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.