Electrodisintegration of C,Cu and Ag by electrons and positrons

Absolute cross sections for the electrodisintegration of ¹²C, ⁶³Cu and ¹⁰⁷Ag by electrons and positrons have been measured in the energy range from 20 to 30 MeV. The cross sections have been determined from the induced activities. The measured cross-section ratio σ⁻/σ⁺ is not equal to 1 and increases with Z. This is in contradiction to the Born-approximation calculations of the virtual-photon spectrum.