Automated measurement of 224Ra and 226Ra in water

We present a new simple approach for automated, non-destructive measurement of the alpha-emitting radium isotopes (223Ra, 224Ra, and 226Ra) in water based on the emanation of their respective radon daughters (219Rn, 220Rn, and 222Rn). The method combines the high adsorption uptake of MnO2 Resin for radium (Kd=2.4×104 ml/g) over a wide pH range with the simplicity of the activity registration using a commercial radon-in-air analyzer (RAD7, DURRIDGE Company, Inc). Radium is first adsorbed onto the MnO2 Resin by passing a water sample through the resin packed in a gas-tight glass cartridge. The same cartridge is then connected to the radon analyzer via a simple tubing system to circulate air through the resin and a drying system. The efficiency of the proposed system is determined by running standards prepared in the same manner. Our results indicate that the efficiency for 226Ra is >22% if both 218Po and 214Po counts are collected. This is comparable with typical efficiencies for alpha spectrometry but with much less sample preparation. We estimate that an MDA of 0.8 pCi/L for 226Ra may be obtained with this new approach using a 1 L water sample and less than 4 h of counting.