Advanced X-ray Systems for the Detection of Special Nuclear Materials

The Dosimetry Group provides support to the Domestic Nuclear Detection Office (DNDO) of the Department of Homeland Security (DHS) for their advanced non-intrusive inspection (NII) initiatives. Our support for these programs falls into three categories.  

The first category is to develop and implement methods to perform radiation dosimetry in and around these high-energy systems. The second thrust is to develop experimental designs, with our colleagues in the NIST Statistical Engineering Division, to evaluate the performance of these systems in terms of pass/fail trials for detection of threat surrogates and using the test methods specified in ANSI N42.46 for image quality.  The NIST team also provides on-site support during testing as well as post-test analysis.  The third area is to consult on other issues related to this type of equipment.

The high-energy photon beams typically utilized in next generation NII systems present dosimetry challenges, as they are of markedly different character compared to those employed in the past. Hence, the methods developed by health physicists to perform dosimetry are of questionable validity. We have developed methodologies to perform measurements of dose to drivers of conveyances under inspection, to evaluate dose to cargo and inadvertent occupants of the conveyance and to determine the radiation footprint of these systems. We have applied these methods to 3 distinct NII systems in a series of tests.

The American National Standards Institute (ANSI) standard for the image quality indicators of non-intrusive cargo and a vehicle inspection system, ANSI N42.46, was previously developed through a series of meetings hosted by NIST.  Application of the test methods described in the standard may not lead to a clear distinction between the performances of different systems. We have developed experimental designs and suggestions that have been, in part, adopted by the DNDO to lend rigor to these tests.  We have also provided substantial input into the development and interpretation of tests of the pass/fail detection of threat surrogates (not a part of ANSI N42.46).  Several test events have taken place and NIST has participated in the field and contributed analysis to the reports describing these events.

Finally, we investigate and provide advice on other effects that could result from deploying such equipment. Such advice is provided based on computations and/or measurements. These effects include compatibility issues with other equipment.

Dose to the driver of a truck (top) and image of the contents of a cargo container (bottom) being scanned by a high-energy non-intrusive inspection system.