Year
2011
Abstract
NaI(Tl) based detection systems, such as HMS-4, are continuing workhorses1,2,3), utilized in the detection of holdup of Special Nuclear Materials4) (SNM). Careful system development and calibration has enabled moderate sized and shielded NaI(Tl) detector elements to quantify uranium bearing deposited compounds (such as UO2F2) over a wide enrichment range, bounded by material self attenuation for the upper thickness limit and to below 0.01gm/cm2 deposit3). With interest evolving in “next generation” systems with enhanced computation and flexibility of use, it is only reasonable to evaluate additional and alternative detector element/collimation solutions that provide improved applicability. In this work, some detector types suitable for portable and transportable assay are investigated that are also available as self contained systems. Upgraded packaged NaI(Tl) crystals are examined together with LaBr3 scintillators. The semiconductor detector element Cadmium Zinc Telluride (CZT) is also examined, as packaged in a complete spectroscopic system. The detector systems tested incorporate a range of detectors with dimensions/volumes ranging 1.0 cm3 for CZT to larger NaI(Tl) crystals 10.0 cm diameter and 2.5 cm thick. Some of the detection systems examined include GPS, wireless communications, cameras and audio recording capability. However in this work, emphasis is placed upon detection and spectral capability as this is primary in defining system potential performance. With the exception of HMS-4, the tested detectors do not incorporate integral shielding or collimation. Therefore the opportunity exists to add these components externally as may be dictated by a given measurement need. Therefore these detectors were also examined using parallel “plate” and “honeycomb” collimator5) structures that provide the ability to control the detector field of view for small total system weight gain. Several differing geometry collimation shapes can be added “in the field” for a given detector These collimators are a significant step beyond HMS-4 both for total system weight and in the ability to match the detector field of view to the object at hand. This paper examines some of these system detection aspects, shows some SNM spectral data and identifies next steps to continue this work.