Title :

Amorphization and D/H fractionation of kerogens during experimental electron irradiation: comparison with chondritic organic matter

Author(s) :

Le Guillou, Corentin [Auteur]
The University of New Mexico [Albuquerque]
Rémusat, Laurent [Auteur]
Laboratoire de Minéralogie et Cosmochimie du Muséum [LMCM]
Bernard, Sylvain [Auteur]
Laboratoire de Minéralogie et Cosmochimie du Muséum [LMCM]
Brearley, Adrian J. [Auteur]
The University of New Mexico [Albuquerque]
Leroux, Hugues [Auteur]
Unité Matériaux et Transformations - UMR 8207 [UMET]

Journal title :

Icarus

Volume number :

226

Pages :

101-110

Publication date :

2013

HAL domain(s) :

Planète et Univers [physics]/Astrophysique [astro-ph]
Physique [physics]/Matière Condensée [cond-mat]/Science des matériaux [cond-mat.mtrl-sci]
Physique [physics]/Astrophysique [astro-ph]
Planète et Univers [physics]/Sciences de la Terre
Chimie/Matériaux
Physique [physics]/Physique [physics]/Géophysique [physics.geo-ph]

English abstract : [en]

Irradiation is common in the interstellar medium and the protosolar nebula. We have investigated the effects of electron irradiation on kerogens of type I and III in a 200 kV transmission electron microscope (TEM), at 293 ...
Show more >Irradiation is common in the interstellar medium and the protosolar nebula. We have investigated the effects of electron irradiation on kerogens of type I and III in a 200 kV transmission electron microscope (TEM), at 293 K and 92 K, using various fluences. Using synchrotron-based scanning transmission X-ray microscopy (STXM) and NanoSIMS, we have demonstrated a progressive amorphization coupled with hydrogen loss and a significant deuterium to hydrogen ratio (D/H) fractionation, with δD increasing by up to 1000‰. Hydrogen loss is non-linearly related to the fluence. Irradiation under cryogenic conditions (92 K) hinders amorphization and D/H elevation. We suggest that these effects are controlled by radiolysis (carbonsingle bondhydrogen bonds are broken and hydrogen is lost), coupled with recombination. The amorphization and hydrogen loss are rate-limited by defect diffusion which controls the recombination probability. The D/H increase appears to follow a Rayleigh distillation law with an apparent fractionation factor similar to the equilibrium fractionation factor of the isotopic exchange reaction CH4 + HD ↔ CH3D + H2. This study represents a first step to estimate the kinetics and timescales of D/H fractionation under ionizing radiation. Extrapolatation of this fractionation behavior to natural environments remains difficult at this point because simultaneous irradiation by protons and other cosmic rays at various energies also occurs. However, the present results show that isotopic fractionation by electron irradiation at 200 kV alone might have been kinetically inhibited at the low temperatures of the interstellar medium and the outer region of the protosolar nebula. In addition, we show that STXM or NanoSIMS experiments should not be performed on organic samples that have already been investigated using TEM, even under low flux electron irradiation conditions.Show less >

Language :

Anglais

Peer reviewed article :

Oui

Audience :

Internationale

Popular science :

Non

Administrative institution(s) :

Université de Lille
ENSCL
CNRS
INRA

Collections :

• Unité Matériaux et Transformations (UMET) - UMR 8207

Research team(s) :

Matériaux Terrestres et Planétaires

Submission date :

2019-05-16T15:31:33Z
2019-10-22T10:04:49Z
2021-02-19T16:53:36Z