Infrared Radiofluorescence (IR-RF) of K-Feldspar: An Interlaboratory Comparison

Abstract

Infrared Radiofluorescence (IR-RF) is a relatively new method for dosimetric dating of the depositional timing of sediments. This contribution presents an interlaboratory comparison of IR-RF measurements of sedimentary feldspar from eight laboratories. A comparison of the variability of instrumental background, bleaching, saturation, and initial rise behaviour of the IR-RF signal was carried out. Two endmember samples, a naturally bleached modern dune sand sample with a zero dose and a naturally saturated sample from a Triassic sandstone (~250 Ma), were used for this interlaboratory comparison. The major findings of this study are that (1) the observed IR-RF signal keeps decreasing beyond 4000 Gy, (2) the saturated sample gives an apparent palaeodose of 1265 ± 329 Gy and (3) in most cases, the natural IR-RF signal of the modern analogue sample (resulting from natural bleaching) is higher than the signal from laboratory-induced bleaching of 6 h, using a solar simulator (SLS). In other words, the laboratory sample bleaching was unable to achieve the level of natural bleaching. The results of the investigations are discussed in detail, along with possible explanations.

Short communication: Synchrotron-based elemental mapping of single grains to investigate variable infrared-radiofluorescence emissions for luminescence dating

“…If we assume typical environmental dose rates of between 3 and 1 Gy ka −1 , then IR-RF dating could produce age estimates ranging from 1.2 to 3.6 Ma, which is around 4 times greater than the upper dating limit of conventional luminescence dating methods. However, more recent studies (Murari et al, 2021b;Kreutzer et al, 2022) indicated a dose saturation at around 1500 Gy, reducing the previously predicted temporal limit of IR-RF dating. Hence, the uncertainty surrounding its upper age limit remains, and further studies on known-age samples are required to assess whether the sample/grain geochemistry influences the age limit.…”

“…A total of five samples were selected to represent a diversity of (i) geological context, (ii) geochemistry, (iii) shape of the IR-RF signal, and (iv) age. Sample Gi326 from a Triassic sandstone from Bayreuth, Germany, is composed of 89 % of K-feldspar (Sontag-González and Fuchs, 2022) and has previously been used as a reference sample in a laboratory comparison of IR-RF dating (Murari et al, 2021b). X7343 was collected from a Pliocene sediment at the Nyayanga site in the Homa peninsula, Kenya (Plummer et al, 2023).…”

Short communication: Synchrotron-based elemental mapping of single grains to investigate variable infrared-radiofluorescence emissions for luminescence dating

“…If we assume typical environmental dose rates of between 3 and 1 Gy ka −1 , then IR-RF dating could produce age estimates ranging from 1.2 to 3.6 Ma, which is around 4 times greater than the upper dating limit of conventional luminescence dating methods. However, more recent studies (Murari et al, 2021b;Kreutzer et al, 2022) indicated a dose saturation at around 1500 Gy, reducing the previously predicted temporal limit of IR-RF dating. Hence, the uncertainty surrounding its upper age limit remains, and further studies on known-age samples are required to assess whether the sample/grain geochemistry influences the age limit.…”

“…A total of five samples were selected to represent a diversity of (i) geological context, (ii) geochemistry, (iii) shape of the IR-RF signal, and (iv) age. Sample Gi326 from a Triassic sandstone from Bayreuth, Germany, is composed of 89 % of K-feldspar (Sontag-González and Fuchs, 2022) and has previously been used as a reference sample in a laboratory comparison of IR-RF dating (Murari et al, 2021b). X7343 was collected from a Pliocene sediment at the Nyayanga site in the Homa peninsula, Kenya (Plummer et al, 2023).…”