Speaker
Description
The AMS technique was implemented for the first time in Spain in 2005, with the arrival at the Centro Nacional de Aceleradores (CNA, Seville) of the first compact and multi-elemental system put in the market by High Voltage Engineering Europa (HVEE, Amersfoort, The Netherlands). Since then, actinides measurement techniques have been in constant development at the CNA. To date, 236U, 237Np, 239Pu, 240Pu and 241Pu can be considered consolidated radionuclides and are routinely measured in a variety of samples [1,2]. Recently, the AMS technique has been setup for 233U [3] and 244Pu [4] analysis. The limelight is now put on Am and Cm analysis.
The compact design of the spectrometer constraints the abundance sensitivity that can be obtained for those nuclides neighboured in mass by naturally occurring isotopes. This is the case of 236U, neighboured by 235U and 238U, and 233U, neighboured by 232Th, 234U and 235U, for which background isotopic ratios of 10-10 (i.e. 236U/238U) and of 5x10-11 (i.e. 233U/238U) have been demonstrated, respectively [3,5]. It has been observed that the survival of molecular isobars in 3+ charge state can limit the sensitivity of the technique is the stripper gas settings are not properly adjusted. This can be especially critical for the extremely minor 244Pu, due to the survival of the diatomic trication 232Th12C3+ [4]. Recent studies on Am (241Am and 243Am) and Cm (244Cm, 245Cm and 246Cm) isotopes point out to detection issues related to the presence of lanthanides (mostly Dy isotopes) in the sample, due to occurrence of pile-up events from 2+ molecular fragments mimicking the electronics signal of 3+ actinides ions in the detector (e.g. 162Dy2+ and 243Am3+). Thus, the best performance of the AMS technique for actinides analysis in environmental samples can be achieved if: i) the AMS technical parameters are thoroughly adjusted in every case (i.e. slits settings and stripper gas pressure), and ii) the radiochemistry of the samples is optimized so that Th is suppressed from the U, Np and Pu samples, and lanthanides from the Am and Cm samples [7].
At the CNA, a synergy between both research fields, AMS technique and radiochemistry, has been achieved, so that the most minor and demanding actinides radionuclides can be analysed in a variety of environmental matrixes. In this work, the overall performance of the technique will be presented. Besides, examples of the most recent studies carried out at the CNA illustrating the potential of the U, Pu and Am isotopic vectors to gain information on the anthropogenic sources of actinides to the environment will be given.
[1] M. López-Lora, E. Chamizo, I. Levy, M. Christl, N. Casacuberta, T.C. Kenna, 236U, 237Np and 239,240Pu as complementary fingerprints of radioactiveeffluents in the western Mediterranean Sea and in the Canada Basin (Arctic Ocean), Sci. Total Environ. 765 (2021) 142741. https://doi.org/10.1016/J.SCITOTENV.2020.142741.
[2] M. López-Lora, G. Olszewski, E. Chamizo, K. Pettersson, M. Eriksson, Plutonium Signatures in a Dated Sediment Core as a Tool to Reveal Nuclear Sources in the Baltic Sea, Environ. Sci. Technol. (2023). https://doi.org/10.1021/acs.est.2c07437.
[3] E. Chamizo, M. López-Lora, M. Christl, Performance of the 1 MV Accelerator Mass Spectrometry system at the Centro Nacional de Aceleradores for the analysis of 233U at environmental levels, Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms. 533 (2022) 81–89. https://doi.org/10.1016/J.NIMB.2022.10.019.
[4] E. Chamizo, M. López-Lora, I. Levy, V. Lérida, Reaching environmental levels of 244Pu by Accelerator Mass Spectrometry at the Centro Nacional de Aceleradores, J. Environ. Radioact. (submitted (2024).
[5] E. Chamizo, M. López-Lora, Accelerator mass spectrometry of 236U with He stripping at the Centro Nacional de Aceleradores, Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms. 438 (2019) 198–206. https://doi.org/10.1016/j.nimb.2018.04.020.
[7] M. López-Lora et al., This conference: Sequential extraction of U, Np, Pu and Am from sediment samples for AMS studies at the Centro Nacional de Aceleradores (CNA, Spain).
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