Determination of the activities of inhomogeneous samples by gamma spectrometry using energy-dependent self-absorption

The 137Cs activities of inhomogeneous model samples, representing solutions with the radionuclide partially dissolved, were measured and compared to the calibrated values. The samples were composed of a thin homogeneous disc and a homogeneous cylinder placed coaxially on top of it, the disc facing the detector. Four samples with different self-absorption values in the cylinder were prepared. The values of the activities in the disc and cylinder were calculated from the countrates in the lines belonging to the X- and γ-rays. The calculated activities agreed with the calibrated ones within the uncertainties of the measurements. The uncertainties of the measured activities are discussed in terms of the self-absorption, which determines the conditionality of the system of equations expressing the countrates in terms of efficiencies and activities.