Inelastic ${}^{6}$Li scattering at 100 MeV/u on ${}^{12}$C and ${}^{93}$Nb have been measured with the high-resolution magnetic spectrometer Grand Raiden. The magnetic-rigidity settings of the spectrometer covered excitation energies from 10 to 40 MeV and scattering angles in the range $0^circ < theta_{text{lab.}}< 2^circ$. The isoscalar giant monopole resonance was selectively excited in the present data. Measurements free of instrumental background and the very favorable resonance-to-continuum ratio of ${}^{6}$Li scattering allowed for precise determination of the $E0$ strengths in ${}^{12}$C and ${}^{93}$Nb. It was found that the monopole strength in ${}^{12}$C exhausts $52 pm 3^text{(stat.)} pm 8 ^text{(sys.)}$% of the energy-weighted sum rule (EWSR), which is considerably higher than results from previous $alpha$-scattering experiments. The monopole strength in ${}^{93}$Nb exhausts $92 pm 4^text{(stat.)} pm 10 ^text{(sys.)}$% of the EWSR, and it is consistent with measurements of nuclei with mass number of $Aapprox90$. Such comparison indicates that the isoscalar giant monopole resonance distributions in these nuclei are very similar, and no influence due to nuclear structure was observed.
Download