The irradiated samples were step heated on-line in a Modifications Ltd. Low-blank furnace. Temperature control is better than 1 degree, and a maximum temperature in excess of 1,600C is achievable to ensure complete sample fusion. The extracted argon was purified in a two-stage process using a liquid-nitrogen cold finger and two SAES Zr-Al getters. The purified Ar gas was measured using a Nuclide 6-60-SGA 15-cm mass spectrometer. Argon isotopic measurements for both samples and standards were corrected for the system blanks, for decay of 37Ar and 39Ar, and for reactor-induced isotopic interferences.