The <i>μ</i>Dose system: determination of environmental dose rates by combined alpha and beta counting – performance tests and practical experiences

The μDose system is a recently developed analytical instrument applying a combined α- and β-sensitive scintillation technique for determining the radioactivity arising from the decay chains of 235U, 238U and 232Th as well as from the decay of 40K. The device was designed to meet the particular requirements of trapped charge dating methods and allows the assessment of environmental (i.e. low) levels of natural radionuclides. The μDose system was developed as a piece of low-cost laboratory equipment, but a systematic test of its performance is still pending. For the first time, we present results from a comprehensive performance test based on an inter-laboratory comparison. We compare the results obtained with μDose measurements with those from thick source alpha counting (TSAC), inductively coupled plasma optical emission spectrometry (ICP-OES) and low-level high-resolution gamma spectrometry (HRGS) applied in five participating laboratories. In addition, the reproducibility and accuracy of μDose measurements were tested on certified reference materials distributed by the International Atomic Energy Agency (IAEA; RGU-1, RGTh-1 and RGK-1) and on two loess standards (Nussy and Volkegem) frequently used in trapped charge dating studies. We compare μDose-based results for a total of 47 sediment samples with results previously obtained for these materials by well-established methods of dose rate determination. The investigated natural samples cover a great variety of environments, including fluvial, aeolian, littoral, colluvial and (geo-)archaeological sites originating from high and low mountain regions as well as from lowlands in tropical areas, drylands and mid-latitude zones of Europe, Africa, Australia, Central Asia and the Americas. Our results suggest the μDose system's capability of assessing low-level radionuclide contents with very good accuracy and precision comparable to well-established dosimetry methods. Based on the results of our comparative study and with respect to the practical experiences gained so far, the μDose system appears to be a promising tool for trapped charge dating studies.

The µDose-system: determination of environmental dose rates by combined alpha and beta counting – performance tests and practical experiences

The µDose-system is a recently developed analytical instrument applying a combined α- and β-sensitive scintillation technique for determining the radioactivity arising from the decay chains of 235U, 238U and 232Th as well as from the decay of 40K. The device was designed to meet the particular requirements of trapped charge dating methods and allows the assessment of environmental (i.e. low) levels of natural radionuclides. The µDose-system was developed as a low-cost laboratory equipment, but a systematic test of its performance is still pending. For the first time, we present results from a comprehensive performance test based on an inter-laboratory comparison. We compare the results gained with µDose-measurements with those from thick source alpha counting (TSAC), inductively coupled plasma optical emission spectrometry (ICP-OES) and low-level high-resolution gamma spectrometry (HRGS) applied in five participating laboratories. In addition, the reproducibility and accuracy of µDose-measurements were tested on certified reference materials distributed by the International Atomic Energy Agency (IAEA; RGU-1, RGTh-1 and RGK-1) and on two loess standards (Nussy and Volkegem) frequently used in trapped charge dating studies. We compare µDose-based results for a total of 47 sediment samples with results previously obtained for these materials by well-established methods of dose rate determination. The investigated natural samples cover a great variety of environments, including fluvial, aeolian, littoral, colluvial and (geo-)archaeological sites originating from high- and low-mountain regions as well as from lowlands in tropical areas, drylands and mid-latitude zones of Europe, Africa, Australia, Central Asia and the Americas. Our results suggest the µDose-system’s capability of assessing low-level radionuclide contents with very good accuracy and precision comparable to well-established dosimetry methods. Based on the results of our comparative study and with respect to the practical experiences gained so far, the µDose-system appears to be a promising tool for trapped charge dating studies.

Attenuation of beta radiation in granular matrices: implications for trapped-charge dating

Mineral grains within sediment or rock absorb a radiation dose from the decay of radionuclides in the host matrix. For the beta dose component, the estimated dose rate must be adjusted for the attenuation of beta particles within the mineral grains. Standard calculations, originally designed for thermoluminescence dating of pottery, assume that the grain is embedded in a homogenous medium. However, most current applications of trapped-charge dating concern sand- or silt-sized dosimeters embedded in granular sediment. In such cases, the radionuclide sources are not homogeneous, but are localized in discrete grains or held on grain surfaces. We show here that the mean dose rate to dosimeter grains in a granular matrix is dependent on the grain-size distributions of the source grains, and of the bulk sediment, as well as on the grain size of the dosimeters. We further argue that U and Th sources are likely to be held primarily on grain surfaces, which causes the dose rate to dosimeter grains to be significantly higher than for sources distributed uniformly throughout grains. For a typical well-sorted medium sand, the beta dose rates derived from surface U and Th sources are higher by 9 % and 14 %, respectively, compared to a homogenous distribution of sources. We account for these effects using an expanded model of beta attenuation, and validate the model against Monte Carlo radiation transport simulations within a geometry of packed spheres.

Deciphering Past Desert-Margin Dynamics in Matmata, Tunisia

&lt;p&gt;The terrestrial dust archives around Matmata (Tunisia) are unique in their morphological setting and grain-size composition (cf. Faust et al., 2020a, b). Located in front of the Grand Erg&amp;#8217;s parlour in a critical zone at the northern edge of the Saharan desert, up to 35 m thick plateau-like loess accumulations cover pre-existing landscapes. In conjunction with intercalated palaeosols, the sandy loess, or rather loess like sediment records, tapped fluctuations in aeolian dynamics related to rapid and large-impact climate boundary shifts. Some of them may have severely threatened local ancient cultures, and future changes may put modern settlements and agriculture projects in this region at risk. Palaeolandscape reconstruction, supported by reliable chronologies, helps us to chart the past landscape, assess today's dynamics, &amp;#160;and maybe predict possible future scenarios.&lt;/p&gt;&lt;p&gt;The &amp;#8216;desert-loess&amp;#8217; records around Matmata seem to engulf a wide temporal range back to Marine Isotope Stage (MIS) 9. Trapped charge dating techniques, such as luminescence and electron spin resonance (ESR) dating, are versatile tools to decipher the timing of past landscape changes. However, for archives such as the one in the neighbourhood of Matmata, conventional luminescence methods (e.g., optically stimulated luminescence, OSL) exceed reported temporal limits. Kreutzer et al. (2018) have convincingly shown that a multi-method approach, using infrared radiofluorescence (IR-RF) and OSL in conjunction with ESR dating, has good potential to tackle long-term landscape dynamics. Our contribution reports first trapped charge dating results from Matmata in Tunisia. We provide preliminary luminescence (IR-RF, OSL) and ESR dating results from seven different sites and discuss the challenges encountered during our methodological work. Finally, we attempt to link our findings to regional climate fluctuations and drainage alterations observed for the large endorheic salt lakes in the Matmata plateau's close purlieu.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Faust, D., Kreutzer, S., Trigui, Y., Pachtmann, M., Mettig, G., Bouaziz, M., Recio Espejo, J.M., Diaz del Olmo, F., Schmidt, C., Lauer, T., Rezek, Z., F&amp;#252;lling, A., Meszner, S., 2020a. New findings of Middle Stone Age lithic artifacts from the Matmata loess region in southern Tunisia. E&amp;G Quaternary Sci. J. 69, 55&amp;#8211;58. doi:10.5194/egqsj-69-55-2020&lt;/p&gt;&lt;p&gt;Faust, D., Pachtmann, M., Mettig, G., Seidel, P., Bouaziz, M., Recio Espejo, J.M., Diaz del Olmo, F., Roettig, C.-B., Kreutzer, S., Hambach, U., Meszner, S., 2020b. Sandy soils in silty loess: the loess system of Matmata (Tunisia). Quaternaire 31, 175&amp;#8211;186. doi:10.4000/quaternaire.14217&lt;/p&gt;&lt;p&gt;Kreutzer, S., Duval, M., Bartz, M., Bertran, P., Bosq, M., Eynaud, F., Verdin, F., Mercier, N., 2018. Deciphering long-term coastal dynamics using IR-RF and ESR dating: A case study from M&amp;#233;doc, south-West France. Quaternary Geochronology 48, 108&amp;#8211;120. doi:10.1016/j.quageo.2018.09.005&lt;/p&gt;