Yields from the reactions ${\mathrm{Be}}^9(e, e^{\prime }n)$ and ${\mathrm{Be}}^9(\gamma , n)$, as well as the relative yields from ${\mathrm{C}}^{12}(e, e^{\prime }n){\mathrm{C}}^{11}$ and ${\mathrm{C}}^{12}(\gamma , n){\mathrm{C}}^{11}$, were measured under conditions which permitted a comparison of the relative effects of electrons and bremsstrahlen from electrons in producing nuclear reactions. The primary electron energies were from 6 to 17 Mev in the case of Be, and 24 to 145 Mev in the case of C. Comparison of the experimental results with the theory of electrodisintegration gives information about the multipole order of the electromagnetic transitions involved. The ${\mathrm{Be}}^9$ results agree with theory if the reaction mechanism is predominantly electric-dipole. For ${\mathrm{C}}^{12}$, a mixture of 92% electric-dipole with 8% electric-quadrupole intensities gives agreement with theory over the energy range 28-145 Mev, provided that the finite size of the C nucleus is taken into account. The method of considering the finite nuclear size in the theory is presented, and the results previously obtained by Reagan for the reactions ${\mathrm{F}}^{19}(e, e^{\prime }2p){\mathrm{N}}^{17}$ and ${\mathrm{F}}^{19}(\gamma , 2p){\mathrm{N}}^{17}$ are shown to be in good agreement with the modified theory for an electric-quadrupole transition.

• Received 31 March 1958

DOI:https://doi.org/10.1103/PhysRev.111.1642