Isotopic Measurements with the Cameca ims 1280 Ion Microprobe at the University of Hawai

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Isotopic Measurements with the Cameca ims 1280
Ion Microprobe at the University of Hawaii

• Gary R. Huss, Kazu Nagashima, Sasha Krot, Kentaro
  Makide, and Lydie Bonal
• W. M. Keck Cosmochemistry Laboratory
• University of Hawaii at Manoa

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Isotopic Systems Studied at UH

• Oxygen isotopes
• 26Al-26Mg systematics
• 60Fe-60Ni systematics
• 53Mn-53Cr systematics
• Carbon isotopes
• Nitrogen isotopes
• Hydrogen isotopes
• Isotope ratio imaging (scanning ion imaging)

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Oxygen Isotopes

• CAIs from CR, CH, CV chondrites
• FUN CAIs from CV chondrites
• Carbonates from lithic clasts in Isheyevo
• Type II chondrules from CR chondrites
• Chondrules from CH and CB chondrites

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Oxygen Isotopes in FUN CAIs
Data from Clayton et al. (1977, EPSL 34, 209),
Clayton et al. (1977, GRL 4, 295), Lee et al.
(1980, GRL 7, 493), Clayton et al. (1984, GCA 48,
535), McKeegan et al. (2005, LPSC 36, 2077).
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Oxygen Isotopes in FUN CAIs
DH8 (Type B), Allende
Normal CAIs from CR chondrites
KT-1 (Type B), NWA 779
Makide et al. (2008)
Krot et al. (2008)
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Oxygen Isotopes Standards

• Standards are critically important for
  calibrating instrumental mass fractionation (IMF)
  and determining accurate oxygen isotopic
  compositions
• At UH, we have standards for
• Olivines of several compositions
• Spinel
• Pyroxenes of several compositions
• Quartz
• Garnet
• Calcite, dolomite, siderite
• Many of these generously provided by the
  WiscSIMS Laboratory

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Oxygen Isotopes Standards

• We need or are working on standards for
• Melilite or melilite glass of several
  compositions
• Ca-Al oxides
• Wollastonite
• Intermediate olivines
• Tochilinite
• Magnetite
• Magnesite
• When we develop a standard, we will try to
  prepare enough to share with other SIMS labs.

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26Al-26Mg Systematics

• CAIs from CR chondrites
• CAIs from CV chondrites
• FUN CAIs from CV chondrites
• Chondrules from CR chondrites
• Chondrules from ordinary chondrites

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26Al-26Mg Systematics
Compact Type A CAI, 2-A1 from Kaba (CV3)
(26Al/27Al)0(4.950.62)x10-5
?26Mg ()
??26Mg)0 -0.470.76
27Al/24Mg
Nagashima et al. (2007)
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26Al-26Mg Systematics Improving the Precision of
the Isochron

• High sensitivity of 1280 can improve precision
• Employ multicollection where possible
• Automated beam centering and careful measurement
  protocol improves reproducibility
• Correct instrumental mass fractionation (IMF) and
  account for intrinsic mass fractionation
  separately
• Correct IMF using standard-sample bracketing
• Calculate 26Mg using appropriate fractionation
  law
• Use appropriate standards to correct for relative
  sensitivities of Al and Mg

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Al-Mg Sensitivity Factors
Makide et al. (2008)
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Mass Fractionation of Magnesium
Makide et al. (2008)
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Measuring of Mass Fractionation of Mg

• Good statistical precision
• Good sample preparation
• Measure samples and standards with the same
  primary beam current and shape and with same
  measurement time.
• Tight control over ion extraction and beam path
  in secondary ion mass spectrometer
• Well-characterized, matrix-matched standards to
  estimate IMF and point-to-point variability
• Demonstrated long-term reproducibility
• Residual uncertainty Do samples and standards
  behave in precisely the same way?

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26Al-26Mg Standards

• Isotopically characterized, matrix-matched
  standards for Mg isotopes to determine
  instrumental and intrinsic mass fractionation and
  to identify 26Mg
• Assuming the published Mg composition for natural
  samples may not be enough
• Matrix-matched standards for relative sensitivity
  factors
• Complete suite for cosmochemistry should include
• Spinel, hibonite, Ca-Al oxides
• Olivines and pyroxenes of various compositions
• Melilites of various compositions
• Plagioclase (with Al/Mg 100)
• Glasses of different compositions

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60Fe-60Ni Systematics

• Sulfides from ordinary chondrites
• Chondrules from ordinary chondrites
• Fayalite from CV chondrites
• Chondrules from CR chondrites

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60Fe-60Ni Systematics Sulfides in Unequilibrated
Ordinary Chondrites
Krymka
26.5 25.5 24.5 23.5 22.5
60Ni/61Ni
0 4 8 12 16
56Fe/61Ni (x106)
(60Fe/56Fe)0 (1.81 0.72) x10-7
Tachibana and Huss (2003)
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60Fe-60Ni Systematics Pyroxene Chondrules in
Unequilibrated Ordinary Chondrites
(60Fe/56Fe)0 (2.23.7) x 10-7
Tachibana et al. (2006)
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60Fe-60Ni Systematics Porphyritic Chondrules in
UOCs
23.6 23.4 23.2 23.0
60Ni/61Ni
0 0.2 0.4 0.6 0.8 1.0 1.2
56Fe/61Ni (x106)
(60Fe/56Fe)0 (1.7 1.1) x10-7
Semarkona SMK3-6
Huss et al. (2007)
Tachibana et al. (2007)
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60Fe-60Ni Systematics Next Steps

• Improve precision of the data
• Develop multicollection (in progress)
• Higher transmission in secondary mass
  spectrometer
• Brute force (measure longer)
• Develop a complete suite of appropriate standards
• Find better samples to measure

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