Background: The purpose of the research is to provide the tools to combat the GWOT by developing a radiation source to detect special nuclear materials (SNM). Neutrons have been shown to produce identifiable signatures in SNM materials. However, the effect range for active detection techniques is limited by the lack of directionality in the neutron beam used to probe the material.
Accomplishment: The generation of neutrons with energies in excess of 10 MeV is of great interest due to demanding applications such as fusion power plant materials testing, contraband detection, and fissile material waste disposal, among others. These applications demand a high flux of neutrons, which is possible with nuclear reactors, spallation sources, and particle accelerators.
Unfortunately these devices not only take up significant space, but are extremely expensive to build and maintain. High-intensity, petawatt class lasers may provide an attractive alternative with relatively lower costs, which is timely due to the rapid advance of high repetition rate, high energy lasers. It has previously been demonstrated experimentally that high-intensity lasers can be used to produce neutrons by directly accelerating deuterons through thick deuterated targets or using accelerated protons impinging on a secondary target. However, due to low exothermic reaction energies, these studies were limited to neutron energies below 3 MeV. A target was proposed for a conceptual design of producing neutrons above 10 MeV using deuterium-tritium targets, though no experiments were carried out to implement this design. Recently, a new scheme was proposed by Davis and Petrov (NRL) et al. to generate neutrons in excess of 10 MeV by accelerating deuterons and interacting them with Lithium or other low Z materials. This technique has the advantage of producing higher and more directional neutron fluence, but experiments have not yet been carried out to validate these predictions. The first experimental results for the production of neutrons with energies up to 18 MeV using high-energy, short pulse lasers was demonstrated and the results will be published in a forthcoming issue of the Physics of Plasmas (Oct).
Significance: The results of this investigation demonstrate the application of intense ultrashort pulse lasers for providing a source of energetic particles for the detection of SNM.
Application: This work is currently being transitioned to ONR as part of the Maritime Weapons of Mass Destruction Detection (M-WMD-D) program. A deployed system could be fielded using a large chirped pulse amplification (CPA) laser on a mobile platform, a target assembly to produce the neutron pulses, and appropriate detectors to analyze the nuclear signatures.