APPLICATION OF THE DIFFERENTIAL PEAK ABSORPTION METHOD AS AN AUXILIARY TOOL IN ENRICHMENT MEASUREMENTS OF UF6 CYLINDERS FOR SAFEGUARDS PURPOSES

The ABACC (Brazilian-Argentine Agency for Accounting and Control of Nuclear Materials) uses the system MMCG (Mini Multi-Channel analyzer and hyper-pure Germanium detector) with the software MGAU in enrichment meter mode for the determination of enrichment of UF6 cylinders during safeguards inspections. One of the important conditions that must be met for this measurement to be acceptable is the infinite- thickness of UF6 in the position where the detector is located during measurement. This is called the Infinite-Thickness Condition (ITC). If this condition is not met, the results obtained by the inspector in the field will be incorrect. With the goal of helping the inspector in this procedure, ABACC is developing a software tool to analyze the spectra achieved, and to determine if the ITC is met. The method under development is based on the Differential Peak Absorption (DPA) technique, in which the relation of count rates measured for different gamma rays photopeaks coming from the same isotope depends on the thickness of the materials present between the isotope and the detector. Applying this technique, the relation between count rates at the photopeaks of 235U in a spectrum obtained from an UF6 cylinder can be compared with the expected value for the ITC. This article presents the theoretical study of the proposed method, and the laboratory tests performed in order to determine the relation between count rates for the photopeaks of 235U in the ITC. The results produced with calibrated laboratory samples and the experiences reached in the field are presented, showing the efficiency of the proposed method as a tool to improve the quality of measurements in safeguards inspections.