Peak energy shift dependent on source position in γ-ray energy measurement by using a closed-ended coaxial HPGe detector

The source position effect in the γ-ray energy measurement by using a closed-ended coaxial HPGe detector is investigated at the energy of 1332 keV. The shift of the γ-ray peak energy is measured as a function of source-to-detector distance for axial and radial positions of the 60Co source. By using Monte Carlo method, the interaction of γ-rays in the detector material is simulated, and then the peak shift due to field increment effect and charge trapping effect is calculated. The measured shift reasonably agrees with the calculated value. For the axial direction, the positive peak shift occurs, and the shift increases significantly within 3 cm from the detector. At the distance of 0.5 cm, the measured shift becomes 42 eV. For the radial direction, the negative peak shift within 9 eV occurs. The dependence of peak shift on the source-to-detector distance for the radial direction is much weaker than that for the axial direction.