Identification Of The Beta(+) Isovector Spin Monopole Resonance Via The Pb-208 And Zr-90(T, He-3) Reactions At 300 Mev/U

The double-differential cross sections for the Pb-208 and Zr-90(t, He-3) reactions at 300 MeV/u have been measured at the RI Beam Factory at RIKEN. This was the first physics experiment with the SHARAQ magnetic spectrometer. The combined analysis of the present (t, He-3) data and previous (n, p) data provides the clearest identification for the beta(+) isovector spin monopole resonance both in the Tl-208 and Y-90 nuclei, and puts the observations of this giant resonance on a firm foundation. The measured distributions of the (t, He-3) monopole cross sections were well reproduced by the distorted-wave Born approximation calculation, where the target transition density was calculated with the self-consistent Hartree-Fock plus random-phase approximation using the T43 Skyrme interaction. A major part of the expected beta(+) isovector spin monopole strength was found in the measured cross section spectra.