Distinguishing Moderated Actinide Metal From Oxide Using Neutron Correlations and Spectroscopy

Determining the amount, chemical form, physical shape, and multiplication of the fissile material in an unknown assembly is a challenging problem that is of great importance in a number of national security contexts. The discrimination of plutonium in metal versus oxide form in special nuclear materials is crucial and yet remains a challenge for current methods. It has previously been shown that the α-ratio for un-moderated plutonium oxides can be rapidly determined by comparing the fast neutron spectrum measured with a liquid scintillator with pure fission and (α,n) neutron spectra measured with the same liquid scintillator. In this paper we show that the chemical form can be obtained for moderated nuclear materials using fast neutron detection systems. We describe a new method to distinguish moderated plutonium metal from oxide using liquid scintillators, neutron spectroscopy and neutron correlations.