²¹⁹Fr, a transitional reflection asymmetric nucleus

Mass-separated sources of ²²³Ac (separated as AcF₂⁺) were used to study the level structure of ²¹⁹Fr following alpha decay. The levels in ²¹⁹Fr are interpreted in terms of K=1/2^±, 3/2^±, and 5/2^± parity doublet bands which have a natural theoretical explanation in terms of reflection asymmetric models. The 9/2^- ground-state member of the K=1/2^- band in ²¹⁹Fr can be understood in terms of both reflection asymmetry and the collapse of the quadrupole-octupole Nilsson orbitals towards the h_9/2 orbitals of spherical symmetry. Comparison of the K=1/2^- ground-state bands in ²¹⁹Fr and ²²¹Fr reveals the details of this transformation. Theoretical analysis of the microscopic structure of several of the positive-parity bands indicates the presence of important Nilsson configurations arising from the shell below.