Efficiency calibration and optimization of a liquid scintillation spectrometer for low level 55Fe and 63Ni measurements

An experimental study on the counting efficiency, background, and Lower Limit of Detection (LLD) of a liquid scintillation spectrometer was carried out for establishing a measurement technique suitable for low level activity measurements of 55Fe and 63Ni in environmental samples. The spectrometer's response, using two scintillators (PerkinElmer Optiphase Hisafe 3 and Meridian Prosafe HC+) and glass and plastic vials, was studied. Colour and chemical quenching effects were also investigated for both scintillators and vials. Finally, a spectrum integration window selection method able to reduce the LLD through a Figure of Merit (FOM) optimization, was tested. Efficiency and LLD curves were obtained for both scintillators and types of vials with this technique.