Performance Analysis of a Gamma-Ray Spectroscopy System Based on a Large-Size HPGe Detector Under Extreme Dead-Time Scenarios

This work is focused on comparing the performance of different gamma-ray spectroscopy systems based on a large-size HPGe detector for a wide range of count rates and dead-times. The project supports an ongoing DTRA DOD project aimed at characterizing many short-lived fission fragments by means of cyclic neutron activation analysis (CNAA) for various actinides of interest for post-detonation nuclear forensics. The CNAA system measures a wide energy range of short-lived fission fragments in high count rate environments; therefore, it is important that we understand how different detection systems perform under extreme dead-time conditions. This performance assessment is done by evaluating how a multi-channel analyzer (MCA) performs while measuring a single or multiple sources at the same time, and at various distances. The main objective of this work is to optimize different gamma detection systems and improve the measurement accuracy under extreme dead-times. To properly analyze the gamma-ray detection system's response to a wide range of dead-times, precise control over a source activity is required. This step is achieved by accurately controlling the solid angle between the HPGe detector's face and various mobile radioactive sources with a pair of one-meter-long stepper motors. This setup gives us the needed flexibility in controlling the detection system's count rate and dead-time impact, thereby observing how different gamma-ray signals affect each another. Additionally, the stepper motor system allows us to accurately mimic a wide range of source half-lives. This capability can be simultaneously extended to up to two sources, thereby creating various parent-daughter decay schemes for a wide range of energies and daughter half-lives.