ISOSCALAR EXCITATIONS IN THE LEAD REGION OBSERVED IN INELASTIC ALPHA-SCATTERING AT E-ALPHA = 120-MEV

Inelastic α-scattering from 197Au, 206Pb, 208Pb and 209Bi has been measured at an α-bombarding energy of 120 MeV. In the giant resonance region an isoscalar resonance (GR2) at Ex ∼ 80A- 1 3, in addition to the well-known GQR resonance (GR1) at Ex ∼ 63 A - 1 3, is observed. DWBA calculations were performed with the collective form factor prescription. The angular distribution of the GQR bump is found to be better fit if a small admixture of 20 % of the E4, energy-weighted sum rule (EWSR) is added to ∼ 100 % of the E2, EWSR. The angular distribution of the higher bump (GR2) is well fit both with an L = 2 and L = 0 transfer in our angular range. If it is L = 0, it then exhausts 100 % of the monopole EWSR. Angular distributions to low-lying states in 208Pb were also obtained. DWBA calculations with collective form factors were performed to fit these data. Around 33 %, 15 % and 7 % ofE3, E4 and E5 EWSR's are exhausted in these low-lying transitions in addition to the 15 % E2, EWSR in the 2+ state at 4.10 MeV. © 1979.