Production and characterization of 60Fe standards for accelerator mass spectrometry

Abstract

Accelerator Mass Spectrometry (AMS) is one of the most sensitive analysis techniques to measure long-lived radionuclides, reaching detection limits for isotopic ratios down to 10 −15 –10 −16 in special cases. Its application portfolio covers nearly every field of environmental research, considering processes in the atmosphere, biosphere, hydrosphere, cryosphere, lithosphere and the cosmosphere. Normally, AMS measures the content of isotopes in comparison to a validated standard. However, in some cases like for example 60 Fe, well characterized standard materials are difficult to produce due to the extreme rareness of the isotope. We report here on the manufacturing of a set of 60 Fe standards, obtained by processing irradiated copper from a beam dump of the high-power proton accelerator (HIPA) at the Paul Scherrer Institute (PSI). The isotopic ratios of the standards have been adjusted via a dilution series of a master solution, isotopic content of which has been characterized by Multi Collector–Inductively Coupled Plasma–Mass Spectrometry (MC-ICP-MS). In total, we produced three samples with isotopic ratios of 1.037(6)·10 −8 , 1.125(7)·10 −10 and 1.234 (7)·10 -12 , respectively. The latter had already been applied in three pioneering AMS studies investigating the remaining signal of injected matter of nearby super novae explosions in sediment archives.

60 Fe deposition during the late Pleistocene and the Holocene echoes past supernova activity

“…The unknown samples were measured relative to standard-type samples (isotope ratios known with ∼10% accuracy) which were based on material from the Technical University of Munich and on material from recent meteorite studies (63). They had been previously cross-calibrated against a material from the Paul Scherrer Institute with well-known isotope ratios (64). These samples confirmed the validity of scaling the system settings between the different masses, with the data showing a reproducibility of ∼5%.…”

Exotic Radionuclides – What are they good for?

“…The neutron capture cross sections both for thermal and stellar energies [20] were the first-ever measurements for this isotope, with which now a much more reliable experimental database exists for the interpretation of related astrophysical processes. Moreover, we manufactured and characterized a series of reference materials for Accelerator Mass Spectrometry (AMS), [21] a very sensitive detection method, which is nowadays able to determine isotopic ratios down to ratios of 10 -14 , in special cases even lower. However, AMS is not an absolute method, but performs the measurements in comparison to reference material with wellknown isotopic ratios.…”

53Mn and 60Fe in iron meteorites—New data, model calculations

“…The nuclide 60 Fe was measured at the ANU Canberra relative to the PSI‐12 standard material, which was produced at the Paul Scherrer Institute (PSI) from a dilution series that is based on material extracted from a beam dump. The 60 Fe/Fe ratio of PSI‐12 is 1.234(7) × 10 −12 (Schumann et al 2019). The original material was used for the half‐life measurements of 60 Fe (e.g., Rugel et al 2009).…”