A procedure for the determination of very low activity levels of tritium in water samples

We describe the procedure developed for the electrolytic concentration of H-3 in water, together with systematically applied checks to guarantee the reproducibility of the process and to minimize the variability between water samples concentrated simultaneously in the different electrolytic cells. Starting from initial volume of 250 mi water, we obtained enrichment parameters normally greater than 70%, with a dispersion always less than 5%. Measuring the concentrated and the unelectrolyzed samples under the same conditions, we found that the lowest detectable activities had been improved from around 1.5 to 0.3 Bq/l. This allowed us to quantify the H-3 activity levels of 100% of the rainwater samples collected in Caceres from 1994 to 1996. The resulting average value for this period was (0.79+/-0.38) Bq/l.