A method to obtain a Maxwell-Boltzmann neutron spectrum at kT=30 keV for nuclear astrophysics studies

A method based on shaping the proton beam energy in order to shape the neutron beam energy to a desired form for accelerator-based neutron sources is proposed. An application to a superconductive RFQ proton accelerator of 5 MeV and 50 mA for the production of a stellar neutron spectrum at thermal energy equal to 30 keV using the (7)Li(p,n)(7) Be reaction is investigated. The chosen energy beam shaper is a carbon foil which shapes the quasi-monochromatic proton beam to a quasi-Gaussian distribution: after the carbon foil, the beam is still shaped by chopping the Gaussian distribution at the reaction energy threshold. The obtained proton beam is impinged in a metallic lithium target. The concepts of the energy shaper, the proposed lithium target and the calculations performed to remove their power load are presented. Calculations show that a power density of 3 kW/cm(2) can be sustained by the target which produces a forward-directed neutron source of 7.3 x 10(10) neutrons/s. The obtained neutron spectrum resembles a Maxwell-Boltzmann distribution at kT=30 keV with a coefficient of determination of 0.997. The method is intended to be applied in activation analysis for measuring the Maxwellian-averaged neutron capture cross-section of elements of interest for astrophysics and validation of integral neutron data in the epithermal energy range. (c) 2009 Elsevier B.V. All rights reserved.