Certain scintillating materials are sensitive to both gamma and neutron radiation and can give information about the type of interacting radiation due to differences in the light output response. By collecting the light pulses and converting them to electrical signals the nature of the radiation can be determined by measuring the amount of electrical charge in the pulse tail -for neutrons, the pulses are longer, with more charge in the tail than for the shorter gamma pulses. This determination called Pulse Shape Discrimination (PSD) can nowadays be performed in real-time onboard digitisers during data collection. In this work several detectors (EJ301, EJ309 liquids; EJ299-33 plastic and p-terphenyl scintillators) of various shapes and sizes were connected to several digital Data Acquisition (DAQ) systems as well as the established digital / analogue hybrid Mesytec MPD8 / MADC-32 set up in a comparative study. The aim of the campaign was to produce a Figures of Merit (FOM) for the PSD performance of the various detector / DAQ combinations to give relative performance estimates of the CAEN V1751 10-bit 1 GSample/s digitiser in comparison with other DAQ solutions within a near-standardised experimental environment. It islikely that the DAQ set ups were not equivalent as significant differences in the matching of the detector outputs to the dynamic range of the digitisers were observed -however, with the configurations used in this campaign the CAEN V1751 digitiser showed superior FOM values to the Struck SiS3320, Bridgeport usbBase and Mesytec MPD-8 DAQ systems tested. Furthermore, there seemed little difference between the FOM from the faster but lower voltage resolution (1 GSample/s with 10 bits) CAEN V1751 compared to the slower but higher resolution (250 MSample/s with 12 bits) CAEN N6720 digitiser for this application.

Artificial neutral networks were developed for use as a potential 'information barrier' technology in the verification of arms control treaty accountable items. They were used to identify and measure specific attributes from g-ray spectra. These attributes included the presence or absence of plutonium, the plutonium Pu-239/Pu-240 isotopic ratio or 239 Pu content and the material age. A set of over 400 training spectra were generated using a spectral simulation software package and various methods for the selection of input data were tested. An input data set which discounted low energy regions susceptible to shielding effects was found to be most effective. Once trained, the network correctly identified the presence or absence of plutonium from real g-ray spectra. Accurate results were also achieved for estimating the content of 239 Pu. In simulated test spectra a root mean squared error (RMSE) of less than 0.1 was found when using the optimum number of inputs. The network was also able to distinguish between spectra from plutonium samples of different ages. Further work is planned to investigate the estimation of a confidence level for whether a specific threshold of 239 Pu content is exceeded. An improved training set is anticipated to improve accuracy in determining the material age, which was not achieved accurately.

A B S T R A C T:The technique of neutron inelastic scattering has demonstrated the presence of longitudinal acoustic phonons in two layer-silicate minerals. Values of the elastic constants determined from the dispersion curves have established the validity of the technique for this class of materials.

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