Determination of a mixture of gamma-emitting radionuclides using solid scintillation detectors and multivariate calibration

Solid scintillation detectors are more efficient than germanium detectors, and thus can be used to quantify gamma-emitting radionuclides with shorter counting times. However, due to the low peak resolution of solid scintillat ion detectors, quantification based on the straightforward calculation of p hotopeak areas becomes extremely inaccurate for mixtures of radionuclides w ith photopeaks of similar energies. In this paper, two multivariate calibra tion methods, partial least squares regression (PLS) and multivariate Linea r regression (MLR), have been investigated for their capacity to determine the activity of gamma-emitting radionuclides with close photopeaks (Sr-85, Cs-134, and Ag-110m) in absence and in presence of potential interferences by using solid scintillation detectors. The influence of different calibrat ion sets on the prediction of activities has also been tested. The predicti on errors obtained when applying either PLS or MLR to the samples without i nterferences are generally lower than 4% and they are comparable with the e rrors obtained with germanium detectors. However, when MLR and PLSR are app lied to samples with interferences, partial least squares is clearly reveal ed as the method of choice, giving accurate quantitative results regardless of the identity and amount of other isotopes present in the samples analys ed. (C) 1999 Published by Elsevier Science B.V.