A Liquid-Lithium Target project for production of high-intensity quasi-stellar neutrons

A windowless Liquid-Lithium Target (LiLiT) is under construction and development at Soreq NRC (Israel). The target is designed to be bombarded by a 2-4 mA proton beam (E_p= 1.8-2.5 MeV) from the high-intensity Soreq Applied Research Accelerator Facility (SARAF), a superconducting linear accelerator for light ions. The liquid-lithium forced flow at a velocity of ∼20 m/s and a thickness of ∼1.8 mm serves both as a power dump (10 kW) for the proton beam and as a neutron-producing target via the ⁷Li(p,n)⁷Be reaction. As known from the work of the Forschungszentrum Karlsruhe group, the energy distribution of neutrons emitted for a proton energy E_p= 1.912 MeV, ∼30 keV above the reaction threshold, and a thick Li target is very similar to that of a Maxwell-Boltzmann flux at a thermal energy of ∼25 keV, well suited for activation measurements relevant to s-process nucleosynthesis. The neutron intensity expected under these conditions from the combination of the SARAF proton beam and the LiLiT thermal properties is of ∼2×10¹⁰ s^-1 mA-and is larger by more than one order of magnitude than currently available. The LiLiT setup is built as a loop circulating liquid lithium at a temperature of ∼200°C and producing a jet (acting as the target) onto a thin concave supporting wall, driven by a rotating magnet inductive electromagnetic pump. The liquid lithium is collected in a reservoir housing a heat exchanger with a mineral-oil closed loop. Circulation and thermal tests of the loop are presently in progress in an offline dedicated electron-gun laboratory and online installation at the SARAF accelerator is planned for end 2010. Characterization of the SARAF proton beam (beam energy, energy width and transverse profile) and of the neutron spectrum obtained under these conditions are studied in parallel using a solid-lithium (lithium fluoride) target at low beam intensities. The SARAF-LiLiT system will be used to measure stellar neutron capture cross sections for stable or radioactive targets demanding high neutron fluxes. Present status and plans are discussed.