Measurement of the isovector spin monopole resonance via the 208Pb,90Zr(t,3He) reactions at 300 MeV/u

Abstract

The isovector spin monopole resonances (IVSMR) of the β+ type were observed via the 208Pb and 90Zr(t, 3He) reactions at 300 MeV/u. The experiment was performed at the RI Beam Factory (RIBF) at RIKEN by using the newly-constructed magnetic spectrometer SHARAQ. The double differential cross sections for the 208Pb and 90Zr(t, 3He) reactions were obtained at the excitation energy of 0 ≤ Ex ≤ 70 MeV and the scattering angles of 0° ≤ θ ≤ 3°. The monopole component was obtained as a difference between the zero-degree and backward-angle spectra. The signatures for the IVSMR were discovered at excitation energies of 12 MeV and 20 MeV in 208Pb and 90Zr, respectively, and they show good correspondences to the theoretical predictions.