KEYWORDS: Scintillators, Liquids, Field programmable gate arrays, Sensors, Digital signal processing, Signal processing, Prototyping, Amplifiers, Data acquisition, Electronic filtering
The nuclear aspect of the CBRN* threat is often divided amongst radiological substances posing no criticality
risk, often referred to as 'dirty bomb' scenarios, and fissile threats. The latter have the theoretical potential for
criticality excursion, resulting in elevated neutron fluxes in addition to the &ggr;-ray component that is common
to dirty bombs. Even in isolation of the highly-unlikely criticality scenario, fissile substances often exhibit
radiation fields comprising a significant neutron component which can require considerably different counterterrorism
measures and clean-up methodologies. The contrast between these threats can indicate important
differences in the relative sophistication of the perpetrators and their organizations. Consequently, the detection
and discrimination of nuclear perils in terms of mixed-field content is an important assay in combating terrorist
threats.
In this paper we report on the design and implementation of a fast digitizer and embedded-processor for onthe-
fly signal processing of events from organic liquid scintillators. A digital technique, known as Pulse Gradient
Analysis (PGA), has been developed at Lancaster University for the digital discrimination of neutrons and &ggr;
rays. PGA has been deployed on bespoke hardware and demonstrates remarkable improvement over analogue
methods for the assay of mixed fields and the real-time discrimination of neutrons and &ggr; rays. In this regard the
technology constitutes an attractive and affordable means for the discrimination of the radiation fields arising
from fissile threats and those from dirty bombs. Data are presented demonstrating this capability with sealed
radioactive sources.
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