Performance of liquid scintillation counting system Quantulus for 14C measurements

To investigate the variation of the solar activity for the long time scale, we have started the measurements of ¹⁴C in an ancient tree, synthesizing benzene from the tree rings and using the liquid scintillation counting system Quantulus. Since the accuracy of 0.2% is necessary for the measurements, we investigated the performance of the liquid scintillation counter system Quantulus. The background rate of the Quantulus was 1 cpm while the counting rate of ¹⁴C was 90 cpm for the ancient tree. The pulse height distribution of β rays from ¹⁴C was well fitted with theoretical β rays spectrum and we confirmed that the Quantulus can detect β rays until the energy as low as 7.5 keV with good efficiency