Detection sensitivity for special nuclear materials with an advanced high-pressure xenon detector and robust fitting analysis

The sensitivity for detection of two special nuclear materials, ²³⁵U and ²³⁹Pu, using an advanced high-pressure xenon detector (HPXe) and robust fitting analysis (RFA) with RobWin is experimentally determined for a set of collections with varying attenuation thicknesses of lead. These measurements provide essential information that enables comparisons with other detector systems for nuclear portal monitoring applications. Advantages of the combined use of HPXe and RFA for nuclear portal monitors are discussed, and recent progress with them is described briefly. An experiment designed to provide data from which models for nuclear portal monitor design can be grounded is described. Spectra were collected at CEA/Saclay with an HPXe unit from MEPhI for both ²³⁵U and ²³⁹Pu with attenuating thicknesses of lead ranging from 0 to 4 mm. A single analysis procedure that yielded consistent results for all spectra was developed to simulate the automated application of analysis without user intervention and without advance knowledge of shielding thickness. These two spectrum series were then analyzed with RFA methodology for detection sensitivity and reported in a form that can be used for comparison with other detector systems and for optimization of design parameters for HPXe/RFA portal monitor systems