The sample is mixed with a liquid scintillator that converts beta radiation into light, which can be detected using photomultiplier tubes (PMTs). Unfortunately, there are various factors that may interfere with the conversion of decay energy emitted from the sample into light photons reaching the PMTs, which usually reduces counting efficiency. This process is called quenching and should be corrected. We usually encounter three major types of quenching:

• Photon quenching occurs with the incomplete transfer of beta particle energy to solvent molecules.

• Chemical (sometimes called “impurity”) quenching causes energy losses in the transfer from solvent to solute.

• Optical or color quenching causes the attenuation of photons produced in the solute. For example, plasma samples contain many different substances in variable amounts, so each sample may absorb light to a different extent.

We can estimate the quenching effect by applying external or internal standards or by using multiple energy channels.