Detection of Shielded Nuclear Material in a Cargo Container Page: 3 of 6
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The Idaho National Laboratory (INL), along
with Los Alamos National Laboratory (LANL) and
Idaho State University's Idaho Accelerator Center
(ISU/IAC), has been developing a high energy
photon interrogation system for non-intrusive
inspections of air-, rail-, and maritime cargo
containers [1, 2]. This energetic photon inspection
technology is referred to as the Pulsed Photonuclear
Assessment (PPA) technology and is supported by
the Department of Homeland Security. The PPA
technology development is addressing one of our
homeland security's most important concerns -
terrorism associated with the transportation of
weapons of mass destruction (WMD), specifically
weapons employing nuclear materials, such as
highly enriched uranium (HEU). While all aspects
of cargo container transportation and security is
important, the focus of this paper is with shielded
nuclear material detection in maritime cargo
containers (or trucks) since these represent the most
common mode of commercial transportation. This
paper briefly describes the prototype PPA
inspection system and then presents detection
results from a selected cargo container inspection
configuration. The photonuclear-induced, radiation
signatures are presented for a nominal 10-MeV
photon interrogation of a 4.8-kg depleted uranium
(DU) sample that is located within well-defined
shielding configurations (i.e., INL "calibration"
pallets) that are then positioned in the center of the
inspected cargo container. This center-positioned
DU, and/or the "calibration" pallet, provides
relatively challenging detection scenarios because it
results in the largest DU-to-detector distances.
2. Inspection technology
The PPA inspection technology uses pulsed,
energetic photons to induce photofissions (and
neutron-induced fissions) in shielded nuclear
materials. The main features of the PPA inspection
system include a pulsed electron accelerator (the
photon source), a neutron and gamma-ray detection
system [1,2], and an inexpensive gray scale
mapping system for cargo loading characterizations
. Note, the PPA "mapping" component will not
be discussed in this paper.
The pulsed photon source for the PPA prototype
is the INL Varitron . The Varitron is a mobile
accelerator system capable of generating electron
pulses of 2-12 MeV electrons at rates up to 1 kHz
with an on-board, electron beam current and energy
monitoring capability. All signature emission data
presented in this paper are provided with a nominal
10-MeV, 125-Hz operation producing about 3-4 pA
(avg.) beam current.
The prototype neutron and gamma-ray detection
system consists of a transportable stand consisting
of an array of nine detector pairs at various
elevations. Each collocated pair consist a neutron
and gamma-ray detector. Figure 1 shows a detector
assembly positioned along side a maritime-cargo
container in a testing device at the IAC that
provides container motion.
Neutron detection is accomplished with the
patent-pending Photonuclear Neutron Detector
(PND) design  that operates within intense
pulsed, photon-flash environments and
differentiates prompt and delayed fission neutrons
emissions between every accelerator pulse. The
unique PND design allows for the detection of 0.1-
keV to 1.0-MeV neutron since this energy range is
representative of almost all delayed fission neutron
- Y; B S6 ' lil i
Figure 1. Deployed PPA detector assembly.
Gamma-ray detection is accomplished with the
use of standard, 1.6-cm, 27.3-cm Geiger-Muller
tubes (model LND 719) collocated with each PND.
A figure-of-merit (FOM)-type parameter is used to
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Jones, J. L.; Norman, D. R.; Haskell, K. J.; Sterbentz, J. W.; Yoon, W. Y.; Watson, S. M. et al. Detection of Shielded Nuclear Material in a Cargo Container, article, June 1, 2005; [Idaho Falls, Idaho]. (digital.library.unt.edu/ark:/67531/metadc886756/m1/3/: accessed September 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.