Investigation of the neutron energy distribution of the IRSN 241Am-Be(alpha,n) source.

The neutron energy distribution of the IRSN standard 241Am-Be(alpha,n) source was measured using a proton recoil liquid scintillator, BC501A, >1.65 MeV. The experimental data were compared with the ISO recommended neutron energy distribution for an Am-Be source and some significant discrepancies were observed. Monte Carlo simulations were then performed to investigate on the neutron source term in order to consider the different parameters between the IRSN Am-Be source and the one used to establish the neutron emission spectrum recommended by the ISO standard. The variation of the parameters of the source did not explain the remaining discrepancies. A good agreement with the experimental results was observed when the theoretical neutron energy distribution from Geiger and Van der Zwan was introduced in the study as new source term. These investigations showed that the ISO recommended Am-Be distribution might not be well suited to represent the neutron energy distribution of all Am-Be sources, and that the manufacturing of the sources might play a major role in the neutron fluence energy distribution.