Electrodisintegration ofCu63,Zn64,Ag109, andTa181

Abstract

The ratio of the ($\ensuremath{\gamma}, n$) photodisintegration cross section to the ($e, {e}^{\ensuremath{'}}n$) electrodisintegration cross section for the isotopes ${\mathrm{Cu}}^{63}$, ${\mathrm{Zn}}^{64}$, ${\mathrm{Ag}}^{109}$, and ${\mathrm{Ta}}^{181}$ was measured for electron energies of 24 to 35 Mev. This ratio was found to decrease with energy in contrast with the Weizs\"acker-Williams approximation which predicts a constant ratio. However, the Weizs\"acker-Williams method does yield a result which is of the right order of magnitude for Cu, Zn, and Ag and which is within a factor of two of the observed value of Ta.Assuming approximately one-half of the total photon absorption of nuclei to be attributed to the ($\ensuremath{\gamma}, n$) reaction, then comparison of the experimental results for Cu, Zn, and Ag with calculations of Blair is consistent with the suggestion of Bethe and Levinger that the main absorption mechanism of nuclei for photons is electric dipole with a contribution of \ensuremath{\sim}6 percent electric quadrupole absorption. However, for Ta no simple correlation between experiment and theory was found. This is attributed to a failure of the Born approximation used in the Blair calculations.