Tritium Measurement and Monitoring in Experimental and Process Systems with Ionization Chambers^a

Historically, ionization chambers have been used successfully to measure low-level tritium concentrations in air for radiation protection purposes. Problems have been encountered in applying this technique to measure much higher concentrations of tritium in gases other than air, particularly to measure tritium in argon and helium. An experimental program was, therefore, initiated to investigate the various factors that affect the response of ionization chambers. Carrier gas effects on the measurement of elemental tritium were investigated in the concentration range 0–150 Ci/m³. Higher than theoretical calibration factors were obtained consistently with low-level tritium gas standards in both helium and argon, while with high-level gas standards the experimental calibration factors were close to the theoretical value. Use of a commercial ionization chamber to measure tritiated water vapour in dry air streams resulted in severe contamination of the chamber. Water swamping of the dry air stream reduced the ionization chamber contamination to a negligible level, allowing reliable measurements to be made. The calibration of ionization chambers with representative process gases and operating conditions is necessary to ensure reliable tritium concentration measurements.