Evidence for predicted level crossing in doubly decoupled structures

High spin states in ${}_{}{}^{174}{}_{}{}^{}\mathrm{Ta}$ have been studied for the first time through in beam spectroscopy techniques following the ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$(${}_{}{}^9{}_{}{}^{}\mathrm{Be}$,4n) fusion-evaporation reaction. A $\Delta I=2\mathrm{}$ doubly decoupled band based on a $3^{+}$ state has been searched for and identified, confirming the predicted deformation dependence of this structure. A remarkable additivity is found for alignments and deviations of moments of inertia with respect to an appropriate even-even core.