Rapid pre-concentration technique for estimation of 226Ra in water

Radium isotopes (224Ra, 226Ra, and 228Ra) in natural waters have been used by several investigators as geochemical tracers to evaluate geophysical and environmental processes in the geosphere. Radium isotopes are also routinely monitored in natural waters for radiation protection. The concentration of 226Ra is so low (3-6mBq/l) that preconcentration of the nuclide from large volume samples is required before radioactivity analysis. Preconcentration of 226Ra in water samples is carried out as carbonate (Ca, Ba and Sr). Ca is separated by nitrate, 226Ra by Ba-chromate. Finally 226Ra is reprecipitated as RaBa (SO4)2 and counted by alpha counter. The yield is determined by BaSO4. The radiochemical method above described is not only time consuming but also laborious. At least three to four days is required for complete radionuclide estimation. Moreover, sometimes 226Ra is not detected in 20L sample. To get a detectable activity it becomes necessary to transport large volumes of water (100-200L) to lab. Besides, it is very difficult to perform the pre-concentration method at sea, and processed at sea, especially when conditions are rough. All these greatly limit the number of samples that can be collected or brought back to the shore-based laboratory. To overcome the limitations of the existing method a large-volume, in-situ samplers based on MnO2 coated Polypropylene (PP) wound cartridges for 226Ra were adopted. The advantages of impregnated cartridges or filters over co-precipitation are ease of use and rapidity, as it enables the rapid preconcentration of radionuclides with high efficiency (in the range of 70-98%) even from hundreds of liters of sample