The determination of tritium, 14C and 35S in milk and crop samples using a combustion technique

The use of a combustion technique for the determination of low energy beta-emitting radionuclides in solid and liquid samples has been in widespread use for a number of years. However, the sensitivity of measurements by existing commercially available combustion apparatus has been limited by the amount of sample that can be combusted before incorporating the combustion products into a liquid scintillator for subsequent counting. Consequently the determination of tritium, 14C and 35S at environmental levels has not been possible using commercially available equipment. This paper describes the apparatus and method that was developed at the Central Veterinary Laboratory for the determination of these low energy beta-emitters in milk and crop samples. A typical sample size of 20-50 g is routinely measured, although the apparatus is designed to be able to make several sequential combustions before measurement of the oxidation products by liquid scintillation counting.