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One of the pressing demands in our western society is the safety and maintenance of our nuclear legacy. In Germany the dismantling, safe processing and storage of nuclear waste have resulted in a multi-national research program. One of the findings was that nondestructive testing methods and material selective imaging of compound large objects is possible using thermal and fast neutrons. They also identified that a powerful, safe, and compact neutron source would be required.
Since the advent of ultra-intense lasers many applications have been investigated using the unique parameter of laser-driven secondary sources. Recently, we have demonstrated the realization of a short-pulse laser- driven neutron source with beam intensities orders of magnitude above earlier attempts. Those sources can lead to a compact and potentially mobile neutron source with a large number of applications. The neutron source is based on a so-called pitcher-catcher approach, where a short burst of energetic, laser-driven deuteron ions are converted into a short pulse of neutrons in a subsequent converter material. Here, in addition to neutron conversion via (d,n) reactions the breakup of energetic deuterons and a non-thermal pre-compound reaction in the converter material result in a directed beam of neutrons and an increase in neutron numbers compared to earlier attempts. The neutron record number so far were produced using high-contrast, high-energy short pulse lasers of a few hundred femtosecond pulse duration and invoking relativistic transparency in solids as a new ion acceleration mechanism.
I will present the underlying mechanism of creating an intense pulsed and highly directed beam of neutrons using ultra-intense lasers and the recent experimental results using laser systems in the US and in Europe. Furthermore, I will focus on a few examples of using such sources for applications that are either important for the security of our countries or will have large economical potential in industrial applications. These range from the remote sensing of illicit nuclear material in cargo to the non-destructive analysis of large civil constructions using compact laser systems.
The initial ion pulse that is converted into neutrons is of only a few picosecond duration and thus the neutron burst is generated with sub-nanosecond pulse length. This allows for precise energy resolution of the neutrons using time-of flight techniques. As the ion acceleration is of only a few millimeter in length, replacing ten's to hundred's of meter of conventional acceleration length the source is extremely compact. As the ion beams are extremely intense and do not suffer from space charge deterioration the fast neutron source is capable of point projection imaging with an initial source size of around a millimeter. As the pulse duration is short, high energy resolution can be achieved at a much reduced time-of-flight length offering more compact systems.
As future laser systems largely increase not only peak power, but also already offer repetition rates up the kHz applications in research and industry become visible.
To fully take advantage of those new sources new detector systems should keep up with enhanced spatial and temporal resolution. Also they need to withstand the unavoidable x-ray flash and electro-magnetic pulse originating from the laser plasma interaction. We have started to explore novel detectors and tested them at high-energy short pulse laser systems for fast and thermal neutron beams.
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