3.1. Sampling and sample treatment
Samples for equivalent dose determination were collected by forcing steel tubes into unconsolidated sand layers and sealing the tubes' ends with aluminum foil. Samples for determination of the environmental dose rate were taken from the direct sedimentary surroundings of the luminescence sample (few centimeters radially around the sampling spot). The light exposed ends of the luminescence sample were later discarded in the laboratory under subdued red light conditions. The samples were dried and sieved to extract the grain size fraction of 100–200 μm. The treatment with 10% hydrochloric acid and 15% hydrogen peroxide removed carbonates and organic matter, Sodium oxalate was added to deflocculate clay minerals. Potassium rich feldspar and quartz were concentrated by mineral gravity separation using LST fastfloat (at a density of 2.58 g/cm3 and 2.68 g/cm3). The quartz concentrate was etched with 40% hydrofluoric acid for 30–40 min to remove the outer layer of the grains affected by alpha radiation and to remove residual plagioclase. The separated quartz was then treated with 15% hydrochloric acid to remove newly formed fluorides. Finally, the etched concentrates were sieved (100–200 μm) to remove smaller grain fragments that resulted from the etching process and may potentially contain feldspar remnants. Feldspar contamination was additionally monitored analytically during the measuring process.