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Fast Neutron Imaging for SNM Detection
V.R. Bom
Delft University of Technology, Delft, Netherlands
Corresponding Author: V.R.Bom@TUDelft.nl
Special Nuclear Materials (SNMs) are difficult to detect because the γ emission are weak and
are being absorbed by surrounding cargo, while the neutron emissions of p.e. 1 kg weapon grade
plutonium (~ 2 MeV) fall below the natural back ground beyond a stand off distance of one meter.
The application of direction sensitive imaging techniques to reduce the back ground, thereby taking
advantage of the isotropy of the back ground, is therefore mandatory for passive as well as active
interrogation methods. A fast neutron imaging detector for the detection of SNMs in containers is
being developed to be applied in the harbor of Rotterdam in cooperation with Customs Rotterdam.
The detection principle is based on two subsequent elastic neutron-proton scatterings in one single
large organic scintillator block. The direction cone of an incident fast neutron can be determined
by observing the event locations, their time difference and the first recoil proton energy.The
scintillator material must have a very short decay time because the time difference is in the nano
second regime. The angular resolution of the detector is estimated from simulations to be better
than 10 degrees, allowing to pinpoint a container holding 1 kg plutonium from a distance of 70 m in
6 minutes. The detector will be applied on the Rotterdam harbor terrain for monitoring containers
in the stack, but would also make possible for instance checking of the full container load of a ship
in one go.
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