This work is focused on comparing different gamma-ray spectroscopy systems based on large-size HPGe detectors for a wide range of dead-time conditions. This project supports an ongoing DTRA DOD project aimed at characterizing a large number of short-lived fission fragments by means of cyclic neutron activation analysis (CNAA) for various actinides of interest for post-detonation nuclear forensics. A CNAA system with a sub-second transit time is currently being finalized at the Pennsylvania State University and it will utilize fast neutrons from the Breazeale Penn State nuclear reactor. The CNAA gamma-spectroscopy system will experience a wide range of (extreme) dead-time conditions; therefore, it is paramount to select the most suitable multi-channel analyzer (MCA) for the CNAA system. The MCAs available for the comparison are CAEN DT5781 with MC2Analyzer software, CAEN Hexagon with Quantus software, GBS Elektronik MCA527 with Winspec software, and Canberra Multiport II with Genie 2000 software. Two large-size HPGe detectors from Canberra are being used for testing with various gamma-ray sources.
Two of the main quantities of interest for any gamma-spectroscopy system are the energy resolution and linearity as a function of dead-time. The energy resolution and linearity are paramount performance characteristics for the aforementioned DTRA DOD project, because the irradiated samples of interest (Th-232, U-233, U-235, U-238, and Am-241) contain many short-lived fission fragments with half-lives on the orders of seconds and minutes that overlap in the energy space. To mimic a wide range of dead-time conditions, a moving gamma-ray source stand has been designed to control the number of gamma-rays impinging on the HPGe detectors through the use of high-precision, fast-moving stepper motor. Additionally, a second moving gamma-ray source stand is being designed to run simultaneously alongside the existing source stand, to mimic a wide dead-time range of different parent/daughter cases (different energies). We are currently finalizing and optimizing the dead-time measurement system, and in the full paper we will describe our experimental observations with various gamma-ray sources and under various parent/daughter and dead-time conditions in detail.