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| Titel |
Structural recovery in zircon under an electron beam |
| VerfasserIn |
T. Váczi, L. Nasdala |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250067741
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| Zusammenfassung |
| Electron beam microanalysis is commonly associated with “beam damage”, a deterioration of
sample structure or chemistry upon interaction with the electron beam. Causes for beam
damage may be e.g. heating, electrolysis and redox reactions. Self-irradiation damage in
natural zircon is caused by the accumulation of alpha decay-induced defects in
crystallinity. This damage is preserved in zircon under normal conditions. However,
damage accumulation may be reversed and damage in zircon may be annealed. Most
commonly this is done by heating (e.g. Nasdala L. et al. 2001, Contrib. Mineral. Petrol.
141:125).
In this study we show that the stationary electron beam used e.g. in electron beam
microanalysis (SEM-EDX, EPMA) also causes a recrystallisation in zircon. Four zircon
samples covering a broad range of initial degrees of damage (ca. 0.9–4.9Ã1018 decay events
per gram calculated alpha dose) were subjected to various electron doses using a
fully focused electron beam (JEOL Superprobe 733, 20 kV accelerating voltage)
by varying the beam current (10–200 nA) and irradiation time (10–500 s). The
annealing effect is demonstrated using the FWHM of the ν3(SiO4) Raman band of
zircon (Nasdala L. et al. 1995, Eur. J. Mineral. 7:471). The rate of recovery has
been found to be proportional to beam current as well as to irradiation time. The
recovery rate has been found to increase with increasing initial damage level. For
a given initial alpha damage, equal electron doses produce essentially the same
degrees of recovery, thus ruling out the role of the heating effect of the electron
beam.
This project is supported by the European Union and co-financed by the European Social
Fund (grant agreement no. TAMOP 4.2.1/B-09/1/KMR-2010-0003). |
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