The electric quadrupole interaction frequencies ${\mathrm{eQV}}_{\mathrm{zz}}/h$ of ${}^{77}\mathrm{Br}$ ( $I^{\pi }=3\mathrm{}/2^{-}$; $T_{1/2}=57\mathrm{}$ h) and ${}^{82}\mathrm{Br}$ ( $I^{\pi }{=5\mathrm{}}^{-}$; $T_{1/2}=35\mathrm{}$ h) in hcp Co were measured with modulated adiabatic fast passage on oriented nuclei. The electric quadrupole moment of ${}^{77}\mathrm{Br}$ is deduced to be $Q=+0.530\mathrm{}\left(22\right)\mathrm{b}$, which, on the condition of strong coupling, implies a nuclear deformation of ${\beta }_2=+0.354\mathrm{}\left(15\right)$. This manifests a drastic increase of the nuclear deformation between ${}^{79}\mathrm{Br}$ ( ${\beta }_2\sim +0.22\mathrm{}$) and ${}^{77}\mathrm{Br}$.

• Received 19 February 1998

DOI:https://doi.org/10.1103/PhysRevLett.80.5289