Assume a copper foil to be irradiated in a thermal neutron flux of \(1.0 \times 10^{9} \mathrm{n} / \mathrm{cm}^{2} / \mathrm{s}\). Using activation cross section for \({ }^{63} \mathrm{Cu}\) as \(4.41 \mathrm{~b}\) and for \({ }^{65} \mathrm{Cu}\) as \(1.8 \mathrm{~b}\), find the ratio of saturation activity due to \({ }^{64} \mathrm{Cu}\) and \({ }^{66} \mathrm{Cu}\).