Abstract:
Background The imperative for compact, high-flux neutron sources extends beyond fundamental nuclear physics into materials science, medical isotope production, and non-destructive inspection. While conventional reactor-based or spallation sources deliver high intensities, their prohibitive scale and regulatory complexity necessitate the exploration of laser-driven alternatives. Recent advances in laser wakefield acceleration (LWFA) present a viable pathway to miniaturize these sources without compromising beam quality.
Purpose This work investigates the feasibility of generating photoneutrons using a compact 45 TW femtosecond laser system. By optimizing laser-plasma coupling, we aim to maximize the laser-to-neutron conversion efficiency, targeting a high-repetition-rate source suitable for practical applications such as fast neutron radiography.
Methods Utilizing a 45 TW Ti:sapphire laser operating at 10 Hz, relativistic electron beams were generated via LWFA by focusing intense pulses onto a supersonic gas jet. Electron beam stability and energy were optimized through precise control of gas density and laser focusing geometry. These electrons impinged on a 1 cm-thick tungsten converter, producing neutrons via bremsstrahlung-induced (γ,n) reactions. Neutron angular distributions were quantified using bubble detectors over 120 accumulated shots, while Monte Carlo simulations (FLUKA) were employed to model the spectral characteristics and yield dependencies.
Results Stable electron beams reaching energies up to 100 MeV facilitated a neutron conversion efficiency of approximately 1×105 n·sr−1·J−1. Measurements revealed a strongly anisotropic angular distribution, with forward-emitted neutrons exceeding lateral yields by a factor of four. Simulation results indicate that while neutron yield scales with electron energy, the growth rate diminishes beyond 100 MeV. Crucially, the neutron spectrum remains concentrated within the 3–8 MeV range—ideal for resonance radiography—provided the driving electron energy exceeds 30 MeV.
Conclusions These findings validate the viability of a compact LWFA-driven photoneutron source operating at 10 Hz. The inherent anisotropy and high specific yield underscore its potential as a complement to conventional facilities. Future upgrades focusing on kHz-level repetition rates and enhanced electron beam quality promise significant improvements in average neutron flux, paving the way for deployable, high-performance neutron sources.
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