  Accurate knowledge of the neutron energy spectra is useful in basic research
and applications. The overall procedure of measuring and unfolding the fast
neutron energy spectra with BC501A liquid scintillation detector is described.
The recoil proton spectrum of Am-Be neutrons was obtained experimentally. With
the NRESP7 code, the response matrix of detector was simulated. Combining the
recoil proton spectrum and response matrix, the unfolding of neutron spectra
was performed by GRAVEL iterative algorithm. A MatLab program based on the
GRAVEL method was developed. The continuous neutron spectrum of Am-Be source
and monoenergetic neutron spectrum of D-T source have been unfolded
successfully and are in good agreement with their standard reference spectra.
The unfolded Am-Be spectrum are more accurate than the spectra unfolded by
artificial neural networks in recent years.
