Dense Plasma Focus Neutron Source for Nuclear Forensics
Andrea Schmidt | 22-FS-036
This feasibility study sought to answer the question of fundamental feasibility: Can a dense plasma focus (DPF) be used for nuclear forensic experiments? We planned to expose a foil stack to a neutron pulse (or several pulses) from a DPF and perform spectrometric measurements at the LLNL counting facility in B151 to independently characterize the integral neutron production rates and neutron spectrum of the DPF. We are also able to do some counting (for short-lived products) locally using a portable counting system that can be co-located with the DPF. This project takes advantage of two unique capabilities at LLNL: nuclear forensic analysis and DPF neutron sources. DPF neutron sources are currently being developed for flash neutron radiography but could potentially serve many other useful NNSA missions, including as a source for nuclear forensic experiments, particularly ones that produce very short-lived isotopes and/or require a rapid shot rate. During FY22, preparations were made in anticipation of making this measurement in FY22. This included setting up a counting detector near the DPF, taking local background measurements, creating a procedure for sample recovery, and performing test runs of sample recovery. Unfortunately, the LLNL DPF was unexpectedly out of commission for the entire one-year duration of this feasibility study. We originally anticipated the machine getting back online in time to take data in FY22, but due to supply chain issues, the machine will not be back up until October 2022.
The nuclear forensics program at LLNL currently relies on facilities such as NIF that provide a very high dose, but also produce a shot approximately once per day. At such facilities, it may take several minutes or hours to recover a sample after a shot, which makes it very difficult to detect short-lived products. The infrequent shot rate makes iteration on experimental set-up difficult. If the DPF were a viable source for such experiments, or even for practice shots leading up to a high-consequence-of-error NIF shot, it could be a valuable tool for the forensics team. It is also possible that, due to the short sample recovery time associated with the DPF, this could open the door to measurements on shorter-lived products that are not possible at the larger flagship facilities.