Development of a low background alpha–beta/gamma coincidence detector

Developing detectors operating in time coincidence is a possible way to increase the sensitivity in gamma spectroscopy. Such design allows both the selection of specific events and the rejection of background. In this work we present a new low background detector mainly developed for the determination of radioactive contamination of liquid samples. The system was constructed by combining a liquid organic scintillator, for the detection of alpha and beta particles, and a High Purity Germanium for the detection of correlated gamma rays. Despite being located in a non-underground laboratory, the instrument can reach sensitivities in the range of tens mBq/kg for 238U, 235U and 232Th, exploiting alpha–gamma and beta–gamma coincidence events.