Measuring Activity Concentrations Using a High Purity Germanium Detector: Extended Source Efficiency Correction and Optimization of Sample Position

An experiment using several calibrated gamma-ray sources located at different positions around a high purity germanium detector was conducted. The efficiency calibration curve for each position was obtained. More than 15 gamma-ray energies for each position point were used. The efficiency calibration curves facilitate the determination of radionuclide concentrations in an extended source such as NORM. These curves are useful for the measurement of a sample that is small enough to be considered as a point source, in order to obtain the position which produces the larger number of counts for the gamma-ray energy of interest. Preliminary results of the resulting efficiency curves and their interpretation are presented. (author)