Accurate Xe Isotope Measurement Using JPL Ion Trap

Abstract

We report an approach for the reproducible and accurate compositional analysis of different mixtures of Xe isotopes using miniature Jet Propulsion Laboratory Quadrupole Ion Trap (JPL-QIT). A major study objective was to validate the recent instrumental improvements to the long-term operational stability under different pressures, temperatures, and trapping conditions. We propose that the present device can be used in certification of trace amounts of isotopes in mixtures dominated by one or more isotopes. Measured isotopic compositions are verified against commercially available standards with accuracy better than 0.07%. To aid the analysis of experimental data, we developed a scalable replica fitting method and use peak areas as descriptors of relative isotopic abundances. This low-power and low-mass device is ideally suited for planetary explorations aimed to enhance quantitative analysis for major isotopes present in small amounts of atmospheric samples.

Computer Modeling of an Ion Trap Mass Analyzer, Part I: Low Pressure Regime

“…For the experimental results presented herein, this assumption is valid as all of the measurements were conducted at low pressures (P ≤ 2 × 10 − 6 Torr) and weak ionization currents (I e ≤ 5 × 10 − 6 A), strictly limiting the number density of confined ions (N i ≤ 2 × 10 5 cm − 3 ). In this regime, ion-ion collisions are a rare event that has been shown previously to affect only the low-mass wing of individual line profiles [21]. Under the stated assumptions, we consider the time evolution of a set of mutually noninteracting particles and numerically integrate a system of equations of motion:…”

“…As illustrated in the xenon mass spectra found in Figure 1, the ion-neutral collisions at low pressures change the decay rate for the low-mass wing of the line profile. The central part of a profile remains unchanged and its full width at half maximum (FWHM) is further used in characterizing the mass resolution of the instrument [21]. This earlier modeling work demonstrated the variation of the mass spectral line shapes subject to trapping conditions.…”

“…A check is performed for collocation in the initial ion cloud to ensure that any random subset is also statistically unbiased and free from particle fusion. Cylindrical geometry is a consequence of axial cylindrical holes present in the endcap electrodes through which electrons are introduced and trapped ions are extracted from the real ion trap [21]. Initial dimensions and position of a cylindrical ion cloud can be controlled either through the pattern file or a command line interface.…”

Response of QIT-MS to Noble Gas Isotopic Ratios in a Simulated Venus Flyby

“…The thermalizer maintains the stainless steel (SS) tube temperature at 70 • C to reduce deposition of sulfuric acid aerosols at the tube's inner surface. The voltage amplitude scan function for the RF drive is detailed in Madzunkov & Nikolic [15].…”

“…When catering to a subset of scientific requirements, each instrument projects its performance based on response function parameters. The QIT-MS sensor is no exception, and details of its response function are found elsewhere [15]. We have also developed a simulation program [16] capable of predicting QIT-MS sensor performance under a wide range of operational parameters.…”