Description
This work tackles the production and experimental characterization of a broad-range ultra-intense neutron source on the LMJ-PETAL facility. Using the PETAL laser ($700~\rm J$, $500~\rm fs$) as a driver of laser-plasma accelerated electron beams, bremsstrahlung gamma-rays were radiated by the relativistic electrons in a $5~\rm cm$-thick lead (Pb) converter in a pitcher-catcher configuration. The high-energy photons were then able to induce the emission of photoneutrons through $(\gamma , xn)$ photonuclear reactions with Pb. The primary electrons were accelerated in the self-modulated laser-wakefield acceleration (SM-LWFA) regime within a supersonic helium gaz jet. This acceleration mechanism is known to generate high electron charges approaching the microCoulomb ($\rm \mu C$), hence its potential for secondary source generation. Using time-of-flight neutron (nToF) scintillator detectors, nuclear activation diagnostics and Geant4 simulations, the setup is shown to have produced up to $2\times 10^{10}$ fast neutrons per shot with energies reaching about $20~\rm MeV$. Such high-flux sources could find application in nuclear physics and astrophysics, as well as in material science.
Moreover, traces of high-energy gamma-induced nuclear fragmentation were recorded on our nuclear activation diagnostic, demonstrating the potential of this scheme to produce radioisotopes akin to conventional spallation facilities but with a more compact setup and a lower overall production cost.