40Ar/39Ar step-heating was performed. Individual samples consisted of up to several grains from each respective irradiated sample, loaded into 2 mm-diameter holes in a copper tray, which was then loaded in an ultra-high vacuum line. Samples were step-heated using a 6-watt argon-ion laser. Argon was purfied using a liquid nitrogen cold trap and a SAES Zr-Al getter aat 400C. Argon isotopes were measured using a VG-3600 mass spectrometer, with corrections for system blanks, decay of 39Ar and 37 Ar, and reactor-induced interferences.