In order to accurately measure the strength of an 241Am Be neutron source, we developed a long counter measurement system, and calibrated its detection efficiency at several neutron energy point on 2.5 MV electrostatic accelerator of Sichuan University. The neutron fluence is determined by 197Au activation technique. We also measured the count of scattering neutrons using retaining cone method. The results show that the long counter’s detection efficiency changes smoothly as the energy changes in the calibrated neutron energy area. The strength of the 241Am Be neutron source is 7.188×105/s measured by this long counter measurement system with the uncertainty of 3.5%.
