High-Specific-Activity ¹⁹⁸Au Low in ¹⁹⁹Au

Gold-198 with a specific activity of 370 Ci/g and containing <0.1% ¹⁹⁹Au was produced by the epithermal neutron-capture reaction, ¹⁹⁷Au(n,γ) ¹⁹⁸Au. The secondary neutron-capture reaction, ¹⁹⁸Au(n,γ)¹⁹⁹Au, was greatly reduced by a thermal-neutron absorber—a cadmium capsule in which the samples of gold foil and gold-aluminum alloy were irradiated. High-specific-activity ¹⁹⁸Au with <0.1% ¹⁹⁹Au is especially useful for medical purposes.