Title: Effects of an Energy Broadened Proton Beam on the Neutron Distribution for the 7Li(p,n)7Be Reaction near Threshold
Citation: Nuclear Measurements, Evaluations and Applications - NEMEA-6 Workshop Proccedings p. 143-152
Publisher: Organisation for Economic Co-operation and Development (OECD)
Publication Year: 2011
JRC Publication N°: JRC61880
URI: http://www.oecd-nea.org/science/docs/2011/index.html
Type: Contributions to Conferences
Abstract: A common method for simulating the thermal neutron conditions in the stellar interior is based on the 7Li(p,n)7Be reaction near threshold energy. This method was pioneered at FZK, Karlsruhe, by Ratynski and Kaeppeler [1]. Maxwellian-averaged neutron capture cross-sections of mean energy 25 keV, relevant to the s-process nucleosynthesis, are measured at existing Van-de-Graaff (VdG) proton accelerators. Soreq NRC Applied Research superconducting linear Accelerator Facility (SARAF) phase 1 [2] is in its final stage of commissioning. Maxwellian averaged neutron capture cross-section measurements are planned to be conducted using a forced-flow closed-loop liquid-lithium target (LiLiT) [3]. The proton beam energy spread of RF linear accelerators, such as SARAF, is typically larger than the spread of proton beams of VdG accelerators. The energy spread of SARAF proton beam at 1912 keV is calculated to be of the order of 20-40 keV FWHM as compared to about 3 keV FWHM for VdG accelerators. For simulating the SARAF proton beam we performed an experiment at the IRMM-Geel VdG using a gold foil degrader positioned before the LiF target. This degrader shifts the mean proton energy to 1912 keV and it broadens the proton beam energy to values simulating the spread of the proton beam at SARAF. For calibrating the cross-sections we also performed a 7Li(p,n)7Be experiment without the gold foil degrader at a proton energy of 1912 keV. The VdG was operated in a pulse mode and the neutron energies were determined by time-of-flight measurements using 6Li glass detectors. Detector efficiencies were obtained by Monte Carlo calculations. We present our study and compare the results for both narrow and broad energy proton beams. Comparison to calculations is also shown.
JRC Institute:Institute for Reference Materials and Measurements

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