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

• Delayed coincidence was used for the detection of Bi-214/Po-214 pairs.
• Measurement of C-14 activity and Rn-222 activity through Bi-214/Po-214 pairs is performed at the same time.
• We report significant Rn-222 contamination of benzene obtained from samples.

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 keVe. 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.