Abstract
The long-lived radioisotope 182Hf (T1/2 = 8.9 Ma) is of high astrophysical interest as its potential abundance in environmental archives would provide insight into recent r-process nucleosynthesis in the vicinity of our solar system. Despite substantial efforts, it could not be measured at natural abundances with conventional AMS so far due to strong isobaric interference from stable 182W. Equally important is an increase in ion source efficiency for the anions of interest. The new Ion Laser InterAction Mass Spectrometry (ILIAMS) technique at VERA tackles the problem of elemental selectivity in AMS with a novel approach. It achieves near-complete suppression of isobar contaminants via selective laser photodetachment of decelerated anion beams in a gas-filled radio-frequency quadrupole (RFQ) ion cooler. The technique exploits differences in electron affinities (EA) within elemental or molecular isobaric systems neutralizing anions with EAs smaller than the photon energy. Alternatively, these differences in EA can also facilitate anion separation via chemical reactions with the buffer gas. We present first results with this approach on AMS-detection of 182Hf. With He +O2 mixtures as buffer gas in the RFQ, suppression of 182WF5− vs 180HfF 5− by >105 has been demonstrated. Mass analysis of the ejected anion beam identified the formation of oxyfluorides as an important reaction channel. The overall Hf-detection efficiency at VERA presently is 1.4% and the W-corrected blank value is 182Hf/180Hf = (3.4 ± 2.1)×10−14. In addition, a survey of different sample materials for highest negative ion yields of HfF 5− with Cs-sputtering has been conducted.
Highlights
Accelerator mass spectrometry (AMS) commonly is the most sensitive technique for the detection of long-lived isotopes, reaching down to the attogram/gram abundance range
It consists of a cesium sputter ion source followed by a 90 bending magnet and the Ion Laser InterAction Mass Spectrometry (ILIAMS) radiofrequency quadrupole ion cooler, a 1 m long linear ion guide based on a 2D Paul trap, where electrostatically-slowed anions gently collide with He bu↵er gas and reach almost thermal energies resulting in transit times of several ms [21]
First AMS measurements were conducted on a set of inhouse reference materials employed in [16] with nominal ratios of 182Hf/180Hf = 5.59⇥10 and 182Hf/180Hf = 5.88⇥10 (Vienna-Hf11) and blank material from commercial HfF4 (Alfa Aesar)
Summary
Accelerator mass spectrometry (AMS) commonly is the most sensitive technique for the detection of long-lived isotopes, reaching down to the attogram/gram abundance range. Over recent years, it has subsequently been employed in the search for signatures from recent nucleosynthesis in the vicinity of the solar system and corresponding signals of 60Fe and 244Pu have been identified in terrestrial and lunar archives [1,2,3,4,5]. The challenge in AMS-detection of 182Hf at these low abundances is interference from the ubiquitous stable isobar 182W This quest started at the 3-MV-Vienna Environmental Research Accelerator (VERA) in 2002 [14]. Ences in electron a nities (EAs) between the isobars may, allow us to reach the required sensitivity
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
