Electroexcitation of the nuclear continuum for ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ at excitation energies up to 100 MeV has been measured at momentum transfers in the range from 0.45 to 1.2 ${\mathrm{fm}}^{-1\mathrm{}}$. Unfolding of the radiation tail was performed using a tail function which takes into account the multiple-photon emission effect. The spectra at these momentum transfers deviate significantly from the prediction of the Fermi-gas model but are consistent with the sum of the multipole strengths of the random-phase approximation; the excess cross section on the low excitation energy side indicates the excitation of multipole resonances. A series of ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ spectra at low momentum transfers was expanded into $E1\mathrm{}$, $E2\mathrm{}\mathrm{}\left(E0\mathrm{}\right)\mathrm{}$, $E3\mathrm{}$, and higher multipole components using the $q$ dependence of the Tassie model for isoscalar modes and the Goldhaber-Teller or Steinwedel-Jensen model for isovector modes. The giant dipole resonance thus obtained is consistent with that from photoreactions. Isoscalar and isovector giant quadrupole resonances are seen, respectively, at 11 and 22.5 MeV and an octupole resonance at 16 MeV. A monopole resonance is suggested at 13.5 MeV. The reduced ${\left|〈r^2〉\right|}^2$, $B\left(E1\mathrm{}\right)\mathrm{}$, $B\left(E2\mathrm{}\right)\mathrm{}$, and $B\left(E3\mathrm{}\right)\mathrm{}$ consume most of the corresponding energy weighted sum rule if the $q$ dependences of the Tassie and Goldhaber-Teller models are assumed. The results with these models are consistent with the random-phase approximation.

NUCLEAR REACTION ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}(e, e^{\prime })$, measured ($E_{e^{\prime }}, {\theta }_{e^{\prime }}$), $E_x=7.4-100\mathrm{}$ MeV, $q=0.45-1.2\mathrm{}$ ${\mathrm{fm}}^{-1\mathrm{}}$, reduced ${\left|〈{\mathcal{r}}^2〉\right|}^2$, $B\left(E1\mathrm{}\right)\mathrm{}$, $B\left(E2\mathrm{}\right)\mathrm{}$, $B\left(E3\mathrm{}\right)\mathrm{}$ for giant multipole resonances, multipole expansion analysis.

• Received 23 October 1975

DOI:https://doi.org/10.1103/PhysRevC.15.217