The radioactive purity of liquid scintillator samples are studied in the C14 Experiment, and in specially the activity of 14C isotope in liquid scintillator.
Liquid scintillator is an oil- or gas-based hydrocarbon compound. As the oils or gases used are very old, the activity of 14C isotope (having the life time nearly 6000 years) is supposed to be very low.
Based on the calculations the concentration of 14C isotope should be less that 10-20. However, the lowest concentration found has the value of 2×10-18 and differs substantially the calculated value.
The calculations do not, for example, take into account the natural activity (like uranium or thorium) of the local environment near the original oil or gas sources which could have been produced the contamination.
Various liquid scintillator samples, based on oil, gas and coal derivatives, will be measured in the C14 Experiment to possibly find out samples having 14C concentration close to or below 10-20.
The instrument for the concentration measurements is pretty simple but it needs very low-background environment and components. It situates at the depth of 1 430 meters in the Pyhäsalmi mine, Finland, in the underground laboratory of Callio Lab.
The instrument consists of a liquid scintillator sample of 1.6 litres, two light quides and photomultiplier tubes. They are surrounded by thick layers of pure copper and lead as radiation shielding against gamma radiation. In addition, the instrument stays in constant compressed air/ nitrogen flow to reduce radon background.
University of Oulu, Finland:
University of Jyväskylä, Finland:
Russian Academy of Sciences, Moscow, Russia:
Dr. Timo Enqvist