The structure of the nucleus ${}_{}{}^{219}{}_{}{}^{}\mathrm{Ac}$(Z=89,N=130) has been studied via the ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$${(}^{13}$C,3n${)}^{219}$Ac reaction. In-beam γ-ray spectroscopic techniques, including γ-ray and α-particle excitation functions, α-γ coincidence, γ-γ coincidence, and γ-ray angular distribution measurements were used in the construction of a level scheme up to a spin of J=(31/2)ħ at an excitation energy of 2245 keV. A total of five bands have been constructed and a series of parity doublets has been observed. For four of the bands the states have been labeled in terms of the simplex quantum number, which should be an appropriate quantum number even for octupole deformed nuclei. However, considerable simplex splitting is observed. The level scheme of ${}_{}{}^{219}{}_{}{}^{}\mathrm{Ac}$ indicates that the nucleus lies in the boundary region between the single-particle shell structure seen in the nuclei immediately surrounding ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ and the collective rotational structure prevalent in the heavier actinides. However, no detailed model predictions are, as yet, available to describe the observed structure, which may require quadrupole, octupole, and nonaxial degrees of freedom.

• Received 24 December 1985

DOI:https://doi.org/10.1103/PhysRevC.33.1344