Study of colour quenching effects in the calibration of liquid scintillation counters: the case of 210Pb

In this work a rigorous method for the calibration of a liquid scintillation counter for 210Pb activity determination is proposed. The variation of the PSA threshold level for alpha/beta discrimination with the colour quenching is analysed for different beta energies. Also the changes in some parameters of the detector response, as the muon-peak, the channel ratio and the centroid of the spectrum, due to colour quenching are studied. The relationship between such parameters and the counting efficiency is described in such a way that the effects of colour in the efficiency are established. 99Tc is proposed as a good standard to calibrate the counter for 210Pb determination in real samples.