Electron irradiation effects on cathodoluminescence in zircon

Abstract

Cathodoluminescence (CL) measurements of zircon sample with two different geological ages have been conducted to clarify the polarization effect of different types of luminescence centers and the effects of electron -irradiation on CL. Polarization of CL has been confirmed in the emissions related to both defect and impurity centers in zircon. Prolonged exposure of electron irradiation reduces the CL intensities of broad bands related to intrinsic defect centers in the blue region and those of narrow bands attributed to Dy 3+ activator, whereas CL intensity of the broad bands attributed to metamictization in the yellow region increases with prolonged irradiation. Therefore, electron irradiation has a different effect on the emission mechanisms of defect centers observed in the blue and yellow regions.

Annealing effects on cathodoluminescence of zircon

“…Microstructures and microtextures such as twins, domains and fractures in the MZ samples were examined under a polarizing microscope and by an electron microscope using secondary electron and backscattered electron imaging as a preliminary observation to the CL and Raman analyses. Kempe et al (2010) and Tsuchiya et al (2014) pointed out a polarization effect of the luminescence in zircon. In this study, square slices (~5.0 × 5.0 × 1.0 mm) with the surfaces having same orientation (001) were prepared for annealing experiments, where the slices were cut off from a same large single crystal of the MZ.…”

“…Malosa, Southern Malawi (termed MZ) was selected for annealing experiments, of which mineralogical properties are referred to Tsuchiya et al (2014). Gamma-ray spectral analysis of MZ indicates the compositions of U: 241 ppm and Th: 177 ppm using JG-3 (GSJ) as a standard sample, where gamma-ray doses of U: 26.8956 Gy, and Th: 8.4783 Gy were calculated according to a method proposed by Guérin et al (2011).…”

“…Recent interests focus on the CL of radiation-damaged minerals such as quartz, feldspar and zircon to characterize the radiation effects of alpha and beta particles (Finch et al, 2004;Okumura et al, 2008;Tsuchiya et al, 2014), to visualize radiation halo produced by alpha radiation (Komuro et al, 2002;Nasdala et al, 2011) and to evaluate a correlation of CL intensity with radiation dose (King et al, 2011;Kayama et al, 2014). These investigations have been eventually conducted to apply CL of minerals for geodosimetry as well as geochronometry, especially using zircon as a radioactive mineral commonly contained in igneous, metamorphic and sedimentary rocks.…”

Cathodoluminescence of synthetic zircon implanted by He⁺ ion

“…Yellow emission has been extensively reported in various types of natural zircon, and assigned to radiation-induced defects by the disintegration of U and Th or to impurity activation of (UO 2 ) +2 (Götze et al, 1999;Nasdala et al, 2002;Gaft et al, 2002;Tsuchiya et al, 2015). According to Tsuchiya et al (2014), young natural zircon extracted from the Takidani granodiorite aged at ~1.4 Ma does not have an obvious emission bands in a yellow region possibly due to very low radiation damage in its structure. However, the present zircon (SZ) without U and Th has a small but discernible emission component in a yellow region.…”

“…Therefore, CL emissions in zircon are attributable to two-types of radiation-induced and intrinsic defects in addition to impurity centers. Recently, luminescent features of radiation damages by simulating the α and β particles in natural and/or synthetic minerals such as quartz, feldspar and zircon have been characterized by a spectroscopic method to assign individual emission centers (e.g., Finch et al, 2004;Okumura et al, 2008;Kayama et al, 2011;Tsuchiya et al, 2014), which suggests an evaluation of dose dependence on luminescence intensity related to radiation-induced defects (King et al, 2011;Kayama et al, 2014). Furthermore, a process of metamictization in radioactive minerals (e.g., zircon) has been estimated by luminescence methods for ionimplanted samples as a simulation of radiation-induced damage on minerals (e.g., Weber et al, 1994;Lian et al, 2003;Ewing et al, 2003;Finch et al, 2004;Nasdala et al, 2011).…”