With an increase in both armed conflicts and terrorist threats, the number of unexploded ordinances is growing rapidly, inducing serious threats for citizens both now and in the future. As well as modern devices, remnants of previous conflicts are also starting to pose severe environmental problems. A good example is the Baltic Sea, which essentially acts as store for hundreds of thousands of tonnes of explosive devices and chemical agents after the two World Wars. It has been recognised as a risk by the governments of the Baltic Sea countries and the European Union.
In this paper, published in Scientific Reports, a collaboration between ISIS, Jagiellonian University and the Polish Academy of Sciences used the Vesuvio beamline to investigate using neutrons for detecting these dangerous materials underwater. Neutron activation analysis (NAA) has been used to detect hazardous materials on the ground, but there are currently no solutions for effectively monitoring threats at sea, both for offshore infrastructure and ports.
Because neutrons are highly penetrating, they can penetrate the object being even if it is concealed in a container or buried in the ground. NAA uses fast neutrons as probes, which interact with the sample material and emit secondary gamma radiation. The energy of the emitted radiation is characteristic of the elemental composition of the sample.
The team studied a commonly used explosive surrogate, melanine, using neutron transmission (NT) and neutron Compton scattering (NCS). When compared to NAA, both NT and NCS can distinguish between isomers present in the material. Secondly, NT and NCS are much less sensitive to background gamma radiation than NAA. Their experiments were supported by first-principles modelling, providing detailed scrutiny of the material structure and the nuclear dynamics behind the neutron scattering observables.
The team were able to determine the signal characteristics of melanine, as well as the limits of detection and quantitation. The protocol presented in this work paves the way towards similar types of experiments that could be performed in the future by automatic underwater drones equipped with compact thermal-to-epithermal neutron sources. These could then be deployed in the Baltic Sea to detect hazardous materials.
The full paper can be found at DOI: 10.1038/s41598-024-69290-x
