Characterization of special nuclear material by neutron resonance spectroscopy

Abstract

Neutrons can be used as a tool to study materials and objects. Cross sections of neutron induced reactions show characteristic resonance structures which can be used as fingerprints to determine the elemental and isotopic composition of materials and objects. They are the basis of two analytical methods which have been developed at the European Commission's Joint Research Centre in Geel (BE): Neutron Resonance Capture Analysis (NRCA) and Neutron Resonance Transmission Analysis (NRTA). The first technique is based on the detection of gamma rays emitted during a neutron capture reaction in the sample being studied; the latter determines the fraction of neutrons transmitted through a sample positioned in a neutron beam. They rely on well-established methodologies in neutron resonance spectroscopy. It has been shown that NRCA is a useful technique to determine the composition of archaeological objects. In contributions to a previous ESARDA symposium in Bruges the use of NRTA to characterize particle-like debris of melted fuel that is formed in severe nuclear accidents has been presented. However, the discussion was primarily based on theoretical studies. In this contribution the performance of NRTA as a non-destructive method to determine the amount of fissile material is discussed based on measurements carried out at the time-of-flight facility GELINA using reference materials containing uranium and plutonium. The results of these experiments demonstrate that the relative amount of special nuclear material in particle like debris can be derived absolutely without the need of calibration materials with an uncertainty less than 2%, even in the presence of strong neutron absorbing matrix materials.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard