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 language | English (US) |
|---|---|
| Pages (from-to) | 653-662 |
| Number of pages | 10 |
| Journal | Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms |
| Volume | 259 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jun 2007 |
| Externally published | Yes |
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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 journal › Article
}
TY - JOUR
T1 - Cosmogenic 41Ca in diogenites
T2 - Production rates, pre-atmospheric size and terrestrial ages
AU - Welten, K. C.
AU - Hillegonds, D. J.
AU - Masarik, J.
AU - Nishiizumi, K.
PY - 2007/6
Y1 - 2007/6
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.
KW - Ca
KW - Antarctic meteorites
KW - Cosmogenic nuclides
KW - Diogenites
KW - Pre-atmospheric size
KW - Production rate
KW - Terrestrial age
UR - http://www.scopus.com/inward/record.url?scp=34248138087&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=34248138087&partnerID=8YFLogxK
U2 - 10.1016/j.nimb.2007.01.204
DO - 10.1016/j.nimb.2007.01.204
M3 - Article
VL - 259
SP - 653
EP - 662
JO - Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
JF - Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
SN - 0168-583X
IS - 1
ER -