Non-destructive assay of fissile materials through active neutron interrogation technique using pulsed neutron (plasma focus) device

摘要

Pulsed neutrons emitted from a plasma focus (PF) device have been used for the first time for the non-destructive assay of ~(235)U content in different chemical forms (oxide and metal). The PF device generates (1.2 ± 0.3) × 10~9 D-D fusion neutrons per shot with a pulse width of 46 ± 5 ns. The method involves the measurement of delayed neutrons from an irradiated sample 50 ms after exposure to the neutron pulse for a time of about 100 s in the multichannel scaling (MCS) mode. The calibration of the active interrogation delayed neutron counter (AIDNEC) system was carried out by irradiating U_3O_8 samples of varying amounts (0.1-40 g) containing enriched ~(235)U (14.8%) in the device. The delayed neutrons were monitored using a bank of six ~3He detectors. The sensitivity of the system was found to be about 100 counts/s/g over the accumulation time of 25 s per neutron pulse of ～10~9. The detection limit of the system is estimated to be 18 mg of ~(235)U. The system can be suitably modified for applications toward non-destructive assay of fissile content in waste packets.