Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> The <span class="inline-formula"><i>μ</i></span>Dose system is a recently developed analytical instrument applying a combined <span class="inline-formula"><i>α</i></span>- and <span class="inline-formula"><i>β</i></span>-sensitive scintillation technique for determining the radioactivity arising from the decay chains of <span class="inline-formula"><sup>235</sup>U</span>, <span class="inline-formula"><sup>238</sup>U</span> and <span class="inline-formula"><sup>232</sup>Th</span> as well as from the decay of <span class="inline-formula"><sup>40</sup>K</span>. 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 <span class="inline-formula"><i>μ</i></span>Dose 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 <span class="inline-formula"><i>μ</i></span>Dose 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 <span class="inline-formula"><i>μ</i></span>Dose 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 <span class="inline-formula"><i>μ</i></span>Dose-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 <span class="inline-formula"><i>μ</i></span>Dose 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 <span class="inline-formula"><i>μ</i></span>Dose system appears to be a promising tool for trapped charge dating studies.
Highlights
We present results from a comprehensive performance test based on an inter-laboratory comparison
We re-investigated a total of 47 environmental samples for which either radionuclide concentra265 tions or activities had already been determined by either thick source alpha counting (TSAC) in combination with inductively coupled plasma optical emission spectrometry (ICP-OES) (Bayreuth) or low-level high-resolution gamma spectrometry (HRGS)
Based on the assumption that 40K is the dominant β-emitter in natural samples that is not part of the above mentioned decay series, the 40K activity is calculated as a residual value derived from the excess of detected β-counts over the number 560 of β-counts expected to arise from the sample-specific decay series of 238U, 235U and 232Th
Summary
20 Over the last two decades, trapped charge dating techniques have become commonly applied standard tools for age determination of sediments in palaeo-environmental and geo-archaeological research. When the 30 minerals are not stimulated any more (e.g. after sediment deposition or after the end of the heating event), they are still exposed to the natural ionizing radiation arising from both, cosmic radiation and the radioactive decay of members of the 238U, 235U and 232Th decay chains as well as from the decay of 40K in the surrounding sediments. 40 While the cosmic component of the environmental dose rate is typically derived from information on the exact sampling position by applying well established formulas (e.g., Prescott and Hutton, 1994), the contribution of ionizing radiation arising from the surrounding sediments is calculated by determining the activity concentrations of the relevant natural radionuclides. We provide recommendations for sample handling and data analysis for the μDose-results derived from practical experiences so 55 far made in the Giessen Luminescence Laboratory
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