The one-body operators \( {\cal O}(\lambda) \) represent a sum over the operators for the individual nucleon degrees of freedom \( i \) $$ {\cal O}(\lambda ) = \sum_{i} O(\lambda ,i). $$

The electric transition operator is given by $$ O(E\lambda ) = r^{\lambda } \; Y^{\lambda }_{\mu }(\hat{r}) \; e_{q} e, $$ were \( Y^{\lambda }_{\mu } \) are the spherical harmonics and \( q \) stands for proton \( q=p \) or neutron \( q=n \).