K.A. Miller and W.S. Charlton,
"An Inverse Transport Approach to Radiation Source Location for Border Security,"
Proceedings of the 29th Annual Meeting of the European Safeguards Research and Development Association
, Aix-en-Provence, France, May 22-24, 2007.
Radiation portal monitors are being deployed at border crossings
throughout the world to help prevent against the smuggling of
nuclear and radiological materials. Many of these borders have
several lanes for vehicles, each equipped with a portal monitor.
With the current technology, if the detectors are alarmed, border
guards must stop traffic and search for the source. In some cases,
it can take hours to get through a busy border crossing. If
radiation detection equipment adds a mere twenty seconds per car,
this wait can increase by more than an hour. Another problem with
these systems derives from the fact that one source can set off
detectors in multiple lanes. If the source is being shielded by a
vehicle in its lane, it may set off detectors in adjacent lanes but
not its own. The purpose of this research is to develop an
algorithm for identifying the location of a radioactive source
using a distributed array of detectors. To locate the source, some
knowledge about the vehicles is needed. When a detector is alarmed,
cameras installed in each lane will take a picture of the vehicles
and a computer algorithm will build a cross section model of the
traffic. The cross section model will be used in neutron and
radiation transport calculations to determine the position of the
radioactive material. There has been a lot of work done using
inverse transport calculations to determine the material properties
of an object, and this work uses some of the same techniques for
source location. Forward transport calculations using a
step-difference approximation are used to define an error
functional describing the difference between the actual and
calculated detector readings given an estimated source location.
Adjoint transport calculations making use of a steepest descent
method are used to minimize that error functional and thus identify
the source location.
Associated Project(s):Inverse Transport for Border Monitoring