Monte Carlo simulation of the spatial response function of a SPECT measurement device for nuclear fuel bundles

Sammanfattning: The PGET device is currently being developed for partial-defect verication purposes on nuclear fuel assemblies. It Comprises CdTe detector elements in a heavy tungsten-alloy collimator, for which collimator slit openings define the field-of-view. This study aims at calculating the spatial response function of this device for further deployment in tomographic reconstruction algorithms. In this work, the detector response for 2 dierent sources (662 keV from Cesium-137 and 1274 keV from Europium-154) was simulated using the MCNPX software package. In the simulations, energy windows used in measurements with the PGET device were deployed. The results show the expected characteristics with strong response for a source position directly in front of the collimator slit opening and decreasing response as the source is moved into the penumbra and umbra region. The uncertainty of the simulated response function was less than 3.5 % for both sources. Separate simulations were made to quantify contributions from septal penetration and scattering from the collimator material into the detector for the energy windows covering the full -energy peak. These contributions were found to be around3% for the source of Cesium-137 and 6% for the source of Europium-154.