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MS: Fachverband Massenspektrometrie

MS 10: Accelerator Mass Spectrometry II

MS 10.3: Talk

Friday, March 14, 2025, 11:45–12:00, HS 2 Chemie

Detecting Environmental ²³¹Pa Using Accelerator Mass Spectrometry — •Janis Wolf¹, Marcus Christl², Sebastian Fichter¹, Habacuc Perez Tribouillier², Stella Winkler¹, and Anton Wallner¹ — ¹Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany — ²ETH Zürich, Laboratory of Ion Beam Physics (LIP), Zürich, Switzerland

While many actinides (e.g., ²³⁶U, ²³⁹Pu, ²⁴¹Am) are routinely measured in environmental samples using accelerator mass spectrometry (AMS), the naturally occurring radionuclide ²³¹Pa (t_1/2 = 3.28· 10⁴ a) is not among them, even though it has been shown that its AMS detection limit is in the lower femtogram range[1]. Challenges in the measurement of ²³¹Pa include the complicated sample preparation and the lack of a long-lived isotope that one could use for normalization.

We developed chemical sample preparation procedures for environmental water and sediment samples, proven successful by our first beam time using MILEA at ETH Zürich. We could achieve a great abundance sensitivity on the mass 231, with no significant background contriburion of ²³²Th. We also investigated complications caused by the short-lived ²³³Pa (t_1/2 = 26.98 days), used for normalization. The ingrowth of ²³³U in our samples causes a lower ²³¹Pa/²³³X ratio to be measured, as UO⁻ has up to 10 times higher negative ion formation efficiency than PaO⁻ in the ion source. This needs to be accounted for by measurement of standards.

[1] M. Christl et al., Nucl. Instrum. Methods Phys. Res., B 262 (2007) 379

Keywords: Protactinium; Accelerator Mass Spectrometry