The long-term stability on basic performances of a diisopropylnaphthalene-based liquid scintillation cocktail

The long-term stability of a cocktail is very important for liquid scintillation counting. The expiry date of a cocktail labeled on the container is usually one to three years later than the manufacture date, which is fairly short for the convenience of purchase, storage and use. Three batches of a diisopropylnaphthalene-based aqueous-miscible cocktail, Ultima Gold AB, with a span of 18 years of storage, have been compared on their basic performances, i.e. background count rate, counting efficiency, quench resistance, and α/β discrimination. We found that the 18-year storage has less impact on the basic performances than batch-to-batch variability in cocktail compositions, which means Ultima Gold AB has very good long-term stability. Therefore, in practice Ultima Gold AB can be used even beyond its expiry date, if it is properly stored for less than 18 years. This result will bring much convenience to plan the purchase, storage and use of the cocktail. In addition, the influence of statistical fluctuations on the quench parameter SQP(E) has been studied.