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 r eproducibility of the process and to minimize the variability between water samples concentrated simultaneously in the different electrolytic cells. S tarting from initial volume of 250 mi water, we obtained enrichment paramet ers normally greater than 70%, with a dispersion always less than 5%. Measu ring the concentrated and the unelectrolyzed samples under the same conditi ons, 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. T he resulting average value for this period was (0.79+/-0.38) Bq/l.