A new liquid scintillation counter for the absolute activity measurement of radionuclides

The detection efficiency of a scintillation counter can be deduced from the knowledge of the statistical distribution of the light emitted by the scintillator. When using traditional photomultiplier tubes (PMT), the resolution of the of photonsʹ spectrum is limited by the multiplication factor of the first dynode. Even with a high-gain PMT, the resolution of the single electron peak is low and the spectrum analysis is difficult. This is no longer the case with a new kind of commercially available photodetector, the hybrid photomultiplier tube (HPMT) in which the mean number of information quanta created by one photoelectron is much greater than those created in a PMT. The photoelectron spectrum resolution is thus dramatically improved and it is possible to deduce the statistical distribution of the number of photons emitted by the scintillator. This paper describes the use of this new photodetector in a liquid scintillation counter, designed for the standardisation of pure beta and electron capture radioactive solutions. The spectrum deconvolution process used to deduce the detection efficiency of the counter is also described.