List Mode Data Acquisition for Safeguards Unattended Monitoring Systems

The International Atomic Energy Agency (IAEA) uses Unattended Monitoring Systems (UMS) to support safeguarding nuclear material in facilities around the world. These UMS are required to operate continuously without the intervention of inspectors or technicians. UMS are also required to reliably operate within space limitations and throughout a variety of conditions that can arise, including loss of external power. Some UMS use shift registers for neutron coincidence counting to verify declared quantities of nuclear material. Shift registers perform both the data acquisition (DAQ) and preliminary data reduction for neutron coincidence counting. Alternatively, list mode (LM) DAQ instruments can be used in combination with software that implements shift register logic to perform neutron coincidence counting. In addition to performing standard shift register analyses (coincidence or multiplicity), LM DAQ can be used to perform additional analyses, such as determining per-preamplifier state-of-health, generating Rossi-alpha distributions, or determining spatial information about a source within a measurement system. It also allows for repeated shift register analysis on already recorded LM data using varied parameters, such as pre-delays, gate widths, and which channels to include in the analysis. However, in the past, LM DAQ was not practical for UMS because of the storage requirements for the quantity of data produced and the computational requirements for data reduction. With the advances in storage capacity and computational capability in compact computers that are suitable for industrial environments, LM advantages may now outweigh their drawbacks for UMS applications. This work presents the results of tests conducted with an Advanced List Mode Module (ALMM) to evaluate the suitability of LM DAQ for neutron coincidence counting UMS.