Adding Water to Liquid Scintillation Cocktail for Laboratory Wipe Tests

Abstract

As part of an ongoing laboratory survey process improvement program, we evaluated the addition of water to liquid scintillation cocktail to improve wipe test counting efficiency. Both polar and non-polar 3H and 14C-labeled compounds were used as model contaminants. Our results support the recommendations in the literature regarding the addition of water to scintillation cocktail We found an increase in the counting efficiency of the water-soluble material as a function of water content of the cocktail, but also observed a decrease in the efficiency of detection of the non-polar compound. The offsetting effects are believed to be the result of increased solubility of the polar compounds in water and increased quench of the already solubilized non-polar compound. The finding that adding water to the cocktail brought counting efficiencies of both polar and non-polar molecules to roughly the same value is novel and allows the use of a single quench curve for each radionuclide, regardless of chemical form.

Temporal Characterization of Tritium Smear Activities

“…The time dependence of measured activity has been previously reported (Santerre et al 1995;Sturchio et al 1999). The reasoning discussed was similar to the reasoning initially hypothesized by TJNAF.…”

“…The initial hypothesis was that tritiated material was collected by the swab during the survey and held within the cotton matrix; after the addition of the LSA cocktail, the tritium migrated into solution. This hypothesis is not unfounded and has been identified by previous research found in literature (Santerre et al 1995;Sturchio et al 1999). Past practice at TJNAF assumed migration would occur rapidly; however, after identifying the changes on the swab counts, the time for full migration was questioned.…”

“…The collection efficiency results are summarized in Table 1. This approach contrasts that of Sturchio et al (1999), where the initial measurement was used to estimate the collection efficiency. By using the later values, the migration of material into solution and the collection efficiency were decoupled, which was important when comparing smears made of different materials.…”

“…The reasoning discussed was similar to the reasoning initially hypothesized by TJNAF. An additional study had the primary purpose of evaluating the effect of water on smear surveys of polar and nonpolar tritiated compounds (Sturchio et al 1999). In a brief aside, the authors documented a clear increase in the counts obtained for samples counted with time elapsed between 0, 4, and 8 h. Santerre et al studied the collection efficiency of filter papers and cotton swabs that were wetted with a variety of solutions; further, the surveys were performed on various surfaces (Santerre et al 1995).…”