Passive and active neutron interrogation techniques at the Joint Research Centre, Ispra

Current methods for non-destructive assay of fissile material using passive and active neutron interrogation at the Joint Research Centre (JRC), Ispra, are described. Passive neutron interrogation is applied for the assay of plutonium under various conditions. An interpretation model was developed at the JRC, Ispra, to be applied in conjunction with the passive neutron detector heads and pulse train analysers. The mode is based on the determination of correlated neutron multiplets derived from the factorial moments of measured signal frequency distributions. A comparison between two active neutron interrogation devices is given. Concerning active neutron interrogation techniques, two different instruments (a photo neutron interrogation device (PHONID) and an active well coincidence counter (AWCC)) have been used for the non-destructive assay of 235U. The two instruments are based on totally different physical aspects. Both systems require a strict categorization of the uranium with respect of geometry, homogeneity of the fissile and moderating material distribution and density. The experimental results of the photo neutron interrogation device are based on results obtained with the newest model of the PHONID series built at the JRC, Ispra, from 1970 onwards by Birkhoff et al. 14 refs, 2 tabs