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

Abstract. 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.