THE DETERMINATION OF RA-226 AND RA-228 IN WATER AND SOLIDS BY THE LEAST-SQUARES GAMMA SPECTROMETRIC METHOD

An extremely simple, fast and accurate method for the simultaneous analysis of both Ra-226 and Ra-228 in water, sludge, sediments, soil and other types of samples has been developed. This method differs from the standard US Environmental Protection Agency methods for radium analysis in that it is used for all types of environmental materials. The radium from a 10- to 100-liter water sample is adsorbed on to a special high-radium-retaining resin, placed in a sealed container and counted on a sodium iodide detector system. The resultant gamma-ray spectrum is analyzed by a least squares method to determine the nuclides present. For a 20-liter water sample, the accuracy approaches +/- 4% at radium concentrations of 90 mBq2 liter-1 (2.5 pCi liter-1). For 20-liter water samples processed in the system at Argonne National Laboratory, the lower limit of detection (4.66-sigma background) for Ra-226 and Ra-228 are 130 mBq (6.5 mBq liter-1) and 240 mBq (12 mBq liter-1), respectively. However, systematic errors increase this limit to about 20 mBq liter-1 for both radionuclides. The lower limits of detection for natural uranium and thorium series nuclides in secular equilibrium in sludge, sediments and other types of solid samples are 240 mBq and 190 mBq, respectively. Thus, only 50- to 100-g quantities of sludge, sediments, soils and other types of solid samples are required and these samples are processed non-destructively. A single operator can process up to 20 water or solid samples per day. When these samples are counted on an analysis system with completely automatic sample changing, a single counting system can process up to 3500 samples per year.