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| Titel |
Combined Raman and photoluminescence spectroscopic investigation of He-irradiation effects in monazite |
| VerfasserIn |
C. Lenz, C. Petautschnig, S. Akhmadaliev, D. Hanf, D. Talla, 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 |
250068727
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| Zusammenfassung |
| We present first results of a study addressing effects of the corpuscular self-irradiation on
stress/strain and optical properties (in particular the photoluminescence behaviour) in
monazite–(Ce). For this, natural samples, and synthetic CePO4 crystals mildly doped
with Nd3+, were irradiated with 7.7 MeV He ions, which are analogues of alpha
particles generated in the 214Po - 210Pb decay event (238U decay series). Light-ion
irradiation was preferred over heavy-ion irradiation (i.e., ~100 keV heavy ions as
analogues of alpha recoils) for two reasons. First, MeV He ions penetrate much
deeper into mineral targets (tens of micrometres vs. a few hundred angstroms),
resulting in irradiated volumes that are “measurable” using micro-spectroscopy
techniques. Second, the depth distribution profiles of nuclear and electronic energy
losses vary appreciably in the case of MeV He ions. The latter is most helpful in
assigning observed effects to either point defects created or target ionisation. The
irradiations were done at the 3 MV Tandem accelerator of the Helmholtz-Zentrum
Dresden-Rossendorf (Germany). The fluences applied varied in the range 1013–1017
He/cm2.
The degree of disturbance of the short-range order in the samples irradiated was evaluated
from the broadening of the ν1(PO4) Raman band (symmetric PO4 stretching; A1g mode) near
970 cm-1 [1,2]. The majority of the damage created was observed near 28 μm into the
monazite–(Ce) targets, i.e., near the ends of the helium trajectories. Here, the ν1(PO4) Raman
band may broaden appreciably, from 2.2 cm-1 (in the case of synthetic CePO4) to well above
20 cm-1. The generation of additional damage was also observed upon He irradiation of
naturally radiation-damaged monazite–(Ce). By contrast, there was no indication of any
annealing effect of the MeV He ions irradiated in these samples (compare [3]; a similar effect
of alpha-assisted annealing was suspected by [4] in the discussion of fission tracks). Sharp
luminescence emissions of REE centres with 4f electronic structure, such as the
2H3-2 - 4I9-2 emission of Nd3+ near 11300 cm-1 (885 nm wavelength), were found
to show similar broadening behaviour. This may potentially be used to develop a
luminescence-based calibration for the non-destructive quantification of the structural
irradiation damage on a micrometre-range. In addition, a brownish-orange, broad-band defect
emission is created at low and depleted at moderate damage (similar to observations on
irradiated zircon by [5]). The presence of this emission may be considered as a simple
indicator of low degrees of damage, for instance in the evaluation of heavy-mineral
concentrates.
[1] Nasdala L, Grötzschel R, Probst S, Bleisteiner B (2010) Can Mineral 48:351–359
[2] Ruschel K, Nasdala L, Kronz A, Hanchar JM, Többens DM, Škoda R, Finger F,
Möller A (2012) Mineral Petrol (submitted)
[3] Ouchani S, Dran J-C, Chaumont J (1997) Nucl Instrum Methods B 132:447–451
[4] Hendricks BWH, Redfield TF (2005) Earth Planet Sci Lett 236:443–458
[5] Nasdala L, Grambole D, Götze J, Kempe U, Váczi T (2011) Contrib Mineral Petrol
161: 777–789 |
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