A NEW QUADRUPOLE ION TRAP MASS SPECTROMETER FOR …Aliquots of gas are first expanded in a 0.5 L...
1
129 Xe/ 132 Xe = 0.9514 ± 0.005 (5‰, 1 , reduced 2 = 0.91) 129 Xe/ 132 Xe 0.94 0.95 0.96 0.97 # of measurement 0 2 4 6 8 10 measured error counting statistics error in % of the 86 Kr/ 84 Kr ratio 0.1 1 10 # accumulated ratios 0 500 1000 1500 Top electrode Alumina ceramic spacer Ring electrode Bottom electrode Photonis 5901 Magnum electron multiplier TM Cathode/Filament holder Anode Focus Exit { Einzel lens z symmetry axis ELECTRON GUN 20 mm A NEW QUADRUPOLE ION TRAP MASS SPECTROMETER FOR MEASURING NOBLE GASES IN PLANETARY ATMOSPHERES G. Avice 1 , A. Belousov 2 , S. Madzunkov 2 , K. A. Farley 1 , J. Simcic 2 , D. Nikolic 2 , M. R. Darrach 2 , C. Sotin 2 *[email protected], 1 California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, USA. 2 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA. Motivation and presentation of the instrument Relative abundances and isotope ratios of noble gases in planetary atmospheres can answer fundamental ques- tions: i) What was the delivery mix (Solar/Chondritic/Cometary) to planetary atmospheres? ii) To what extent are silicate portions (mantle, crust) of ter- restrial planets degassed? iii) How much of the atmosphere was lost by atmospheric escape and what is the timing of this escape? Venus is a missing piece of the noble gaz puzzle [1]. Com- pact missions recently suggested to use a noble gas qua- drupole ion trap mass spectrometer (QITMS) [2] deve- loped at JPL (Fig. 1) [3] to measure noble gases in the Venus atmosphere. [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. - Is the instrument able to measure small amounts (<10 -13 mol) of noble gases in static mode & without a cooling gas? Main questions Preliminary Conclusions and Potential Improvements - Does the precision meet requirements for answering questions in planetary sciences? - JPL QITMS is able to measure noble gases in static mode for extended periods of time (>10 h) Standard gases, samples and procedure Fig. 1: Picture of the ion trap. Ions are created by electron-impact in the mm-sized 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 to the ring electrode ejects ions in both directions along the z-axis. Light masses are ejected first. An electron multiplier (channeltron) detects the ejected ions. 1 shot from the standard bottle = 2x10 -14 mol of 84 Kr and 8x10 -16 mol of 132 Xe. Atmopheric isotope ratios. Precision Sensitivity and signal evolution One complete isotopic spectrum is collected every cycle (20-50 ms) meaning that measuring the gas during few minutes allows to compile hundreds of isotope ratios (Fig. 5). The precision fol- lows closely the counting statis- tics predicted by the Poisson’s law (Fig. 6). Reproducibility Several aliquots (10 over 3 days) of the standard were measured to characte- rize the external reproducibility (Fig. 7). It matches the internal precision meaning that the QITMS is able to pro- duce virtually identical results over time. Changing the source conditions (energy and focus) changes the values of isotope ratios. Sensitivity depends on the emission current and reaches 1.2x10 13 cps/torr of gas. Potential improvements: i) collecting all ions with a second detector ii) changing the type of filament to get a more focused electron beam iii) changing the type of getter for a better puri- fication of the residual gas Signal decreases faster than predicted by ion consumption (Fig. 4). This is likely due to a growing contribution from residual gas (mainly CH 4 ). - Counting statistics follows the Poisson’s law - Precision and reproducibility meet requirements for a mission sampling the Venus atmosphere - Future investigations: potential improvements in sensitivity, RF stability, measurement of light noble gases Adapted from [4] Fig. 2: Measurement sequence with ionization and ejection. Results obtained on samples Fig. 4: Evolution of the Kr and CH 4 signals with time. Fig. 3: Isotopic spectrum showing Kr and Xe from a standard shot. Note the log scale. Other peaks are hydrocarbon fragments. Kr, Xe Aliquots of gas are first expanded in a 0.5 L volume. Resi- dual reactive gases are purified with D50/D100 capacitorr getters (SAES) during 10 mn. Gas is introduced into the 4 L chamber enclosing the QITMS and in static vacuum (pumped closed). Pressure equilibrates within 2 mn after introduction. Standard shots Gas from acid-resistant residues of the Allende meteo- rite was extracted by laser step-heating. Reactive gases were removed by a Ti sponge getter at 650 ºC. Kr and Xe were separated by condensation on the walls of a quartz tube held at liquid nitrogen temperature. Samples Fig. 6: Evolution of the error on the 86 Kr/ 84 K ratio with accumulation of the isotope ratios. The error follows closely the Poisson’s law. Fig. 5: Example of the distribution of 10 3 86 Kr/ 84 Kr ratios collected over 1h of measurement. Fig. 7: Reproducibility of the 86 Kr/ 84 Kr (a) and 129 Xe/ 132 Xe (b) ratios. Results of the measurement of gases extracted from HF-HCl residue of the meteorite Allende are similar to values reported in the literature [5]. For example, the 40 Ar/ 36 Ar ratio is lower than 50. The isotopic composition of Xe (Fig. 8) matches the Q component found in meteorites [5]. Kr signal (2x10 3 cps) Methane signal (~10 4 cps) normalized signal 0.7 0.8 0.9 1.0 time (s) 0 1000 2000 Fig. 8: Isotopic spectrum of Xe in the Allende meteorite. - QITMS would be proposed for integration on the Cupid’s Arrow small satellite mission (see Abstract #1763) 86 Kr/ 84 Kr = 0.3182 ± 0.0007 (2‰, 1 , reduced 2 = 1.8) 86 Kr/ 84 Kr 0.317 0.318 0.319 0.320 # of measurement 0 2 4 6 8 10 Abstract #1158 (LPI nº 2083) ion trap measurement Chondritic Xe, Busemann et al. (2000) Air Allende meteorite (HF/HCl residue) i Xe/ 132 Xe relative to air 0.95 1.00 1.05 1.10 1.15 1.20 mass 128 130 132 134 136 a b 86 Kr/ 84 Kr = 0.3181 ± 0.0005 (1.6 ‰, 60 mn, N = 1005) s.e.m = N density 0 20 40 60 80 86 Kr/ 84 Kr 0.26 0.28 0.30 0.32 0.34 0.36 Krypton Xenon Xe ++ total counts 1 10 1 10 2 10 3 10 4 mass Anode (Ionizer) Detector Neg. Grid Sequence 1 RF (ring) Ionization Ejection Detector Pos. Grid Sequence 2 +120V -120V -110V 0V 0V 0V Trapping Detection time (ms) 0 5 10 15 20 25
Transcript of A NEW QUADRUPOLE ION TRAP MASS SPECTROMETER FOR …Aliquots of gas are first expanded in a 0.5 L...
129Xe/132Xe = 0.9514 ± 0.005 (5‰, 1 , reduced 2 = 0.91)
129 Xe
/132 Xe
0.94
0.95
0.96
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# of measurement0 2 4 6 8 10
measured errorcounting statistics
erro
r in
% o
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86Kr
/84Kr
ratio
0.1
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# accumulated ratios0 500 1000 1500
Top electrodeAlumina ceramicspacer
Ring electrode
Bottom electrode
Photonis 5901 Magnumelectron multiplierTM
Cathode/Filamentholder
AnodeFocusExit{Einzel lens
z symmetry axis
ELEC
TRO
N G
UN
20 m
m
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 instrumentRelative abundances and isotope ratios of noble gases in planetary atmospheres can answer fundamental ques-tions:
i) What was the delivery mix (Solar/Chondritic/Cometary) to planetary atmospheres?
ii) To what extent are silicate portions (mantle, crust) of ter-restrial planets degassed?
iii) How much of the atmosphere was lost by atmospheric escape and what is the timing of this escape?
Venus is a missing piece of the noble gaz puzzle [1]. Com-pact missions recently suggested to use a noble gas qua-drupole ion trap mass spectrometer (QITMS) [2] deve-loped at JPL (Fig. 1) [3] to measure noble gases in the Venus atmosphere.
[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.
- Is the instrument able to measure small amounts (<10-13 mol)of noble gases in static mode & without a cooling gas?
Main questions
Preliminary Conclusions and Potential Improvements
- Does the precision meet requirements for answering questions in planetary sciences?
- JPL QITMS is able to measure noble gases in static mode for extended periods of time (>10 h)
Standard gases, samples and procedure
Fig. 1: Picture of the ion trap. Ions are created by electron-impact in the mm-sized 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 to the ring electrode ejects ions in both directions along the z-axis. Light masses are ejected first. An electron multiplier (channeltron) detects the ejected ions.
1 shot from the standard bottle = 2x10-14 mol of 84Kr and 8x10-16 mol of 132Xe. Atmopheric isotope ratios.
Precision
Sensitivity and signal evolution
One complete isotopic spectrum is collected every cycle (20-50 ms) meaning that measuring the gas during few minutes allows to compile hundreds of isotope ratios (Fig. 5). The precision fol-lows closely the counting statis-tics predicted by the Poisson’s law (Fig. 6).
Reproducibility
Several aliquots (10 over 3 days) of the standard were measured to characte-rize the external reproducibility (Fig. 7). It matches the internal precision meaning that the QITMS is able to pro-duce virtually identical results over time. Changing the source conditions (energy and focus) changes the values of isotope ratios.
Sensitivity depends on the emission current and reaches 1.2x1013 cps/torr of gas.Potential improvements:i) collecting all ions with a second detector ii) changing the type of filament to get a more focused electron beamiii) changing the type of getter for a better puri-fication of the residual gasSignal decreases faster than predicted by ion consumption (Fig. 4). This is likely due to a growing contribution from residual gas (mainly CH4).
- Counting statistics follows the Poisson’s law- Precision and reproducibility meet requirements for a mission sampling the Venus atmosphere- Future investigations: potential improvements in sensitivity, RF stability, measurement of light noble gases
Adapted from [4]
Fig. 2: Measurement sequence with ionization and ejection.
Results obtained on samples
Fig. 4: Evolution of the Kr and CH4 signals with time.
Fig. 3: Isotopic spectrum showing Kr and Xe from a standard shot.Note the log scale. Other peaks are hydrocarbon fragments.
Kr, Xe
Aliquots of gas are first expanded in a 0.5 L volume. Resi-dual reactive gases are purified with D50/D100 capacitorr getters (SAES) during 10 mn. Gas is introduced into the 4 L chamber enclosing the QITMS and in static vacuum (pumped closed). Pressure equilibrates within 2 mn after introduction.
Standard shotsGas from acid-resistant residues of the Allende meteo-rite was extracted by laser step-heating. Reactive gases were removed by a Ti sponge getter at 650 ºC. Kr and Xe were separated by condensation on the walls of a quartz tube held at liquid nitrogen temperature.
Samples
Fig. 6: Evolution of the error on the 86Kr/84K ratio with accumulation of the isotope ratios. The error followsclosely the Poisson’s law.
Fig. 5: Example of the distribution of 103 86Kr/84Kr ratioscollected over 1h of measurement.
Fig. 7: Reproducibility of the 86Kr/84Kr (a) and 129Xe/132Xe (b) ratios.
Results of the measurement of gases extracted from HF-HCl residue of the meteorite Allende are similar to values reported in the literature [5]. For example, the 40Ar/36Ar ratio is lower than 50. The isotopic composition of Xe (Fig. 8) matches the Q component found in meteorites [5].
Kr signal (2x103 cps)Methane signal (~104 cps)
norm
alize
d sig
nal
0.7
0.8
0.9
1.0
time (s)0 1000 2000
Fig. 8: Isotopic spectrum of Xe in the Allende meteorite.
- QITMS would be proposed for integration on the Cupid’s Arrow small satellite mission (see Abstract #1763)
86Kr/84Kr = 0.3182 ± 0.0007 (2‰, 1 , reduced 2 = 1.8)
86Kr
/84Kr
0.317
0.318
0.319
0.320
# of measurement0 2 4 6 8 10
Abstract #1158 (LPI nº 2083)
ion trap measurementChondritic Xe, Busemann et al. (2000)
Air
Allende meteorite (HF/HCl residue)
i Xe/13
2 Xe re
lativ
e to
air
0.95
1.00
1.05
1.10
1.15
1.20
mass128 130 132 134 136
a
b
86Kr/84Kr = 0.3181 ± 0.0005 (1.6 ‰, 60 mn, N = 1005)
s.e.m = N
dens
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0
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86Kr/84Kr0.26 0.28 0.30 0.32 0.34 0.36
Krypton
XenonXe++
tota
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+120V-120V-110V
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time (ms)0 5 10 15 20 25
