Following the heavy-ion fusion-evaporation reaction ${}^{32}\mathrm{S}+{}^{24}\mathrm{M}\mathrm{g}$ at 95 MeV beam energy the lifetimes of analogue states in the $T_z=\pm 1/2$ $A=51$ mirror nuclei ${}^{51}\mathrm{F}\mathrm{e}$ and ${}^{51}\mathrm{M}\mathrm{n}$ have been measured using the Cologne plunger device coupled to the GASP $\gamma$-ray spectrometer. The deduced $B(E2;27/2^{-}\to 23/2^{-})$ values afford a unique opportunity to probe isoscalar and isovector polarization charges and to derive effective proton and neutron charges, ${\epsilon }_p$ and ${\epsilon }_n$, in the $fp$ shell. A comparison between the experimental results and several different large-scale shell-model calculations yields ${\epsilon }_p\sim 1.15e$ and ${\epsilon }_n\sim 0.80e$.

• Received 16 August 2004

DOI:https://doi.org/10.1103/PhysRevLett.93.222501