Testing of different true coincidence correction approaches for gamma-ray spectrometry of voluminous sources

To achieve the highest possible sensitivity of analysis for environmental samples it is common practice to use both a high efficiency detector and a close measurement geometry with a large sample size (e.g. Marinelli beaker). Under such conditions, the typical efficiency calibration procedure results in a biased activity value for many nuclides due to the true coincidence summing effect. While there are a few methods to correct for this effect with special calibration standards, such calibrations can be both time consuming and expensive. Due to these calibration difficulties, the true coincidence summing effect is often simply ignored. Recently, it has been demonstrated that the coincidence summing correction can be performed mathematically even for voluminous sources. This new method consists of an integration of the coincidence correction factor over the sample volume while taking into account its chemical composition and the container. In this paper, we will discuss the latest approaches for establishing the peak efficiency and peak-to-total efficiency curves, which are required for this method. These approaches have been tested for HPGe detectors of two different relative efficiencies.