Active Activation Diagnostics for High Energy X-ray and Neutron Measurements
Dean Rusby | 21-FS-047
The goal of this project was to identify materials that can be used to detect high-energy x rays during National Ignition Facility Advanced Radiographic Capability (NIF-ARC) experiments and be incorporated into the existing real-time nuclear activation detectors (RTNADs), with minimal impact to the RTNAD deuterium–tritium (DT) neutron measurement capability. First, we conducted a search of authoritative compilations of nuclear data for alternative materials. As part of this work, we identified activation products with short half-lives, hence suitable for future high-repetition rate laser systems, for measuring high-energy x rays. Next, a few explorative experiments were conducted at the Photonuclear Reactions for Isotopic Signature Measurements (PRISM) facility at Lawrence Livermore National Laboratory to investigate some possible reactions that could be useful for NIF-ARC experiments. Finally, to understand the impact of introducing new materials to the existing RTNAD setup, we used a Monte Carlo model to investigate the impact of introducing materials suitable for x-ray measurements within the existing RTNADs. We have identified two materials, gold and neodymium, that appear to be the best candidates to complement the RTNADs, by adding a new high-energy x-ray measurement capability.
The Monte Carlo code GEANT4 was used to investigate the impact of introducing new materials to the existing RTNAD setup. The configuration where a new sample was introduced under the existing zirconium cap had the highest geometric collection efficiency but would impact, by approximately 10%, the measurement at 909 kiloelectron-Volts (keV), which is used for the spatial measurement of neutrons from ignition experiments. Finally, using a previously measured x-ray spectrum from a NIF-ARC experiment, the estimated activity from the previously measured configuration was found to be approximately 5 decays per second. This is slightly higher than the background after a typical NIF-ARC experiment, suggesting that this setup would be a method of increasing the capabilities of the RTNADs.
The goal of investigating using multiple (additional) activation materials with the existing RTNADs is to develop a flexible platform to diagnose both high-energy x rays and DT neutrons at the NIF facility, which is used to develop science and technology tools and capabilities to meet future national security challenges. This work also can also be translated to other high-energy lasers (e.g., the Omega laser) or other facilities (e.g., the Z Facility) within the NNSA complex that may require fluxes of high-energy x-ray bremsstrahlung radiation, and potentially, other high-repetition-rate laser facilities.