Pakistan Journal of Biological Sciences1028-88801812-5735Asian Network for Scientific Information10.3923/pjbs.2006.681.685Shahbazi-MoghadamMorteza Emaddedin Faghahati 4200694The design and performance of a system for the measurement of very low tritium concentrations in natural waters are described and discussed in the light of analytical and accuracy. The system consists of a sensitive flow-type proportional counter with a controllable inlet gas. Along with this counter, a reliable method for preparation of the samples has been used. Low tritium concentrations are determined on samples that have been preconcentrated electrolytically, necessitating samples of about 300 mL at least to allow for repeated measurements. Water samples were converted to hydrogen gas and then reacted with ethylene to yield ethane. A special proportional counter of about 1.9 L was designed and constructed for this purpose. Appropriate electronic equipment allowed the registration of tritium counts and background below and mainly background above about 15 kev. Water samples were collected from two ground sources and two main rivers and in two different seasons. The rivers` concentrations were higher in summer than in winter. The ground water concentrations were of about a factor of two smaller than the river concentration in summer.]]>Brown, R.M. and W.E. Grummit,195634214220Geyh, M.A.,197214C and 3H measurements.]]>2227234Hufen, T.H., L.S. Lau and R.W. Buddenmeier,197413C and tritium in water samples from basaltic aquifers and carbonate aquifers on the island of Oahu, Hawall.]]>2111127Theodorsson, P. and J. Part,199117419427Theodorsson, P.,199133913Theodorsson, P.,199234420427Theodorsson, P.,1996pp: 227-256pp: 227-256Theodorsson, P.,199950311316Cameron, J.F.,19651965pp: 542573IAEA, International Atomic Energy Agency,19631963IAEA, International Atomic Energy Agency,19641964