Many techniques have been developed and applied in the US and other countries for the control of the special nuclear materials (SNM) plutonium and uranium, but no standard methods exist for the determination of neptunium in bulk containers. Such methods are needed because the U.S. Department of Energy requires all Government-owned (sup 237)Np be treated as if it were SNM and the International Atomic Energy Agency is considering how to monitor this material. We present the results of the measurements of several samples of neptunium metal with a variety of techniques. Analysis of passive gamma-ray spectra uniquely identifies the material, provides isotopic ratios for contaminants, such as (sup 243)Am, and may provide information about the shielding, mass, and time since processing. Active neutron interrogation, using the delayed neutron technique in a package monitor, provides useful data even if the neptunium is shielded. The tomographic gamma scanner yields a map of the distribution of the neptunium and shielding in a container. Active photon interrogation with pulses from a 10-MeV linac produces delayed neutrons between pulses, even when the container is heavily shielded. Data from one or more of these techniques can be used to identify the material and estimate a mass in a bulk container.
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