Ultrasensitive detection of ²⁴⁴Pu in environmental samples by accelerator mass spectrometry

For the ultrasensitive determination of ²⁴⁴Pu by accelerator mass spectrometry, a suitable methodology was developed at the IFIN-HH AMS laboratory. Alpha spectrometry was used to verify the performance of the radiochemical procedure for plutonium extraction, including preparation of alpha sources by electrodeposition and microprecipitation. The chemical yield for plutonium extraction from environmental samples was found to be reasonable (∼86%) for our purposes. The ²⁴⁴Pu AMS measurements were performed using two AMS systems, 1 MV (IFIN-HH) and 3 MV (CIRCE) accelerators. The spectra collected using chemical blanks clearly show the zero background when measuring mass 244, while a total measurement efficiency for both systems of the order of 10⁻⁴ was estimated. Regarding the concentration of ²⁴⁴Pu per gram of sediment, we obtained hundreds of atto-grams per gram for the sediment of Bikini Atoll, while for the sediment of the Pacific Ocean the level is of the order of several tens of atto-grams per gram. In addition, we determined isotopic ratios for ²⁴⁰Pu/²³⁹Pu and ²⁴⁴Pu/²³⁹Pu for both certified reference materials, and they are in fine agreement within the 2σ limits when comparing the two AMS systems used in this work as well as compared to other published results.