A comparison of two calibration methods of the 229 Th spike for uranium age dating by 230 Th/ 234 U radiochronometer

230 Th/ 234 U radiochronometer was commonly used for uranium age determination which could help to reveal the origin of the nuclear material. 229 Th was a relatively appropriate spike for measuring 230 Th by isotope dilution mass spectrometry and its concentration needs to be calibrated before using as spike. A prepared 229 Th solution which was used as Th isotope spike for age dating of CRM U850 sample were calibrated separately by 232 Th and 230 Th standard materials. The calibrated results were compared and evaluated.