CHILI – the Chicago Instrument for Laser Ionization – a new tool for isotope measurements in cosmochemistry

Abstract

Graphi cal Abstract 3 Highlights• CHILI is a new resonance ionization mass spectrometer at the University of Chicago • CHILI has been developed for isotopic analysis of small samples in cosmochemistry • CHILI combines high spatial resolution and high sensitivity • Sr, Ba, Fe, and Ni isotopes have been measured in presolar grains • A new timing scheme allows analysis of all Fe and Ni isotopes without interferences 4 ABSTRACT We describe CHILI, the Chicago Instrument for Laser Ionization, a new resonance ionization mass spectrometer developed for isotopic analysis at high spatial resolution and high sensitivity of small samples like contemporary interstellar dust grains returned by the Stardust spacecraft. We explain how CHILI addresses the technical challenges associated with such analyses by pushing most technical specifications towards their physical limits. As an initial demonstration, after many years of designing and developing CHILI, we have analyzed presolar silicon carbide grains for their isotopic compositions of strontium, zirconium, and barium. Subsequently, after further technical improvements, we have used CHILI to analyze, for the first time without interference, all stable isotopes of iron and nickel simultaneously in presolar silicon carbide grains. With a special timing scheme for the ionization lasers, we separated iron and nickel isotopes in the time-of-flight spectrum such that the isobaric interference between 58 Fe and 58 Ni was resolved. In-depth discussion of the astrophysical implications of the presolar grain results is deferred to dedicated later publications. Here we focus on the technical aspects of CHILI, its status quo, and further developments necessary to achieve CHILI's ultimate goals, ~10 nm lateral resolution and 30-40 % useful yield.

J-type Carbon Stars: A Dominant Source of 14N-rich Presolar SiC Grains of Type AB

“…CHILI is equipped with six Ti:sapphire lasers for resonance ionization (Stephan et al 2016). All of the Sr, Mo, and Ba isotopes were simultaneously measured in each grain using the procedure described by Stephan et al (2017).…”

New Constraints on the Major Neutron Source in Low-mass AGB Stars

“…Such detailed analyses have demonstrated that the majority of presolar SiC grains (>90%), known as mainstream (MS) SiC grains, came from low-mass AGB stars and contain heavy trace elements with s-process isotopic signatures (Nicolussi et al 1997(Nicolussi et al , 1998Lugaro et al 2003). Analysis of heavy element isotopic compositions of MS SiC grains with precision on the order of 1−10% (e.g., Savina et al 2003;Stephan et al 2016), therefore, provides a unique opportunity to investigate the s-process nucleosynthesis in AGB stars at a level of detail that cannot be achieved by current astronomical observations.…”

Electronic data acquisition and operational control system for time‐of‐flight sputtered neutral mass spectrometer

“…If a single event involves multiple ions, it is difficult to apply the event counting methods to determine accurate ion numbers, but the ADC method may be available. Recent development of time‐of‐flight sputtered neutral mass spectrometry (TOF‐SNMS) using laser postionization is expected ultimate increase of ionization efficiency of atoms and molecules (eg, Stephan et al and Ebata et al). The ionization efficiencies for various elements increase up to 100 times by irradiation of femtosecond laser of 2.5 mJ of the pulse energy and 120‐femtosecond pulse width .…”