Vial effect and background subtraction method in low-level tritium measurement by liquid scintillation counter.

Counting efficiencies of individual Teflon vials used in low-level tritium measurement by a liquid scintillation counter were investigated. The efficiency observed was fairly varied among vials in spite of being prepared in the same way. And the plots of the efficiency vs the external standard ratio give a straight line. More detailed investigation showed that this vial quenching and chemical quenching are simultaneously corrected by an external standard ratio. On the basis of the above results an appropriate background subtraction method is proposed.