Origin of Excess 176Hf in Meteorites

Details Origin of Excess 176Hf in Meteorites Origin of Excess 176Hf in Meteorites

Jul 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010apj...717..861t&link_type=abstract

The Astrophysical Journal, Volume 717, Issue 2, pp. 861-867 (2010).

Astronomy and Astrophysics

Astronomy

6

Atomic Processes, Meteorites, Meteors, Meteoroids

Scientific paper

After considerable controversy regarding the 176Lu decay constant (λ176Lu), there is now widespread agreement that (1.867 ± 0.008) × 10-11 yr-1 as confirmed by various terrestrial objects and a 4557 Myr meteorite is correct. This leaves the 176Hf excesses that are correlated with Lu/Hf elemental ratios in meteorites older than ~4.56 Ga meteorites unresolved. We attribute 176Hf excess in older meteorites to an accelerated decay of 176Lu caused by excitation of the long-lived 176Lu ground state to a short-lived 176m Lu isomer. The energy needed to cause this transition is ascribed to a post-crystallization spray of cosmic rays accelerated by nearby supernova(e) that occurred after 4564.5 Ma. The majority of these cosmic rays are estimated to penetrate accreted material down to 10-20 m, whereas a small fraction penetrate as deep as 100-200 m, predicting decreased excesses of 176Hf with depth of burial at the time of the irradiation event.

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