High-power electron beam tests of a liquid-lithium target and characterization study of 7Li(p,n) near-threshold neutrons for accelerator-based boron neutron capture therapy

• A Liquid-Lithium Target (LiLiT) was built as a high-intensity neutron source via the 7Li(p,n) reaction.
• The target was tested with a high-power electron gun.
• The target dissipates power densities >4 kW/cm2 and ~2 MW/cm3 at a lithium flow velocity of ~4 m/s.
• Ionizing particles from the BNCT reaction 10B(n,a)7Li were detected using a novel approach based on CR-39 track detectors.
• Measured doses are in good agreement with simulations using MCNP and Geant4 codes.

A compact Liquid-Lithium Target (LiLiT) was built and tested with a high-power electron gun at Soreq Nuclear Research Center (SNRC). The target is intended to demonstrate liquid-lithium target capabilities to constitute an accelerator-based intense neutron source for Boron Neutron Capture Therapy (BNCT) in hospitals. The lithium target will produce neutrons through the 7Li(p,n)7Be reaction and it will overcome the major problem of removing the thermal power >5 kW generated by high-intensity proton beams, necessary for sufficient therapeutic neutron flux.In preliminary experiments liquid lithium was flown through the target loop and generated a stable jet on the concave supporting wall. Electron beam irradiation demonstrated that the liquid-lithium target can dissipate electron power densities of more than 4 kW/cm2 and volumetric power density around 2 MW/cm3 at a lithium flow of ~4 m/s, while maintaining stable temperature and vacuum conditions. These power densities correspond to a narrow (σ=~2 mm) 1.91 MeV, 3 mA proton beam. A high-intensity proton beam irradiation (1.91–2.5 MeV, 2 mA) is being commissioned at the SARAF (Soreq Applied Research Accelerator Facility) superconducting linear accelerator.In order to determine the conditions of LiLiT proton irradiation for BNCT and to tailor the neutron energy spectrum, a characterization of near threshold (~1.91 MeV) 7Li(p,n) neutrons is in progress based on Monte-Carlo (MCNP and Geant4) simulation and on low-intensity experiments with solid LiF targets. In-phantom dosimetry measurements are performed using special designed dosimeters based on CR-39 track detectors.