Helm's model for nuclear transition charge densities, assuming these to extend over a smeared-out shell at the nuclear radius, has been found useful in describing coulomb-type electroexcitation of individual nuclear levels. We have extended the model by obtaining corresponding nuclear transition current densities (satisfying the continuity equation) and magnetization densities, which permit calculation of transverse matrix elements, and hence offer a description of electroexcitation of single levels at large electron scattering angles. The model yields a good numerical fit to the 15.1-MeV level in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and to other examples. In addition, the relation between the $M$, $T$ and the $B$ notation for electroexcitation matrix elements is established, and the Isabelle-Bishop expansion in powers of the momentum transfer is rederived.

• Received 8 June 1967

DOI:https://doi.org/10.1103/PhysRev.163.927