Measurement of Tritium with Plastic Scintillator Surface Improvement with Plasma Treatment

Tritium is usually measured by using a liquid scintillation counter. However, liquid scintillator used for measurement will be radioactive waste fluid. To solve this issue, we have developed the method of measuring tritium samples with plasma-treated plastic scintillator sheets instead of liquid scintillator (Plasma method). With the Plasma method of 2-min plasma treatment, we had obtained measurement efficiency of 48 ± 2 % for 2 min measurement of tritium except for tritiated water. On the other hand, it needed almost 6 hours to obtain constant measurement efficiency. We tried putting silica gel beads into vials to remove H₂O molecules from PS sheet surface quickly. The silica gel beads worked well and we got constant measurement efficiency within 1-3 hours. Also, we tried using other kinds of PS treated with plasma to obtain higher measurement efficiencies of tritium samples.