Physical description of nuclear materials identification system (NMIS) signatures

This paper describes all time and frequency analysis parameters measured wi th a new correlation processor (capability up to 1 GHz sampling rates and u p to five input data channels) for three input channels: (1) the Cf-252 sou rce ionization chamber; (2) a detection channel; and (3) a second detection channel. An intuitive and physical description of the various measured qua ntities is given as well as a brief mathematical description and a brief de scription of how the data are acquired. If the full five-channel capability is used, the number of measured quantities increases in number but not in type. The parameters provided by this new processor can be divided into two general classes: time analysis signatures and their related frequency anal ysis signatures. The time analysis signatures include the number of time In pulses occurs in a time interval, that is triggered randomly, upon a detec tion event, or upon a source fission event triggered. From the number of pu lses in a time interval, the moments, factorial moments, and Feynmann varia nce can be obtained. Recent implementations of third- and fourth-order time and frequency analysis signatures in this processor are also briefly descr ibed. Thus, this processor used with a timed source of input neutrons conta ins all of the information from a pulsed neutron measurement, one and two d etector Rossi-alpha measurements, multiplicity measurements, and third- and fourth-order correlation functions. This processor, although originally de signed for active measurements with a 252Cf interrogating source, has been successfully used passively (without Cf-252 source) for systems with inhere nt neutron sources such as fissile systems of plutonium. Data from active m easurements with an 18.75 kg highly enriched uranium (93.2 wt%, U-235) meta l casting for storage are presented to illustrate some of the various time and frequency analysis parameters. This processor, which is a five-channel time correlation analyzer with time channel widths as small as 1 ns, was de veloped at the Oak Ridge National Laboratory and the Oak Ridge Y-12 Plant w here it is in use for verification and confirmation of weapons components a nd other fissile materials in storage and for receipts from other Departmen t of Energy and Department of Defense Facilities. (C) 2000 Elsevier Science B.V. All rights reserved.