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Fast neutrons propagate significantly in free space with interaction properties that contrast markedly with those of electromagnetic radiation, the latter being fundamental to most wireless communications. Here, we report on the configuration and operation of a nuclear instrumentation set-up designed to transmit digitally encoded information using fast neutrons. We demonstrate the potential of fast neutron radiation as a medium for wireless communications for applications where conventional electromagnetic transmission is either not feasible or is inherently limited.

Systems that adopt organic scintillation detector arrays often require a calibration process prior to the intended measurement campaign to correct for significant performance variances between detectors within the array. These differences exist because of low tolerances associated with photo-multiplier tube technology and environmental influences. Differences in detector response can be corrected for by adjusting the supplied photo-multiplier tube voltage to control its gain and the effect that this has on the pulse height spectra from a gamma-only calibration source with a defined photo-peak. Automated methods that analyze these spectra and adjust the photomultiplier tube bias accordingly are emerging for hardware that integrate acquisition electronics and high voltage control. However, development of such algorithms require access to the hardware, multiple detectors and calibration source for prolonged periods, all with associated constraints and risks. In this work, we report on a software function and related models developed to rescale and regenerate pulse height data acquired from a single scintillation detector. Such a function could be used to generate significant and varied pulse height data that can be used to integration-test algorithms that are capable of automatically response matching multiple detectors using pulse height spectra analysis. Furthermore, a function of this sort removes the dependence on multiple detectors, digital analyzers and calibration source. Results show a good match between the real and regenerated pulse height data. The function has also been used successfully to develop auto-calibration algorithms.

Scintillation detectors offer a single-step detection method for fast neutrons and necessitate real-time acquisition, whereas this is redundant in two-stage thermal detection systems using helium-3 and lithium-6, where the fast neutrons need to be thermalized prior to detection. The relative affordability of scintillation detectors and the associated fast digital acquisition systems have enabled entirely new measurement setups that can consist of sizeable detector arrays. These detectors in most cases rely on photomultiplier tubes, which have significant tolerances and result in variations in detector response functions. The detector tolerances and other environmental instabilities must be accounted for in measurements that depend on matched detector performance. This paper presents recent advances made to a high-speed FPGA-based digitizer. The technology described offers a complete solution for fast-neutron scintillation detectors by integrating multichannel high-speed data acquisition technology with dedicated detector high-voltage supplies. This configuration has significant advantages for large detector arrays that require uniform detector responses. We report on bespoke control software and firmware techniques that exploit real-time functionality to reduce setup and acquisition time, increase repeatability, and reduce statistical uncertainties.

The design, principle of operation and the results of the first measurements made with a 4-channel multiplexed analyzer for real-time parallel processing of fast scintillation detectors is described. Recent advancements in the performance of organic scintillation media for the detection of fast neutrons, not least the reduction in hazard and the recent advent of plastic scintillation materials exhibiting Pulse Shape Discrimination (PSD), has highlighted the possibility of using multiple detectors in systems based on detectors exploiting these media. In this paper a real-time, digital multiple-channel PSD analyzer is described based on a single-board solution with an integrated high-voltage supply and graphical user interface. It has been developed to meet the requirements of nuclear materials assay of relevance to safeguards and security, and tested in a variety of related laboratory-based environments.

A novel algorithm for the digital discrimination of neutrons and gamma-rays in a mixed radiation field is presented. Most of the pulse shape discrimination methods in scintillation detection systems use time-domain features of the signal (e. g. charge comparison method or constant-time discrimination). However, there are no frequency-domain discrimination methods up to date in the literature. Our method employs the wavelet transform to extract frequency-domain features for discrimination. Compared to the pulse gradient analysis (PGA) algorithm, it provides an improvement in reducing the overlap area between neutron and gamma events and also in increasing the Figure of Merit (FoM). Another advantage of this method consists in the removal of the dependency of the discrimination method on timing features. Since the light output in the scintillation process is very noisy, this kind of dependency may degrade the performance of the algorithm.