Quenching Correction with Two-Dimensional Scintillation Spectrum in Tritium Measurement

Liquid scintillation counters (LSCs) have been widely used for low-level tritium measurements. To obtain an accurate tritium activity using a LSC, a quenching correction is required. The quenching occurs from interruptions to the scintillation process (chemical quenching) and by absorption of scintillation photons by colored substances (color quenching). There is no common method for the correction of color quenching. Here, two-dimensional (2-D) scintillation spectra were measured with a conventional LSC connected to an external multichannel analyzer. The LSC had two photomultiplier tubes (PMTs). A 2-D spectrum was constructed from pulse heights from both PMTs. In a less-quenching cocktail, the 2-D scintillation spectra extended along a 45-deg line. However, the shape of the spectrum broadened with increasing color quenching and thus gave information about the color quenching. The effect of color quenching was qualitatively less significant in the relationship between the tritium counting efficiency and the quenching index parameter.