A spectral radioluminescence study for dating and dosimetry

Site-selective mapping of metastable states using electron-beam induced luminescence microscopy

Metastable states created by electron or hole capture in crystal defects are widely used in dosimetry and photonic applications. Feldspar, the most abundant mineral in the Earth’s crust (> 50%), generates metastable states with lifetimes of millions of years upon exposure to ionizing radiation. Although feldspar is widely used in dosimetry and geochronometry, the creation of metastable states and charge transfer across them is poorly understood. Understanding such phenomena requires next-generation methods based on high-resolution, site-selective probing of the metastable states. Recent studies using site-selective techniques such as photoluminescence (PL), and radioluminescence (RL) at 7 K have revealed that feldspar exhibits two near-infrared (NIR) emission bands peaking at 880 nm and 955 nm, which are believed to arise from the principal electron-trapping states. Here, we map for the first time the electron-trapping states in potassium-rich feldspar using spectrally-resolved cathodoluminescence microscopy at a spatial resolution of ~ 6 to 22 µm. Each pixel probed by a scanning electron microscope provides us a cathodoluminescence spectrum (SEM-CL) in the range 600–1000 nm, and elemental data from energy-dispersive x-ray (EDX) spectroscopy. We conclude that the two NIR emissions are spatially variable and, therefore, originate from different sites. This conclusion contradicts the existing model that the two emissions arise from two different excited states of a principal trap. Moreover, we are able to link the individual NIR emission peaks with the geochemical variations (K, Na and Fe concentration), and propose a model that explains the quenching of the NIR emission by Fe⁴⁺. Our study contributes to an improved understanding of charge storage in feldspathic minerals, with implications for developing sub-single grain (micrometer scale) measurement techniques in radiation dosimetry.

Synthesis and stimulated luminescence property of Zn(BO2)2:Tb3

Zinc borate, Zn(BO₂)₂, doped with different concentrations of terbium (0.5-8mol%) was synthesized and polycrystalline samples were characterized by Scanning Electron Microscopy and X-Ray Diffraction. The Zn(BO₂)₂ was formed in the pure samples sintered at 750 and 800°C which has the body centered cubic structure, and a ZnB₄O₇ primitive orthorhombic phase was present. The thermoluminescent intensity was dependents on the thermal treatment (250-500°C) and also on the impurity concentration. The linear dose-response was obtained between 0.022-27.7Gy and 0.5-50Gy when the samples were exposed to beta and gamma radiation, respectively. The complex structure of the glow curves was analyzed by the Computerized Glow Curve Deconvolution method. The kinetics parameters were calculated assuming the general order kinetics model describing accurately the TL process. The glow curves of Tb³⁺-doped zinc borate phosphor were well deconvolved by six glow peaks. Zinc borate with 8mol% of impurity concentration exhibited an intense radioluminescent emission. The radioluminescent spectra show their maximum bands at 370, 490, 545 and 700nm related to the terbium ion in the zinc borate. These obtained results suggest that the terbium doped zinc borate is a promising phosphor for use in radiation dosimetry because of its high TL sensitivity to the ionizing radiation.