Measurement of highly enriched uranium in some materials with active coincidence neutron count

The technique for measuring highly enriched uranium (HEU) in some samples are described. The high level neutron coincidence counter is modified into an active well neutron coincidence counter using two Am-Li neutron sources. The fission neutron of HEU induced by neutron of Am-Li source is measured for determining the 235U content in material, the calibration function is determined with U3O8 powder, the function between the real coincidence counts and mass of U3O8 powder under 500 g is approximately linear with a fast neutron mode measurement. The U content in some materials are determined and the corrections about their density, matrix (mainly carbon), the material position etc are discussed. The most of the measurement uncertainty is 4%-11%. The carbon in material is one of the most important interference source