Browsing by Author "Buffler, Andrew"

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    A compact neutron spectrometer for detecting neutrons produced by cosmic rays
    (2023) Jarvie, Erin; Buffler, Andrew; Hutton Tanya
    The high energy secondary neutron fields from cosmic radiation that are found in aviation and space environments have impacts on both biological and technological systems. A compact neutron spectrometer that is safe to operate in an aviation environment and suitable for detecting these secondary neutrons has been developed. The detector consisting of a (0.6×0.6×12.0 cm3 ) EJ-276 plastic scintillator coupled to a silicon photomultiplier (SiPM) has been designed, constructed and characterised with neutrons up to 62.5 MeV at the UCT n-lab, IRSN AMANDE and iThemba LABS fast neutron facilities. The compact detector displays good quality pulse shape discrimination for the separation of neutron and gamma ray events. Neutron energy spectra were obtained through time-of-flight (ToF) measurements and spectrum unfolding. The energy spectra obtained from ToF display energy resolution similar to that obtained by a BC-501A reference detector. A matrix of measured response functions for neutrons with energies between 11 MeV and 62 MeV at 3 MeV intervals selected by ToF has been constructed for the detector. The response functions have been used to successfully unfold neutron energy spectra across the entire range of energies.
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    A new compact neutron spectrometer
    (2016) Comrie, Angus; Buffler, Andrew; Smit, Ricky
    A new compact neutron spectrometer has been designed, developed and characterized. The detector is based on EJ299-33 plastic scintillator coupled to silicon photomultipliers, and a digital implementation of pulse shape discrimination is used to separate events associated with neutrons from those associated with gamma-rays. The spectrometer is suitable over the neutron energy range 1 – 100 MeV, and the development illustrated with measurements made using an Am-Be radioisotopic source, a D-T sealed tube neutron generator and quasi-monoenergetic neutron beams produced using the iThemba LABS cyclotron. A segmented variation of the spectrometer is capable of providing directional information through the comparison of count rates between scintillator cells.
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    A New Digital Data Acquisition System for Neutron Metrology
    (2022) Sole, Chloe; Buffler, Andrew; Hutton,Tanya
    Within the neutron metrology and spectrometry community digital pulse processing systems are being developed for measurements of Fast neutron fields in a wide variety of contexts, for example at accelerator and medical radiation facilities, around nuclear power plants, in airplanes in flight and space stations. These fields often vary widely with respect to both energy and intensity, which complicates measurements of energy dependent fluence. Investigations have been completed into the suitability of a CAEN DT5730 digitiser unit as a viable alternative to a traditional analogue system for data acquisition for fast neutron metrology. Experiments were completed at the fast neutron facilities of AMANDE (IRSN, Cadarache) using a BC501A scintillation detector and both the DT5730 digitiser and an analogue system based on NIM electronics and an MPA-3 multichannel analyser acquisition unit. Follow-up measurements were made at the n-lab facility at the University of Cape Town. The measurements covered an energy range from 0.5 MeV to 20 MeV, over a large range of intensities. The energy and intensity response for both systems and digital configurations were investigated based on the unfolding of measured light output spectra using an existing neutron response matrix for the detectors. Deadtime behaviour, rate dependent losses and linearity over the energy range were explored. The quality of the measured neutron spectra was compared through both uncertainty budgets and shape comparison analyses. Factors to consider when migrating from analogue signal processing to digital signal processing are discussed for the measured energy and intensity range, including advantages and disadvantages using digital pulse processing for metrology both in the laboratory and in the field. While there is more research required for a thorough bench-marking, the present results indicate that digital data acquisition technology has matured to the point where it can now be considered for use within neutron metrology.
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    An uncertainty budget for the precursor Watt balance for South Africa
    (2019) Mametja, Thapelo Given; Buffler, Andrew; Karsten, Aletta
    The 26th General Conference on Weights and Measures (CGPM) held on the 16th November 2018 has adopted the revision of the International system of units (SI) to be based on the fundamental physical constants.
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    Observing flow using fast neutron radiography and positron emission particle tracking
    (2021) Daniels, Graham Clinton; Buffler, Andrew
    Dynamic flow of material has been studied using fast neutron radiography (FNR) and positron emission particle tracking (PEPT). A new fast neutron imaging system was commissioned at The South African Nuclear Energy Corporation, Pretoria, as part of this study, although FNR measurements were ultimately performed at PhysikalischTechnische Bundesanstalt (PTB), Braunschweig. The PEPT studies were undertaken at the PEPT Cape Town facility located at iThemba LABS, Cape Town. The steady state motion of media, within a laboratory-scale tumbling mill, was studied for a range of speed and media mixes, using both FNR and PEPT. Several operational parameters were derived from the data, which could be related to potential improvements to the milling efficiency. The blending of FNR and PEPT data for the study of steady state flow, was explored for the first time. In addition, the flow of water through porous media was studied using FNR, which enabled the determination of the hydraulic conductivity, and hence intrinsic permeability, of the media within the column. The potential of using FNR, without or without PEPT, for the study of material in motion is discussed.