Microscopic interpretation of the ( t , $^3$He) reaction at 130 MeV on $^{90}$Zr and isovector monopole strength

The 130-MeV primary tritium beam of the AGOR facility with an intensity of up to 108 pps and the Big Bite Spectrometer experimental setup have been used to study the (t, 3He) reaction between 0° and 5° lab angles on 12C and 90Zr targets. The standard ray-tracing procedure has allowed us to obtain excitation-energy spectra up to 30 MeV in six angular bins for each residual nucleus, with an average energy resolution of 350 keV. We have used the DWBA reaction mechanism model to reproduce those spectra and their angular distributions. In this approximation, the form factor was treated as a folding of an effective projectile-nucleon interaction with a transition density. The effective projectile-nucleon interaction has been adjusted to reproduce the 0° cross section of the 1+ ground state of 12B populated in the 12C(t, 3He) reaction. We have employed RPA wave functions of excited states to construct the form factors. This DWBA+RPA analysis is used to compare calculated and experimental cross sections directly and to discuss the giant resonance excitations in the 90Y nucleus. In this talk, we give some details on this analysis. We show that there are important contributions of L = 2 transitions in the observed cross sections for the 1+ final states that explain the previous difficulties in clearly identifying the monopole strength distributions. We then have a better indication of where the L = 0 part is located with this reaction and its microscopic analysis