  The quadrupole-octupole coupling and the related spectroscopic properties
have been studied for the even-even light actinides $^{218-238}$Ra and
$^{220-240}$Th. The Hartree-Fock-Bogoliubov approximation, based on the
Gogny-D1M energy density functional, has been employed as a microscopic input,
i.e., to obtain (axially symmetric) mean-field potential energy surfaces as
functions of the quadrupole and octupole deformation parameters. The mean-field
potential energy surfaces have been mapped onto the corresponding bosonic
potential energy surfaces using the expectation value of the $sdf$ Interacting
Boson Model (IBM) Hamiltonian in the boson condensate state. The strength
parameters of the $sdf$-IBM Hamiltonian have been determined via this mapping
procedure. The diagonalization of the mapped IBM Hamiltonian provides energies
for positive- and negative-parity states as well as wave functions which are
employed to obtain transitional strengths. The results of the calculations
compare well with available data from Coulomb excitation experiments and point
towards a pronounced octupole collectivity around $^{224}$Ra and $^{226}$Th.
