Reexamination of ${}^6$Li scattering as a Probe to Investigate the Isoscalar Giant Resonances in Nuclei

Abstract

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 $0^{\circ }<\hat{I}{¸}_{\text{lab.}}<2^{\circ }$. 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 $\hat{I}\pm$-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 $A\approx 90$. 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.

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