A 2D imaging system for mapping luminescence-depth profiles for rock surface dating

Spatially resolved optically stimulated luminescence (OSL) offers a means for rapid assessment of dose distributions in retrospective dosimetry and geochronology. Until recently, OSL imaging systems have largely been restricted to measurements of millimetre scale samples; this approach is not well suited for applications where the physical process of interest operates on centimetre scale (e.g., depth dependent trap eviction in exposed rocks, sediment mixing in soils, attenuation of gamma radiation, etc.). Here we describe and demonstrate the Risø Luminescence Imager - an electron multiplying charge-coupled device (EMCCD) based imaging system for measuring infrared photoluminescence (IRPL) and infrared stimulated luminescence (IRSL) from centimetre scale samples. While these signals specifically arise from feldspar, the stimulation and detection configuration may be modified to suit other target materials/dosimeters. We characterise the stability and reproducibility of the system through IRPL and IRSL measurements from a large (~4 × 5 cm) heterogeneous rock sample, and a slice of K-feldspar mineral. Finally, we present examples of suitable applications, including the reconstruction of luminescence-depth profiles from IRPL and IRSL images, and reconstruction of IRSL decay curves. Measurement of luminescence-depth profiles with high resolution using 2D imaging using the Risø Luminescence Imager is expected to improve our understanding of the trap emptying mechanisms (kinetics) in rocks. This system also opens new avenues for the development of field imaging instrumentation and provides opportunity to study feldspar luminescence in relation to its geochemistry.