  The applicability of MCNP6 to simulate quasi-monoenergetic neutron sources
from interactions of proton beams with energies below 150 MeV on thick 7Li
targets have been studied. Neutron spectra at zero degrees from a 2-mm 7Li
layer backed by a 12-mm carbon beam stopper in an Al flange bombarded with
protons of 20, 25, 30, 35, and 40 MeV have been calculated with MCNP6 using the
recent Los Alamos data library as well as using the Bertini+Dresner and
CEM03.03 event generators. A comparison with the experimental neutron spectra
shows that the event generators do not do well in describing such reactions,
while MCNP6 using the LANL data library simulates production of neutrons from p
+ 7Li in good agreement with the measured data.
