The 4.438 MeV gamma to neutron ratio for the Am–Be neutron source

An accurate measurement of the 4.438 MeV $\gamma$-ray to total neutron ratio, namely $R=S_{\gamma }/S_n$, for a Chinese-made Am–Be neutron source is described. The neutron strength of the source relative to a previously standardized source was determined by the manganese bath technique. The $\gamma$-rays spectra of the source were measured using a $\varnothing 75\times 75$ mm NaI(Tl) detector. The background induced by neutrons and the absolute full energy peak efficiency of the detector were calculated using the MCNP code. The experimental ratio so obtained agrees well with the calculated value. A synthetic evaluated and recommended value of $R=0.575\pm 4.8\%$ was given. We conclude that the experimental R-value appears an important characteristic for an Am–Be source.