A team of the LOEWE research-initiative Nuclear Photonics, led by the TU Darmstadt, shows that neutrons, which are produced compactly with lasers, can be used in non-destructive material testing. As electrically neutral particles, neutrons penetrate matter relatively easily. This results in a wide range of industrial applications, such as testing containers with radioactive waste. The results were published in the renowned journal "Nature Communications".
Until now, science has used X-rays to examine the contents of objects. However, light elements such as hydrogen or organic substances are difficult to recognize and distinguish, especially when they are behind heavier, shielding elements. Neutrons are particularly sensitive to these materials and shields such as lead easily penetrate them. In addition, there is the unique ability that different isotopes can be distinguished with the help of neutrons, which makes it possible to unambiguously determine the spatial distribution of isotopes within an object. If you "bombard" an object to be examined with neutrons, you can deduce its content from the isotope distribution.
This is particularly important for the dismantling of nuclear facilities. Before the casks with radioactive waste housed in the interim storage facility can be taken to the repository, their contents must be clearly identified. This proves to be difficult with classic X-ray technology, since the containers are often designed in such a way that they are as opaque as possible for this type of radiation.
The neutron beams are usually generated in large particle accelerator facilities, which are extremely expensive to build and operate. A further complication is that the objects to be examined cannot be transported to the few existing large-scale facilities. This technology is therefore not accessible to a large part of the industry.
Researchers from the LOEWE focus area Nuclear Photonics headed by Dr. Marc Zimmer and Professor Markus Roth from the Institute for Nuclear Physics at the TU Darmstadt have replaced the conventional accelerator with a high-intensity laser and used it to generate neutrons. This reduced the typical distance of hundreds of meters needed to accelerate and measure the samples to less than two meters. On the one hand, this was made possible by the use of ultra-short-pulse lasers based on the "Chirped Pulse Amplification" method, for which the Nobel Prize was awarded in 2018. On the other hand, the conditions for the investigations at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt were optimized to such an extent that several industrially relevant applications could be demonstrated at the same time.
The experiment was able to show that such a compact laser-driven neutron source can be used to identify different isotopes in workpieces non-destructively and even to make them spatially "visible". A previously unknown contamination was also detected in one of the workpieces. In addition to use for radioactive waste, other applications are also conceivable with the neutron source, such as the non-destructive examination of archaeological finds or the visualization of the fuel flow within an engine during operation.