E0,E1,E2,E3, andE4giant resonances in theN=82nucleusCe140between 4 and 48 MeV excitation energy with inelastic electron scattering

Abstract

The cross section for electron scattering from natural cerium (89% $^{140}\mathrm{Ce}$) has been measured with electrons of 80 and 92 MeV at 90 and 105\ifmmode^\circ\else\textdegree\fi{} between 4 and 48 MeV excitation energy. The nine resonances or resonance-like structures identified at ${E}_{x}=6(31{A}^{\ensuremath{-}\frac{1}{3}}), 7.4(38{A}^{\ensuremath{-}\frac{1}{3}}), 10(52{A}^{\ensuremath{-}\frac{1}{3}}), 12(62{A}^{\ensuremath{-}\frac{1}{3}}), 15.3(79{A}^{\ensuremath{-}\frac{1}{3}}), 22(114{A}^{\ensuremath{-}\frac{1}{3}}), 25(130{A}^{\ensuremath{-}\frac{1}{3}}), 31(160{A}^{\ensuremath{-}\frac{1}{3}})$, and $37.5(195{A}^{\ensuremath{-}\frac{1}{3}})$ MeV were classified on the basis of their momentum transfer dependence and discussed in the framework of the shell model. Since some of the arguments used are intricate we refer for quantitative particulars to the text. It is shown that the $E2$ sum rule strength not exhausted in the excitation range of this experiment may contribute up to 50% of the classical dipole sum rule to the photon cross section between 50 MeV and the pion threshold. The resonance at 10 MeV might be due to a separate oscillation of the excess neutrons against the rest of the nucleus.NUCLEAR REACTIONS $^{140}\mathrm{Ce}$($e$,${e}^{\ensuremath{'}}$, ${E}_{0}=50 \mathrm{to} 92$ MeV, Measured $\frac{{d}^{2}\ensuremath{\sigma}}{d\ensuremath{\Omega}d{E}_{x}}$, bound and continuum states (giant resonances). Deduced multipolarity, reduced matrix element $B(E\ensuremath{\lambda})$, radiative width ${\ensuremath{\Gamma}}_{y}^{\ensuremath{\circ}}$, sum rule exhaustion of giant resonances, photon cross section to pion threshold, total width of continuum and clustered states.