Abstract
The level structure of La143 has been investigated by measurement of gamma-ray and conversion-electron singles, gamma-gamma coincidence, and gamma-gamma angular correlation spectra following the decay of 15.0-s Ba143. Comparison of the observed structure of La143 with the structures of isotopic La and isotonic N=86 nuclides, as well as those of the adjacent Cs isotopes and N=84 isotones, suggests the presence of unusual low-lying (3/2+ and (5/2- levels that are not readily accounted for by theoretical calculations. The observed structures suggest that the deformation in this mass region is influenced by different factors than that of the nuclides above Z=64, and that reflection asymmetric structures play an important role in the structure of the nuclides in the A=145 mass region. © 1988 The American Physical Society.