COMPETING ELECTRIC AND MAGNETIC EXCITATIONS IN BACKWARD ELECTRON-SCATTERING FROM HEAVY DEFORMED-NUCLEI

Important E2 contributions to the (e,e') cross sections of low-lying o rbital M1 excitations are found in heavy deformed nuclei, arising from the small energy separation between the two excitations with (IK)-K-p i=2(+)1 and 1(+)1, respectively. They are studied microscopically in Q RPA using DWBA. The accompanying E2 response is negligible at small mo mentum transfer q but contributes substantially to the cross sections measured at theta=165 degrees for 0.6<q(eff)<0.9 fm(-1) (40 less than or equal to E(i) less than or equal to 70 MeV) and leads to a very goo d agreement with experiment. The electric response is of longitudinal C2 type for theta less than or equal to 175 degrees but becomes almost purely transverse E2 for larger backward angles. The transverse E2 re sponse remains comparable with the M1 response for q(eff)>1.2 fm(-1) ( E(i)>100 MeV) and even dominant for E(i)>200 MeV. This happens even at large backward angles theta>175 degrees, where the M1 dominance is li mited to the lower q region.