ANALYSIS OF RA-228 AND RA-226 IN PUBLIC WATER-SUPPLIES BY A GAMMA-RAY SPECTROMETER

Methods for measuring 128Ra were reviewed to select a brief and simple screening procedure under NIPDW Regulations for public water supplies. A two-step method was considered to concentrate Ra by evaporation or co-precipitation and to count it with a gas ionization detector, a liquid-scintillation detector, or a Ge detector with multichannel analyzer. Gross /8 particle counting appears to be feasible for screening to meet the 0.04 Bq L-1 detection limit. One can utilize the same sample volume as currently collected and measure radiation with commonly available equipment in reasonable time. The required sample volumes were estimated on the basis of known counting efficiencies and background count rates. Gamma-ray spectral analysis is the recommended option, however, because 226Ra and 228Ra can be determined directly and simultaneously. Several aspects of the method were examined to assure that the concentration procedure is nearly quantitative and that the detection limit can be reached with a 3.8-L sample in a 6000-s counting period. The method was tested with Ra tracer solutions and EPA intercomparison samples over the range of 0.04 to 1 Bq L-1. It was found appropriate for 22SRa and 226Ra analyses. © 1990 Health Physics Society Pergamon Press plc.