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) |
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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 |
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