Behaviour of 137Cs and 210Pb inventory at three candidate reference sites for erosion study in the upstream Citarum watershed area, West Java, Indonesia

The fallout radionuclide (FRN) analysis needs a reference site (RS)inventory to determine erosion and sedimentation in the studyarea. The investigated area is in the upstream Citarum watershed,West Java, Indonesia. Twenty-seven corings and 22 scrap sampleshave been prepared well and measured using HPGe gamma spectroscopy. The data below the minimum detectable activity (MDA) was found for 137CsinRS6cor4and7(<0.16±0.08Bqkg–1).MDA quantification implies that the inventory below MDA eroded greater than its maximum value (76.02 tons ha–1 a–1). The comparison 137Cs inventory in this study is lower than the three estimation models; however, the inventory of Mt. Papandayan is
closer to the model. This study found the depth percentage of 20 30 cm using the proportion of 0–20cm/0–30cm ratio and predicted the portion of the existence of 137Cs and 210Pbex in the 20–30cm in the bulk sample. The highest H0 (142.04kg m–2), the relaxation length λ, and proportion of 20% of 137Cs in 20–30cm depth imply that 137Cs inventory activity is possibly deeper than 30cm. This study recommends that Mt. Papandayan could be the alternative RS for the upstream Citarum watershed