Cosmogenic 41Ca in diogenites

Production rates, pre-atmospheric size and terrestrial ages

K. C. Welten, D. J. Hillegonds, J. Masarik, K. Nishiizumi

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

We measured concentrations of cosmogenic 41Ca in 37 diogenites, including 8 falls and 29 Antarctic finds, using accelerator mass spectrometry (AMS). The measured 41Ca concentrations in falls range from 2.8 to 9.3 dpm/kg, those in Antarctic finds range from 1.6 to 28 dpm/kg. The 41Ca concentrations in four of the falls agree within 10% with estimated saturation values based on spallation from Ti, Cr, Mn and the main target element, Fe. Four other diogenite falls and several Antarctic finds show elevated 41Ca concentrations, which are attributed to capture of thermal neutrons on 40Ca. The neutron-capture 41Ca contributions range from 0.1 to 1.5 dpm/g Ca. Monte Carlo based model calculations show that contributions of neutron-capture 41Ca are negligible (<0.05 dpm/g Ca) in diogenites with pre-atmospheric radii <20 cm, but become dominant in diogenites larger than 30 cm in radius and reach a maximum value of ∼5.6 dpm/g Ca in the center of objects with radii of 80-100 cm. The contributions of neutron-capture 41Ca in diogenites were used to constrain their pre-atmospheric radii. Many Antarctic diogenites show low 41Ca concentrations, up to 60% below the saturation value determined for falls. From these low 41Ca concentrations we derive terrestrial ages up to ∼135 kyr. We compare these terrestrial ages with those of other Antarctic achondrites and Antarctic chondrites and discuss the role of terrestrial weathering in limiting the lifetime of meteorites falling in different environments, i.e. Antarctic versus hot desert conditions.

Original languageEnglish (US)
Pages (from-to)653-662
Number of pages10
JournalNuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
Volume259
Issue number1
DOIs
StatePublished - Jun 2007
Externally publishedYes

Fingerprint

Neutrons
radii
neutrons
low concentrations
ice environments
achondrites
Meteorites
saturation
deserts
chondrites
weathering
spallation
meteorites
Weathering
thermal neutrons
falling
Particle accelerators
Mass spectrometry
accelerators
mass spectroscopy

Keywords

  • Ca
  • Antarctic meteorites
  • Cosmogenic nuclides
  • Diogenites
  • Pre-atmospheric size
  • Production rate
  • Terrestrial age

ASJC Scopus subject areas

  • Surfaces, Coatings and Films
  • Instrumentation
  • Surfaces and Interfaces

Cite this

Cosmogenic 41Ca in diogenites : Production rates, pre-atmospheric size and terrestrial ages. / Welten, K. C.; Hillegonds, D. J.; Masarik, J.; Nishiizumi, K.

In: Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms, Vol. 259, No. 1, 06.2007, p. 653-662.

Research output: Contribution to journalArticle

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abstract = "We measured concentrations of cosmogenic 41Ca in 37 diogenites, including 8 falls and 29 Antarctic finds, using accelerator mass spectrometry (AMS). The measured 41Ca concentrations in falls range from 2.8 to 9.3 dpm/kg, those in Antarctic finds range from 1.6 to 28 dpm/kg. The 41Ca concentrations in four of the falls agree within 10{\%} with estimated saturation values based on spallation from Ti, Cr, Mn and the main target element, Fe. Four other diogenite falls and several Antarctic finds show elevated 41Ca concentrations, which are attributed to capture of thermal neutrons on 40Ca. The neutron-capture 41Ca contributions range from 0.1 to 1.5 dpm/g Ca. Monte Carlo based model calculations show that contributions of neutron-capture 41Ca are negligible (<0.05 dpm/g Ca) in diogenites with pre-atmospheric radii <20 cm, but become dominant in diogenites larger than 30 cm in radius and reach a maximum value of ∼5.6 dpm/g Ca in the center of objects with radii of 80-100 cm. The contributions of neutron-capture 41Ca in diogenites were used to constrain their pre-atmospheric radii. Many Antarctic diogenites show low 41Ca concentrations, up to 60{\%} below the saturation value determined for falls. From these low 41Ca concentrations we derive terrestrial ages up to ∼135 kyr. We compare these terrestrial ages with those of other Antarctic achondrites and Antarctic chondrites and discuss the role of terrestrial weathering in limiting the lifetime of meteorites falling in different environments, i.e. Antarctic versus hot desert conditions.",
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N2 - We measured concentrations of cosmogenic 41Ca in 37 diogenites, including 8 falls and 29 Antarctic finds, using accelerator mass spectrometry (AMS). The measured 41Ca concentrations in falls range from 2.8 to 9.3 dpm/kg, those in Antarctic finds range from 1.6 to 28 dpm/kg. The 41Ca concentrations in four of the falls agree within 10% with estimated saturation values based on spallation from Ti, Cr, Mn and the main target element, Fe. Four other diogenite falls and several Antarctic finds show elevated 41Ca concentrations, which are attributed to capture of thermal neutrons on 40Ca. The neutron-capture 41Ca contributions range from 0.1 to 1.5 dpm/g Ca. Monte Carlo based model calculations show that contributions of neutron-capture 41Ca are negligible (<0.05 dpm/g Ca) in diogenites with pre-atmospheric radii <20 cm, but become dominant in diogenites larger than 30 cm in radius and reach a maximum value of ∼5.6 dpm/g Ca in the center of objects with radii of 80-100 cm. The contributions of neutron-capture 41Ca in diogenites were used to constrain their pre-atmospheric radii. Many Antarctic diogenites show low 41Ca concentrations, up to 60% below the saturation value determined for falls. From these low 41Ca concentrations we derive terrestrial ages up to ∼135 kyr. We compare these terrestrial ages with those of other Antarctic achondrites and Antarctic chondrites and discuss the role of terrestrial weathering in limiting the lifetime of meteorites falling in different environments, i.e. Antarctic versus hot desert conditions.

AB - We measured concentrations of cosmogenic 41Ca in 37 diogenites, including 8 falls and 29 Antarctic finds, using accelerator mass spectrometry (AMS). The measured 41Ca concentrations in falls range from 2.8 to 9.3 dpm/kg, those in Antarctic finds range from 1.6 to 28 dpm/kg. The 41Ca concentrations in four of the falls agree within 10% with estimated saturation values based on spallation from Ti, Cr, Mn and the main target element, Fe. Four other diogenite falls and several Antarctic finds show elevated 41Ca concentrations, which are attributed to capture of thermal neutrons on 40Ca. The neutron-capture 41Ca contributions range from 0.1 to 1.5 dpm/g Ca. Monte Carlo based model calculations show that contributions of neutron-capture 41Ca are negligible (<0.05 dpm/g Ca) in diogenites with pre-atmospheric radii <20 cm, but become dominant in diogenites larger than 30 cm in radius and reach a maximum value of ∼5.6 dpm/g Ca in the center of objects with radii of 80-100 cm. The contributions of neutron-capture 41Ca in diogenites were used to constrain their pre-atmospheric radii. Many Antarctic diogenites show low 41Ca concentrations, up to 60% below the saturation value determined for falls. From these low 41Ca concentrations we derive terrestrial ages up to ∼135 kyr. We compare these terrestrial ages with those of other Antarctic achondrites and Antarctic chondrites and discuss the role of terrestrial weathering in limiting the lifetime of meteorites falling in different environments, i.e. Antarctic versus hot desert conditions.

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