Fast neutrons are produced from cosmic ray interactions with matter posing particular dosimetric challenges for aviation and space exploration. Progress towards a compact detector system suitable for measurements of cosmic ray induced neutrons with energies up to 120 MeV is presented. The detector was comprised of a 6 mm × 6 mm × 120 mm prism of EJ-276 scintillator and a pair of MicroFC-60035 silicon photomultipliers, coupled with a digital data acquisition system. A comparison was made of pulse shape discrimination capabilities and light output resolution for single and dual silicon photomultiplier detector systems. The dual SiPM detector was characterised in mono-energetic fast neutron fields between 2.5-19.0 MeV. The simulation of detector response functions with Geant4 was explored, using measurements in mono-energetic fields to derive scaling and broadening parameters. Quasi-monoenergetic detector response functions were measured for neutrons with energies up to 16 MeV using Time-of-Flight techniques, and were used to demonstrate the spectroscopic capabilities of the prototype device through the unfolding of known neutron fields.

Background Coal plays a central role in the production of electricity in South Africa and in other countries. The knowledge of the elemental composition of coal is thus most valued in the coal industry as it is used to determine its quality and potential impact on the environment. There are many analysis techniques used for characterising coal that have been developed over several decades and are well established. However, most techniques used require sampling, are destructive to the sample, and are limited in their capability to analyse samples in bulk. Techniques that use neutrons are among the desirable techniques because of their capability to measure elemental composition of samples in bulk. Methods In this work a new analysis technique that combines neutron-based techniques to characterise bulk materials using neutron-induced elemental signatures has been developed. Beams of fast neutrons were used to measure signatures for the elements H, C, N, O, Al, Si, S and Fe derived from neutron transmission and prompt gamma-ray measurements. Transmitted neutron energy spectra were measured utilising a cylindrical organic liquid scintillation detector with a 51 mm diameter and 51 mm height, and spectrum unfolding with MAXED, while de-excitation gamma-ray energy spectra were measured utilising a pair of cylindrical NaI (Tl) detectors with a 76 mm diameter and 76 mm height. Results and conclusions The measured elemental responses were used to construct a library of standardised elemental signatures, which were then used to deconvolve mass fractions of elements present in simple composite samples. Mass fractions of hydrogen, carbon, silicon and oxygen were determined from high density polyethylene, quartz sand and aluminium oxide. The results were in agreement with the expected mass fractions, which demonstrates the technique’s potential capability to accurately determine the presence and quantity of composite elements of materials with complex compositions.

The metrology of high energy neutrons is increasing in relevance for dosimetry in space and aviation, and around accelerator facilities (for both hadron therapy and research activities). High energy neutron fields are produced naturally by galactic cosmic rays and solar particle events interacting with matter such as in spacecraft or the atmosphere, and also in and around high energy accelerators. The neutron energy spectra in both cases have similar features: lower energy neutrons peaking at a neutron energy of around 1 MeV as evaporation products; and high energy neutrons peaking around 100 MeV originating as knock-on neutrons in peripheral collisions or in charge exchange reactions. Reliable measurement of high energy neutron fields requires instrumentation which has traceability to internationally recognised reference standards within facilities offering well characterised beams. However, above 20 MeV only a few such facilities exist, and metrology is more challenging as a consequence of both physical and technological complexity. We discuss the present urgent need for high energy neutron reference fields, illustrated by measurements made at the high energy neutron facility at iThemba LABS, South Africa.

Positron emission particle tracking (PEPT) is an applied nuclear technique for measuring the trajectory of a single tracer particle moving in a system of granular or liquid flow or attached to a moving rigid body. The tracer particle is labeled with a positron emission tomography (PET) radionuclide that decays via positron emission. The nearly collinear 511keV annihilation gamma rays are detected in coincidence by a modified PET camera, which defines their line of response (LOR). The chronologically measured LORs may then be used to triangulate the position of the moving tracer particle. We report on recent developments at PEPT Cape Town positron emission particle tracking facility.

A metrological characterisation of a high-energy neutron field at the iThemba Laboratory for Accelerator-Based Sciences (LABS) was combined with Monte Carlo radiation transport simulations to estimate the absorbed dose delivered to vials of human blood for an experimental setup relevant to conducting radiobiology experiments at this facility. Neutrons with a peak energy of 62.34(37) MeV were produced by a 66.48 MeV proton beam irradiating an 8.0 mm lithium target. The neutron beam energy distribution and fluence were characterised at emission angles of 0 degrees and 16 degrees via Time-of-Flight measurements with a BC-501A liquid scintillation detector, a 238U fission ionisation chamber, and two beam monitors. These measurements were combined with Monte Carlo radiation transport simulations developed in Geant4 to calculate the absorbed dose that would be delivered to four vials of human blood contained in high-density polyethylene phantoms placed at a distance of 4.300 m from the target during a typical irradiation. The absorbed dose delivered to each blood vial per unit monitor count was estimated and combined with measured monitor count rates to determine the absorbed dose rate. Depending on the vial position in the phantom, dose rates ranged from 24.36(78) mGy hour-1 to 26.22(84) mGy hour-1 at 0 degrees, and from 13.16(42) mGy hour-1 to 14.21(46) mGy hour-1 at 16 degrees.

A compact neutron spectrometer consisting of a 6 mm × 6 mm × 120 mm prism of EJ-276 plastic scintillator capable of pulse shape discrimination coupled to a single silicon photomultiplier is described. In principle this device will be capable of spectroscopic measurements exceeding 100 MeV using unfolding analyses with detector response functions measured at neutron time-of-flight facilities. A characterisation of the device is described and illustrated with measurements of the detector response made at three fast neutron facilities with energies between 5.0 MeV and 63.5 MeV. Nearly mono-energetic detector response functions were used to produce neutron energy spectra by unfolding light output distributions measured with the detector in the energy range of interest.

The n-lab is a fast neutron facility based in the Department of Physics, University of Cape Town, offering collimated neutron beams produced by an MP 320 deuterium-tritium sealed tube neutron generator, and a 220 GBq americium-beryllium radioisotopic source. Characterisations of the spatial and energy distributions of the fast neutron beams were performed using an EJ-301 organic liquid scintillator detector and digital data acquisition system. Neutron energy spectra were obtained through unfolding analyses with MAXED, and a Monte Carlo approach to the propagation of uncertainties was implemented. Measurements of fluence and neutron emission rates were determined through the neutron activation of copper foils and subsequently used to validate the scaling of the unfolded neutron energy spectra.

Positron Emission Particle Tracking (PEPT) is a radioactive tracer-based approach to studying dynamic physical processes and multiphase flows. Short-lived positron-emitting isotopes are loaded onto suitable substrates used as tracer particle flow followers in physical and engineering-relevant systems. Coincident photons from electron-positron annihilation are detected using large arrays of pixelated scintillators, with the reconstructed photon trajectories collectively used to determine tracer particle dynamics. We have developed indirect radiochemical, and direct physical activation, techniques for producing tracer particles for such studies, and we report on the current state of the art with focus on the direct approach with high-energy alpha-particle beams. The O-16(alpha,x)F-18 reactions have been explored as viable candidates in producing the pure positron emitter F-18 from natural O-16-bearing targets. Silicon dioxide (SiO2) glass spheres of diameters of 5 to 10 mm were irradiated in a 100-MeV alpha-particle beam of around 800-nA current for approximately 2 h. Radioisotope activation yields were characterized by half-life measurements and gamma-ray spectroscopy, with the highest yield being F-18 (<2.5 mCi). Contaminants from other reaction channels were observed and characterized, including the positron emitter Sc-43 and negative beta emitter Na-24, produced from alpha and neutron activation of contaminant species in the target material, respectively. The activation technique is shown to be a reasonable candidate to complement and enhance existing tracer particle production techniques for PEPT and other radiotracer-based studies.

The application of a CAEN DT5730 digitizer unit for fast neutron metrology and applications has been explored. The standard methods implemented to obtain a calibrated light output parameter from the integrated anode output has a high sensitivity to the selection of pulse integration time. We report on measurements made at the n-lab within the Department of Physics at the University of Cape Town which explored alternative approaches to determining the light output parameter with the digital acquisition system, aiming for a high degree of consistency.

Positron emission particle tracking (PEPT) has offered important insights into the internal dynamics of multiphase flows. High precision and frequency measurements of the location of the tracer particle are required to resolve individual eddies at the millimetre scale or smaller. To explore the potential of PEPT to perform these measurements, a model was developed of the Siemens ECAT “EXACT3D” HR++ positron emission tomography (PET) scanner at the PEPT Cape Town facility in South Africa with the software Geant4 Application for Tomographic Emission (GATE) and was used to generate Lagrangian tracks from simulations of moving tracer particles. The model was validated with measurements from both experiment and simulation and was extended to two virtual scenarios inspired by turbulent flows. The location data from the simulation accurately captured linear portions of an oscillating path up to high speeds of 25 m s−1; however, tracking tended to undercut the turning points due to the high tracer acceleration. For a particle moving on a spiral path of decreasing radius, the location data tracked the path above a radius of 2.0 mm with an uncertainty equivalent to the radius of the tracer particle, 300 μm. Improvements to the measurement are required to track sub-millimetre flow structures, such as the application of PET scanners with higher spatial resolution and upgrades to the sampling processes used in location algorithms.

A compact neutron spectrometer is described, which consists of four square prisms of plastic scintillator capable of pulse shape discrimination, eight silicon photomultipliers and a high density polyethylene moderator. The device is capable, in principle, of spectroscopic measurements up to around 60 MeV, although extendable to higher energies, and is also able to discern the direction of neutron radiation impinging on the detector. Results from simulations using Geant4, together with measurements with neutrons from an 241Am-9Be radioisotopic source, are used to characterise the detector in both spectroscopic and direction-sensitive modes. Field applications of the detector are discussed.

Positron Emission Particle Tracking (PEPT) techniques allow the tracking of a radioactive tracer particle moving within a system of flow, enabling non-invasive study of dynamic systems. On the micro-scale, PEPT performance is limited by the achievable activity in radiolabelling a suitable tracer particle, and the fixed geometry of conventional detector systems. To enable application of PEPT towards these scales advanced instrumentation is required, and a hybrid detection system has been developed combining scintillator and semiconductor devices. A bismuth germanate oxide (BGO) scintillator array consisting of 1024 detector elements derived from CTI/Siemens PET scanners (512 pixels of 6.75 x 6.25 x 30 mm(3) and 512 pixels of 4.1 x 4.0 x 30 mm(3)) forms a field of view of 150 x 196 x 101 mm(3). A pair of pixelated cadmium zinc telluride room temperature semiconductors (9680 pixels of 1.8 x 1.8 x 0.5 mm(3)) form a high spatial resolution region of 62 x 42 x 20 mm(3) placed within the larger field of view. The design choice maximizes absolute efficiency by merit of the scintillators and enhances spatial resolution through the semiconductors. Energy and timing resolutions of the BGO elements were determined, and sensitivity profiles of the system modelled numerically, enabling the characterization of the system absolute efficiency and spatial resolution. The results suggest the applicability of PEPT in the study of microscale flows for the first time, including investigating flows in capillaries and micro-fluidic devices.

Within nuclear installations concrete is widely used for its structural and radiation shielding properties. Developing methods to independently, and non-destructively, verify the composition of such materials in situ is of high priority for the regulation of existing and future nuclear installations. This work reports on the ongoing development of measurement techniques utilising fast neutron beams for the elemental analysis of concrete and its constituents.

Neutrons and gamma rays are effective probes for the elemental characterisation of bulk samples. Neutrons interactions with matter are characteristic of the nature of the target nucleus, and the incident neutron energy. Most nuclides exhibit distinctive structure in their total and differential cross sections, thus elements can be differentiated via their total, elastic and inelastic scattering cross sections, and the energies of prompt gamma rays produced in inelastic collisions. In this work we report on the use of the fast neutron transmission analysis technique for the analysis of 12 C in graphite. We also present results of prompt gamma ray neutron activation analysis of graphite using 14 MeV neutrons, which was explored for the purpose of developing a multimodal neutron-based technique for elemental analysis of materials in bulk.

Positron emission particle tracking (PEPT) is a powerful non-invasive technique used to study the underlying dynamics of granular and multiphase flowing systems. The essence of PEPT is to attach (chemically or otherwise) sufficient positron-emitting radioisotope to a particle chosen as representative of the bulk material under study, and hence used as a flow-following tracer. We report on standardised methods for creating density-modified tracer particles to expand the range of applications feasible to research with the PEPT technique.

A compact neutron spectrometer consisting of a (0.6 x 0.6 x 12.0 cm(3)) EJ-276 plastic scintillator coupled to a silicon photomultiplier has been designed. An essential aspect of the characterisation of the spectrometer is the measurement of detector response functions for neutron energies above 20 MeV. The process of producing response functions for neutron energies between 10 MeV and 60 MeV for the compact detector using neutron time-of-flight measurements at iThemba LABS is presented.

Positron emission particle tracking measures the trajectory of a single radioactively labelled tracer particle by coincident detection of emitted annihilation photons. The technique enables the non-invasive study of dense opaque flows, with the tracer acting as a small neutrally buoyant flow-follower. The University of Cape Town has established a PEPT facility at iThemba LABS, utilising tracer particles produced through radiochemical methods, and measured using adapted positron tomographs. An activation approach producing the positron emitter 18 F inside glass target spheres of diameter between 5.0 and 10 mm using accelerated beams of alpha-particles has been explored. The reaction 16 O(O, x) 18 F is used, exploiting the high concentration of natural oxygen and the correspondingly high cross-sections for 18 F formation. A standard target holder for the batch production of radionuclides at iThemba LABS was modified, reducing the entrance window thickness, allowing ingress of circulating cooling water, and adapted for a primary tparticle beam of 100 MeV energy delivered by the separated sector cyclotron (SSC) of iThemba LABS. Two-hour bombardment at nominal beam current 0.8 eµA produced activities up to ~ 110 MBq (3 mCi), with over 95% of the activity being 18 F.

Short lived positron emitting species are used to produce flow-following tracer particles to study flow dynamics in a technique known as positron emission particle tracking (PEPT). The photon pairs produced by positron annihilation are detected in time coincidence by arrays of high-speed position sensitive detectors. Reconstruction of consecutive annihilations are used to determine the near-instantaneous position of the tracer particle. Hence, the resulting bulk flow dynamics are derived, including residence times, velocities, accelerations, and related kinematic properties. The Department of Physics at the University of Cape Town uses PEPT to study dynamic physical processes, turbulent, and multiphase flows. Studies aim to address global challenge topics including problems in water scarce environments, reducing industrial wastes, and enhancing developments towards sustainable economies through improved process efficiencies and design led approaches. The PEPT Cape Town enterprise is discussed, including the development of flow metrology systems and complementary nuclear measurement techniques. Research encompasses four key themes: radioisotope tracer production, instrumentation & detector development, data acquisition & processing, and flow metrology.

Establishing a deep underground physics laboratory to study, amongst others, double beta decay, geoneutrinos, reactor neutrinos and dark matter has been discussed for more than a decade within the austral African physicists' community. PAUL, the Paarl Africa Underground Laboratory, is an initiative foreseeing an open international laboratory devoted to the development of competitive science in the austral region. It has the advantage that the location, the Huguenot tunnel, exists already and the geology and the environment of the site is appropriate for an experimental facility. The paper describes the PAUL initiative, presents the physics prospects and discusses the capacity for building the future experimental facility.