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 study area. The investigated area is in the upstream Citarum watershed, West Java, Indonesia. Twenty-seven corings and 22 scrap samples have been prepared well and measured using HPGe gamma spectroscopy. The data below the minimum detectable activity (MDA) was found for ¹³⁷Cs in RS6 cor 4 and 7 (<0.16 ± 0.08 Bq kg^-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 0-20 cm/0-30 cm ratio and predicted the portion of the existence of ¹³⁷Cs and ²¹⁰Pb_ex in the 20-30 cm in the bulk sample. The highest H₀ (142.04 kg m^-2), the relaxation length λ, and proportion of 20% of ¹³⁷Cs in 20-30 cm depth imply that ¹³⁷Cs inventory activity is possibly deeper than 30 cm. This study recommends that Mt. Papandayan could be the alternative RS for the upstream Citarum watershed.