Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1261766 | Marine Chemistry | 2012 | 6 Pages |
We describe a method for measuring 224Ra and 228Th activities in coastal sediments based on a delayed-coincidence counting system (the RaDeCC system). Milli-Q water is added to bulk sediment to form a slurry. 224Ra in interstitial water is co-precipitated by MnO2 suspension. The MnO2 suspension and the sediment with absorbed 224Ra and 228Th are filtered onto a 142-mm 0.7 μm (nominal pore size) GFF filter. The filter is placed onto a sample holder specified for sediment samples and counted in a RaDeCC system. 224Ra and 228Th activities are calculated from two measurements that are conducted within 6–12 h and in 8–10 days after sample collection. The RaDeCC system is calibrated with a 232U-228Th standard using the method of standard addition. The reproducibility and the overall accuracy of 224Ra and 228Th measurements based on this method are estimated to be ± 5% and ± 5–7%, respectively. We have applied this method to a coastal sediment and observed a significant deficit of 224Ra with respect to 228Th in the upper 3–4 cm.
►224Ra and 228Th activities in coastal sediments were measured using a RadeCC system. ► Counting efficiency doesn't change with water content in the range of ~ 0.4–0.5. ► Counting efficiency doesn't change with sample load in the range of 2–25 g. ► The reproducibility and the overall accuracy are ± 5% and ± 5–7%, respectively. ► A deficit of 224Ra relative to 228Th was observed in a coastal sediment.