High sensitivity measurement of 224Ra and 226Ra in water with an improved hydrous titanium oxide technique at the Sudbury Neutrino Observatory

TL;DR

This paper presents an improved, faster hydrous titanium oxide technique for measuring trace levels of radium isotopes in large volumes of water at the SNO, enhancing sensitivity and efficiency.

Contribution

The method introduces a streamlined process combining HTiO filters and co-precipitation, achieving high chemical efficiency and low detection limits for radium isotopes in heavy water.

Findings

Achieved detection limits of 2.0x10^3 uBq/kg for 224Ra.

Achieved detection limits of 3.7x10^3 uBq/kg for 226Ra.

Capable of analyzing 200-450 tonnes of water with high efficiency.

Abstract

The existing hydrous titanium oxide (HTiO) technique for the measurement of 224Ra and 226Ra in the water at the Sudbury Neutrino Observatory (SNO) has been changed to make it faster and less sensitive to trace impurities in the HTiO eluate. Using HTiO-loaded filters followed by cation exchange adsorption and HTiO co-precipitation, Ra isotopes from 200-450 tonnes of heavy water can be extracted and concentrated into a single sample of a few millilitres with a total chemical efficiency of 50%. Combined with beta-alpha coincidence counting, this method is capable of measuring 2.0x10^3 uBq/kg of 224Ra and 3.7x10^3 uBq/kg of 226Ra from the 232Th and 238U decay chains, respectively, for a 275 tonne D2O assay, which are equivalent to 5x10^16 g Th/g and 3x10^16 g U/g in heavy water.