Signature to detect the isovector giant quadrupole resonance

We calculate the γ decay from the isoscalar and isovector giant quadrupole resonances in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ into the low-lying spectrum. Whereas the γ decay from the isoscalar giant quadrupole resonance into the first excited $3^{\mathrm{-}}$ state is very small, the corresponding transition from the isovector giant quadrupole resonance is strongly enhanced. According to preliminary calculations, these results hold rather generally for other heavy mass nuclei. We suggest using this property in experimental investigation of the isovector giant quadrupole resonance.