Asher Shor

SARAF Phase I linac in 2012

This report outlines the status of beam operations at the SARAF accelerator during 2012. Performance of various accelerator subsystems, their limiting factors and the recent improvements are presented. The accumulated experience of proton beam operation is summarized. Future prospects are discussed.

SARAF Phase I linac operation in 2013–2014

Phase I of the SARAF superconducting RF linac is under operation at the Soreq Nuclear Research Center. The present status of Phase I main components is reported, as well as, the beam operation experience accumulated in 2013–2014. The latter include acceleration of a 2 mA and 1.6 mA CW proton beams at energies of 2 MeV and 3.9 MeV correspondingly and 1 mA pulsed, duty cycle of few %, deuteron beams up to 5.6 MeV. The recent experiments include operation of intense CW proton beams on the liquid lithium target.

Detectors for the gamma-ray resonant absorption (GRA) method of explosives detection in cargo: a comparative study

Gamma-Ray Resonant Absorption (GRA) is an automatic-decision radiographic screening technique that combines high radiation penetration with very good sensitivity and specificity to nitrogenous explosives. The method is particularly well-suited to inspection of large, massive objects (since the resonant γ-ray probe is at 9.17 MeV) such as aviation and marine containers, heavy vehicles and railroad cars. Two kinds of γ-ray detectors have been employed to date in GRA systems: 1) Resonant-response nitrogen-rich liquid scintillators and 2) BGO detectors. This paper analyses and compares the response of these detector-types to the resonant radiation, in terms of single-pixel figures of merit. The latter are sensitive not only to detector response, but also to accelerator-beam quality, via the properties of the nuclear reaction that produces the resonant-γ-rays. Generally, resonant detectors give rise to much higher nitrogen-contrast sensitivity in the radiographic image than their non-resonant detector counterparts and furthermore, do not require proton beams of high energy-resolution. By comparison, the non-resonant detectors have higher γ-detection efficiency, but their contrast sensitivity is very sensitive to the quality of the accelerator beam. Implications of these detector/accelerator characteristics for eventual GRA field systems are discussed.

Scientific opportunities at SARAF with a liquid lithium jet target neutron source

SARAF (Soreq Applied Research Accelerator Facility) is based on a 5 mA, 40 MeV, proton/deuteron accelerator. Phase-I, operational since 2010, provides proton and deuteron beams up to 4 and 5 MeV, respectively, for basic and applied research activities. The high power Liquid-Lithium jet Target (LiLiT), with 1.912 MeV proton beam, provides high flux quasi-Maxwellian neutrons at kT ~30 keV (about 2 × 1010 n/s/cm2/mA on the irradiated sample, about 1 cm from the target), enabling studies of s-process reactions relevant to nucleo-synthesis of the heavy elements in giant AGB stars. With higher energy proton beams and with deuterons, LiLiT can provide higher fluxes of high energy neutrons up to 20 MeV. The experimental program with SARAF phase-I will be enhanced shortly with a new target room complex which is under construction. Finally, SARAF phase-II, planned to start operation at ~2023, will enable full capabilities with proton/ deuteron beams at 5 mA and 40 MeV. Liquid lithium targets will then be used to produce neutron sources with intensities of 1015 n/s, which after thermalization will provide thermal neutron (25 meV) fluxes of about 1012 n/s/cm2 at the entrance to neutron beam lines to diffraction and radiography stations.SARAF (Soreq Applied Research Accelerator Facility) is based on a 5 mA, 40 MeV, proton/deuteron accelerator. Phase-I, operational since 2010, provides proton and deuteron beams up to 4 and 5 MeV, respectively, for basic and applied research activities. The high power Liquid-Lithium jet Target (LiLiT), with 1.912 MeV proton beam, provides high flux quasi-Maxwellian neutrons at kT ~30 keV (about 2 × 1010 n/s/cm2/mA on the irradiated sample, about 1 cm from the target), enabling studies of s-process reactions relevant to nucleo-synthesis of the heavy elements in giant AGB stars. With higher energy proton beams and with deuterons, LiLiT can provide higher fluxes of high energy neutrons up to 20 MeV. The experimental program with SARAF phase-I will be enhanced shortly with a new target room complex which is under construction. Finally, SARAF phase-II, planned to start operation at ~2023, will enable full capabilities with proton/ deuteron beams at 5 mA and 40 MeV. Liquid lithium targets will then be used to pr...

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 (Ep= 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 7 Li(p,n) 7 Be reaction. As known from the work of the Forschungszentrum Karlsruhe group, the energy distribution of neutrons emitted for a proton energy Ep= 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 ~2×10 10 s -1 mA -1 , 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 o 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.

Nucleosynthesis Reactions With The High-intensity Saraf-lilit Neutron Source

We present a status report of recent neutron capture experiments performed with the mA-proton beam (1.92 MeV, 3 kW) of the Soreq Applied Research Accelerator Facility (SARAF) and the Liquid-Lithium Target (LiLiT). Experiments and preliminary results for (n,gamma) reactions on 36,38Ar, studied for the first time with 30-keV neutrons, on natKr, natCe and on radioactive targets 147Pm and 171Tm are described.

FIRST NUCLEAR-ASTROPHYSICS EXPERIMENTS WITH HIGH-INTENSITY NEUTRONS FROM THE LIQUID-LITHIUM TARGET LiLiT

A high-intensity neutron source based on a Liquid-Lithium Target (LiLiT) and the Li(p,n) reaction was developed at SARAF (Soreq Applied Research Accelerator Facility, Israel). The setup is used for nuclear-astrophysics experiments owing to the quasi-Maxwellian shape of the neutron energy distribution at stellar thermal energies (kT ~ 30 keV). The LiLiT device consists of a forced-flown (> 2 m/s) film of liquid lithium (~200 C) whose free surface is bombarded by a proton beam. The lithium film acts both as the neutron-producing target and as a power beam dump. The setup was commissioned with a 1.2 mA proton beam at 1.91 MeV, producing a neutron yield (peaked at ~28 keV) of ~ 3 ×10 n/s, more than one order of magnitude larger than conventional Li(p,n)-based neutron sources. The target dissipates a peak power areal density of 2.5 kW/cm and a peak power volume density of 500 kW/cm with no significant temperature or vacuum pressure elevation in the target chamber. We present preliminary results of first activation measurements on Zr and Ce stable isotopes performed with the SARAF-LiLiT setup, using Au as neutron monitor and of the determination of their Maxwellian-averaged neutron capture cross section.

Energy-broadened proton beam for production of quasi-stellar neutrons from the 7Li(p,n)7Be reaction

Production of quasi-stellar neutrons by the 7Li(p,n)7Be reaction has been used for measuring s-process cross sections and efforts to upgrade the proton beam intensity with RF linear accelerators are presently ongoing. We investigated the effect of an energy-broadened proton beam, as is expected for a RF linear accelerator, on the produced 25-keV quasi-Maxwellian neutron spectrum and compared it to that of a Van de Graaff accelerator with well-defined proton energy. Neutron spectrum measurements from 0° to 80° were carried out with a pulsed proton beam at the IRMM Van de Graaff accelerator using time-of-flight techniques, both with a narrow energy spread (σ≈1.5 keV) proton beam and with an energy-broadened beam (σ≈20 keV) obtained by straggling through a Au-foil degrader. In the latter case, the neutron spectrum is closer to the Maxwellian flux distribution in the high neutron energy region.