Techniques of groundwater tracing using radionuclides

The properties of the various radionuclides commonly used for tracing groundǎter were discussed. Comparisons were made of their movement through the soil, half-lives, permissible levels, price, and ease of handling and measurement. Tritium is cheap, easy to handle, and moves with the groundwater but is difficult to count. Anions that are pure beta emitters (S³⁵O₄^—, P³²O₄^—, C¹⁴O₃^—) are easy to count, but the last two may be fixed by soil bacteria. Of the halogens, Cl³⁶ is expensive, and Br⁸² and I¹³¹ have short half-lives. Gamma emitters (Br⁸², I¹³¹) can be detected in the field but may require shielding during handling. EDTA complexes of gamma emitters (Co⁶⁰, Cr⁵¹, Sb¹²⁵) are also used, but biodegradation of the organic chelate is possible. Care must be exercised when using long-lived radionuclides that the environment is not contaminated for a long period.