A low level liquid scintillation spectrometer with five counting modules for 14C, 222Rn and delayed coincidence measurements

This paper presents a low-level liquid scintillation counting spectrometer with five identical counting units that allow simultaneous measurements to be performed. The counting chambers are enclosed in high purity copper and lead shielding which significantly decreases the background count rate. Each of the five counting chambers is equipped with a high stability software-controllable power supply, and each counting module contains a signal analyzer that measures the pulse height, pulse shape and the time between subsequent pulses, returning all the data as a time-stamped sequence which enables the identification of pulse pairs. Such pulse pairs, arising from the decay of 214Bi/214Po, provides a sensitive tool for 222Rn contamination determination in low-level 14C measurements. This enables radiocarbon dating or bio-component determination to be performed directly after liquid scintillator production without the risk of 222Rn interfering with the measurement of 14C.