The quadrupole moment of the ${11}^{-}$ isomer in ${}^{196}\mathrm{Pb}$ has been measured by the level mixing spectroscopy method. This state has a $\pi \left({3s}_{1/2}^{-2\mathrm{}}{1h}_{9/2}1i_{13/2}\right){11}^{-}$ configuration which is involved in most of the shears band heads in the Pb region. The first directly measured value of $Q_s\left({11}^{-}\right)=(-)3.41\left(66\right)\mathrm{b}$, coupled to the previously known quadrupole moment of the $\nu \left({1i}_{13/2}^{-2\mathrm{}}\right){12}^{+}$ isomer allows us to estimate the quadrupole moment of the ${16}^{-}$ shears band head as $Q_s\left({16}^{-}\right)=-0.32\mathrm{}\left(10\right)\mathrm{b}$. The experimental values are compared to tilted axis cranking calculations, giving insight into the validity of the additivity approach to couple quadrupole moments and on the amount of deformation in the shears bands.

• Received 31 October 2001

DOI:https://doi.org/10.1103/PhysRevLett.88.102502