A distribution apparatus has been developed for preparing the gaseous tritium standard sources in ampoules suitable for calibration of gas-monitors. The apparatus consists of a gas handling loop for mixing and exhausting, ampoule racks and a radioactivity measurement loop.
The radioactivity measurement loop contains a standard spherical glass ionization chamber which has an effective volume of 1, 210cm3. The ionization chamber was calibrated with the gaseous standard sources supplied by LMRI in France. The dependences of the ionization efficiency of a spherical ionization chamber on effective volume and internal air pressure were derived on the basis of Monte Carlo calculation. They could give a good explanation of the measured results.
The standard sources prepared by this apparatus could cover the activity range from 1×10-2μCi to 1mCi. The uncertainty of the activity in an ampoule was estimated to be within ±5% in consideration of the errors of radioactivity measurement and ampoule sealing.
