Low level ¹⁴C measurements in freshly prepared benzene samples with simultaneous ²¹⁴Bi/²¹⁴Po pairs counting for routine ²²²Rn contamination correction

In this paper, we present the application of a known method for simultaneous measurements of the ¹⁴C and ²²²Rn in benzene dating samples. Measurements are performed with a laboratory-made multichannel analyzer that records the height of each pulse and the time interval between the subsequent pulses. This feature is used to detect pairs of pulses from two subsequent decays of ²²²Rn products, ²¹⁴Bi and ²¹⁴Po, what occur in less than 800 μs and have amplitudes corresponding to more than 160 keV_e. The measured decay pairs' background count rate is 3.4 day^-1 which is much larger than the theoretically expected rate of 0.36 day^-1, this suggests a possible source of ²²²Rn in the LSC cocktails. The ²¹⁴Bi/²¹⁴Po pairs count rate is used to correct a count rate in the fixed energy ¹⁴C window. Prolonged measurements were performed on a set of 4 test samples starting immediately after the benzene synthesis. The obtained results show good reproducibility and high efficiency in detecting ²²²Rn presence. The measurements of the chemically prepared benzene from the samples tend to be contaminated with ²²²Rn are also presented and these clearly show the influence the of ²²²Rn contamination on the ¹⁴C activity measurements.