Characterization of laser-driven neutron emissions

Ultra-intense lasers represent a new way to produce neutron fields, more compact than nuclear reactors or accelerators and with fewer radiological constraints than these conventional sources. The electric field induced by an ultra-intense laser pulse within a micrometer-sized target can reach several TV/m, allowing for the acceleration of protons to several tens of MeV. These protons can then be intercepted by a second target, called a converter, in which they induce nuclear reactions and thus produce neutrons. This technique, known as the pitcher-catcher technique, is capable of generating very intense fluxes (> 10¹⁷ n/cm²/s) at energies up to several tens of MeV, making it possible to envision applications such as neutron imaging or the laboratory reproduction of the rapid nucleosynthesis process responsible for the creation of the heaviest elements.

To demonstrate the feasibility of these applications and ensure the radiological protection of these laser facilities, these neutron fields must be optimally characterized. Detectors with ultra-fast electronics or passive detectors appear to be most compatible to the characteristics of laser-driven neutron sources (very brief and intense emissions, noisy environment, etc.).

This thesis work focuses on optimizing the development of a neutron activation spectrometer (SPAC), particularly suitable for measuring intense neutron fields with a strong gamma component. In addition to simulations of the expected source terms and detector responses using Geant4 & MCNP Monte Carlo codes, bubble dosimeters, Time-of-Flight detectors and activation samples were used on various laser facilities such as ALLS (Canada) and Apollon (France), to optimize and characterize the produced neutron emissions.

ultra-Intense lasers, neutrons, laser-driven neutron sources, detection, nuclear physics

Full document (EN): HAL-04957025