Cascade summing in gamma-ray spectrometry in marinelli-beaker geometries: the third efficiency curve

Radionuclides emitting multiple gamma-rays in cascade give rise to summing effects that may be a source of error in the efficiency-curve based interpretation of gamma-ray spectra obtained in highly efficient counting geometries. Correction methods for sources that are small enough for the detector efficiency to be constant over the source volume are well-known. However, in geometries where the detector efficiency is not constant throughout the sample volume, such as Marinelli-beaker geometries, appreciable underestimation of the source activity may still occur if the variation of the efficiencies over the source volume is not accounted for. By introducing a third efficiency curve that accounts for the variation of the detector efficiency over the source volume, we have developed a practical, easy-to-use method that allows for determination of all three efficiency curves from a single, high-resolution gamma-ray spectrum, as well as for accurate correction for cascade summing effects.