The relative strength (ΔS=1)/[(ΔS=0)+(ΔS=1)] of isovector spin excitations, ${\mathit{P}}_{\mathrm{sf}}$, in the high-lying resonance region of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ was investigated with the ${(}^7$Li${,}^7$Be) reaction at ${\mathit{E}}_{\mathit{L}}$=26 MeV/nucleon and ${\mathrm{\theta }}_{\mathit{L}}$=0° by separately measuring the ${(}^7$Li${,}^7$${\mathrm{Be}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}$) and ${(}^7$Li${,}^7$${\mathrm{Be}}_{0.43}$ MeV) reaction channels with the ${}_{}{}^7{}_{}{}^{}\gamma$ coincidence technique. The relative strength ${\mathit{P}}_{\mathrm{sf}}$ was derived up to an excitation energy of 18 MeV in ${}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ and found to have a constant value of 0.4–0.5 for the continuum irrespective of excitation energy and 0.5 for the isovector dipole resonance centered at ${\mathit{E}}_{\mathit{x}}$=7.6 MeV.

• Received 26 April 1991

DOI:https://doi.org/10.1103/PhysRevLett.67.1082