Variation of the Background Levels of Tritium Monitors due to Nat Radioactivity

Variation of the background levels of tritium monitors due to natural radioactivity in air was measured by measured by means of tritium monitors, each of which was equipped with an ionization chamber as a detector. The background levels of the monitors varied significantly depending on the ventilator-on and -off mode. The decay curve of the result of 222Rn. The concentration of 222Rn in the laboratory room amounted about 1x10-8 μCi/cm3 when the ventilator was not used for a day. The variation of the background level of a low-background liquid scintillation counter also fluctuated due to the variation of the concentration of 222Rn in air. Although the fluctuation could be partially prevented by weather-stripping the counter, other counterplans such as gas-purging might be necessary in order to measure tritium in a low concentration