Sampling and selection of analytical methods for radium

Selecting samples for radium isotope analysis will normally be done to provide quantitative measurements for research studies, monitoring of mine-mill operations, investigation of contaminated sites (tailings piles, waste deposit sites, manufacturing facilities employing radium, etc.) and general environmental assessment. The greatest emphasis should be placed on those sample types which are the primary transfer media (air and water). Next would be vegetation and animal species that are part of the human food chain and, finally, sediments, soil and rock that can act as collectors of sources of radium. There are several factors that restrict the choice of an appropriate radiochemical procedure from the available options. The largest cost in radiochemical determinations is the labour required to process and prepare the samples for counting. Large soil and sediment samples may be analysed directly by gamma spectroscopy, thereby eliminating sample digestions and radium isolation procedures. Gross alpha counting procedures are the least time consuming for the determination of 226Ra. In the absence of significant amounts of 224Ra, this method is capable of accurate, low detection limit results. Alpha spectroscopy is the method of choice when radium isotopes must be determined. This technique approaches the gross alpha procedures in speed. Single samples can be prepared and analysed in as little as two to three hours. The radon emanation method is more time consuming than either of the foregoing methods. When the other radium isotopes are present, the specificity of the emanation method for 226Ra makes it preferable to the gross alpha procedures. The foregoing methods are generally equivalent in terms of sensitivity and precision. For equal counting times their detection limits are comparable. 30 refs