Abstract #1158 (LPI nº 2083) A NEW QUADRUPOLE ION TRAP MASS SPECTROMETER FOR MEASURING NOBLE GASES IN PLANETARY ATMOSPHERES G. Avice1, A. Belousov2, S. Madzunkov2, K. A. Farley1, J. Simcic2, D. Nikolic2, M. R. Darrach2, C. Sotin2 *[email protected], 1California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, USA. 2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA. Motivation and presentation of the instrument Sequence 1 Sequence 2 Kr, Xe Relative abundances and isotope ratios of noble gases in Ionization Ejection planetary atmospheres can answer fundamental ques- Top electrode Alumina ceramic Trapping Detection tions: Cathode/Filament spacer holder Adapted from [4] i) What was the delivery mix (Solar/Chondritic/Cometary) Ring electrode to planetary atmospheres? Anode Einzel lens Focus { Exit Bottom electrode ii) To what extent are silicate portions (mantle, crust) of ter- ELECTRON GUN restrial planets degassed? RF (ring) iii) How much of the atmosphere was lost by atmospheric escape and what is the timing of this escape? Photonis 5901 Magnum Anode (Ionizer) 0V 20 mm TM electron multiplier -110V Detector Neg. Grid 0V z symmetry axis -120V Venus is a missing piece of the noble gaz puzzle [1]. Com- Detector Pos. Grid Fig. 1: Picture of the ion trap. Ions are created by electron-impact in the mm-sized +120V pact missions recently suggested to use a noble gas qua- 0V drupole ion trap mass spectrometer (QITMS) [2] deve- space between the top and bottom electrodes. A radiofrequency signal (about 1 MHz) applied to the ring electrode traps the ions [2]. Ramping the voltage applied 0 5 10 15 20 25 loped at JPL (Fig. 1) [3] to measure noble gases in the to the ring electrode ejects ions in both directions along the z-axis. Light masses time (ms) Venus atmosphere. are ejected first. An electron multiplier (channeltron) detects the ejected ions. Fig. 2: Measurement sequence with ionization and ejection. Main questions Standard gases, samples and procedure - Is the instrument able to measure small amounts (<10-13 mol) 1 shot from the standard bottle = 2x10-14 mol of 84Kr and 8x10-16 mol of 132Xe. Atmopheric isotope ratios. of noble gases in static mode & without a cooling gas? Standard shots Samples - Does the precision meet requirements for answering Aliquots of gas are first expanded in a 0.5 L volume. Resi- Gas from acid-resistant residues of the Allende meteo- questions in planetary sciences? dual reactive gases are purified with D50/D100 capacitorr rite was extracted by laser step-heating. Reactive gases getters (SAES) during 10 mn. Gas is introduced into the were removed by a Ti sponge getter at 650 ºC. Kr and 4 L chamber enclosing the QITMS and in static vacuum Xe were separated by condensation on the walls of a Krypton (pumped closed). Pressure equilibrates within 2 mn after quartz tube held at liquid nitrogen temperature. 4 10 introduction. ++ Xenon 80 Xe 86 84 103 Precision Kr/ Kr = 0.3181 ± 0.0005 (1.6 ‰, 60 mn, N = 1005) s.e.m = N measured error 60 2 One complete isotopic spectrum counting statistics 10 10 total counts is collected every cycle (20-50 40 1 ms) meaning that measuring the 10 density gas during few minutes allows Kr ratio to compile hundreds of isotope 20 84 1 ratios (Fig. 5). The precision fol- Kr/ mass 86 Fig. 3: Isotopic spectrum showing Kr and Xe from a standard shot. lows closely the counting statis- 0 1 Note the log scale. Other peaks are hydrocarbon fragments. tics predicted by the Poisson’s 0.26 0.28 0.30 0.32 0.34 0.36 86Kr/84Kr law (Fig. 6). Fig. 5: Example of the distribution of 103 86Kr/84Kr ratios Sensitivity and signal evolution collected over 1h of measurement. error in % of the Sensitivity depends on the emission current 1.0 Reproducibility and reaches 1.2x1013 cps/torr of gas. a 86 84 2 0.1 Potential improvements: Kr/ Kr = 0.3182 ± 0.0007 (2‰, 1 , reduced = 1.8) 0.9 0.320 i) collecting all ions with a second detector 0 500 1000 1500 ii) changing the type of filament to get a more Kr 0.319 84 # accumulated ratios focused electron beam Kr/ 0.318 86 84 normalized signal Fig. 6: Evolution of the error on the Kr/ K ratio with 0.8 86 iii) changing the type of getter for a better puri- 0.317 accumulation of the isotope ratios. The error follows fication of the residual gas Kr signal (2x103 cps) closely the Poisson’s law. Methane signal (~104 cps) 0 2 4 6 8 10 Signal decreases faster than predicted by ion 0.7 # of measurement 0 1000 2000 b Several aliquots (10 over 3 days) of the consumption (Fig. 4). This is likely due to a 129Xe/132Xe = 0.9514 ± 0.005 (5‰, 1 , reduced 2 = 0.91) time (s) standard were measured to characte- growing contribution from residual gas (mainly 0.97 CH ). Fig. 4: Evolution of the Kr and CH4 signals with time. rize the external reproducibility (Fig. 7). 4 Xe 0.96 It matches the internal precision 132 1.20 0.95 Xe/ meaning that the QITMS is able to pro- Allende meteorite (HF/HCl residue) Results obtained on samples 129 0.94 duce virtually identical results over 1.15 time. Changing the source conditions Results of the measurement of gases 0 2 4 6 8 10 (energy and focus) changes the values 1.10 extracted from HF-HCl residue of the # of measurement 86 84 129 132 of isotope ratios. meteorite Allende are similar to values Fig. 7: Reproducibility of the Kr/ Kr (a) and Xe/ Xe (b) ratios. 1.05 reported in the literature [5]. For Xe relative to air example, the 40Ar/36Ar ratio is lower Preliminary Conclusions and Potential Improvements 132 Air - JPL QITMS is able to measure noble gases in static mode for extended periods of time (>10 h) Xe/ i 1.00 than 50. The isotopic composition of - Counting statistics follows the Poisson’s law Xe (Fig. 8) matches the Q component - Precision and reproducibility meet requirements for a mission sampling the Venus atmosphere 0.95 ion trap measurement found in meteorites [5]. Chondritic Xe, Busemann et al. (2000) - Future investigations: potential improvements in sensitivity, RF stability, measurement of light noble gases - QITMS would be proposed for integration on the Cupid’s Arrow small satellite mission (see Abstract #1763) 128 130 132 134 136 mass Fig. 8: Isotopic spectrum of Xe in the Allende meteorite. [1] Chassefière et al. (2012) Planet. & Space Sci. 63-64; [2] Paul & Steinwedel (1953) Zeit. fur Naturforsch. A 8; [3] Madzunkov & Nikolic (2014) J. Am. Soc. Mass Spectrom. 25; [4] March (1997) J. of Mass Spectrom. 32; [5] Busemann et al. (2000) MAPS 35..