Development of a chemical separation strategy for Pu, Am and Cm from rare-earth rich geological archives

The understanding of the formation of the elements has been an intriguing topic within the last decades. It is now approved that the heaviest naturally occurring elements on earth, the actinides, are produced in the astrophysical r-process. However, the exact site of this process is still debated. Recently, the amount of interstellar 244Pu (T1/2 = 81.3 Myr) in various geological archives like deep-sea ferromanganese crusts and sediments has been investigated by applying highly sensitive accelerator mass spectrometry measurements (AMS).[1,2] Correlation of the influx of 244Pu with 60Fe (T1/2 = 2.6 Myr) which is produced by the weak s-process in massive stars and ejected into the interstellar medium by supernovae could point to a possible origin of the r-process in the universe. To further prove this hypothesis, recent investigations focus on the determination of other long-lived radionuclides which are also produced in the r-process, e.g. 247Cm (T1/2 = 15.6 Myr) and 182Hf (T1/2 = 8.9 Myr). However, the separation of the expected ultra-trace amounts of these nuclides (a few 100 atoms per gram) from huge amounts of matrix and interfering elements represents a major analytical challenge. Thus, this contribution aims to probe existing chemical treatment strategies for the determination of minute amounts of actinides and Hf from various geological archives. The separation method is based on anion exchange for Pu separation and extraction chromatography for Cm and Hf, respectively.[3] The yield of the different elements is monitored by a combination of AMS, γ-counting and ICP-MS measurements. The effective separation strategy of different actinides and Hf from major matrix elements allow for processing multi-gram amounts of different geological samples. This is a prerequisite for the detection of live interstellar 247Cm and 182Hf in geological archives. Furthermore, this adapted method can be used for the analysis of environmental samples regarding their content and isotopic ratio of anthropogenically produced Pu, Am and Cm which holds potential for nuclear safeguards and nuclear forensics studies.