decay of oriented 124Sb. Several excited O+ states have been established. The results reveal discrepancies between results derived from average resonance (A.R.C.) and thermal neutron capture experiments. In addition substantial L=2 mixing has been established in several first forbidden β-transitions from 124Sb. The nucleus 76Se has been studied following the β-decay of oriented 76As. Many gamma-transition multipole mixing ratios have been extracted and in particular several supposed El transitions have had their character confirmed. The Interacting Boson Model has been used to describe the neutron rich barium nuclei 140-146Ba and both 124Te and 76As. (author)