High fluences of neutrons determined from Sm and Gd isotopic compositions in aubrites

Hiroshi Hidaka, Mitsuru Ebihara, Shigekazu Yoneda

Research output: Contribution to journalArticle

36 Citations (Scopus)

Abstract

Large isotopic deviations of 149Sm-150Sm and 157Gd-158Gd derived from neutron capture effects were observed in five enstatite achondrites (aubrites); Norton County, ALH78113, Cumberland Falls, Bishopville and Mayo Belwa. The isotopic variations of these aubrites (ε149Sm = -32 to -7, ε150Sm = +11 to +57, ε157Gd = -42 to -14 and ε158Gd = +9 to +26) correspond to irradiation with neutron fluence of (1.17 - 3.99) x 1016 n cm-2, which is within the range of estimated neutron fluence values of some lunar samples. These results indicate that aubrites may have been located near the surface of their parent body for several hundreds of Ma. Furthermore, the neutron energy spectrum obtained from the combination of Sm and Gd isotope systematics (ε(Sm)/ε(Gd)) suggests that the energy of thermalized neutrons in five aubrites was in the range of 200-400 K, and was lower than those in lunar samples A-12 and A-15. In addition, we analyzed one anomalous aubrite (Mt. Egerton), and two enstatite chondrites (Happy Canyon and Abee) to investigate the relationship of their origin with aubrites. However, these three meteorites showed no evidence for intensive neutron irradiation observed in the aubrites.

Original languageEnglish
Pages (from-to)41-51
Number of pages11
JournalEarth and Planetary Science Letters
Volume173
Issue number1-2
DOIs
Publication statusPublished - 1999 Nov 15

    Fingerprint

Keywords

  • Chladnite
  • Gadolinium
  • Isotope ratios
  • Neutrons
  • Samarium

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Cite this