Determination of emission rates and spectra of neutrons from ²⁴¹Am-Li sources

We studied the application of ²⁴¹Am-Li interrogation neutron sources, which were originally deployed in non-destructive assay apparatus for nuclear safeguard, to calibration work. To determine the emission rate, the angular distribution of neutron fluence was measured using a a portable long counter. On the measurement day (October 23, 2015), the emission rate was determined to be 1.00 × 10⁶ n/s. The expanded measurement uncertainty of the emission rate was 4.1% at the coverage factor k = 2. The mean energy of neutron spectrum was 0.41 MeV based on a Bonner multi-sphere spectrometer. The ambient dose equivalent rate at 1.0 m was evaluated to be 7.5 μSv/h. (author)