Isoscalar giant monopole strength in ${}^{58}$Ni, ${}^{90}$Zr, ${}^{120}$Sn and ${}^{208}$Pb

Abstract

Inelastic $\hat{I}\pm$-particle scattering at energies of a few hundred MeV and very-forward scattering angles including $0^{\circ }$ has been established as a tool for the study of the isoscalar giant monopole (IS0) strength distributions in nuclei. An independent investigation of the IS0 strength in nuclei across a wide mass range was performed using the $0^{\circ }$ facility at iThemba Laboratory for Accelerator Based Sciences (iThemba LABS), South Africa, to understand differences observed between IS0 strength distributions in previous experiments performed at the Texas A\&M University (TAMU) Cyclotron Institute, USA and the Research Center for Nuclear Physics (RCNP), Japan. The isoscalar giant monopole resonance (ISGMR) was excited in ${}^{58}$Ni, ${}^{90}$Zr, ${}^{120}$Sn and ${}^{208}$Pb using $\hat{I}\pm$-particle inelastic scattering with $196$ MeV $\hat{I}\pm$ beam and scattering angles $\hat{I}{¸}_{\text{Lab}}=0^{\circ }$ and $4^{\circ }$. The K$600$ magnetic spectrometer at iThemba LABS was used to detect and momentum analyze the inelastically scattered $\hat{I}\pm$ particles. The IS0 strength distributions in the nuclei studied were deduced with the difference-of-spectra (DoS) technique including a correction factor for the $4^{\circ }$ data based on the decomposition of $L>0$ cross sections in previous experiments. IS0 strength distributions for ${}^{58}$Ni, ${}^{90}$Zr, ${}^{120}$Sn and ${}^{208}$Pb are extracted in the excitation-energy region $E_{\mathrm{x}}=9-25$ MeV.Using correction factors extracted from the RCNP experiments, there is a fair agreement with their published IS0 results. Good agreement for IS0 strength in ${}^{58}$Ni is also obtained with correction factors deduced from the TAMU results, while marked differences are found for ${}^{90}$Zr and ${}^{208}$Pb.

12 pages, 10 figures, regular article submitted to PRC