Simulations and experiments have been carried out to explore using a plastic scintillator as a dosimetry probe in the
vicinity of a pulsed bremsstrahlung source in the range 4 to 20 MeV. Taking advantage of the tissue-equivalent
properties of this detector in conjunction with the use of a fast digital signal processor near real-time dosimetry was
shown to be possible. The importance of accounting for a broad energy electron beam in bremsstrahlung production,
and photon scattering and build-up, in correctly interpreting dosimetry results at long stand-off distances is highlighted
by comparing real world experiments with ideal geometry simulations. Close agreement was found between absorbed
energy calculations based upon spectroscopic techniques and calculations based upon signal integration, showing a ratio
between 10 MeV absorbed dose to 12 MeV absorbed dose of 0.58 at a distance of 91.4 m from the accelerator. This is
compared with an idealized model simulation with a monoenergetic electron beam and without scattering, where the
ratio was 0.46.
Current requirements of some Homeland Security active interrogation projects for the detection of Special Nuclear Material
(SNM) necessitate the development of faster inspection and acquisition capabilities. In order to do so, fast detectors which
can operate during and shortly after intense interrogation radiation flashes are being developed. Novel silicon carbide (SiC)
semiconductor Schottky diodes have been utilized as robust neutron and photon detectors in both pulsed photon and pulsed
neutron fields and are being integrated into active inspection environments to allow exploitation of both prompt and delayed
emissions. These detectors have demonstrated the capability of detecting both photon and neutron events during intense
photon flashes typical of an active inspection environment. Beyond the inherent insensitivity of SiC to gamma radiation,
fast digitization and processing has demonstrated that pulse shape discrimination (PSD) in combination with amplitude
discrimination can further suppress unwanted gamma signals and extract fast neutron signatures. Usable neutron signals
have been extracted from mixed radiation fields where the background has exceeded the signals of interest by >1000:1.
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