The electrodisintegration of ${\mathrm{Cu}}^{63}$ and ${\mathrm{Mn}}^{55}$ has been investigated for total electron energies from 29.5 Mev to 81.5 Mev by a stacked-foil experiment using the internal electron beam of a synchrotron. The value of $\overline{F}$, which is essentially the ratio of photon induced foil activity to electron induced foil activity, is found to be 8.32±0.54 at 29.5 Mev, 5.47±0.36 at 46.5 Mev, 5.31±0.25 at 63.5 Mev, and 4.97±0.05 at 81.5 Mev for the ${\mathrm{Cu}}^{63}(e, e^{\prime }n){\mathrm{Cu}}^{62}$ reaction. For the ${\mathrm{Mn}}^{55}(e, e^{\prime }3n){\mathrm{Mn}}^{52*}$ reaction, which has an effective excitation energy of 42 Mev, $\overline{F}$ is found to be 6.67±0.41 at 63.5 Mev and 7.43±0.40 at 81.5 Mev. Upon comparing these values with the theoretical values of $\overline{F}$ for different multipole photon absorption processes, it appears that the resonance peak in the nuclear photon absorption cross section for copper is due to a mixture of 97% of an electric dipole process and 3% of an electric quadrupole process. Nuclear size effects might make the experimental results compatible with a larger proportion of electric quadrupole process. Above the resonance peak, at energies near 42 Mev, the photon absorption appears to be due to either an electric dipole or a magnetic dipole process, but not an electric quadrupole process.

• Received 18 June 1956

DOI:https://doi.org/10.1103/PhysRev.105.1534