NEW Video: Triple to Double Coincidence Ratio explained

7th June 2022

Three Photomultiplier Tubes are better than two in liquid scintillation counting

Triple to Double Coincidence Ratio – TDCR – is unique to the Hidex line of liquid scintillation counters. Both the 300 SL and 600 SL use three PMT detectors as opposed to two like traditional counters use.

This three-detector system can automatically calculate counting efficiency, which correlates to quenching. This eliminates the need for an internal radiation source, offering benefits such as no disposal costs, no health hazards when servicing, and no transportation restrictions.

Calculating TDCR

TDCR uses two sets of counts. The first is a triple count detected by all three PMTs, and the second is a summation of double counts, which two PMTs detect. The triple count is divided by the summation of all counts (triples plus doubles) and this gives us the Triple to Double Coincidence Ratio.


For more information, please see Hidex’s application notes here:

Two sets of spectral data generated

The benefits of TDCR lie in the spectral data it generates. For example, for a spectrum for Tritium, TDCR gives us two different types of spectral data per sample. One sample that three detectors register, which we call triple counts, and another that two detectors register, which we call double counts.

The difference between the triple and double counts is a factor of quench and energy of the isotope. The more the isotope is quenched, the greater this difference will be.

Another way to think about this is inside the chamber we have photons being emitted in all directions to each of the PMT detectors, and we have a quenching event where something blocks the signal to one of the PMTs. This will give us a smaller triple count spectrum, but a larger double count spectrum because we have more accumulation on the doubles than the triples.

Find out more

You can learn more about TDCR and the Hidex line of liquid scintillation counters by watching our video or by clicking the button below to request a one-to-one product demonstration.