High-Power Electron Beam Tests of a Liquid-Lithium Target and 7Li(p,n) Near-Threshold Neutrons: Characterization Study for Accelerator-Based Boron Neutron Capture Therapy


  S. Halfon [1,2]  ,  M. Paul [1]  ,  A. Arenshtam [2]  ,  D. Berkovits [2]  ,  D. Cohen [1]  ,  I. Eliyahu [2]  ,  G. Feinberg [1,2]  ,  D. Kijel [2]  ,  I. Mardor [2]  ,  I .Silverman [2]  
[1] The Hebrew University of Jerusalem
[2] Soreq NRC

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 epithermal neutron source with possible application for Boron Neutron Capture Therapy (BNCT) cancer treatment in hospitals. The LiLiT 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 a 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 at velocity higher than 5 m/s on the concave supporting wall. A high-intensity (26 kV, 100 mA) electron gun was attached to the system, and the electron beam is directed to the lithium surface. The 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, 2 mA proton beam. LiLiT high-intensity proton beam irradiation (1.91- 2.5 MeV, 2 mA) is in commissioning stage at SARAF (Soreq Applied Research Accelerator Facility) superconducting linear accelerator. In order to determine conditions of LiLiT proton irradiation for BNCT and tailoring of 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) simulations and on low-intensity experiments with solid LiF targets using a Van De Graaff accelerator at the Weizmann Institute of Science. A 3He spectrometer was used to evaluate the neutron spectrum before and after a polyethylene moderator. In-phantom dosimetry measurements are performed using specially designed dosimeters based on CR-39 plastic track detectors.