Independent measurements of 129I content in environmental reference materials using accelerator and thermal ionization mass spectrometry

Iodine environmental measurement programs are in need of new materials with certified 129I activity. Frequently 129I measurements are validated in the literature using the standard material IAEA-375, Chernobyl soil, which is the only soil/sediment material with a recommended 129I activity. IAEA-375 has not been available for purchase since 2010. This study is an extension of previous work at INL to include four additional standard materials that are commercially available (NIST materials: RM 8704, Buffalo River sediment, SRM 2710a, Montana I soil, and IAEA materials: SL-1, lake sediment, IAEA-385, Irish Sea sediment). These materials have certified or recommended activities for a variety of radionuclides but not for 129I. This paper reports a comparison of accelerator mass spectrometry (AMS) and thermal ionization mass spectrometry (TIMS) data for 129I activity, as well as the 129/127I ratios for these standards to assist in identifying a suitable alternative for IAEA-375. Two independent chemical separation and mass spectrometric analysis techniques have been applied in an effort to corroborate the data. Both methods were validated via analyses of IAEA-375 for 129I and show good agreement with the recommended activity of 1.7 × 10−3 Bq kg−1 for 129I; (1.6 × 10−3 Bq kg−1 by AMS and 1.8 × 10−3 Bq kg−1 by TIMS) with both sets of results within the 95% confidence interval of the recommended value.